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* [PATCH v9 0/8] Count rlimits in each user namespace
@ 2021-03-23 20:59 Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 1/8] Increase size of ucounts to atomic_long_t Alexey Gladkov
                   ` (8 more replies)
  0 siblings, 9 replies; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

Preface
-------
These patches are for binding the rlimit counters to a user in user namespace.
This patch set can be applied on top of:

git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v5.12-rc4

Problem
-------
The RLIMIT_NPROC, RLIMIT_MEMLOCK, RLIMIT_SIGPENDING, RLIMIT_MSGQUEUE rlimits
implementation places the counters in user_struct [1]. These limits are global
between processes and persists for the lifetime of the process, even if
processes are in different user namespaces.

To illustrate the impact of rlimits, let's say there is a program that does not
fork. Some service-A wants to run this program as user X in multiple containers.
Since the program never fork the service wants to set RLIMIT_NPROC=1.

service-A
 \- program (uid=1000, container1, rlimit_nproc=1)
 \- program (uid=1000, container2, rlimit_nproc=1)

The service-A sets RLIMIT_NPROC=1 and runs the program in container1. When the
service-A tries to run a program with RLIMIT_NPROC=1 in container2 it fails
since user X already has one running process.

The problem is not that the limit from container1 affects container2. The
problem is that limit is verified against the global counter that reflects
the number of processes in all containers.

This problem can be worked around by using different users for each container
but in this case we face a different problem of uid mapping when transferring
files from one container to another.

Eric W. Biederman mentioned this issue [2][3].

Introduced changes
------------------
To address the problem, we bind rlimit counters to user namespace. Each counter
reflects the number of processes in a given uid in a given user namespace. The
result is a tree of rlimit counters with the biggest value at the root (aka
init_user_ns). The limit is considered exceeded if it's exceeded up in the tree.

[1]: https://lore.kernel.org/containers/87imd2incs.fsf@x220.int.ebiederm.org/
[2]: https://lists.linuxfoundation.org/pipermail/containers/2020-August/042096.html
[3]: https://lists.linuxfoundation.org/pipermail/containers/2020-October/042524.html

Changelog
---------
v9:
* Used a negative value to check that the ucounts->count is close to overflow.
* Rebased onto v5.12-rc4.

v8:
* Used atomic_t for ucounts reference counting. Also added counter overflow
  check (thanks to Linus Torvalds for the idea).
* Fixed other issues found by lkp-tests project in the patch that Reimplements
  RLIMIT_MEMLOCK on top of ucounts.

v7:
* Fixed issues found by lkp-tests project in the patch that Reimplements
  RLIMIT_MEMLOCK on top of ucounts.

v6:
* Fixed issues found by lkp-tests project.
* Rebased onto v5.11.

v5:
* Split the first commit into two commits: change ucounts.count type to atomic_long_t
  and add ucounts to cred. These commits were merged by mistake during the rebase.
* The __get_ucounts() renamed to alloc_ucounts().
* The cred.ucounts update has been moved from commit_creds() as it did not allow
  to handle errors.
* Added error handling of set_cred_ucounts().

v4:
* Reverted the type change of ucounts.count to refcount_t.
* Fixed typo in the kernel/cred.c

v3:
* Added get_ucounts() function to increase the reference count. The existing
  get_counts() function renamed to __get_ucounts().
* The type of ucounts.count changed from atomic_t to refcount_t.
* Dropped 'const' from set_cred_ucounts() arguments.
* Fixed a bug with freeing the cred structure after calling cred_alloc_blank().
* Commit messages have been updated.
* Added selftest.

v2:
* RLIMIT_MEMLOCK, RLIMIT_SIGPENDING and RLIMIT_MSGQUEUE are migrated to ucounts.
* Added ucounts for pair uid and user namespace into cred.
* Added the ability to increase ucount by more than 1.

v1:
* After discussion with Eric W. Biederman, I increased the size of ucounts to
  atomic_long_t.
* Added ucount_max to avoid the fork bomb.

--

Alexey Gladkov (8):
  Increase size of ucounts to atomic_long_t
  Add a reference to ucounts for each cred
  Use atomic_t for ucounts reference counting
  Reimplement RLIMIT_NPROC on top of ucounts
  Reimplement RLIMIT_MSGQUEUE on top of ucounts
  Reimplement RLIMIT_SIGPENDING on top of ucounts
  Reimplement RLIMIT_MEMLOCK on top of ucounts
  kselftests: Add test to check for rlimit changes in different user
    namespaces

 fs/exec.c                                     |   6 +-
 fs/hugetlbfs/inode.c                          |  16 +-
 fs/proc/array.c                               |   2 +-
 include/linux/cred.h                          |   4 +
 include/linux/hugetlb.h                       |   4 +-
 include/linux/mm.h                            |   4 +-
 include/linux/sched/user.h                    |   7 -
 include/linux/shmem_fs.h                      |   2 +-
 include/linux/signal_types.h                  |   4 +-
 include/linux/user_namespace.h                |  26 ++-
 ipc/mqueue.c                                  |  41 ++---
 ipc/shm.c                                     |  26 +--
 kernel/cred.c                                 |  50 +++++-
 kernel/exit.c                                 |   2 +-
 kernel/fork.c                                 |  18 +-
 kernel/signal.c                               |  57 +++----
 kernel/sys.c                                  |  14 +-
 kernel/ucount.c                               | 133 ++++++++++++---
 kernel/user.c                                 |   3 -
 kernel/user_namespace.c                       |   9 +-
 mm/memfd.c                                    |   4 +-
 mm/mlock.c                                    |  23 ++-
 mm/mmap.c                                     |   4 +-
 mm/shmem.c                                    |   8 +-
 tools/testing/selftests/Makefile              |   1 +
 tools/testing/selftests/rlimits/.gitignore    |   2 +
 tools/testing/selftests/rlimits/Makefile      |   6 +
 tools/testing/selftests/rlimits/config        |   1 +
 .../selftests/rlimits/rlimits-per-userns.c    | 161 ++++++++++++++++++
 29 files changed, 493 insertions(+), 145 deletions(-)
 create mode 100644 tools/testing/selftests/rlimits/.gitignore
 create mode 100644 tools/testing/selftests/rlimits/Makefile
 create mode 100644 tools/testing/selftests/rlimits/config
 create mode 100644 tools/testing/selftests/rlimits/rlimits-per-userns.c

-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 1/8] Increase size of ucounts to atomic_long_t
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 2/8] Add a reference to ucounts for each cred Alexey Gladkov
                   ` (7 subsequent siblings)
  8 siblings, 0 replies; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

RLIMIT_MSGQUEUE and RLIMIT_MEMLOCK use unsigned long to store their
counters. As a preparation for moving rlimits based on ucounts, we need
to increase the size of the variable to long.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 include/linux/user_namespace.h |  4 ++--
 kernel/ucount.c                | 16 ++++++++--------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 64cf8ebdc4ec..0bb833fd41f4 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -85,7 +85,7 @@ struct user_namespace {
 	struct ctl_table_header *sysctls;
 #endif
 	struct ucounts		*ucounts;
-	int ucount_max[UCOUNT_COUNTS];
+	long ucount_max[UCOUNT_COUNTS];
 } __randomize_layout;
 
 struct ucounts {
@@ -93,7 +93,7 @@ struct ucounts {
 	struct user_namespace *ns;
 	kuid_t uid;
 	int count;
-	atomic_t ucount[UCOUNT_COUNTS];
+	atomic_long_t ucount[UCOUNT_COUNTS];
 };
 
 extern struct user_namespace init_user_ns;
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 11b1596e2542..04c561751af1 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -175,14 +175,14 @@ static void put_ucounts(struct ucounts *ucounts)
 	kfree(ucounts);
 }
 
-static inline bool atomic_inc_below(atomic_t *v, int u)
+static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
 {
-	int c, old;
-	c = atomic_read(v);
+	long c, old;
+	c = atomic_long_read(v);
 	for (;;) {
 		if (unlikely(c >= u))
 			return false;
-		old = atomic_cmpxchg(v, c, c+1);
+		old = atomic_long_cmpxchg(v, c, c+1);
 		if (likely(old == c))
 			return true;
 		c = old;
@@ -196,17 +196,17 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 	struct user_namespace *tns;
 	ucounts = get_ucounts(ns, uid);
 	for (iter = ucounts; iter; iter = tns->ucounts) {
-		int max;
+		long max;
 		tns = iter->ns;
 		max = READ_ONCE(tns->ucount_max[type]);
-		if (!atomic_inc_below(&iter->ucount[type], max))
+		if (!atomic_long_inc_below(&iter->ucount[type], max))
 			goto fail;
 	}
 	return ucounts;
 fail:
 	bad = iter;
 	for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
-		atomic_dec(&iter->ucount[type]);
+		atomic_long_dec(&iter->ucount[type]);
 
 	put_ucounts(ucounts);
 	return NULL;
@@ -216,7 +216,7 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 {
 	struct ucounts *iter;
 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
-		int dec = atomic_dec_if_positive(&iter->ucount[type]);
+		long dec = atomic_long_dec_if_positive(&iter->ucount[type]);
 		WARN_ON_ONCE(dec < 0);
 	}
 	put_ucounts(ucounts);
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 2/8] Add a reference to ucounts for each cred
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 1/8] Increase size of ucounts to atomic_long_t Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 3/8] Use atomic_t for ucounts reference counting Alexey Gladkov
                   ` (6 subsequent siblings)
  8 siblings, 0 replies; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov, kernel test robot

For RLIMIT_NPROC and some other rlimits the user_struct that holds the
global limit is kept alive for the lifetime of a process by keeping it
in struct cred. Adding a pointer to ucounts in the struct cred will
allow to track RLIMIT_NPROC not only for user in the system, but for
user in the user_namespace.

Updating ucounts may require memory allocation which may fail. So, we
cannot change cred.ucounts in the commit_creds() because this function
cannot fail and it should always return 0. For this reason, we modify
cred.ucounts before calling the commit_creds().

Changelog

v6:
* Fix null-ptr-deref in is_ucounts_overlimit() detected by trinity. This
  error was caused by the fact that cred_alloc_blank() left the ucounts
  pointer empty.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/exec.c                      |  4 ++++
 include/linux/cred.h           |  2 ++
 include/linux/user_namespace.h |  4 ++++
 kernel/cred.c                  | 40 ++++++++++++++++++++++++++++++++++
 kernel/fork.c                  |  6 +++++
 kernel/sys.c                   | 12 ++++++++++
 kernel/ucount.c                | 40 +++++++++++++++++++++++++++++++---
 kernel/user_namespace.c        |  3 +++
 8 files changed, 108 insertions(+), 3 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 18594f11c31f..d7c4187ca023 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1360,6 +1360,10 @@ int begin_new_exec(struct linux_binprm * bprm)
 	WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
 	flush_signal_handlers(me, 0);
 
+	retval = set_cred_ucounts(bprm->cred);
+	if (retval < 0)
+		goto out_unlock;
+
 	/*
 	 * install the new credentials for this executable
 	 */
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 4c6350503697..66436e655032 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -144,6 +144,7 @@ struct cred {
 #endif
 	struct user_struct *user;	/* real user ID subscription */
 	struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
+	struct ucounts *ucounts;
 	struct group_info *group_info;	/* supplementary groups for euid/fsgid */
 	/* RCU deletion */
 	union {
@@ -170,6 +171,7 @@ extern int set_security_override_from_ctx(struct cred *, const char *);
 extern int set_create_files_as(struct cred *, struct inode *);
 extern int cred_fscmp(const struct cred *, const struct cred *);
 extern void __init cred_init(void);
+extern int set_cred_ucounts(struct cred *);
 
 /*
  * check for validity of credentials
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 0bb833fd41f4..f71b5a4a3e74 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -97,11 +97,15 @@ struct ucounts {
 };
 
 extern struct user_namespace init_user_ns;
+extern struct ucounts init_ucounts;
 
 bool setup_userns_sysctls(struct user_namespace *ns);
 void retire_userns_sysctls(struct user_namespace *ns);
 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
 void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
+struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
+struct ucounts *get_ucounts(struct ucounts *ucounts);
+void put_ucounts(struct ucounts *ucounts);
 
 #ifdef CONFIG_USER_NS
 
diff --git a/kernel/cred.c b/kernel/cred.c
index 421b1149c651..58a8a9e24347 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -60,6 +60,7 @@ struct cred init_cred = {
 	.user			= INIT_USER,
 	.user_ns		= &init_user_ns,
 	.group_info		= &init_groups,
+	.ucounts		= &init_ucounts,
 };
 
 static inline void set_cred_subscribers(struct cred *cred, int n)
@@ -119,6 +120,8 @@ static void put_cred_rcu(struct rcu_head *rcu)
 	if (cred->group_info)
 		put_group_info(cred->group_info);
 	free_uid(cred->user);
+	if (cred->ucounts)
+		put_ucounts(cred->ucounts);
 	put_user_ns(cred->user_ns);
 	kmem_cache_free(cred_jar, cred);
 }
@@ -222,6 +225,7 @@ struct cred *cred_alloc_blank(void)
 #ifdef CONFIG_DEBUG_CREDENTIALS
 	new->magic = CRED_MAGIC;
 #endif
+	new->ucounts = get_ucounts(&init_ucounts);
 
 	if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
 		goto error;
@@ -284,6 +288,11 @@ struct cred *prepare_creds(void)
 
 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
 		goto error;
+
+	new->ucounts = get_ucounts(new->ucounts);
+	if (!new->ucounts)
+		goto error;
+
 	validate_creds(new);
 	return new;
 
@@ -363,6 +372,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 		ret = create_user_ns(new);
 		if (ret < 0)
 			goto error_put;
+		if (set_cred_ucounts(new) < 0)
+			goto error_put;
 	}
 
 #ifdef CONFIG_KEYS
@@ -653,6 +664,31 @@ int cred_fscmp(const struct cred *a, const struct cred *b)
 }
 EXPORT_SYMBOL(cred_fscmp);
 
+int set_cred_ucounts(struct cred *new)
+{
+	struct task_struct *task = current;
+	const struct cred *old = task->real_cred;
+	struct ucounts *old_ucounts = new->ucounts;
+
+	if (new->user == old->user && new->user_ns == old->user_ns)
+		return 0;
+
+	/*
+	 * This optimization is needed because alloc_ucounts() uses locks
+	 * for table lookups.
+	 */
+	if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
+		return 0;
+
+	if (!(new->ucounts = alloc_ucounts(new->user_ns, new->euid)))
+		return -EAGAIN;
+
+	if (old_ucounts)
+		put_ucounts(old_ucounts);
+
+	return 0;
+}
+
 /*
  * initialise the credentials stuff
  */
@@ -719,6 +755,10 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
 	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
 		goto error;
 
+	new->ucounts = get_ucounts(new->ucounts);
+	if (!new->ucounts)
+		goto error;
+
 	put_cred(old);
 	validate_creds(new);
 	return new;
diff --git a/kernel/fork.c b/kernel/fork.c
index 54cc905e5fe0..37498cca6a1d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2995,6 +2995,12 @@ int ksys_unshare(unsigned long unshare_flags)
 	if (err)
 		goto bad_unshare_cleanup_cred;
 
+	if (new_cred) {
+		err = set_cred_ucounts(new_cred);
+		if (err)
+			goto bad_unshare_cleanup_cred;
+	}
+
 	if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
 		if (do_sysvsem) {
 			/*
diff --git a/kernel/sys.c b/kernel/sys.c
index 2e2e3f378d97..cabfc5b86175 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -552,6 +552,10 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
 	if (retval < 0)
 		goto error;
 
+	retval = set_cred_ucounts(new);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:
@@ -610,6 +614,10 @@ long __sys_setuid(uid_t uid)
 	if (retval < 0)
 		goto error;
 
+	retval = set_cred_ucounts(new);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:
@@ -685,6 +693,10 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
 	if (retval < 0)
 		goto error;
 
+	retval = set_cred_ucounts(new);
+	if (retval < 0)
+		goto error;
+
 	return commit_creds(new);
 
 error:
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 04c561751af1..50cc1dfb7d28 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -8,6 +8,12 @@
 #include <linux/kmemleak.h>
 #include <linux/user_namespace.h>
 
+struct ucounts init_ucounts = {
+	.ns    = &init_user_ns,
+	.uid   = GLOBAL_ROOT_UID,
+	.count = 1,
+};
+
 #define UCOUNTS_HASHTABLE_BITS 10
 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
 static DEFINE_SPINLOCK(ucounts_lock);
@@ -125,7 +131,15 @@ static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struc
 	return NULL;
 }
 
-static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
+static void hlist_add_ucounts(struct ucounts *ucounts)
+{
+	struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
+	spin_lock_irq(&ucounts_lock);
+	hlist_add_head(&ucounts->node, hashent);
+	spin_unlock_irq(&ucounts_lock);
+}
+
+struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
 	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
 	struct ucounts *ucounts, *new;
@@ -160,7 +174,26 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
 	return ucounts;
 }
 
-static void put_ucounts(struct ucounts *ucounts)
+struct ucounts *get_ucounts(struct ucounts *ucounts)
+{
+	unsigned long flags;
+
+	if (!ucounts)
+		return NULL;
+
+	spin_lock_irqsave(&ucounts_lock, flags);
+	if (ucounts->count == INT_MAX) {
+		WARN_ONCE(1, "ucounts: counter has reached its maximum value");
+		ucounts = NULL;
+	} else {
+		ucounts->count += 1;
+	}
+	spin_unlock_irqrestore(&ucounts_lock, flags);
+
+	return ucounts;
+}
+
+void put_ucounts(struct ucounts *ucounts)
 {
 	unsigned long flags;
 
@@ -194,7 +227,7 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 {
 	struct ucounts *ucounts, *iter, *bad;
 	struct user_namespace *tns;
-	ucounts = get_ucounts(ns, uid);
+	ucounts = alloc_ucounts(ns, uid);
 	for (iter = ucounts; iter; iter = tns->ucounts) {
 		long max;
 		tns = iter->ns;
@@ -237,6 +270,7 @@ static __init int user_namespace_sysctl_init(void)
 	BUG_ON(!user_header);
 	BUG_ON(!setup_userns_sysctls(&init_user_ns));
 #endif
+	hlist_add_ucounts(&init_ucounts);
 	return 0;
 }
 subsys_initcall(user_namespace_sysctl_init);
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index af612945a4d0..516db53166ab 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1281,6 +1281,9 @@ static int userns_install(struct nsset *nsset, struct ns_common *ns)
 	put_user_ns(cred->user_ns);
 	set_cred_user_ns(cred, get_user_ns(user_ns));
 
+	if (set_cred_ucounts(cred) < 0)
+		return -EINVAL;
+
 	return 0;
 }
 
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 3/8] Use atomic_t for ucounts reference counting
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 1/8] Increase size of ucounts to atomic_long_t Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 2/8] Add a reference to ucounts for each cred Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-04-05 17:01   ` Eric W. Biederman
  2021-03-23 20:59 ` [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts Alexey Gladkov
                   ` (5 subsequent siblings)
  8 siblings, 1 reply; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

The current implementation of the ucounts reference counter requires the
use of spin_lock. We're going to use get_ucounts() in more performance
critical areas like a handling of RLIMIT_SIGPENDING.

Now we need to use spin_lock only if we want to change the hashtable.

v9:
* Use a negative value to check that the ucounts->count is close to
  overflow.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 include/linux/user_namespace.h |  4 +--
 kernel/ucount.c                | 53 ++++++++++++----------------------
 2 files changed, 21 insertions(+), 36 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index f71b5a4a3e74..d84cc2c0b443 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -92,7 +92,7 @@ struct ucounts {
 	struct hlist_node node;
 	struct user_namespace *ns;
 	kuid_t uid;
-	int count;
+	atomic_t count;
 	atomic_long_t ucount[UCOUNT_COUNTS];
 };
 
@@ -104,7 +104,7 @@ void retire_userns_sysctls(struct user_namespace *ns);
 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
 void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
-struct ucounts *get_ucounts(struct ucounts *ucounts);
+struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);
 void put_ucounts(struct ucounts *ucounts);
 
 #ifdef CONFIG_USER_NS
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 50cc1dfb7d28..7bac19bb3f1e 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -11,7 +11,7 @@
 struct ucounts init_ucounts = {
 	.ns    = &init_user_ns,
 	.uid   = GLOBAL_ROOT_UID,
-	.count = 1,
+	.count = ATOMIC_INIT(1),
 };
 
 #define UCOUNTS_HASHTABLE_BITS 10
@@ -139,6 +139,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts)
 	spin_unlock_irq(&ucounts_lock);
 }
 
+struct ucounts *get_ucounts(struct ucounts *ucounts)
+{
+	if (ucounts && atomic_add_negative(1, &ucounts->count)) {
+		atomic_dec(&ucounts->count);
+		ucounts = NULL;
+	}
+	return ucounts;
+}
+
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
 	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
@@ -155,7 +164,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 
 		new->ns = ns;
 		new->uid = uid;
-		new->count = 0;
+		atomic_set(&new->count, 1);
 
 		spin_lock_irq(&ucounts_lock);
 		ucounts = find_ucounts(ns, uid, hashent);
@@ -163,33 +172,12 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 			kfree(new);
 		} else {
 			hlist_add_head(&new->node, hashent);
-			ucounts = new;
+			spin_unlock_irq(&ucounts_lock);
+			return new;
 		}
 	}
-	if (ucounts->count == INT_MAX)
-		ucounts = NULL;
-	else
-		ucounts->count += 1;
 	spin_unlock_irq(&ucounts_lock);
-	return ucounts;
-}
-
-struct ucounts *get_ucounts(struct ucounts *ucounts)
-{
-	unsigned long flags;
-
-	if (!ucounts)
-		return NULL;
-
-	spin_lock_irqsave(&ucounts_lock, flags);
-	if (ucounts->count == INT_MAX) {
-		WARN_ONCE(1, "ucounts: counter has reached its maximum value");
-		ucounts = NULL;
-	} else {
-		ucounts->count += 1;
-	}
-	spin_unlock_irqrestore(&ucounts_lock, flags);
-
+	ucounts = get_ucounts(ucounts);
 	return ucounts;
 }
 
@@ -197,15 +185,12 @@ void put_ucounts(struct ucounts *ucounts)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&ucounts_lock, flags);
-	ucounts->count -= 1;
-	if (!ucounts->count)
+	if (atomic_dec_and_test(&ucounts->count)) {
+		spin_lock_irqsave(&ucounts_lock, flags);
 		hlist_del_init(&ucounts->node);
-	else
-		ucounts = NULL;
-	spin_unlock_irqrestore(&ucounts_lock, flags);
-
-	kfree(ucounts);
+		spin_unlock_irqrestore(&ucounts_lock, flags);
+		kfree(ucounts);
+	}
 }
 
 static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
                   ` (2 preceding siblings ...)
  2021-03-23 20:59 ` [PATCH v9 3/8] Use atomic_t for ucounts reference counting Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-04-05 16:56   ` Eric W. Biederman
  2021-03-23 20:59 ` [PATCH v9 5/8] Reimplement RLIMIT_MSGQUEUE " Alexey Gladkov
                   ` (4 subsequent siblings)
  8 siblings, 1 reply; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

To illustrate the impact of rlimits, let's say there is a program that
does not fork. Some service-A wants to run this program as user X in
multiple containers. Since the program never fork the service wants to
set RLIMIT_NPROC=1.

service-A
 \- program (uid=1000, container1, rlimit_nproc=1)
 \- program (uid=1000, container2, rlimit_nproc=1)

The service-A sets RLIMIT_NPROC=1 and runs the program in container1.
When the service-A tries to run a program with RLIMIT_NPROC=1 in
container2 it fails since user X already has one running process.

We cannot use existing inc_ucounts / dec_ucounts because they do not
allow us to exceed the maximum for the counter. Some rlimits can be
overlimited by root or if the user has the appropriate capability.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/exec.c                      |  2 +-
 include/linux/cred.h           |  2 ++
 include/linux/sched/user.h     |  1 -
 include/linux/user_namespace.h | 13 ++++++++
 kernel/cred.c                  | 10 +++---
 kernel/exit.c                  |  2 +-
 kernel/fork.c                  |  9 ++---
 kernel/sys.c                   |  2 +-
 kernel/ucount.c                | 61 ++++++++++++++++++++++++++++++++++
 kernel/user.c                  |  1 -
 kernel/user_namespace.c        |  3 +-
 11 files changed, 91 insertions(+), 15 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index d7c4187ca023..f2bcdbeb3afb 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1878,7 +1878,7 @@ static int do_execveat_common(int fd, struct filename *filename,
 	 * whether NPROC limit is still exceeded.
 	 */
 	if ((current->flags & PF_NPROC_EXCEEDED) &&
-	    atomic_read(&current_user()->processes) > rlimit(RLIMIT_NPROC)) {
+	    is_ucounts_overlimit(current_ucounts(), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
 		retval = -EAGAIN;
 		goto out_ret;
 	}
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 66436e655032..5ca1e8a1d035 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -372,6 +372,7 @@ static inline void put_cred(const struct cred *_cred)
 
 #define task_uid(task)		(task_cred_xxx((task), uid))
 #define task_euid(task)		(task_cred_xxx((task), euid))
+#define task_ucounts(task)	(task_cred_xxx((task), ucounts))
 
 #define current_cred_xxx(xxx)			\
 ({						\
@@ -388,6 +389,7 @@ static inline void put_cred(const struct cred *_cred)
 #define current_fsgid() 	(current_cred_xxx(fsgid))
 #define current_cap()		(current_cred_xxx(cap_effective))
 #define current_user()		(current_cred_xxx(user))
+#define current_ucounts()	(current_cred_xxx(ucounts))
 
 extern struct user_namespace init_user_ns;
 #ifdef CONFIG_USER_NS
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index a8ec3b6093fc..d33d867ad6c1 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -12,7 +12,6 @@
  */
 struct user_struct {
 	refcount_t __count;	/* reference count */
-	atomic_t processes;	/* How many processes does this user have? */
 	atomic_t sigpending;	/* How many pending signals does this user have? */
 #ifdef CONFIG_FANOTIFY
 	atomic_t fanotify_listeners;
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d84cc2c0b443..9d1ca370c201 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -50,9 +50,12 @@ enum ucount_type {
 	UCOUNT_INOTIFY_INSTANCES,
 	UCOUNT_INOTIFY_WATCHES,
 #endif
+	UCOUNT_RLIMIT_NPROC,
 	UCOUNT_COUNTS,
 };
 
+#define MAX_PER_NAMESPACE_UCOUNTS UCOUNT_RLIMIT_NPROC
+
 struct user_namespace {
 	struct uid_gid_map	uid_map;
 	struct uid_gid_map	gid_map;
@@ -107,6 +110,16 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
 struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);
 void put_ucounts(struct ucounts *ucounts);
 
+static inline long get_ucounts_value(struct ucounts *ucounts, enum ucount_type type)
+{
+	return atomic_long_read(&ucounts->ucount[type]);
+}
+
+bool inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v);
+bool inc_rlimit_ucounts_and_test(struct ucounts *ucounts, enum ucount_type type, long v, long max);
+void dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v);
+bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max);
+
 #ifdef CONFIG_USER_NS
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
diff --git a/kernel/cred.c b/kernel/cred.c
index 58a8a9e24347..dcfa30b337c5 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -360,7 +360,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 		kdebug("share_creds(%p{%d,%d})",
 		       p->cred, atomic_read(&p->cred->usage),
 		       read_cred_subscribers(p->cred));
-		atomic_inc(&p->cred->user->processes);
+		inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 		return 0;
 	}
 
@@ -395,8 +395,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 	}
 #endif
 
-	atomic_inc(&new->user->processes);
 	p->cred = p->real_cred = get_cred(new);
+	inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	alter_cred_subscribers(new, 2);
 	validate_creds(new);
 	return 0;
@@ -496,12 +496,12 @@ int commit_creds(struct cred *new)
 	 * in set_user().
 	 */
 	alter_cred_subscribers(new, 2);
-	if (new->user != old->user)
-		atomic_inc(&new->user->processes);
+	if (new->user != old->user || new->user_ns != old->user_ns)
+		inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
 	rcu_assign_pointer(task->real_cred, new);
 	rcu_assign_pointer(task->cred, new);
 	if (new->user != old->user)
-		atomic_dec(&old->user->processes);
+		dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
 	alter_cred_subscribers(old, -2);
 
 	/* send notifications */
diff --git a/kernel/exit.c b/kernel/exit.c
index 04029e35e69a..61c0fe902b50 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -188,7 +188,7 @@ void release_task(struct task_struct *p)
 	/* don't need to get the RCU readlock here - the process is dead and
 	 * can't be modifying its own credentials. But shut RCU-lockdep up */
 	rcu_read_lock();
-	atomic_dec(&__task_cred(p)->user->processes);
+	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	rcu_read_unlock();
 
 	cgroup_release(p);
diff --git a/kernel/fork.c b/kernel/fork.c
index 37498cca6a1d..d8a4956463ae 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -819,9 +819,11 @@ void __init fork_init(void)
 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
 		init_task.signal->rlim[RLIMIT_NPROC];
 
-	for (i = 0; i < UCOUNT_COUNTS; i++)
+	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++)
 		init_user_ns.ucount_max[i] = max_threads/2;
 
+	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
+
 #ifdef CONFIG_VMAP_STACK
 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
 			  NULL, free_vm_stack_cache);
@@ -1972,8 +1974,7 @@ static __latent_entropy struct task_struct *copy_process(
 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
 #endif
 	retval = -EAGAIN;
-	if (atomic_read(&p->real_cred->user->processes) >=
-			task_rlimit(p, RLIMIT_NPROC)) {
+	if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
 		if (p->real_cred->user != INIT_USER &&
 		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
 			goto bad_fork_free;
@@ -2376,7 +2377,7 @@ static __latent_entropy struct task_struct *copy_process(
 #endif
 	delayacct_tsk_free(p);
 bad_fork_cleanup_count:
-	atomic_dec(&p->cred->user->processes);
+	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 	exit_creds(p);
 bad_fork_free:
 	p->state = TASK_DEAD;
diff --git a/kernel/sys.c b/kernel/sys.c
index cabfc5b86175..00266a65a000 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -473,7 +473,7 @@ static int set_user(struct cred *new)
 	 * for programs doing set*uid()+execve() by harmlessly deferring the
 	 * failure to the execve() stage.
 	 */
-	if (atomic_read(&new_user->processes) >= rlimit(RLIMIT_NPROC) &&
+	if (is_ucounts_overlimit(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) &&
 			new_user != INIT_USER)
 		current->flags |= PF_NPROC_EXCEEDED;
 	else
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 7bac19bb3f1e..77699231e002 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -7,6 +7,7 @@
 #include <linux/hash.h>
 #include <linux/kmemleak.h>
 #include <linux/user_namespace.h>
+#include <linux/security.h>
 
 struct ucounts init_ucounts = {
 	.ns    = &init_user_ns,
@@ -80,6 +81,7 @@ static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_inotify_instances"),
 	UCOUNT_ENTRY("max_inotify_watches"),
 #endif
+	{ },
 	{ }
 };
 #endif /* CONFIG_SYSCTL */
@@ -207,6 +209,19 @@ static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
 	}
 }
 
+static inline long atomic_long_dec_value(atomic_long_t *v, long n)
+{
+	long c, old;
+	c = atomic_long_read(v);
+	for (;;) {
+		old = atomic_long_cmpxchg(v, c, c - n);
+		if (likely(old == c))
+			return c;
+		c = old;
+	}
+	return c;
+}
+
 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
 			   enum ucount_type type)
 {
@@ -240,6 +255,51 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 	put_ucounts(ucounts);
 }
 
+bool inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
+{
+	struct ucounts *iter;
+	bool overlimit = false;
+
+	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+		long max = READ_ONCE(iter->ns->ucount_max[type]);
+		if (atomic_long_add_return(v, &iter->ucount[type]) > max)
+			overlimit = true;
+	}
+
+	return overlimit;
+}
+
+bool inc_rlimit_ucounts_and_test(struct ucounts *ucounts, enum ucount_type type,
+		long v, long max)
+{
+	bool overlimit = inc_rlimit_ucounts(ucounts, type, v);
+	if (!overlimit && get_ucounts_value(ucounts, type) > max)
+		overlimit = true;
+	return overlimit;
+}
+
+void dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
+{
+	struct ucounts *iter;
+	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+		long dec = atomic_long_dec_value(&iter->ucount[type], v);
+		WARN_ON_ONCE(dec < 0);
+	}
+}
+
+bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max)
+{
+	struct ucounts *iter;
+	if (get_ucounts_value(ucounts, type) > max)
+		return true;
+	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+		max = READ_ONCE(iter->ns->ucount_max[type]);
+		if (get_ucounts_value(iter, type) > max)
+			return true;
+	}
+	return false;
+}
+
 static __init int user_namespace_sysctl_init(void)
 {
 #ifdef CONFIG_SYSCTL
@@ -256,6 +316,7 @@ static __init int user_namespace_sysctl_init(void)
 	BUG_ON(!setup_userns_sysctls(&init_user_ns));
 #endif
 	hlist_add_ucounts(&init_ucounts);
+	inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
 	return 0;
 }
 subsys_initcall(user_namespace_sysctl_init);
diff --git a/kernel/user.c b/kernel/user.c
index a2478cddf536..7f5ff498207a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -98,7 +98,6 @@ static DEFINE_SPINLOCK(uidhash_lock);
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
 	.__count	= REFCOUNT_INIT(1),
-	.processes	= ATOMIC_INIT(1),
 	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
 	.uid		= GLOBAL_ROOT_UID,
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 516db53166ab..2434b13b02e5 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -118,9 +118,10 @@ int create_user_ns(struct cred *new)
 	ns->owner = owner;
 	ns->group = group;
 	INIT_WORK(&ns->work, free_user_ns);
-	for (i = 0; i < UCOUNT_COUNTS; i++) {
+	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++) {
 		ns->ucount_max[i] = INT_MAX;
 	}
+	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 5/8] Reimplement RLIMIT_MSGQUEUE on top of ucounts
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
                   ` (3 preceding siblings ...)
  2021-03-23 20:59 ` [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING " Alexey Gladkov
                   ` (3 subsequent siblings)
  8 siblings, 0 replies; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 include/linux/sched/user.h     |  4 ----
 include/linux/user_namespace.h |  1 +
 ipc/mqueue.c                   | 41 ++++++++++++++++++----------------
 kernel/fork.c                  |  1 +
 kernel/ucount.c                |  1 +
 kernel/user_namespace.c        |  1 +
 6 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index d33d867ad6c1..8a34446681aa 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -18,10 +18,6 @@ struct user_struct {
 #endif
 #ifdef CONFIG_EPOLL
 	atomic_long_t epoll_watches; /* The number of file descriptors currently watched */
-#endif
-#ifdef CONFIG_POSIX_MQUEUE
-	/* protected by mq_lock	*/
-	unsigned long mq_bytes;	/* How many bytes can be allocated to mqueue? */
 #endif
 	unsigned long locked_shm; /* How many pages of mlocked shm ? */
 	unsigned long unix_inflight;	/* How many files in flight in unix sockets */
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9d1ca370c201..d0fea0306394 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -51,6 +51,7 @@ enum ucount_type {
 	UCOUNT_INOTIFY_WATCHES,
 #endif
 	UCOUNT_RLIMIT_NPROC,
+	UCOUNT_RLIMIT_MSGQUEUE,
 	UCOUNT_COUNTS,
 };
 
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 8031464ed4ae..f0f8f013dae2 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -144,7 +144,7 @@ struct mqueue_inode_info {
 	struct pid *notify_owner;
 	u32 notify_self_exec_id;
 	struct user_namespace *notify_user_ns;
-	struct user_struct *user;	/* user who created, for accounting */
+	struct ucounts *ucounts;	/* user who created, for accounting */
 	struct sock *notify_sock;
 	struct sk_buff *notify_cookie;
 
@@ -292,7 +292,6 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		struct ipc_namespace *ipc_ns, umode_t mode,
 		struct mq_attr *attr)
 {
-	struct user_struct *u = current_user();
 	struct inode *inode;
 	int ret = -ENOMEM;
 
@@ -321,7 +320,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		info->notify_owner = NULL;
 		info->notify_user_ns = NULL;
 		info->qsize = 0;
-		info->user = NULL;	/* set when all is ok */
+		info->ucounts = NULL;	/* set when all is ok */
 		info->msg_tree = RB_ROOT;
 		info->msg_tree_rightmost = NULL;
 		info->node_cache = NULL;
@@ -371,19 +370,24 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 		if (mq_bytes + mq_treesize < mq_bytes)
 			goto out_inode;
 		mq_bytes += mq_treesize;
-		spin_lock(&mq_lock);
-		if (u->mq_bytes + mq_bytes < u->mq_bytes ||
-		    u->mq_bytes + mq_bytes > rlimit(RLIMIT_MSGQUEUE)) {
+		info->ucounts = get_ucounts(current_ucounts());
+		if (info->ucounts) {
+			bool overlimit;
+
+			spin_lock(&mq_lock);
+			overlimit = inc_rlimit_ucounts_and_test(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE,
+					mq_bytes, rlimit(RLIMIT_MSGQUEUE));
+			if (overlimit) {
+				dec_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes);
+				spin_unlock(&mq_lock);
+				put_ucounts(info->ucounts);
+				info->ucounts = NULL;
+				/* mqueue_evict_inode() releases info->messages */
+				ret = -EMFILE;
+				goto out_inode;
+			}
 			spin_unlock(&mq_lock);
-			/* mqueue_evict_inode() releases info->messages */
-			ret = -EMFILE;
-			goto out_inode;
 		}
-		u->mq_bytes += mq_bytes;
-		spin_unlock(&mq_lock);
-
-		/* all is ok */
-		info->user = get_uid(u);
 	} else if (S_ISDIR(mode)) {
 		inc_nlink(inode);
 		/* Some things misbehave if size == 0 on a directory */
@@ -497,7 +501,6 @@ static void mqueue_free_inode(struct inode *inode)
 static void mqueue_evict_inode(struct inode *inode)
 {
 	struct mqueue_inode_info *info;
-	struct user_struct *user;
 	struct ipc_namespace *ipc_ns;
 	struct msg_msg *msg, *nmsg;
 	LIST_HEAD(tmp_msg);
@@ -520,8 +523,7 @@ static void mqueue_evict_inode(struct inode *inode)
 		free_msg(msg);
 	}
 
-	user = info->user;
-	if (user) {
+	if (info->ucounts) {
 		unsigned long mq_bytes, mq_treesize;
 
 		/* Total amount of bytes accounted for the mqueue */
@@ -533,7 +535,7 @@ static void mqueue_evict_inode(struct inode *inode)
 					  info->attr.mq_msgsize);
 
 		spin_lock(&mq_lock);
-		user->mq_bytes -= mq_bytes;
+		dec_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes);
 		/*
 		 * get_ns_from_inode() ensures that the
 		 * (ipc_ns = sb->s_fs_info) is either a valid ipc_ns
@@ -543,7 +545,8 @@ static void mqueue_evict_inode(struct inode *inode)
 		if (ipc_ns)
 			ipc_ns->mq_queues_count--;
 		spin_unlock(&mq_lock);
-		free_uid(user);
+		put_ucounts(info->ucounts);
+		info->ucounts = NULL;
 	}
 	if (ipc_ns)
 		put_ipc_ns(ipc_ns);
diff --git a/kernel/fork.c b/kernel/fork.c
index d8a4956463ae..85c6094f5a48 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -823,6 +823,7 @@ void __init fork_init(void)
 		init_user_ns.ucount_max[i] = max_threads/2;
 
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
+	init_user_ns.ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = task_rlimit(&init_task, RLIMIT_MSGQUEUE);
 
 #ifdef CONFIG_VMAP_STACK
 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 77699231e002..03ed158e810f 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -81,6 +81,7 @@ static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_inotify_instances"),
 	UCOUNT_ENTRY("max_inotify_watches"),
 #endif
+	{ },
 	{ },
 	{ }
 };
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 2434b13b02e5..cc90d5203acf 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -122,6 +122,7 @@ int create_user_ns(struct cred *new)
 		ns->ucount_max[i] = INT_MAX;
 	}
 	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
+	ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE);
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING on top of ucounts
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
                   ` (4 preceding siblings ...)
  2021-03-23 20:59 ` [PATCH v9 5/8] Reimplement RLIMIT_MSGQUEUE " Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-04-05 16:58   ` Eric W. Biederman
  2021-03-23 20:59 ` [PATCH v9 7/8] Reimplement RLIMIT_MEMLOCK " Alexey Gladkov
                   ` (2 subsequent siblings)
  8 siblings, 1 reply; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/proc/array.c                |  2 +-
 include/linux/sched/user.h     |  1 -
 include/linux/signal_types.h   |  4 ++-
 include/linux/user_namespace.h |  1 +
 kernel/fork.c                  |  1 +
 kernel/signal.c                | 57 ++++++++++++++++------------------
 kernel/ucount.c                |  1 +
 kernel/user.c                  |  1 -
 kernel/user_namespace.c        |  1 +
 9 files changed, 34 insertions(+), 35 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index bb87e4d89cd8..74b0ea4b7e38 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -284,7 +284,7 @@ static inline void task_sig(struct seq_file *m, struct task_struct *p)
 		collect_sigign_sigcatch(p, &ignored, &caught);
 		num_threads = get_nr_threads(p);
 		rcu_read_lock();  /* FIXME: is this correct? */
-		qsize = atomic_read(&__task_cred(p)->user->sigpending);
+		qsize = get_ucounts_value(task_ucounts(p), UCOUNT_RLIMIT_SIGPENDING);
 		rcu_read_unlock();
 		qlim = task_rlimit(p, RLIMIT_SIGPENDING);
 		unlock_task_sighand(p, &flags);
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 8a34446681aa..8ba9cec4fb99 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -12,7 +12,6 @@
  */
 struct user_struct {
 	refcount_t __count;	/* reference count */
-	atomic_t sigpending;	/* How many pending signals does this user have? */
 #ifdef CONFIG_FANOTIFY
 	atomic_t fanotify_listeners;
 #endif
diff --git a/include/linux/signal_types.h b/include/linux/signal_types.h
index 68e06c75c5b2..34cb28b8f16c 100644
--- a/include/linux/signal_types.h
+++ b/include/linux/signal_types.h
@@ -13,6 +13,8 @@ typedef struct kernel_siginfo {
 	__SIGINFO;
 } kernel_siginfo_t;
 
+struct ucounts;
+
 /*
  * Real Time signals may be queued.
  */
@@ -21,7 +23,7 @@ struct sigqueue {
 	struct list_head list;
 	int flags;
 	kernel_siginfo_t info;
-	struct user_struct *user;
+	struct ucounts *ucounts;
 };
 
 /* flags values. */
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d0fea0306394..6e8736c7aa29 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -52,6 +52,7 @@ enum ucount_type {
 #endif
 	UCOUNT_RLIMIT_NPROC,
 	UCOUNT_RLIMIT_MSGQUEUE,
+	UCOUNT_RLIMIT_SIGPENDING,
 	UCOUNT_COUNTS,
 };
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 85c6094f5a48..741f896c156e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -824,6 +824,7 @@ void __init fork_init(void)
 
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = task_rlimit(&init_task, RLIMIT_MSGQUEUE);
+	init_user_ns.ucount_max[UCOUNT_RLIMIT_SIGPENDING] = task_rlimit(&init_task, RLIMIT_SIGPENDING);
 
 #ifdef CONFIG_VMAP_STACK
 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
diff --git a/kernel/signal.c b/kernel/signal.c
index f2a1b898da29..1b537d9de447 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -413,49 +413,44 @@ void task_join_group_stop(struct task_struct *task)
 static struct sigqueue *
 __sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimit)
 {
-	struct sigqueue *q = NULL;
-	struct user_struct *user;
-	int sigpending;
+	struct sigqueue *q = kmem_cache_alloc(sigqueue_cachep, flags);
 
-	/*
-	 * Protect access to @t credentials. This can go away when all
-	 * callers hold rcu read lock.
-	 *
-	 * NOTE! A pending signal will hold on to the user refcount,
-	 * and we get/put the refcount only when the sigpending count
-	 * changes from/to zero.
-	 */
-	rcu_read_lock();
-	user = __task_cred(t)->user;
-	sigpending = atomic_inc_return(&user->sigpending);
-	if (sigpending == 1)
-		get_uid(user);
-	rcu_read_unlock();
+	if (likely(q != NULL)) {
+		bool overlimit;
 
-	if (override_rlimit || likely(sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) {
-		q = kmem_cache_alloc(sigqueue_cachep, flags);
-	} else {
-		print_dropped_signal(sig);
-	}
-
-	if (unlikely(q == NULL)) {
-		if (atomic_dec_and_test(&user->sigpending))
-			free_uid(user);
-	} else {
 		INIT_LIST_HEAD(&q->list);
 		q->flags = 0;
-		q->user = user;
+
+		/*
+		 * Protect access to @t credentials. This can go away when all
+		 * callers hold rcu read lock.
+		 */
+		rcu_read_lock();
+		q->ucounts = get_ucounts(task_ucounts(t));
+		if (q->ucounts) {
+			overlimit = inc_rlimit_ucounts_and_test(q->ucounts, UCOUNT_RLIMIT_SIGPENDING,
+					1, task_rlimit(t, RLIMIT_SIGPENDING));
+
+			if (override_rlimit || likely(!overlimit)) {
+				rcu_read_unlock();
+				return q;
+			}
+		}
+		rcu_read_unlock();
 	}
 
-	return q;
+	print_dropped_signal(sig);
+	return NULL;
 }
 
 static void __sigqueue_free(struct sigqueue *q)
 {
 	if (q->flags & SIGQUEUE_PREALLOC)
 		return;
-	if (atomic_dec_and_test(&q->user->sigpending))
-		free_uid(q->user);
+	if (q->ucounts) {
+		dec_rlimit_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING, 1);
+		put_ucounts(q->ucounts);
+	}
 	kmem_cache_free(sigqueue_cachep, q);
 }
 
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 03ed158e810f..29976c8942f3 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -81,6 +81,7 @@ static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_inotify_instances"),
 	UCOUNT_ENTRY("max_inotify_watches"),
 #endif
+	{ },
 	{ },
 	{ },
 	{ }
diff --git a/kernel/user.c b/kernel/user.c
index 7f5ff498207a..6737327f83be 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -98,7 +98,6 @@ static DEFINE_SPINLOCK(uidhash_lock);
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
 	.__count	= REFCOUNT_INIT(1),
-	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
 	.uid		= GLOBAL_ROOT_UID,
 	.ratelimit	= RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index cc90d5203acf..df1bed32dd48 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -123,6 +123,7 @@ int create_user_ns(struct cred *new)
 	}
 	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
 	ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE);
+	ns->ucount_max[UCOUNT_RLIMIT_SIGPENDING] = rlimit(RLIMIT_SIGPENDING);
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 7/8] Reimplement RLIMIT_MEMLOCK on top of ucounts
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
                   ` (5 preceding siblings ...)
  2021-03-23 20:59 ` [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING " Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-03-23 20:59 ` [PATCH v9 8/8] kselftests: Add test to check for rlimit changes in different user namespaces Alexey Gladkov
  2021-04-05 17:03 ` [PATCH v9 0/8] Count rlimits in each user namespace Eric W. Biederman
  8 siblings, 0 replies; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov, kernel test robot

The rlimit counter is tied to uid in the user_namespace. This allows
rlimit values to be specified in userns even if they are already
globally exceeded by the user. However, the value of the previous
user_namespaces cannot be exceeded.

Changelog
v8:
* Fix issues found by lkp-tests project.

v7:
* Keep only ucounts for RLIMIT_MEMLOCK checks instead of struct cred.

v6:
* Fix bug in hugetlb_file_setup() detected by trinity.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/hugetlbfs/inode.c           | 16 ++++++++--------
 include/linux/hugetlb.h        |  4 ++--
 include/linux/mm.h             |  4 ++--
 include/linux/sched/user.h     |  1 -
 include/linux/shmem_fs.h       |  2 +-
 include/linux/user_namespace.h |  1 +
 ipc/shm.c                      | 26 +++++++++++++-------------
 kernel/fork.c                  |  1 +
 kernel/ucount.c                |  1 +
 kernel/user.c                  |  1 -
 kernel/user_namespace.c        |  1 +
 mm/memfd.c                     |  4 ++--
 mm/mlock.c                     | 23 +++++++++++++++--------
 mm/mmap.c                      |  4 ++--
 mm/shmem.c                     |  8 ++++----
 15 files changed, 53 insertions(+), 44 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 701c82c36138..be519fc9559a 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -1443,7 +1443,7 @@ static int get_hstate_idx(int page_size_log)
  * otherwise hugetlb_reserve_pages reserves one less hugepages than intended.
  */
 struct file *hugetlb_file_setup(const char *name, size_t size,
-				vm_flags_t acctflag, struct user_struct **user,
+				vm_flags_t acctflag, struct ucounts **ucounts,
 				int creat_flags, int page_size_log)
 {
 	struct inode *inode;
@@ -1455,20 +1455,20 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
 	if (hstate_idx < 0)
 		return ERR_PTR(-ENODEV);
 
-	*user = NULL;
+	*ucounts = NULL;
 	mnt = hugetlbfs_vfsmount[hstate_idx];
 	if (!mnt)
 		return ERR_PTR(-ENOENT);
 
 	if (creat_flags == HUGETLB_SHMFS_INODE && !can_do_hugetlb_shm()) {
-		*user = current_user();
-		if (user_shm_lock(size, *user)) {
+		*ucounts = current_ucounts();
+		if (user_shm_lock(size, *ucounts)) {
 			task_lock(current);
 			pr_warn_once("%s (%d): Using mlock ulimits for SHM_HUGETLB is deprecated\n",
 				current->comm, current->pid);
 			task_unlock(current);
 		} else {
-			*user = NULL;
+			*ucounts = NULL;
 			return ERR_PTR(-EPERM);
 		}
 	}
@@ -1495,9 +1495,9 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
 
 	iput(inode);
 out:
-	if (*user) {
-		user_shm_unlock(size, *user);
-		*user = NULL;
+	if (*ucounts) {
+		user_shm_unlock(size, *ucounts);
+		*ucounts = NULL;
 	}
 	return file;
 }
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index cccd1aab69dd..96d63dbdec65 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -434,7 +434,7 @@ static inline struct hugetlbfs_inode_info *HUGETLBFS_I(struct inode *inode)
 extern const struct file_operations hugetlbfs_file_operations;
 extern const struct vm_operations_struct hugetlb_vm_ops;
 struct file *hugetlb_file_setup(const char *name, size_t size, vm_flags_t acct,
-				struct user_struct **user, int creat_flags,
+				struct ucounts **ucounts, int creat_flags,
 				int page_size_log);
 
 static inline bool is_file_hugepages(struct file *file)
@@ -454,7 +454,7 @@ static inline struct hstate *hstate_inode(struct inode *i)
 #define is_file_hugepages(file)			false
 static inline struct file *
 hugetlb_file_setup(const char *name, size_t size, vm_flags_t acctflag,
-		struct user_struct **user, int creat_flags,
+		struct ucounts **ucounts, int creat_flags,
 		int page_size_log)
 {
 	return ERR_PTR(-ENOSYS);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 64a71bf20536..7466eab000d0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1658,8 +1658,8 @@ extern bool can_do_mlock(void);
 #else
 static inline bool can_do_mlock(void) { return false; }
 #endif
-extern int user_shm_lock(size_t, struct user_struct *);
-extern void user_shm_unlock(size_t, struct user_struct *);
+extern int user_shm_lock(size_t, struct ucounts *);
+extern void user_shm_unlock(size_t, struct ucounts *);
 
 /*
  * Parameter block passed down to zap_pte_range in exceptional cases.
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 8ba9cec4fb99..82bd2532da6b 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -18,7 +18,6 @@ struct user_struct {
 #ifdef CONFIG_EPOLL
 	atomic_long_t epoll_watches; /* The number of file descriptors currently watched */
 #endif
-	unsigned long locked_shm; /* How many pages of mlocked shm ? */
 	unsigned long unix_inflight;	/* How many files in flight in unix sockets */
 	atomic_long_t pipe_bufs;  /* how many pages are allocated in pipe buffers */
 
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d82b6f396588..aa77dcd1646f 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -65,7 +65,7 @@ extern struct file *shmem_file_setup_with_mnt(struct vfsmount *mnt,
 extern int shmem_zero_setup(struct vm_area_struct *);
 extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags);
-extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
+extern int shmem_lock(struct file *file, int lock, struct ucounts *ucounts);
 #ifdef CONFIG_SHMEM
 extern const struct address_space_operations shmem_aops;
 static inline bool shmem_mapping(struct address_space *mapping)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 6e8736c7aa29..82851fba7278 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -53,6 +53,7 @@ enum ucount_type {
 	UCOUNT_RLIMIT_NPROC,
 	UCOUNT_RLIMIT_MSGQUEUE,
 	UCOUNT_RLIMIT_SIGPENDING,
+	UCOUNT_RLIMIT_MEMLOCK,
 	UCOUNT_COUNTS,
 };
 
diff --git a/ipc/shm.c b/ipc/shm.c
index febd88daba8c..003234fbbd17 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -60,7 +60,7 @@ struct shmid_kernel /* private to the kernel */
 	time64_t		shm_ctim;
 	struct pid		*shm_cprid;
 	struct pid		*shm_lprid;
-	struct user_struct	*mlock_user;
+	struct ucounts		*mlock_ucounts;
 
 	/* The task created the shm object.  NULL if the task is dead. */
 	struct task_struct	*shm_creator;
@@ -286,10 +286,10 @@ static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
 	shm_rmid(ns, shp);
 	shm_unlock(shp);
 	if (!is_file_hugepages(shm_file))
-		shmem_lock(shm_file, 0, shp->mlock_user);
-	else if (shp->mlock_user)
+		shmem_lock(shm_file, 0, shp->mlock_ucounts);
+	else if (shp->mlock_ucounts)
 		user_shm_unlock(i_size_read(file_inode(shm_file)),
-				shp->mlock_user);
+				shp->mlock_ucounts);
 	fput(shm_file);
 	ipc_update_pid(&shp->shm_cprid, NULL);
 	ipc_update_pid(&shp->shm_lprid, NULL);
@@ -625,7 +625,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 
 	shp->shm_perm.key = key;
 	shp->shm_perm.mode = (shmflg & S_IRWXUGO);
-	shp->mlock_user = NULL;
+	shp->mlock_ucounts = NULL;
 
 	shp->shm_perm.security = NULL;
 	error = security_shm_alloc(&shp->shm_perm);
@@ -650,7 +650,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 		if (shmflg & SHM_NORESERVE)
 			acctflag = VM_NORESERVE;
 		file = hugetlb_file_setup(name, hugesize, acctflag,
-				  &shp->mlock_user, HUGETLB_SHMFS_INODE,
+				  &shp->mlock_ucounts, HUGETLB_SHMFS_INODE,
 				(shmflg >> SHM_HUGE_SHIFT) & SHM_HUGE_MASK);
 	} else {
 		/*
@@ -698,8 +698,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 no_id:
 	ipc_update_pid(&shp->shm_cprid, NULL);
 	ipc_update_pid(&shp->shm_lprid, NULL);
-	if (is_file_hugepages(file) && shp->mlock_user)
-		user_shm_unlock(size, shp->mlock_user);
+	if (is_file_hugepages(file) && shp->mlock_ucounts)
+		user_shm_unlock(size, shp->mlock_ucounts);
 	fput(file);
 	ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
 	return error;
@@ -1105,12 +1105,12 @@ static int shmctl_do_lock(struct ipc_namespace *ns, int shmid, int cmd)
 		goto out_unlock0;
 
 	if (cmd == SHM_LOCK) {
-		struct user_struct *user = current_user();
+		struct ucounts *ucounts = current_ucounts();
 
-		err = shmem_lock(shm_file, 1, user);
+		err = shmem_lock(shm_file, 1, ucounts);
 		if (!err && !(shp->shm_perm.mode & SHM_LOCKED)) {
 			shp->shm_perm.mode |= SHM_LOCKED;
-			shp->mlock_user = user;
+			shp->mlock_ucounts = ucounts;
 		}
 		goto out_unlock0;
 	}
@@ -1118,9 +1118,9 @@ static int shmctl_do_lock(struct ipc_namespace *ns, int shmid, int cmd)
 	/* SHM_UNLOCK */
 	if (!(shp->shm_perm.mode & SHM_LOCKED))
 		goto out_unlock0;
-	shmem_lock(shm_file, 0, shp->mlock_user);
+	shmem_lock(shm_file, 0, shp->mlock_ucounts);
 	shp->shm_perm.mode &= ~SHM_LOCKED;
-	shp->mlock_user = NULL;
+	shp->mlock_ucounts = NULL;
 	get_file(shm_file);
 	ipc_unlock_object(&shp->shm_perm);
 	rcu_read_unlock();
diff --git a/kernel/fork.c b/kernel/fork.c
index 741f896c156e..a3a5e317c3c0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -825,6 +825,7 @@ void __init fork_init(void)
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = task_rlimit(&init_task, RLIMIT_MSGQUEUE);
 	init_user_ns.ucount_max[UCOUNT_RLIMIT_SIGPENDING] = task_rlimit(&init_task, RLIMIT_SIGPENDING);
+	init_user_ns.ucount_max[UCOUNT_RLIMIT_MEMLOCK] = task_rlimit(&init_task, RLIMIT_MEMLOCK);
 
 #ifdef CONFIG_VMAP_STACK
 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 29976c8942f3..1db2c8744cde 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -84,6 +84,7 @@ static struct ctl_table user_table[] = {
 	{ },
 	{ },
 	{ },
+	{ },
 	{ }
 };
 #endif /* CONFIG_SYSCTL */
diff --git a/kernel/user.c b/kernel/user.c
index 6737327f83be..c82399c1618a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -98,7 +98,6 @@ static DEFINE_SPINLOCK(uidhash_lock);
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
 	.__count	= REFCOUNT_INIT(1),
-	.locked_shm     = 0,
 	.uid		= GLOBAL_ROOT_UID,
 	.ratelimit	= RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
 };
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index df1bed32dd48..5ef0d4b182ba 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -124,6 +124,7 @@ int create_user_ns(struct cred *new)
 	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);
 	ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE);
 	ns->ucount_max[UCOUNT_RLIMIT_SIGPENDING] = rlimit(RLIMIT_SIGPENDING);
+	ns->ucount_max[UCOUNT_RLIMIT_MEMLOCK] = rlimit(RLIMIT_MEMLOCK);
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
diff --git a/mm/memfd.c b/mm/memfd.c
index 2647c898990c..081dd33e6a61 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -297,9 +297,9 @@ SYSCALL_DEFINE2(memfd_create,
 	}
 
 	if (flags & MFD_HUGETLB) {
-		struct user_struct *user = NULL;
+		struct ucounts *ucounts = NULL;
 
-		file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user,
+		file = hugetlb_file_setup(name, 0, VM_NORESERVE, &ucounts,
 					HUGETLB_ANONHUGE_INODE,
 					(flags >> MFD_HUGE_SHIFT) &
 					MFD_HUGE_MASK);
diff --git a/mm/mlock.c b/mm/mlock.c
index f8f8cc32d03d..b874d0436976 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -817,9 +817,10 @@ SYSCALL_DEFINE0(munlockall)
  */
 static DEFINE_SPINLOCK(shmlock_user_lock);
 
-int user_shm_lock(size_t size, struct user_struct *user)
+int user_shm_lock(size_t size, struct ucounts *ucounts)
 {
 	unsigned long lock_limit, locked;
+	bool overlimit;
 	int allowed = 0;
 
 	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -828,21 +829,27 @@ int user_shm_lock(size_t size, struct user_struct *user)
 		allowed = 1;
 	lock_limit >>= PAGE_SHIFT;
 	spin_lock(&shmlock_user_lock);
-	if (!allowed &&
-	    locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
+	overlimit = inc_rlimit_ucounts_and_test(ucounts, UCOUNT_RLIMIT_MEMLOCK,
+			locked, lock_limit);
+
+	if (!allowed && overlimit && !capable(CAP_IPC_LOCK)) {
+		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
+		goto out;
+	}
+	if (!get_ucounts(ucounts)) {
+		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
 		goto out;
-	get_uid(user);
-	user->locked_shm += locked;
+	}
 	allowed = 1;
 out:
 	spin_unlock(&shmlock_user_lock);
 	return allowed;
 }
 
-void user_shm_unlock(size_t size, struct user_struct *user)
+void user_shm_unlock(size_t size, struct ucounts *ucounts)
 {
 	spin_lock(&shmlock_user_lock);
-	user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, (size + PAGE_SIZE - 1) >> PAGE_SHIFT);
 	spin_unlock(&shmlock_user_lock);
-	free_uid(user);
+	put_ucounts(ucounts);
 }
diff --git a/mm/mmap.c b/mm/mmap.c
index 3f287599a7a3..99f97d200aa4 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1605,7 +1605,7 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
 			goto out_fput;
 		}
 	} else if (flags & MAP_HUGETLB) {
-		struct user_struct *user = NULL;
+		struct ucounts *ucounts = NULL;
 		struct hstate *hs;
 
 		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
@@ -1621,7 +1621,7 @@ unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
 		 */
 		file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
 				VM_NORESERVE,
-				&user, HUGETLB_ANONHUGE_INODE,
+				&ucounts, HUGETLB_ANONHUGE_INODE,
 				(flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
 		if (IS_ERR(file))
 			return PTR_ERR(file);
diff --git a/mm/shmem.c b/mm/shmem.c
index b2db4ed0fbc7..45b71a002ab1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2227,7 +2227,7 @@ static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
 }
 #endif
 
-int shmem_lock(struct file *file, int lock, struct user_struct *user)
+int shmem_lock(struct file *file, int lock, struct ucounts *ucounts)
 {
 	struct inode *inode = file_inode(file);
 	struct shmem_inode_info *info = SHMEM_I(inode);
@@ -2239,13 +2239,13 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
 	 * no serialization needed when called from shm_destroy().
 	 */
 	if (lock && !(info->flags & VM_LOCKED)) {
-		if (!user_shm_lock(inode->i_size, user))
+		if (!user_shm_lock(inode->i_size, ucounts))
 			goto out_nomem;
 		info->flags |= VM_LOCKED;
 		mapping_set_unevictable(file->f_mapping);
 	}
-	if (!lock && (info->flags & VM_LOCKED) && user) {
-		user_shm_unlock(inode->i_size, user);
+	if (!lock && (info->flags & VM_LOCKED) && ucounts) {
+		user_shm_unlock(inode->i_size, ucounts);
 		info->flags &= ~VM_LOCKED;
 		mapping_clear_unevictable(file->f_mapping);
 	}
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v9 8/8] kselftests: Add test to check for rlimit changes in different user namespaces
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
                   ` (6 preceding siblings ...)
  2021-03-23 20:59 ` [PATCH v9 7/8] Reimplement RLIMIT_MEMLOCK " Alexey Gladkov
@ 2021-03-23 20:59 ` Alexey Gladkov
  2021-04-05 17:03 ` [PATCH v9 0/8] Count rlimits in each user namespace Eric W. Biederman
  8 siblings, 0 replies; 15+ messages in thread
From: Alexey Gladkov @ 2021-03-23 20:59 UTC (permalink / raw)
  To: LKML, Kernel Hardening, Linux Containers, linux-mm
  Cc: Alexey Gladkov, Andrew Morton, Christian Brauner,
	Eric W . Biederman, Jann Horn, Jens Axboe, Kees Cook,
	Linus Torvalds, Oleg Nesterov

The testcase runs few instances of the program with RLIMIT_NPROC=1 from
user uid=60000, in different user namespaces.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 tools/testing/selftests/Makefile              |   1 +
 tools/testing/selftests/rlimits/.gitignore    |   2 +
 tools/testing/selftests/rlimits/Makefile      |   6 +
 tools/testing/selftests/rlimits/config        |   1 +
 .../selftests/rlimits/rlimits-per-userns.c    | 161 ++++++++++++++++++
 5 files changed, 171 insertions(+)
 create mode 100644 tools/testing/selftests/rlimits/.gitignore
 create mode 100644 tools/testing/selftests/rlimits/Makefile
 create mode 100644 tools/testing/selftests/rlimits/config
 create mode 100644 tools/testing/selftests/rlimits/rlimits-per-userns.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 6c575cf34a71..a4ea1481bd9a 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -48,6 +48,7 @@ TARGETS += proc
 TARGETS += pstore
 TARGETS += ptrace
 TARGETS += openat2
+TARGETS += rlimits
 TARGETS += rseq
 TARGETS += rtc
 TARGETS += seccomp
diff --git a/tools/testing/selftests/rlimits/.gitignore b/tools/testing/selftests/rlimits/.gitignore
new file mode 100644
index 000000000000..091021f255b3
--- /dev/null
+++ b/tools/testing/selftests/rlimits/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+rlimits-per-userns
diff --git a/tools/testing/selftests/rlimits/Makefile b/tools/testing/selftests/rlimits/Makefile
new file mode 100644
index 000000000000..03aadb406212
--- /dev/null
+++ b/tools/testing/selftests/rlimits/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+CFLAGS += -Wall -O2 -g
+TEST_GEN_PROGS := rlimits-per-userns
+
+include ../lib.mk
diff --git a/tools/testing/selftests/rlimits/config b/tools/testing/selftests/rlimits/config
new file mode 100644
index 000000000000..416bd53ce982
--- /dev/null
+++ b/tools/testing/selftests/rlimits/config
@@ -0,0 +1 @@
+CONFIG_USER_NS=y
diff --git a/tools/testing/selftests/rlimits/rlimits-per-userns.c b/tools/testing/selftests/rlimits/rlimits-per-userns.c
new file mode 100644
index 000000000000..26dc949e93ea
--- /dev/null
+++ b/tools/testing/selftests/rlimits/rlimits-per-userns.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Author: Alexey Gladkov <gladkov.alexey@gmail.com>
+ */
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sched.h>
+#include <signal.h>
+#include <limits.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <err.h>
+
+#define NR_CHILDS 2
+
+static char *service_prog;
+static uid_t user   = 60000;
+static uid_t group  = 60000;
+
+static void setrlimit_nproc(rlim_t n)
+{
+	pid_t pid = getpid();
+	struct rlimit limit = {
+		.rlim_cur = n,
+		.rlim_max = n
+	};
+
+	warnx("(pid=%d): Setting RLIMIT_NPROC=%ld", pid, n);
+
+	if (setrlimit(RLIMIT_NPROC, &limit) < 0)
+		err(EXIT_FAILURE, "(pid=%d): setrlimit(RLIMIT_NPROC)", pid);
+}
+
+static pid_t fork_child(void)
+{
+	pid_t pid = fork();
+
+	if (pid < 0)
+		err(EXIT_FAILURE, "fork");
+
+	if (pid > 0)
+		return pid;
+
+	pid = getpid();
+
+	warnx("(pid=%d): New process starting ...", pid);
+
+	if (prctl(PR_SET_PDEATHSIG, SIGKILL) < 0)
+		err(EXIT_FAILURE, "(pid=%d): prctl(PR_SET_PDEATHSIG)", pid);
+
+	signal(SIGUSR1, SIG_DFL);
+
+	warnx("(pid=%d): Changing to uid=%d, gid=%d", pid, user, group);
+
+	if (setgid(group) < 0)
+		err(EXIT_FAILURE, "(pid=%d): setgid(%d)", pid, group);
+	if (setuid(user) < 0)
+		err(EXIT_FAILURE, "(pid=%d): setuid(%d)", pid, user);
+
+	warnx("(pid=%d): Service running ...", pid);
+
+	warnx("(pid=%d): Unshare user namespace", pid);
+	if (unshare(CLONE_NEWUSER) < 0)
+		err(EXIT_FAILURE, "unshare(CLONE_NEWUSER)");
+
+	char *const argv[] = { "service", NULL };
+	char *const envp[] = { "I_AM_SERVICE=1", NULL };
+
+	warnx("(pid=%d): Executing real service ...", pid);
+
+	execve(service_prog, argv, envp);
+	err(EXIT_FAILURE, "(pid=%d): execve", pid);
+}
+
+int main(int argc, char **argv)
+{
+	size_t i;
+	pid_t child[NR_CHILDS];
+	int wstatus[NR_CHILDS];
+	int childs = NR_CHILDS;
+	pid_t pid;
+
+	if (getenv("I_AM_SERVICE")) {
+		pause();
+		exit(EXIT_SUCCESS);
+	}
+
+	service_prog = argv[0];
+	pid = getpid();
+
+	warnx("(pid=%d) Starting testcase", pid);
+
+	/*
+	 * This rlimit is not a problem for root because it can be exceeded.
+	 */
+	setrlimit_nproc(1);
+
+	for (i = 0; i < NR_CHILDS; i++) {
+		child[i] = fork_child();
+		wstatus[i] = 0;
+		usleep(250000);
+	}
+
+	while (1) {
+		for (i = 0; i < NR_CHILDS; i++) {
+			if (child[i] <= 0)
+				continue;
+
+			errno = 0;
+			pid_t ret = waitpid(child[i], &wstatus[i], WNOHANG);
+
+			if (!ret || (!WIFEXITED(wstatus[i]) && !WIFSIGNALED(wstatus[i])))
+				continue;
+
+			if (ret < 0 && errno != ECHILD)
+				warn("(pid=%d): waitpid(%d)", pid, child[i]);
+
+			child[i] *= -1;
+			childs -= 1;
+		}
+
+		if (!childs)
+			break;
+
+		usleep(250000);
+
+		for (i = 0; i < NR_CHILDS; i++) {
+			if (child[i] <= 0)
+				continue;
+			kill(child[i], SIGUSR1);
+		}
+	}
+
+	for (i = 0; i < NR_CHILDS; i++) {
+		if (WIFEXITED(wstatus[i]))
+			warnx("(pid=%d): pid %d exited, status=%d",
+				pid, -child[i], WEXITSTATUS(wstatus[i]));
+		else if (WIFSIGNALED(wstatus[i]))
+			warnx("(pid=%d): pid %d killed by signal %d",
+				pid, -child[i], WTERMSIG(wstatus[i]));
+
+		if (WIFSIGNALED(wstatus[i]) && WTERMSIG(wstatus[i]) == SIGUSR1)
+			continue;
+
+		warnx("(pid=%d): Test failed", pid);
+		exit(EXIT_FAILURE);
+	}
+
+	warnx("(pid=%d): Test passed", pid);
+	exit(EXIT_SUCCESS);
+}
-- 
2.29.3



^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts
  2021-03-23 20:59 ` [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts Alexey Gladkov
@ 2021-04-05 16:56   ` Eric W. Biederman
  2021-04-06 15:44     ` Alexey Gladkov
  0 siblings, 1 reply; 15+ messages in thread
From: Eric W. Biederman @ 2021-04-05 16:56 UTC (permalink / raw)
  To: Alexey Gladkov
  Cc: LKML, Kernel Hardening, Linux Containers, linux-mm,
	Alexey Gladkov, Andrew Morton, Christian Brauner, Jann Horn,
	Jens Axboe, Kees Cook, Linus Torvalds, Oleg Nesterov

Alexey Gladkov <gladkov.alexey@gmail.com> writes:

> The rlimit counter is tied to uid in the user_namespace. This allows
> rlimit values to be specified in userns even if they are already
> globally exceeded by the user. However, the value of the previous
> user_namespaces cannot be exceeded.
>
> To illustrate the impact of rlimits, let's say there is a program that
> does not fork. Some service-A wants to run this program as user X in
> multiple containers. Since the program never fork the service wants to
> set RLIMIT_NPROC=1.
>
> service-A
>  \- program (uid=1000, container1, rlimit_nproc=1)
>  \- program (uid=1000, container2, rlimit_nproc=1)
>
> The service-A sets RLIMIT_NPROC=1 and runs the program in container1.
> When the service-A tries to run a program with RLIMIT_NPROC=1 in
> container2 it fails since user X already has one running process.
>
> We cannot use existing inc_ucounts / dec_ucounts because they do not
> allow us to exceed the maximum for the counter. Some rlimits can be
> overlimited by root or if the user has the appropriate capability.

In general this looks good.

My comments are going to be on the infrastructure this patch
introduces rather than the change to RLIMIT_NPROC.  Perhaps
these would fare better as separate patches.

To preserve the existing semantics of incrementing and decrementing
rlimits in places separate from where the limits are checked you
correctly introduce inc_rlimit_ucounts and dec_rlimit_ucounts.

This separation means that for a short period of time the values
in the counts can overflow.  Which is something that the current
ucount helpers don't allow.  Taking advantage of the entire
negative range for the counts, just like we take advantage
of the entire negative range in get_ucounts seems a reasonable thing
to do.

On 32bit using "atomic_long_t" instead of "unsigned long" to hold the
counts has the downside that RLIMIT_MSGQUEUE and RLIMIT_MEMLOCK are
limited to 2GiB instead of 4GiB.  I don't think anyone cares but
it should be mentioned in case someone does.

The functions inc_rlimit_ucounts and inc_rlimit_ucounts_test need
to return overflow in the unlikely event the count values becomes
negative.

Also when setting ns->ucount_max[] in create_user_ns because one value
is signed and the other is unsigned.  Care should be taken so that
rlimit_infinity is translated into the largest positive value the
type can hold.

Eric

> Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
> ---
>  fs/exec.c                      |  2 +-
>  include/linux/cred.h           |  2 ++
>  include/linux/sched/user.h     |  1 -
>  include/linux/user_namespace.h | 13 ++++++++
>  kernel/cred.c                  | 10 +++---
>  kernel/exit.c                  |  2 +-
>  kernel/fork.c                  |  9 ++---
>  kernel/sys.c                   |  2 +-
>  kernel/ucount.c                | 61 ++++++++++++++++++++++++++++++++++
>  kernel/user.c                  |  1 -
>  kernel/user_namespace.c        |  3 +-
>  11 files changed, 91 insertions(+), 15 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index d7c4187ca023..f2bcdbeb3afb 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1878,7 +1878,7 @@ static int do_execveat_common(int fd, struct filename *filename,
>  	 * whether NPROC limit is still exceeded.
>  	 */
>  	if ((current->flags & PF_NPROC_EXCEEDED) &&
> -	    atomic_read(&current_user()->processes) > rlimit(RLIMIT_NPROC)) {
> +	    is_ucounts_overlimit(current_ucounts(), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
>  		retval = -EAGAIN;
>  		goto out_ret;
>  	}
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 66436e655032..5ca1e8a1d035 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -372,6 +372,7 @@ static inline void put_cred(const struct cred *_cred)
>  
>  #define task_uid(task)		(task_cred_xxx((task), uid))
>  #define task_euid(task)		(task_cred_xxx((task), euid))
> +#define task_ucounts(task)	(task_cred_xxx((task), ucounts))
>  
>  #define current_cred_xxx(xxx)			\
>  ({						\
> @@ -388,6 +389,7 @@ static inline void put_cred(const struct cred *_cred)
>  #define current_fsgid() 	(current_cred_xxx(fsgid))
>  #define current_cap()		(current_cred_xxx(cap_effective))
>  #define current_user()		(current_cred_xxx(user))
> +#define current_ucounts()	(current_cred_xxx(ucounts))
>  
>  extern struct user_namespace init_user_ns;
>  #ifdef CONFIG_USER_NS
> diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
> index a8ec3b6093fc..d33d867ad6c1 100644
> --- a/include/linux/sched/user.h
> +++ b/include/linux/sched/user.h
> @@ -12,7 +12,6 @@
>   */
>  struct user_struct {
>  	refcount_t __count;	/* reference count */
> -	atomic_t processes;	/* How many processes does this user have? */
>  	atomic_t sigpending;	/* How many pending signals does this user have? */
>  #ifdef CONFIG_FANOTIFY
>  	atomic_t fanotify_listeners;
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index d84cc2c0b443..9d1ca370c201 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -50,9 +50,12 @@ enum ucount_type {
>  	UCOUNT_INOTIFY_INSTANCES,
>  	UCOUNT_INOTIFY_WATCHES,
>  #endif
> +	UCOUNT_RLIMIT_NPROC,
>  	UCOUNT_COUNTS,
>  };
>  
> +#define MAX_PER_NAMESPACE_UCOUNTS UCOUNT_RLIMIT_NPROC
> +
>  struct user_namespace {
>  	struct uid_gid_map	uid_map;
>  	struct uid_gid_map	gid_map;
> @@ -107,6 +110,16 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
>  struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);
>  void put_ucounts(struct ucounts *ucounts);
>  
> +static inline long get_ucounts_value(struct ucounts *ucounts, enum ucount_type type)
> +{
> +	return atomic_long_read(&ucounts->ucount[type]);
> +}
> +
> +bool inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v);
> +bool inc_rlimit_ucounts_and_test(struct ucounts *ucounts, enum ucount_type type, long v, long max);
> +void dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v);
> +bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max);
> +
>  #ifdef CONFIG_USER_NS
>  
>  static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
> diff --git a/kernel/cred.c b/kernel/cred.c
> index 58a8a9e24347..dcfa30b337c5 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -360,7 +360,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
>  		kdebug("share_creds(%p{%d,%d})",
>  		       p->cred, atomic_read(&p->cred->usage),
>  		       read_cred_subscribers(p->cred));
> -		atomic_inc(&p->cred->user->processes);
> +		inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
>  		return 0;
>  	}
>  
> @@ -395,8 +395,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
>  	}
>  #endif
>  
> -	atomic_inc(&new->user->processes);
>  	p->cred = p->real_cred = get_cred(new);
> +	inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
>  	alter_cred_subscribers(new, 2);
>  	validate_creds(new);
>  	return 0;
> @@ -496,12 +496,12 @@ int commit_creds(struct cred *new)
>  	 * in set_user().
>  	 */
>  	alter_cred_subscribers(new, 2);
> -	if (new->user != old->user)
> -		atomic_inc(&new->user->processes);
> +	if (new->user != old->user || new->user_ns != old->user_ns)
> +		inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
>  	rcu_assign_pointer(task->real_cred, new);
>  	rcu_assign_pointer(task->cred, new);
>  	if (new->user != old->user)
> -		atomic_dec(&old->user->processes);
> +		dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
>  	alter_cred_subscribers(old, -2);
>  
>  	/* send notifications */
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 04029e35e69a..61c0fe902b50 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -188,7 +188,7 @@ void release_task(struct task_struct *p)
>  	/* don't need to get the RCU readlock here - the process is dead and
>  	 * can't be modifying its own credentials. But shut RCU-lockdep up */
>  	rcu_read_lock();
> -	atomic_dec(&__task_cred(p)->user->processes);
> +	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
>  	rcu_read_unlock();
>  
>  	cgroup_release(p);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 37498cca6a1d..d8a4956463ae 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -819,9 +819,11 @@ void __init fork_init(void)
>  	init_task.signal->rlim[RLIMIT_SIGPENDING] =
>  		init_task.signal->rlim[RLIMIT_NPROC];
>  
> -	for (i = 0; i < UCOUNT_COUNTS; i++)
> +	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++)
>  		init_user_ns.ucount_max[i] = max_threads/2;
>  
> +	init_user_ns.ucount_max[UCOUNT_RLIMIT_NPROC] = task_rlimit(&init_task, RLIMIT_NPROC);
> +
>  #ifdef CONFIG_VMAP_STACK
>  	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
>  			  NULL, free_vm_stack_cache);
> @@ -1972,8 +1974,7 @@ static __latent_entropy struct task_struct *copy_process(
>  	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
>  #endif
>  	retval = -EAGAIN;
> -	if (atomic_read(&p->real_cred->user->processes) >=
> -			task_rlimit(p, RLIMIT_NPROC)) {
> +	if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
>  		if (p->real_cred->user != INIT_USER &&
>  		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
>  			goto bad_fork_free;
> @@ -2376,7 +2377,7 @@ static __latent_entropy struct task_struct *copy_process(
>  #endif
>  	delayacct_tsk_free(p);
>  bad_fork_cleanup_count:
> -	atomic_dec(&p->cred->user->processes);
> +	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
>  	exit_creds(p);
>  bad_fork_free:
>  	p->state = TASK_DEAD;
> diff --git a/kernel/sys.c b/kernel/sys.c
> index cabfc5b86175..00266a65a000 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -473,7 +473,7 @@ static int set_user(struct cred *new)
>  	 * for programs doing set*uid()+execve() by harmlessly deferring the
>  	 * failure to the execve() stage.
>  	 */
> -	if (atomic_read(&new_user->processes) >= rlimit(RLIMIT_NPROC) &&
> +	if (is_ucounts_overlimit(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) &&
>  			new_user != INIT_USER)
>  		current->flags |= PF_NPROC_EXCEEDED;
>  	else
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 7bac19bb3f1e..77699231e002 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -7,6 +7,7 @@
>  #include <linux/hash.h>
>  #include <linux/kmemleak.h>
>  #include <linux/user_namespace.h>
> +#include <linux/security.h>
>  
>  struct ucounts init_ucounts = {
>  	.ns    = &init_user_ns,
> @@ -80,6 +81,7 @@ static struct ctl_table user_table[] = {
>  	UCOUNT_ENTRY("max_inotify_instances"),
>  	UCOUNT_ENTRY("max_inotify_watches"),
>  #endif
> +	{ },
>  	{ }
>  };
>  #endif /* CONFIG_SYSCTL */
> @@ -207,6 +209,19 @@ static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
>  	}
>  }
>  
> +static inline long atomic_long_dec_value(atomic_long_t *v, long n)
> +{
> +	long c, old;
> +	c = atomic_long_read(v);
> +	for (;;) {
> +		old = atomic_long_cmpxchg(v, c, c - n);
> +		if (likely(old == c))
> +			return c;
> +		c = old;
> +	}
> +	return c;
> +}

Just use atomic_add_long_return.


> +
>  struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
>  			   enum ucount_type type)
>  {
> @@ -240,6 +255,51 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
>  	put_ucounts(ucounts);
>  }
>  
> +bool inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
> +{
> +	struct ucounts *iter;
> +	bool overlimit = false;
> +
> +	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> +		long max = READ_ONCE(iter->ns->ucount_max[type]);
> +		if (atomic_long_add_return(v, &iter->ucount[type]) > max)
> +			overlimit = true;

Please check for negative to detect counter overflow.
At least the mq code already checks for overflow.

> +	}
> +
> +	return overlimit;
> +}
> +
> +bool inc_rlimit_ucounts_and_test(struct ucounts *ucounts, enum ucount_type type,
> +		long v, long max)
> +{
> +	bool overlimit = inc_rlimit_ucounts(ucounts, type, v);
> +	if (!overlimit && get_ucounts_value(ucounts, type) > max)
> +		overlimit = true;

The return of get_ucounts_value also needs to be checked for negative.

> +	return overlimit;
> +}
> +
> +void dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
> +{
> +	struct ucounts *iter;
> +	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> +		long dec = atomic_long_dec_value(&iter->ucount[type], v);
                           atomic_long_add_return(&iter->ucount[type], -v);
> +		WARN_ON_ONCE(dec < 0);
> +	}
> +}
> +
> +bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max)
> +{
> +	struct ucounts *iter;
> +	if (get_ucounts_value(ucounts, type) > max)
> +		return true;
> +	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> +		max = READ_ONCE(iter->ns->ucount_max[type]);
> +		if (get_ucounts_value(iter, type) > max)
> +			return true;
> +	}
> +	return false;
> +}
> +
>  static __init int user_namespace_sysctl_init(void)
>  {
>  #ifdef CONFIG_SYSCTL
> @@ -256,6 +316,7 @@ static __init int user_namespace_sysctl_init(void)
>  	BUG_ON(!setup_userns_sysctls(&init_user_ns));
>  #endif
>  	hlist_add_ucounts(&init_ucounts);
> +	inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
>  	return 0;
>  }
>  subsys_initcall(user_namespace_sysctl_init);
> diff --git a/kernel/user.c b/kernel/user.c
> index a2478cddf536..7f5ff498207a 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -98,7 +98,6 @@ static DEFINE_SPINLOCK(uidhash_lock);
>  /* root_user.__count is 1, for init task cred */
>  struct user_struct root_user = {
>  	.__count	= REFCOUNT_INIT(1),
> -	.processes	= ATOMIC_INIT(1),
>  	.sigpending	= ATOMIC_INIT(0),
>  	.locked_shm     = 0,
>  	.uid		= GLOBAL_ROOT_UID,
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 516db53166ab..2434b13b02e5 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -118,9 +118,10 @@ int create_user_ns(struct cred *new)
>  	ns->owner = owner;
>  	ns->group = group;
>  	INIT_WORK(&ns->work, free_user_ns);
> -	for (i = 0; i < UCOUNT_COUNTS; i++) {
> +	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++) {
>  		ns->ucount_max[i] = INT_MAX;
>  	}
> +	ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC);

This should have a special case that translates RLIMIT_INFINITY
to LONG_MAX.

>  	ns->ucounts = ucounts;
>  
>  	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */


^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING on top of ucounts
  2021-03-23 20:59 ` [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING " Alexey Gladkov
@ 2021-04-05 16:58   ` Eric W. Biederman
  0 siblings, 0 replies; 15+ messages in thread
From: Eric W. Biederman @ 2021-04-05 16:58 UTC (permalink / raw)
  To: Alexey Gladkov
  Cc: LKML, Kernel Hardening, Linux Containers, linux-mm,
	Alexey Gladkov, Andrew Morton, Christian Brauner, Jann Horn,
	Jens Axboe, Kees Cook, Linus Torvalds, Oleg Nesterov


A small bug below.

Eric


> diff --git a/kernel/signal.c b/kernel/signal.c
> index f2a1b898da29..1b537d9de447 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -413,49 +413,44 @@ void task_join_group_stop(struct task_struct *task)
>  static struct sigqueue *
>  __sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimit)
>  {
> -	struct sigqueue *q = NULL;
> -	struct user_struct *user;
> -	int sigpending;
> +	struct sigqueue *q = kmem_cache_alloc(sigqueue_cachep, flags);
>  
> -	/*
> -	 * Protect access to @t credentials. This can go away when all
> -	 * callers hold rcu read lock.
> -	 *
> -	 * NOTE! A pending signal will hold on to the user refcount,
> -	 * and we get/put the refcount only when the sigpending count
> -	 * changes from/to zero.
> -	 */
> -	rcu_read_lock();
> -	user = __task_cred(t)->user;
> -	sigpending = atomic_inc_return(&user->sigpending);
> -	if (sigpending == 1)
> -		get_uid(user);
> -	rcu_read_unlock();
> +	if (likely(q != NULL)) {
> +		bool overlimit;
>  
> -	if (override_rlimit || likely(sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) {
> -		q = kmem_cache_alloc(sigqueue_cachep, flags);
> -	} else {
> -		print_dropped_signal(sig);
> -	}
> -
> -	if (unlikely(q == NULL)) {
> -		if (atomic_dec_and_test(&user->sigpending))
> -			free_uid(user);
> -	} else {
>  		INIT_LIST_HEAD(&q->list);
>  		q->flags = 0;
> -		q->user = user;
> +
> +		/*
> +		 * Protect access to @t credentials. This can go away when all
> +		 * callers hold rcu read lock.
> +		 */
> +		rcu_read_lock();
> +		q->ucounts = get_ucounts(task_ucounts(t));
> +		if (q->ucounts) {
> +			overlimit = inc_rlimit_ucounts_and_test(q->ucounts, UCOUNT_RLIMIT_SIGPENDING,
> +					1, task_rlimit(t, RLIMIT_SIGPENDING));
> +
> +			if (override_rlimit || likely(!overlimit)) {
> +				rcu_read_unlock();
> +				return q;
> +			}
> +		}
> +		rcu_read_unlock();

I believe you need to call __sigqueue_free here.

>  	}
>  
> -	return q;
> +	print_dropped_signal(sig);
> +	return NULL;
>  }
>  
>  static void __sigqueue_free(struct sigqueue *q)
>  {
>  	if (q->flags & SIGQUEUE_PREALLOC)
>  		return;
> -	if (atomic_dec_and_test(&q->user->sigpending))
> -		free_uid(q->user);
> +	if (q->ucounts) {
> +		dec_rlimit_ucounts(q->ucounts, UCOUNT_RLIMIT_SIGPENDING, 1);
> +		put_ucounts(q->ucounts);
> +	}
>  	kmem_cache_free(sigqueue_cachep, q);
>  }
>  

Eric


^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v9 3/8] Use atomic_t for ucounts reference counting
  2021-03-23 20:59 ` [PATCH v9 3/8] Use atomic_t for ucounts reference counting Alexey Gladkov
@ 2021-04-05 17:01   ` Eric W. Biederman
  0 siblings, 0 replies; 15+ messages in thread
From: Eric W. Biederman @ 2021-04-05 17:01 UTC (permalink / raw)
  To: Alexey Gladkov
  Cc: LKML, Kernel Hardening, Linux Containers, linux-mm,
	Alexey Gladkov, Andrew Morton, Christian Brauner, Jann Horn,
	Jens Axboe, Kees Cook, Linus Torvalds, Oleg Nesterov

Alexey Gladkov <gladkov.alexey@gmail.com> writes:

> The current implementation of the ucounts reference counter requires the
> use of spin_lock. We're going to use get_ucounts() in more performance
> critical areas like a handling of RLIMIT_SIGPENDING.
>
> Now we need to use spin_lock only if we want to change the hashtable.
>
> v9:
> * Use a negative value to check that the ucounts->count is close to
>   overflow.


Overall this looks good, one small issue below.

Eric

> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 50cc1dfb7d28..7bac19bb3f1e 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -11,7 +11,7 @@
>  struct ucounts init_ucounts = {
>  	.ns    = &init_user_ns,
>  	.uid   = GLOBAL_ROOT_UID,
> -	.count = 1,
> +	.count = ATOMIC_INIT(1),
>  };
>  
>  #define UCOUNTS_HASHTABLE_BITS 10
> @@ -139,6 +139,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts)
>  	spin_unlock_irq(&ucounts_lock);
>  }
>  
> +struct ucounts *get_ucounts(struct ucounts *ucounts)
> +{
> +	if (ucounts && atomic_add_negative(1, &ucounts->count)) {
> +		atomic_dec(&ucounts->count);
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^

To handle the pathological case of all of the other uses calling
put_ucounts after the value goes negative, the above should
be put_ucounts intead of atomic_dec.


> +		ucounts = NULL;
> +	}
> +	return ucounts;
> +}
> +
>  struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
>  {
>  	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
> @@ -155,7 +164,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
>  
>  		new->ns = ns;
>  		new->uid = uid;
> -		new->count = 0;
> +		atomic_set(&new->count, 1);
>  
>  		spin_lock_irq(&ucounts_lock);
>  		ucounts = find_ucounts(ns, uid, hashent);
> @@ -163,33 +172,12 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
>  			kfree(new);
>  		} else {
>  			hlist_add_head(&new->node, hashent);
> -			ucounts = new;
> +			spin_unlock_irq(&ucounts_lock);
> +			return new;
>  		}
>  	}
> -	if (ucounts->count == INT_MAX)
> -		ucounts = NULL;
> -	else
> -		ucounts->count += 1;
>  	spin_unlock_irq(&ucounts_lock);
> -	return ucounts;
> -}
> -
> -struct ucounts *get_ucounts(struct ucounts *ucounts)
> -{
> -	unsigned long flags;
> -
> -	if (!ucounts)
> -		return NULL;
> -
> -	spin_lock_irqsave(&ucounts_lock, flags);
> -	if (ucounts->count == INT_MAX) {
> -		WARN_ONCE(1, "ucounts: counter has reached its maximum value");
> -		ucounts = NULL;
> -	} else {
> -		ucounts->count += 1;
> -	}
> -	spin_unlock_irqrestore(&ucounts_lock, flags);
> -
> +	ucounts = get_ucounts(ucounts);
>  	return ucounts;
>  }
>  
> @@ -197,15 +185,12 @@ void put_ucounts(struct ucounts *ucounts)
>  {
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&ucounts_lock, flags);
> -	ucounts->count -= 1;
> -	if (!ucounts->count)
> +	if (atomic_dec_and_test(&ucounts->count)) {
> +		spin_lock_irqsave(&ucounts_lock, flags);
>  		hlist_del_init(&ucounts->node);
> -	else
> -		ucounts = NULL;
> -	spin_unlock_irqrestore(&ucounts_lock, flags);
> -
> -	kfree(ucounts);
> +		spin_unlock_irqrestore(&ucounts_lock, flags);
> +		kfree(ucounts);
> +	}
>  }
>  
>  static inline bool atomic_long_inc_below(atomic_long_t *v, int u)


^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v9 0/8] Count rlimits in each user namespace
  2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
                   ` (7 preceding siblings ...)
  2021-03-23 20:59 ` [PATCH v9 8/8] kselftests: Add test to check for rlimit changes in different user namespaces Alexey Gladkov
@ 2021-04-05 17:03 ` Eric W. Biederman
  8 siblings, 0 replies; 15+ messages in thread
From: Eric W. Biederman @ 2021-04-05 17:03 UTC (permalink / raw)
  To: Alexey Gladkov
  Cc: LKML, Kernel Hardening, Linux Containers, linux-mm,
	Alexey Gladkov, Andrew Morton, Christian Brauner, Jann Horn,
	Jens Axboe, Kees Cook, Linus Torvalds, Oleg Nesterov

Alexey Gladkov <gladkov.alexey@gmail.com> writes:

> Preface
> -------
> These patches are for binding the rlimit counters to a user in user namespace.
> This patch set can be applied on top of:
>
> git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v5.12-rc4
>
> Problem
> -------
> The RLIMIT_NPROC, RLIMIT_MEMLOCK, RLIMIT_SIGPENDING, RLIMIT_MSGQUEUE rlimits
> implementation places the counters in user_struct [1]. These limits are global
> between processes and persists for the lifetime of the process, even if
> processes are in different user namespaces.
>
> To illustrate the impact of rlimits, let's say there is a program that does not
> fork. Some service-A wants to run this program as user X in multiple containers.
> Since the program never fork the service wants to set RLIMIT_NPROC=1.
>
> service-A
>  \- program (uid=1000, container1, rlimit_nproc=1)
>  \- program (uid=1000, container2, rlimit_nproc=1)
>
> The service-A sets RLIMIT_NPROC=1 and runs the program in container1. When the
> service-A tries to run a program with RLIMIT_NPROC=1 in container2 it fails
> since user X already has one running process.
>
> The problem is not that the limit from container1 affects container2. The
> problem is that limit is verified against the global counter that reflects
> the number of processes in all containers.
>
> This problem can be worked around by using different users for each container
> but in this case we face a different problem of uid mapping when transferring
> files from one container to another.
>
> Eric W. Biederman mentioned this issue [2][3].
>
> Introduced changes
> ------------------
> To address the problem, we bind rlimit counters to user namespace. Each counter
> reflects the number of processes in a given uid in a given user namespace. The
> result is a tree of rlimit counters with the biggest value at the root (aka
> init_user_ns). The limit is considered exceeded if it's exceeded up in the tree.
>
> [1]: https://lore.kernel.org/containers/87imd2incs.fsf@x220.int.ebiederm.org/
> [2]: https://lists.linuxfoundation.org/pipermail/containers/2020-August/042096.html
> [3]: https://lists.linuxfoundation.org/pipermail/containers/2020-October/042524.html
>
> Changelog
> ---------
> v9:
> * Used a negative value to check that the ucounts->count is close to overflow.
> * Rebased onto v5.12-rc4.
>
> v8:
> * Used atomic_t for ucounts reference counting. Also added counter overflow
>   check (thanks to Linus Torvalds for the idea).
> * Fixed other issues found by lkp-tests project in the patch that Reimplements
>   RLIMIT_MEMLOCK on top of ucounts.
>
> v7:
> * Fixed issues found by lkp-tests project in the patch that Reimplements
>   RLIMIT_MEMLOCK on top of ucounts.
>
> v6:
> * Fixed issues found by lkp-tests project.
> * Rebased onto v5.11.
>
> v5:
> * Split the first commit into two commits: change ucounts.count type to atomic_long_t
>   and add ucounts to cred. These commits were merged by mistake during the rebase.
> * The __get_ucounts() renamed to alloc_ucounts().
> * The cred.ucounts update has been moved from commit_creds() as it did not allow
>   to handle errors.
> * Added error handling of set_cred_ucounts().
>
> v4:
> * Reverted the type change of ucounts.count to refcount_t.
> * Fixed typo in the kernel/cred.c
>
> v3:
> * Added get_ucounts() function to increase the reference count. The existing
>   get_counts() function renamed to __get_ucounts().
> * The type of ucounts.count changed from atomic_t to refcount_t.
> * Dropped 'const' from set_cred_ucounts() arguments.
> * Fixed a bug with freeing the cred structure after calling cred_alloc_blank().
> * Commit messages have been updated.
> * Added selftest.
>
> v2:
> * RLIMIT_MEMLOCK, RLIMIT_SIGPENDING and RLIMIT_MSGQUEUE are migrated to ucounts.
> * Added ucounts for pair uid and user namespace into cred.
> * Added the ability to increase ucount by more than 1.
>
> v1:
> * After discussion with Eric W. Biederman, I increased the size of ucounts to
>   atomic_long_t.
> * Added ucount_max to avoid the fork bomb.
>
> --
>
> Alexey Gladkov (8):
>   Increase size of ucounts to atomic_long_t
>   Add a reference to ucounts for each cred
>   Use atomic_t for ucounts reference counting
>   Reimplement RLIMIT_NPROC on top of ucounts
>   Reimplement RLIMIT_MSGQUEUE on top of ucounts
>   Reimplement RLIMIT_SIGPENDING on top of ucounts
>   Reimplement RLIMIT_MEMLOCK on top of ucounts
>   kselftests: Add test to check for rlimit changes in different user namespaces
>

Overall this looks good, and it is a very good sign that the automatic
testing bots have not found anything.  I found a few little nits.
But thing are looking very good.

Eric



^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts
  2021-04-05 16:56   ` Eric W. Biederman
@ 2021-04-06 15:44     ` Alexey Gladkov
  2021-04-07 16:56       ` Eric W. Biederman
  0 siblings, 1 reply; 15+ messages in thread
From: Alexey Gladkov @ 2021-04-06 15:44 UTC (permalink / raw)
  To: Eric W. Biederman
  Cc: LKML, Kernel Hardening, Linux Containers, linux-mm,
	Andrew Morton, Christian Brauner, Jann Horn, Jens Axboe,
	Kees Cook, Linus Torvalds, Oleg Nesterov

On Mon, Apr 05, 2021 at 11:56:35AM -0500, Eric W. Biederman wrote:
>
> Also when setting ns->ucount_max[] in create_user_ns because one value
> is signed and the other is unsigned.  Care should be taken so that
> rlimit_infinity is translated into the largest positive value the
> type can hold.

You mean like that ?

ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC) <= LONG_MAX ?
	rlimit(RLIMIT_NPROC) : LONG_MAX;
ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE) <= LONG_MAX ?
	rlimit(RLIMIT_MSGQUEUE) : LONG_MAX;
ns->ucount_max[UCOUNT_RLIMIT_SIGPENDING] = rlimit(RLIMIT_SIGPENDING) <= LONG_MAX ?
	rlimit(RLIMIT_SIGPENDING) : LONG_MAX;
ns->ucount_max[UCOUNT_RLIMIT_MEMLOCK] = rlimit(RLIMIT_MEMLOCK) <= LONG_MAX ?
	rlimit(RLIMIT_MEMLOCK) : LONG_MAX;

-- 
Rgrds, legion



^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts
  2021-04-06 15:44     ` Alexey Gladkov
@ 2021-04-07 16:56       ` Eric W. Biederman
  0 siblings, 0 replies; 15+ messages in thread
From: Eric W. Biederman @ 2021-04-07 16:56 UTC (permalink / raw)
  To: Alexey Gladkov
  Cc: LKML, Kernel Hardening, Linux Containers, linux-mm,
	Andrew Morton, Christian Brauner, Jann Horn, Jens Axboe,
	Kees Cook, Linus Torvalds, Oleg Nesterov

Alexey Gladkov <gladkov.alexey@gmail.com> writes:

> On Mon, Apr 05, 2021 at 11:56:35AM -0500, Eric W. Biederman wrote:
>>
>> Also when setting ns->ucount_max[] in create_user_ns because one value
>> is signed and the other is unsigned.  Care should be taken so that
>> rlimit_infinity is translated into the largest positive value the
>> type can hold.
>
> You mean like that ?
>
> ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC) <= LONG_MAX ?
> 	rlimit(RLIMIT_NPROC) : LONG_MAX;
> ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE) <= LONG_MAX ?
> 	rlimit(RLIMIT_MSGQUEUE) : LONG_MAX;
> ns->ucount_max[UCOUNT_RLIMIT_SIGPENDING] = rlimit(RLIMIT_SIGPENDING) <= LONG_MAX ?
> 	rlimit(RLIMIT_SIGPENDING) : LONG_MAX;
> ns->ucount_max[UCOUNT_RLIMIT_MEMLOCK] = rlimit(RLIMIT_MEMLOCK) <= LONG_MAX ?
> 	rlimit(RLIMIT_MEMLOCK) : LONG_MAX;

Yes.

I only got as far as:
if (rlimit(RLIMI_NNN) == RLIM_INFINITY) {
	ns->ucount_max[UCOUNT_LIMIT_NNN] = LONG_MAX;
} else {
	ns->ucount_max[UCOUNT_LMIT_NNN] = rlmit(RLIMIT_NNN);
}
But forcing everything about LONG_MAX to LONG_MAX actually looks better
in practice.  Especially as that is effectively RLIMIT_INFINITY anyway.

Eric


^ permalink raw reply	[flat|nested] 15+ messages in thread

end of thread, other threads:[~2021-04-07 16:56 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-03-23 20:59 [PATCH v9 0/8] Count rlimits in each user namespace Alexey Gladkov
2021-03-23 20:59 ` [PATCH v9 1/8] Increase size of ucounts to atomic_long_t Alexey Gladkov
2021-03-23 20:59 ` [PATCH v9 2/8] Add a reference to ucounts for each cred Alexey Gladkov
2021-03-23 20:59 ` [PATCH v9 3/8] Use atomic_t for ucounts reference counting Alexey Gladkov
2021-04-05 17:01   ` Eric W. Biederman
2021-03-23 20:59 ` [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts Alexey Gladkov
2021-04-05 16:56   ` Eric W. Biederman
2021-04-06 15:44     ` Alexey Gladkov
2021-04-07 16:56       ` Eric W. Biederman
2021-03-23 20:59 ` [PATCH v9 5/8] Reimplement RLIMIT_MSGQUEUE " Alexey Gladkov
2021-03-23 20:59 ` [PATCH v9 6/8] Reimplement RLIMIT_SIGPENDING " Alexey Gladkov
2021-04-05 16:58   ` Eric W. Biederman
2021-03-23 20:59 ` [PATCH v9 7/8] Reimplement RLIMIT_MEMLOCK " Alexey Gladkov
2021-03-23 20:59 ` [PATCH v9 8/8] kselftests: Add test to check for rlimit changes in different user namespaces Alexey Gladkov
2021-04-05 17:03 ` [PATCH v9 0/8] Count rlimits in each user namespace Eric W. Biederman

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