From: legion@kernel.org
To: LKML <linux-kernel@vger.kernel.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Linux Containers <containers@lists.linux-foundation.org>,
linux-mm@kvack.org
Cc: Jens Axboe <axboe@kernel.dk>, Kees Cook <keescook@chromium.org>,
Jann Horn <jannh@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alexey Gladkov <legion@kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH v11 3/9] Use atomic_t for ucounts reference counting
Date: Thu, 22 Apr 2021 14:27:10 +0200 [thread overview]
Message-ID: <94d1dbecab060a6b116b0a2d1accd8ca1bbb4f5f.1619094428.git.legion@kernel.org> (raw)
In-Reply-To: <cover.1619094428.git.legion@kernel.org>
From: Alexey Gladkov <legion@kernel.org>
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.
v10:
* Always try to put ucounts in case we cannot increase ucounts->count.
This will allow to cover the case when all consumers will return
ucounts at once.
v9:
* Use a negative value to check that the ucounts->count is close to
overflow.
Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
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..365865f368ec 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)) {
+ put_ucounts(ucounts);
+ 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
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next prev parent reply other threads:[~2021-04-22 12:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 12:27 [PATCH v11 0/9] Count rlimits in each user namespace legion
2021-04-22 12:27 ` [PATCH v11 1/9] Increase size of ucounts to atomic_long_t legion
2021-04-22 12:27 ` [PATCH v11 2/9] Add a reference to ucounts for each cred legion
2021-04-22 12:27 ` legion [this message]
2021-04-22 12:27 ` [PATCH v11 4/9] Reimplement RLIMIT_NPROC on top of ucounts legion
2021-04-29 14:04 ` Dan Carpenter
2021-04-30 18:09 ` [PATCH] ucounts: Silence warning in dec_rlimit_ucounts Eric W. Biederman
2021-04-22 12:27 ` [PATCH v11 5/9] Reimplement RLIMIT_MSGQUEUE on top of ucounts legion
2021-04-22 12:27 ` [PATCH v11 6/9] Reimplement RLIMIT_SIGPENDING " legion
2021-04-22 12:27 ` [PATCH v11 7/9] Reimplement RLIMIT_MEMLOCK " legion
2021-04-22 12:27 ` [PATCH v11 8/9] kselftests: Add test to check for rlimit changes in different user namespaces legion
2021-04-22 12:27 ` [PATCH v11 9/9] ucounts: Set ucount_max to the largest positive value the type can hold legion
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