Kernel-hardening Archive on lore.kernel.org
 help / color / Atom feed
From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
	mathieu.desnoyers@efficios.com, willy@infradead.org,
	peterz@infradead.org, will.deacon@arm.com,
	paulmck@linux.vnet.ibm.com, elena.reshetova@intel.com,
	keescook@chromium.org,
	Andrea Parri <andrea.parri@amarulasolutions.com>,
	kernel-team@android.com, kernel-hardening@lists.openwall.com,
	jannh@google.com, Andrew Morton <akpm@linux-foundation.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	KJ Tsanaktsidis <ktsanaktsidis@zendesk.com>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH v3] Convert struct pid count to refcount_t
Date: Mon,  1 Jul 2019 14:38:26 -0400
Message-ID: <20190701183826.191936-1-joel@joelfernandes.org> (raw)

struct pid's count is an atomic_t field used as a refcount. Use
refcount_t for it which is basically atomic_t but does additional
checking to prevent use-after-free bugs.

For memory ordering, the only change is with the following:
 -	if ((atomic_read(&pid->count) == 1) ||
 -	     atomic_dec_and_test(&pid->count)) {
 +	if (refcount_dec_and_test(&pid->count)) {
 		kmem_cache_free(ns->pid_cachep, pid);

Here the change is from:
Fully ordered --> RELEASE + ACQUIRE (as per refcount-vs-atomic.rst)
This ACQUIRE should take care of making sure the free happens after the
refcount_dec_and_test().

The above hunk also removes atomic_read() since it is not needed for the
code to work and it is unclear how beneficial it is. The removal lets
refcount_dec_and_test() check for cases where get_pid() happened before
the object was freed.

Cc: mathieu.desnoyers@efficios.com
Cc: willy@infradead.org
Cc: peterz@infradead.org
Cc: will.deacon@arm.com
Cc: paulmck@linux.vnet.ibm.com
Cc: elena.reshetova@intel.com
Cc: keescook@chromium.org
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: kernel-team@android.com
Cc: kernel-hardening@lists.openwall.com
Cc: jannh@google.com
Reviewed-by: keescook@chromium.org
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

---
v1->v2 is to get rid of the atomic_read().
v2->v3 replaces ATOMIC_INIT with REFCOUNT_INIT

 include/linux/pid.h | 5 +++--
 kernel/pid.c        | 9 ++++-----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 14a9a39da9c7..8cb86d377ff5 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -3,6 +3,7 @@
 #define _LINUX_PID_H
 
 #include <linux/rculist.h>
+#include <linux/refcount.h>
 
 enum pid_type
 {
@@ -56,7 +57,7 @@ struct upid {
 
 struct pid
 {
-	atomic_t count;
+	refcount_t count;
 	unsigned int level;
 	/* lists of tasks that use this pid */
 	struct hlist_head tasks[PIDTYPE_MAX];
@@ -69,7 +70,7 @@ extern struct pid init_struct_pid;
 static inline struct pid *get_pid(struct pid *pid)
 {
 	if (pid)
-		atomic_inc(&pid->count);
+		refcount_inc(&pid->count);
 	return pid;
 }
 
diff --git a/kernel/pid.c b/kernel/pid.c
index 20881598bdfa..86b526bd59e1 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -37,12 +37,12 @@
 #include <linux/init_task.h>
 #include <linux/syscalls.h>
 #include <linux/proc_ns.h>
-#include <linux/proc_fs.h>
+#include <linux/refcount.h>
 #include <linux/sched/task.h>
 #include <linux/idr.h>
 
 struct pid init_struct_pid = {
-	.count 		= ATOMIC_INIT(1),
+	.count		= REFCOUNT_INIT(1),
 	.tasks		= {
 		{ .first = NULL },
 		{ .first = NULL },
@@ -106,8 +106,7 @@ void put_pid(struct pid *pid)
 		return;
 
 	ns = pid->numbers[pid->level].ns;
-	if ((atomic_read(&pid->count) == 1) ||
-	     atomic_dec_and_test(&pid->count)) {
+	if (refcount_dec_and_test(&pid->count)) {
 		kmem_cache_free(ns->pid_cachep, pid);
 		put_pid_ns(ns);
 	}
@@ -210,7 +209,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 	}
 
 	get_pid_ns(ns);
-	atomic_set(&pid->count, 1);
+	refcount_set(&pid->count, 1);
 	for (type = 0; type < PIDTYPE_MAX; ++type)
 		INIT_HLIST_HEAD(&pid->tasks[type]);
 
-- 
2.22.0.410.gd8fdbe21b5-goog

                 reply index

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190701183826.191936-1-joel@joelfernandes.org \
    --to=joel@joelfernandes.org \
    --cc=akpm@linux-foundation.org \
    --cc=andrea.parri@amarulasolutions.com \
    --cc=ebiederm@xmission.com \
    --cc=elena.reshetova@intel.com \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=kernel-team@android.com \
    --cc=ktsanaktsidis@zendesk.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mathieu.desnoyers@efficios.com \
    --cc=mhocko@suse.com \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peterz@infradead.org \
    --cc=will.deacon@arm.com \
    --cc=willy@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Kernel-hardening Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kernel-hardening/0 kernel-hardening/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kernel-hardening kernel-hardening/ https://lore.kernel.org/kernel-hardening \
		kernel-hardening@lists.openwall.com
	public-inbox-index kernel-hardening

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/com.openwall.lists.kernel-hardening


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git