[PATCH v2] audit: annotate the lockless read of the audit control lock owner

[PATCH v2] audit: annotate the lockless read of the audit control lock owner

[Babanpreet Singh]

audit_ctl_owner_current() reads the lock owner without taking the lock
and KCSAN complains about it. Only the current task can store itself as
owner, so the check can't give a wrong answer. Mark the accesses with
READ_ONCE() and WRITE_ONCE().

Reported-by: syzbot+39b8fea0641107a1ccee@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=39b8fea0641107a1ccee
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Babanpreet Singh <bbnpreetsingh@gmail.com>
---
v2: drop the comment in audit_ctl_owner_current(). The KCSAN build of
audit.o disassembles the same as v1.
v1: https://lore.kernel.org/all/20261002011712.7-1-bbnpreetsingh@gmail.com/
Compile tested only (gcc W=1 and the KCSAN instrumentation diff); I
could not reproduce the race in QEMU.

 kernel/audit.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index 631d6d4a23cfd..d0c2036bde759 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -247,7 +247,7 @@ int auditd_test_task(struct task_struct *task)
 void audit_ctl_lock(void)
 {
 	mutex_lock(&audit_cmd_mutex.lock);
-	audit_cmd_mutex.owner = current;
+	WRITE_ONCE(audit_cmd_mutex.owner, current);
 }
 
 /**
@@ -255,7 +255,7 @@ void audit_ctl_lock(void)
  */
 void audit_ctl_unlock(void)
 {
-	audit_cmd_mutex.owner = NULL;
+	WRITE_ONCE(audit_cmd_mutex.owner, NULL);
 	mutex_unlock(&audit_cmd_mutex.lock);
 }
 
@@ -268,7 +268,7 @@ void audit_ctl_unlock(void)
  */
 static bool audit_ctl_owner_current(void)
 {
-	return (current == audit_cmd_mutex.owner);
+	return (current == READ_ONCE(audit_cmd_mutex.owner));
 }
 
 /**

base-commit: a8bdcf944504980635c2069b4a4cfcf677b09bbb
-- 
2.43.0

Re: [PATCH v2] audit: annotate the lockless read of the audit control lock owner

[Bradley Morgan]

On 8 October 2026 04:44:03 BST, Babanpreet Singh <bbnpreetsingh@gmail.com>
wrote:
>audit_ctl_owner_current() reads the lock owner without taking the lock
>and KCSAN complains about it. Only the current task can store itself as
>owner, so the check can't give a wrong answer. Mark the accesses with
>READ_ONCE() and WRITE_ONCE().
>
>Reported-by: syzbot+39b8fea0641107a1ccee@syzkaller.appspotmail.com
>Closes: https://syzkaller.appspot.com/bug?extid=39b8fea0641107a1ccee
>Assisted-by: Claude:claude-opus-5-5

Reviewed-by: Bradley Morgan <brads@mainlining.org>

Tested-by: Bradley Morgan <brads@mainlining.org> # Power10


>Signed-off-by: Babanpreet Singh <bbnpreetsingh@gmail.com>
>---
>v2: drop the comment in audit_ctl_owner_current(). The KCSAN build of
>audit.o disassembles the same as v1.
>v1: https://lore.kernel.org/all/20261002011712.7-1-bbnpreetsingh@gmail.com/
>Compile tested only (gcc W=1 and the KCSAN instrumentation diff); I
>could not reproduce the race in QEMU.
>
> kernel/audit.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/kernel/audit.c b/kernel/audit.c
>index 631d6d4a23cfd..d0c2036bde759 100644
>--- a/kernel/audit.c
>+++ b/kernel/audit.c
>@@ -247,7 +247,7 @@ int auditd_test_task(struct task_struct *task)
> void audit_ctl_lock(void)
> {
> 	mutex_lock(&audit_cmd_mutex.lock);
>-	audit_cmd_mutex.owner = current;
>+	WRITE_ONCE(audit_cmd_mutex.owner, current);
> }
> 
> /**
>@@ -255,7 +255,7 @@ void audit_ctl_lock(void)
>  */
> void audit_ctl_unlock(void)
> {
>-	audit_cmd_mutex.owner = NULL;
>+	WRITE_ONCE(audit_cmd_mutex.owner, NULL);
> 	mutex_unlock(&audit_cmd_mutex.lock);
> }
> 
>@@ -268,7 +268,7 @@ void audit_ctl_unlock(void)
>  */
> static bool audit_ctl_owner_current(void)
> {
>-	return (current == audit_cmd_mutex.owner);
>+	return (current == READ_ONCE(audit_cmd_mutex.owner));
> }
> 
> /**

Clean!

>
>base-commit: a8bdcf944504980635c2069b4a4cfcf677b09bbb
>

--- Thanks!
"I'm not a very positive person" - Linus torvalds