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@xxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx
>Closes: https://syzkaller.appspot.com/bug?extid=39b8fea0641107a1ccee
>Assisted-by: Claude:claude-opus-5-5

Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>

Tested-by: Bradley Morgan <brads@xxxxxxxxxxxxxx> # Power10


>Signed-off-by: Babanpreet Singh <bbnpreetsingh@xxxxxxxxx>
>---
>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@xxxxxxxxx/
>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