Re: [PATCH v2 4/5] audit: check if audit_queue is full after prepare_to_wait_exclusive()

[Paul Moore]

On May 11, 2023 Eiichi Tsukata <eiichi.tsukata@xxxxxxxxxxx> wrote:
> 
> Commit 7ffb8e317bae ("audit: we don't need to
> __set_current_state(TASK_RUNNING)") accidentally moved queue full check
> before add_wait_queue_exclusive() which introduced the following race:
> 
>     CPU1                           CPU2
>   ========                       ========
>   (in audit_log_start())         (in kauditd_thread())
> 
>   @audit_queue is full
>                                  wake_up(&audit_backlog_wait)
>                                  wait_event_freezable()
>   add_wait_queue_exclusive()
>   ...
>   schedule_timeout()
> 
> Once this happens, both audit_log_start() and kauditd_thread() can cause
> deadlock for up to backlog_wait_time waiting for each other. To prevent
> the race, this patch adds @audit_queue full check after
> prepare_to_wait_exclusive() and call schedule_timeout() only if the
> queue is full.
> 
> Fixes: 7ffb8e317bae ("audit: we don't need to __set_current_state(TASK_RUNNING)")
> Signed-off-by: Eiichi Tsukata <eiichi.tsukata@xxxxxxxxxxx>
> ---
>  kernel/audit.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

I discussed my concerns with this patch in the last patchset, and I
believe they still apply here.

--
paul-moore.com