Messages in this thread | | | From | Eiichi Tsukata <> | Subject | Re: [PATCH v2 4/5] audit: check if audit_queue is full after prepare_to_wait_exclusive() | Date | Mon, 22 May 2023 04:28:14 +0000 |
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> On May 20, 2023, at 5:54, Paul Moore <paul@paul-moore.com> wrote: > > On May 11, 2023 Eiichi Tsukata <eiichi.tsukata@nutanix.com> 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@nutanix.com> >> --- >> 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. >
Please refer to the implementation of ___wait_event(). It checks the condition *after* prepare_to_wait_event().
Another similar example in the kernel code is unix_wait_for_peer(). It checks unix_recvq_full() after prepare_to_wait_exclusive().
I’m assuming this is a logical bug needs to be fixed.
Eiichi
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