Re: [PATCH v3 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled

[Peter Zijlstra]

On Tue, Jan 11, 2022 at 03:23:09PM -0800, Suren Baghdasaryan wrote:
> With write operation on psi files replacing old trigger with a new one,
> the lifetime of its waitqueue is totally arbitrary. Overwriting an
> existing trigger causes its waitqueue to be freed and pending poll()
> will stumble on trigger->event_wait which was destroyed.
> Fix this by disallowing to redefine an existing psi trigger. If a write
> operation is used on a file descriptor with an already existing psi
> trigger, the operation will fail with EBUSY error.
> Also bypass a check for psi_disabled in the psi_trigger_destroy as the
> flag can be flipped after the trigger is created, leading to a memory
> leak.
> 
> Fixes: 0e94682b73bf ("psi: introduce psi monitor")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: syzbot+cdb5dd11c97cc532efad@xxxxxxxxxxxxxxxxxxxxxxxxx
> Analyzed-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---

Thanks, I'll go stick this in sched/urgent unless Linus picks it up
himself.