linux-kernel - Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled

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Message-ID: <Yd7nlpb5C1asdT9p@cmpxchg.org>
Date:   Wed, 12 Jan 2022 09:37:10 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     torvalds@...ux-foundation.org, ebiggers@...nel.org, tj@...nel.org,
        lizefan.x@...edance.com, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, corbet@....net,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, stable@...r.kernel.org,
        kernel-team@...roid.com,
        syzbot+cdb5dd11c97cc532efad@...kaller.appspotmail.com
Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed
 while being polled

On Mon, Jan 10, 2022 at 11:12:12PM -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@...r.kernel.org
> Reported-by: syzbot+cdb5dd11c97cc532efad@...kaller.appspotmail.com
> Analyzed-by: Eric Biggers <ebiggers@...nel.org>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

That looks good to me, thanks Suren.

Acked-by: Johannes Weiner <hannes@...xchg.org>

Peter, would you mind picking this up and routing this to Linus
through the sched tree, please?