From: Christian Brauner <christian.brauner@ubuntu.com>
To: Marco Elver <elver@google.com>
Cc: Andrea Parri <parri.andrea@gmail.com>,
bsingharora@gmail.com, Dmitry Vyukov <dvyukov@google.com>,
LKML <linux-kernel@vger.kernel.org>,
stable@vger.kernel.org,
syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com,
syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] taskstats: fix data-race
Date: Wed, 9 Oct 2019 13:53:25 +0200 [thread overview]
Message-ID: <20191009115324.iczitezqqkotpocj@wittgenstein> (raw)
In-Reply-To: <CANpmjNMgVub_pSGVfjBOtXg1ufdBvpXC_XUTnvNyQeF17JSCSw@mail.gmail.com>
On Wed, Oct 09, 2019 at 01:48:27PM +0200, Marco Elver wrote:
> On Wed, 9 Oct 2019 at 13:31, Christian Brauner
> <christian.brauner@ubuntu.com> wrote:
> >
> > When assiging and testing taskstats in taskstats_exit() there's a race
> > when writing and reading sig->stats when a thread-group with more than
> > one thread exits:
> >
> > cpu0:
> > thread catches fatal signal and whole thread-group gets taken down
> > do_exit()
> > do_group_exit()
> > taskstats_exit()
> > taskstats_tgid_alloc()
> > The tasks reads sig->stats without holding sighand lock seeing garbage.
> >
> > cpu1:
> > task calls exit_group()
> > do_exit()
> > do_group_exit()
> > taskstats_exit()
> > taskstats_tgid_alloc()
> > The task takes sighand lock and assigns new stats to sig->stats.
> >
> > Fix this by using smp_load_acquire() and smp_store_release().
> >
> > Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
> > Fixes: 34ec12349c8a ("taskstats: cleanup ->signal->stats allocation")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
> > Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> > ---
> > /* v1 */
> > Link: https://lore.kernel.org/r/20191005112806.13960-1-christian.brauner@ubuntu.com
> >
> > /* v2 */
> > Link: https://lore.kernel.org/r/20191006235216.7483-1-christian.brauner@ubuntu.com
> > - Dmitry Vyukov <dvyukov@google.com>, Marco Elver <elver@google.com>:
> > - fix the original double-checked locking using memory barriers
> >
> > /* v3 */
> > Link: https://lore.kernel.org/r/20191007110117.1096-1-christian.brauner@ubuntu.com/
> > - Andrea Parri <parri.andrea@gmail.com>:
> > - document memory barriers to make checkpatch happy
> >
> > /* v4 */
> > - Andrea Parri <parri.andrea@gmail.com>:
> > - use smp_load_acquire(), not READ_ONCE()
> > - update commit message
>
> Acked-by: Marco Elver <elver@google.com>
>
> Note that this now looks almost like what I suggested, except the
Right, I think we all just needed to get our heads clear about what
exactly is happening here. This codepath is not a very prominent one. :)
> return at the end of the function is accessing sig->stats again. In
> this case, it seems it's fine assuming sig->stats cannot be written
> elsewhere. Just wanted to point it out to make sure it's considered.
Yes, I considered that but thanks for mentioning it.
Note that this patch has a bug. It should be
smp_load_acquire(&sig->stats) and not smp_load_acquire(sig->stats).
I accidently didn't automatically recompile the patchset after the last
change I made. Andrea thankfully caught this.
Thanks!
Christian
prev parent reply other threads:[~2019-10-09 11:53 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20191007104039.GA16085@andrea.guest.corp.microsoft.com>
2019-10-07 11:01 ` [PATCH v2] taskstats: fix data-race Christian Brauner
2019-10-07 13:18 ` Andrea Parri
2019-10-07 13:28 ` Christian Brauner
2019-10-07 13:50 ` Dmitry Vyukov
2019-10-07 13:55 ` Christian Brauner
2019-10-07 14:08 ` Dmitry Vyukov
2019-10-07 14:10 ` Christian Brauner
2019-10-07 14:14 ` Andrea Parri
2019-10-07 14:18 ` Dmitry Vyukov
2019-10-08 14:20 ` Andrea Parri
2019-10-08 14:24 ` Christian Brauner
2019-10-08 15:26 ` Andrea Parri
2019-10-08 15:35 ` Christian Brauner
2019-10-08 15:44 ` Andrea Parri
2019-10-09 11:31 ` [PATCH] " Christian Brauner
2019-10-09 11:40 ` Christian Brauner
2019-10-09 11:48 ` [PATCH v5] " Christian Brauner
2019-10-09 12:08 ` Andrea Parri
2019-10-09 13:26 ` Christian Brauner
2019-10-21 11:33 ` [PATCH v6] " Christian Brauner
2019-10-21 12:19 ` Rasmus Villemoes
2019-10-21 13:04 ` Christian Brauner
2019-11-29 17:56 ` Will Deacon
2019-11-30 15:08 ` Christian Brauner
2019-10-23 12:16 ` Andrea Parri
2019-10-23 12:39 ` Dmitry Vyukov
2019-10-23 13:11 ` Christian Brauner
2019-10-23 13:20 ` Dmitry Vyukov
2019-10-24 11:31 ` Andrea Parri
2019-10-24 11:51 ` Dmitry Vyukov
2019-10-24 13:05 ` Andrea Parri
2019-10-24 13:13 ` Dmitry Vyukov
2019-10-24 13:21 ` Christian Brauner
2019-10-24 13:34 ` Dmitry Vyukov
2019-10-24 13:43 ` Andrea Parri
2019-10-24 13:58 ` Dmitry Vyukov
2019-10-24 14:40 ` Andrea Parri
2019-10-24 14:49 ` Dmitry Vyukov
2019-11-29 17:57 ` Will Deacon
2019-10-09 11:48 ` [PATCH] " Marco Elver
2019-10-09 11:53 ` Christian Brauner [this message]
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