linux-kernel - Re: [PATCH] taskstats: fix data-race

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Date:   Mon, 7 Oct 2019 11:29:28 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     bsingharora@...il.com, Marco Elver <elver@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzbot <syzbot+c5d03165a1bd1dead0c1@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH] taskstats: fix data-race

On Mon, Oct 07, 2019 at 09:31:16AM +0200, Dmitry Vyukov wrote:
> On Mon, Oct 7, 2019 at 1:52 AM Christian Brauner
> <christian.brauner@...ntu.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 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 READ_ONCE() and smp_store_release().
> >
> > Reported-by: syzbot+c5d03165a1bd1dead0c1@...kaller.appspotmail.com
> > Cc: Dmitry Vyukov <dvyukov@...gle.com>
> > Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> > ---
> > /* v1 */
> > Link: https://lore.kernel.org/r/20191005112806.13960-1-christian.brauner@ubuntu.com
> >
> > /* v2 */
> > - Dmitry Vyukov <dvyukov@...gle.com>, Marco Elver <elver@...gle.com>:
> >   - fix the original double-checked locking using memory barriers
> > ---
> >  kernel/taskstats.c | 19 ++++++++++---------
> >  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>

Applied to:
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=fixes

Should show up in linux-next tomorrow.
Targeting v5.4-rc3.
Cced stable.

Christian