From: Dmitry Vyukov <dvyukov@google.com>
To: Andrea Parri <parri.andrea@gmail.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
bsingharora@gmail.com, Marco Elver <elver@google.com>,
LKML <linux-kernel@vger.kernel.org>,
syzbot <syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
stable <stable@vger.kernel.org>
Subject: Re: [PATCH v2] taskstats: fix data-race
Date: Mon, 7 Oct 2019 15:50:47 +0200 [thread overview]
Message-ID: <CACT4Y+YG23qbL16MYH3GTK4hOPsM9tDfbLzrTZ7k_ocR2ABa6A@mail.gmail.com> (raw)
In-Reply-To: <20191007131804.GA19242@andrea.guest.corp.microsoft.com>
On Mon, Oct 7, 2019 at 3:18 PM Andrea Parri <parri.andrea@gmail.com> wrote:
>
> On Mon, Oct 07, 2019 at 01:01:17PM +0200, Christian Brauner 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.
>
> You meant "without holding sighand lock" here, right?
>
>
> >
> > 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@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>
> > Link: https://lore.kernel.org/r/20191006235216.7483-1-christian.brauner@ubuntu.com
> > ---
> > /* v1 */
> > Link: https://lore.kernel.org/r/20191005112806.13960-1-christian.brauner@ubuntu.com
> >
> > /* v2 */
> > - Dmitry Vyukov <dvyukov@google.com>, Marco Elver <elver@google.com>:
> > - fix the original double-checked locking using memory barriers
> >
> > /* v3 */
> > - Andrea Parri <parri.andrea@gmail.com>:
> > - document memory barriers to make checkpatch happy
> > ---
> > kernel/taskstats.c | 21 ++++++++++++---------
> > 1 file changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> > index 13a0f2e6ebc2..978d7931fb65 100644
> > --- a/kernel/taskstats.c
> > +++ b/kernel/taskstats.c
> > @@ -554,24 +554,27 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
> > static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
> > {
> > struct signal_struct *sig = tsk->signal;
> > - struct taskstats *stats;
> > + struct taskstats *stats_new, *stats;
> >
> > - if (sig->stats || thread_group_empty(tsk))
> > - goto ret;
> > + /* Pairs with smp_store_release() below. */
> > + stats = READ_ONCE(sig->stats);
>
> This pairing suggests that the READ_ONCE() is heading an address
> dependency, but I fail to identify it: what is the target memory
> access of such a (putative) dependency?
I would assume callers of this function access *stats. So the
dependency is between loading stats and accessing *stats.
> > + if (stats || thread_group_empty(tsk))
> > + return stats;
> >
> > /* No problem if kmem_cache_zalloc() fails */
> > - stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
> > + stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
> >
> > spin_lock_irq(&tsk->sighand->siglock);
> > if (!sig->stats) {
> > - sig->stats = stats;
> > - stats = NULL;
> > + /* Pairs with READ_ONCE() above. */
> > + smp_store_release(&sig->stats, stats_new);
>
> This is intended to 'order' the _zalloc() (zero initializazion)
> before the update of sig->stats, right? what else am I missing?
>
> Thanks,
> Andrea
>
>
> > + stats_new = NULL;
> > }
> > spin_unlock_irq(&tsk->sighand->siglock);
> >
> > - if (stats)
> > - kmem_cache_free(taskstats_cache, stats);
> > -ret:
> > + if (stats_new)
> > + kmem_cache_free(taskstats_cache, stats_new);
> > +
> > return sig->stats;
> > }
> >
> > --
> > 2.23.0
> >
next prev parent reply other threads:[~2019-10-07 13:51 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-05 4:26 KCSAN: data-race in taskstats_exit / taskstats_exit syzbot
2019-10-05 4:29 ` Dmitry Vyukov
2019-10-05 11:29 ` Christian Brauner
2019-10-05 11:28 ` [PATCH] taskstats: fix data-race Christian Brauner
2019-10-05 13:33 ` Marco Elver
2019-10-05 14:15 ` Christian Brauner
2019-10-05 14:34 ` Marco Elver
2019-10-06 10:00 ` Dmitry Vyukov
2019-10-06 10:59 ` Christian Brauner
2019-10-06 23:52 ` Christian Brauner
2019-10-07 7:31 ` Dmitry Vyukov
2019-10-07 9:29 ` Christian Brauner
2019-10-07 10:40 ` Andrea Parri
2019-10-07 10:50 ` Christian Brauner
2019-10-07 11:01 ` [PATCH v2] " Christian Brauner
2019-10-07 13:18 ` Andrea Parri
2019-10-07 13:28 ` Christian Brauner
2019-10-07 13:50 ` Dmitry Vyukov [this message]
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
2019-11-06 0:27 ` Balbir Singh
2019-11-06 0:09 ` KCSAN: data-race in taskstats_exit / taskstats_exit Balbir Singh
2019-11-06 10:23 ` Marco Elver
2019-11-07 10:39 ` Balbir Singh
2019-11-08 0:54 ` Balbir Singh
2019-11-08 8:55 ` Dmitry Vyukov
2019-11-09 3:42 ` Balbir Singh
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