From: Christian Brauner <christian.brauner@ubuntu.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: syzbot <syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com>,
bsingharora@gmail.com, Marco Elver <elver@google.com>,
LKML <linux-kernel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: [PATCH] taskstats: fix data-race
Date: Sun, 6 Oct 2019 12:59:31 +0200 [thread overview]
Message-ID: <20191006105930.5a5jxislaqpzmo22@wittgenstein> (raw)
In-Reply-To: <CACT4Y+YiVE52xkADKgpfzRgofHbVxtRpcbKo_RU81jjOV_0TvA@mail.gmail.com>
On Sun, Oct 06, 2019 at 12:00:32PM +0200, Dmitry Vyukov wrote:
> On Sat, Oct 5, 2019 at 1:28 PM Christian Brauner
> <christian.brauner@ubuntu.com> wrote:
> >
> > When assiging and testing taskstats in taskstats
> > taskstats_exit() there's a race around writing and reading sig->stats.
> >
> > cpu0:
> > task calls exit()
> > do_exit()
> > -> taskstats_exit()
> > -> taskstats_tgid_alloc()
> > The task takes sighand lock and assigns new stats to sig->stats.
> >
> > cpu1:
> > task catches signal
> > do_exit()
> > -> taskstats_tgid_alloc()
> > -> taskstats_exit()
> > The tasks reads sig->stats __without__ holding sighand lock seeing
> > garbage.
> >
> > Fix this by taking sighand lock when reading sig->stats.
> >
> > Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
> > Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
> > ---
> > kernel/taskstats.c | 28 +++++++++++++++++-----------
> > 1 file changed, 17 insertions(+), 11 deletions(-)
> >
> > diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> > index 13a0f2e6ebc2..58b145234c4a 100644
> > --- a/kernel/taskstats.c
> > +++ b/kernel/taskstats.c
> > @@ -553,26 +553,32 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
> >
> > static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
> > {
> > + int empty;
> > + struct taskstats *stats_new, *stats = NULL;
> > struct signal_struct *sig = tsk->signal;
> > - struct taskstats *stats;
> > -
> > - if (sig->stats || thread_group_empty(tsk))
> > - goto ret;
> >
> > /* No problem if kmem_cache_zalloc() fails */
> > - stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
> > + stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
>
> This seems to be over-pessimistic wrt performance b/c:
> 1. We always allocate the object and free it on every call, even if
> the stats are already allocated, whereas currently we don't.
> 2. We always allocate the object and free it if thread_group_empty,
> whereas currently we don't.
> 3. We do lock/unlock on every call.
>
> I would suggest to fix the double-checked locking properly.
As I said in my reply to Marco: I'm integrating this. I just haven't
had time to update the patch.
Christian
next prev parent reply other threads:[~2019-10-06 10:59 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 [this message]
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
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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