Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 9 Oct 2019 15:26:17 +0200
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     bsingharora@gmail.com, dvyukov@google.com, elver@google.com,
        linux-kernel@vger.kernel.org, parri.andrea@gmail.com,
        stable@vger.kernel.org,
        syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com,
        syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH v5] taskstats: fix data-race
Message-ID: <20191009132616.at3yspm6y3mzp5wg@wittgenstein>
References: <20191009113134.5171-1-christian.brauner@ubuntu.com>
 <20191009114809.8643-1-christian.brauner@ubuntu.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20191009114809.8643-1-christian.brauner@ubuntu.com>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Oct 09, 2019 at 01:48:09PM +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 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>

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

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

Targeting v5.4-rc3.

Thanks!
Christian