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

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Message-ID: <20191009114040.tqbbdxmkvvt6mia5@wittgenstein>
Date:   Wed, 9 Oct 2019 13:40:41 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     parri.andrea@...il.com
Cc:     bsingharora@...il.com, dvyukov@...gle.com, elver@...gle.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+c5d03165a1bd1dead0c1@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] taskstats: fix data-race

On Wed, Oct 09, 2019 at 01:31:34PM +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@...kaller.appspotmail.com
> Fixes: 34ec12349c8a ("taskstats: cleanup ->signal->stats allocation")
> Cc: stable@...r.kernel.org
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>

_sigh_, let me resend since i fcked this one up.

Christian