Re: [PATCH] umh: fix UAF when the process is being killed

From: Luis Chamberlain <mcgrof@kernel.org>
To: Schspa Shi <schspa@gmail.com>
Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, vschneid@redhat.com,
	linux-kernel@vger.kernel.org,
	syzbot+10d19d528d9755d9af22@syzkaller.appspotmail.com,
	syzbot+70d5d5d83d03db2c813d@syzkaller.appspotmail.com,
	syzbot+83cb0411d0fcf0a30fc1@syzkaller.appspotmail.com
Subject: Re: [PATCH] umh: fix UAF when the process is being killed
Date: Tue, 13 Dec 2022 15:03:53 -0800	[thread overview]
Message-ID: <Y5kE2eAa8EZUxx5b@bombadil.infradead.org> (raw)
In-Reply-To: <m2pmcoag55.fsf@gmail.com>

On Mon, Dec 12, 2022 at 09:38:31PM +0800, Schspa Shi wrote:
> I'd like to upload a V2 patch with the new solution if you prefer the
> following way.
> 
> diff --git a/kernel/umh.c b/kernel/umh.c
> index 850631518665..8023f11fcfc0 100644
> --- a/kernel/umh.c
> +++ b/kernel/umh.c
> @@ -452,6 +452,11 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
>                 /* umh_complete() will see NULL and free sub_info */
>                 if (xchg(&sub_info->complete, NULL))
>                         goto unlock;
> +               /*
> +                * kthreadd (or new kernel thread) will call complete()
> +                * shortly.
> +                */
> +               wait_for_completion(&done);
>         }

Yes much better. Did you verify it fixes the splat found by the bots?

  Luis