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

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Message-ID: <Y5kE2eAa8EZUxx5b@bombadil.infradead.org>
Date:   Tue, 13 Dec 2022 15:03:53 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Schspa Shi <schspa@...il.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org,
        syzbot+10d19d528d9755d9af22@...kaller.appspotmail.com,
        syzbot+70d5d5d83d03db2c813d@...kaller.appspotmail.com,
        syzbot+83cb0411d0fcf0a30fc1@...kaller.appspotmail.com
Subject: Re: [PATCH] umh: fix UAF when the process is being killed

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