linux-kernel - Re: arm64/v4.16-rc1: KASAN: use-after-free Read in finish_task

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Message-ID: <20180215153307.GA11712@arm.com>
Date:   Thu, 15 Feb 2018 15:33:07 +0000
From:   Will Deacon <will.deacon@....com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: arm64/v4.16-rc1: KASAN: use-after-free Read in finish_task_switch

On Thu, Feb 15, 2018 at 02:22:39PM +0000, Will Deacon wrote:
> Assuming others agree with this diagnosis, I'm not sure how to fix it.
> It's basically not safe to set current->mm = NULL with preemption enabled.

One thing we could try would be to leave current->mm alone and just do the
mmdrop in finish_task_switch at the point where we put the task_struct for
DEAD tasks. mm_update_next_owner might need updating so that it doesn't
re-assign current as the owner and run into a BUG_ON.


Will