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Date:   Thu, 22 Dec 2022 20:34:15 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Phil Auld <pauld@redhat.com>,
        Wenjie Li <wenjieli@qti.qualcomm.com>,
        David Wang =?utf-8?B?546L5qCH?= <wangbiao3@xiaomi.com>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH-tip v2] sched: Fix use-after-free bug in
 dup_user_cpus_ptr()
Message-ID: <Y6SxNwUn7/4/8IQa@hirez.programming.kicks-ass.net>
References: <20221205164832.2151247-1-longman@redhat.com>
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On Mon, Dec 05, 2022 at 11:48:32AM -0500, Waiman Long wrote:
> Since commit 07ec77a1d4e8 ("sched: Allow task CPU affinity to be
> restricted on asymmetric systems"), the setting and clearing of
> user_cpus_ptr are done under pi_lock for arm64 architecture. However,
> dup_user_cpus_ptr() accesses user_cpus_ptr without any lock
> protection. When racing with the clearing of user_cpus_ptr in
> __set_cpus_allowed_ptr_locked(), it can lead to user-after-free and
> double-free in arm64 kernel.

How? the task cannot be in migrate_enable() and fork() at the same time,
no?