linux-kernel - Re: perf: use-after-free in perf

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Message-ID: <20170307140414.GA31678@redhat.com>
Date:   Tue, 7 Mar 2017 15:04:14 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: perf: use-after-free in perf_release

On 03/06, Peter Zijlstra wrote:
>
> and this is a failed fork().
>
>
> However, inherited events don't have a filedesc to fput(), and
> similarly, a task that fails for has never been visible to attach a perf
> event to because it never hits the pid-hash.

Yes, it is not visible to find_task_by_vpid() until copy_process() does
attach_pid(PIDTYPE_PID), and copy_process() can't fail after that.

Oleg.