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Date: Tue, 7 Mar 2017 15:04:14 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dmitry Vyukov <dvyukov@google.com>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        syzkaller <syzkaller@googlegroups.com>
Subject: Re: perf: use-after-free in perf_release
Message-ID: <20170307140414.GA31678@redhat.com>
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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.