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

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Message-ID: <20170307132741.GB3358@twins.programming.kicks-ass.net>
Date:   Tue, 7 Mar 2017 14:27:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     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>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: perf: use-after-free in perf_release

On Tue, Mar 07, 2017 at 02:16:49PM +0100, Peter Zijlstra wrote:
> So I _think_ find_task_by_vpid() can return an already dead task; and
> we'll happily increase task->usage.

Hurm, so find_get_context() already does the PF_EXITING test. And then
the put_ctx would've been from find_get_context(), not fput().

So still puzzled.