linux-kernel - Re: [PATCH] perf/core: fix use-after-free in uprobe_perf

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Date:   Mon, 9 Apr 2018 14:25:53 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/core: fix use-after-free in uprobe_perf_close

On 04/09, Prashant Bhole wrote:
>
> It occurs because task_struct is freed before perf_event which refers
> to the task and task flags are checked while teardown of the event.
> perf_event_alloc() assigns task_struct to hw.target of perf_event,
> but there is no reference counting for it.
>
> As a fix we get_task_struct() in perf_event_alloc() at above mentioned
> assignment and put_task_struct() in _free_event().
>
> Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>

Agreed, lets make a simple fix for the start. I'd suggest cc:stable,
afaics this fixes the commit 63b6da39bb38e8f1a1ef3180d32a39d6
("perf: Fix perf_event_exit_task() race").

Reviewed-by: Oleg Nesterov <oleg@...hat.com>