linux-kernel - Re: uprobes/perf: KASAN: use-after-free in uprobe_perf

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Date:   Mon, 9 Apr 2018 13:40:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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: uprobes/perf: KASAN: use-after-free in uprobe_perf_close

On Mon, Apr 09, 2018 at 12:40:10PM +0200, Oleg Nesterov wrote:
> But I still think that we should (try to) remove put_task_struct() from put_ctx().
> 
> Quite possibly I missed something, but I think it only adds some confusion. Once
> again, even if ctx can't go away you can't use ctx->task without TASK_TOMBSTONE
> check, exactly because this task can exit. So why perf_event_context should add
> another reference?

Ah, I see what you mean. Yes that might be possible.