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

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Message-ID: <CACT4Y+bzNOrMHmfP_cv3Jzaqs0zB3qHY9eu0y4JdKvVw0mgveA@mail.gmail.com>
Date:   Tue, 7 Mar 2017 15:17:34 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Oleg Nesterov <oleg@...hat.com>
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>,
        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 Tue, Mar 7, 2017 at 3:04 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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.


I would what is that that is failed in copy_process. Could it be
perf_event_init_task itself? Maybe it leaves a pointer to p in some
shared state on some error conditions?