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

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Message-ID: <20170307165131.GA6097@redhat.com>
Date:   Tue, 7 Mar 2017 17:51:32 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.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 03/07, Dmitry Vyukov wrote:
>
> 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?

I am looking at perf_event_init_task() too and I can't understand the
error handling...

perf_event_init_context() can return success even if inherit_task_group() in
the first list_for_each_entry(pinned_groups) fails, "ret" will be overwritten
by the 2nd list_for_each_entry(flexible_groups) loop. "inherited_all" should
be cleared, still this looks confusing at least.

inherit_event() returns NULL under is_orphaned_event() check, not ERR_PTR().
Is it correct?

Oleg.