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Date: Tue, 7 Mar 2017 17:51:32 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        syzkaller <syzkaller@googlegroups.com>
Subject: Re: perf: use-after-free in perf_release
Message-ID: <20170307165131.GA6097@redhat.com>
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On 03/07, Dmitry Vyukov wrote:
>
> On Tue, Mar 7, 2017 at 3:04 PM, Oleg Nesterov <oleg@redhat.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.