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

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Message-ID: <20170307172958.GB3312@twins.programming.kicks-ass.net>
Date:   Tue, 7 Mar 2017 18:29:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, 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 07, 2017 at 05:51:32PM +0100, Oleg Nesterov wrote:
> On 03/07, Dmitry Vyukov wrote:

> > 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?

Urgh, there was something tricky there, but I cannot remember, and it
seems we didn't put a comment in either :/

Alexander, can you remember?

But yes, this all looks a tad dodgy, I'll try and have a look, but I
feel like I'm coming down with something :-(