Re: perf: use-after-free in perf_release

From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	syzkaller <syzkaller@googlegroups.com>
Subject: Re: perf: use-after-free in perf_release
Date: Tue, 7 Mar 2017 18:29:58 +0100	[thread overview]
Message-ID: <20170307172958.GB3312@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20170307165131.GA6097@redhat.com>

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 :-(