netdev - Re: bpf: use-after-free in array_map

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Date:	Sun, 17 Apr 2016 18:45:44 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	ast@...nel.org, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: bpf: use-after-free in array_map_alloc

On 04/17/2016 01:29 PM, Alexei Starovoitov wrote:
> On Sun, Apr 17, 2016 at 12:58:21PM -0400, Sasha Levin wrote:
>> > Hi all,
>> > 
>> > I've hit the following while fuzzing with syzkaller inside a KVM tools guest
>> > running the latest -next kernel:
> thanks for the report. Adding Tejun...
> if I read the report correctly it's not about bpf, but rather points to
> the issue inside percpu logic.
> First __alloc_percpu_gfp() is called, then the memory is freed with
> free_percpu() which triggers async pcpu_balance_work and then
> pcpu_extend_area_map is hitting use-after-free.
> I guess bpf percpu array map is stressing this logic the most.
> Any simpler steps to reproduce ?

No simple way to reproduce. I blamed bpf because I saw a few traces
and it was only bpf that was causing it, there was no other reasoning
behind it.


Thanks,
Sasha