netdev - Re: [offlist] Re: Crash in netlink/sk_filter_trim

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Date:   Fri, 17 Aug 2018 20:30:16 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Peter Robinson <pbrobinson@...il.com>,
        Marc Haber <mh+netdev@...schlus.de>,
        linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        labbott@...hat.com, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on
 4.18rc1

On 08/17/2018 06:17 PM, Russell King - ARM Linux wrote:
> On Fri, Aug 17, 2018 at 02:40:19PM +0200, Daniel Borkmann wrote:
>> I'd have one potential bug suspicion, for the 4.18 one you were trying,
>> could you run with the below patch to see whether it would help?
> 
> I think this is almost certainly the problem - looking at the history,
> it seems that the "-4" was assumed to be part of the scratch stuff in
> commit 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack space")
> but it isn't - it's because "off" of zero refers to the top word in the
> stack (iow at STACK_SIZE-4).

Yeah agree, my thinking as well (albeit bit late, sigh, sorry about that).
Waiting for Peter to get back with results for definite confirmation. Your
rework in 1c35ba122d4a ("ARM: net: bpf: use negative numbers for stacked
registers") and 96cced4e774a ("ARM: net: bpf: access eBPF scratch space using
ARM FP register") fixes this in mainline, so unless I'm missing something this
would only need a stand-alone fix for 4.18/stable which I can cook up and
submit then.

Thanks,
Daniel