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

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Message-ID: <20180817161743.GX30658@n2100.armlinux.org.uk>
Date:   Fri, 17 Aug 2018 17:17:43 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Daniel Borkmann <daniel@...earbox.net>
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 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).

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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