netdev - Re: [PATCH net] net: filter: be more defensive on div/mod by X==0

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Date:	Mon, 07 Apr 2014 12:55:09 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	dborkman@...hat.com
Cc:	ast@...mgrid.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: filter: be more defensive on div/mod by X==0

From: Daniel Borkmann <dborkman@...hat.com>
Date: Sat,  5 Apr 2014 01:04:03 +0200

> The old interpreter behaviour was that we returned with 0
> whenever we found a division by 0 would take place. In the new
> interpreter we would currently just skip that instead and
> continue execution.
> 
> It's true that a value of 0 as return might not be appropriate
> in all cases, but current users (socket filters -> drop
> packet, seccomp -> SECCOMP_RET_KILL, cls_bpf -> unclassified,
> etc) seem fine with that behaviour. Better this than undefined
> BPF program behaviour as it's expected that A contains the
> result of the division. In future, as more use cases open up,
> we could further adapt this return value to our needs, if
> necessary.
> 
> So reintroduce return of 0 for division by 0 as in the old
> interpreter. Also in case of K which is guaranteed to be 32bit
> wide, sk_chk_filter() already takes care of preventing division
> by 0 invoked through K, so we can generally spare us these tests.
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> Reviewed-by: Alexei Starovoitov <ast@...mgrid.com>

Applied, thanks Daniel.
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