linux-kernel - Re: [PATCH 2/2] [net-next] bpf: fix out-of-bounds access warning in bpf

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Date:   Thu, 02 Nov 2017 23:35:22 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Arnd Bergmann <arnd@...db.de>, Alexei Starovoitov <ast@...nel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Edward Cree <ecree@...arflare.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] [net-next] bpf: fix out-of-bounds access warning
 in bpf_check

On 11/02/2017 12:05 PM, Arnd Bergmann wrote:
> The bpf_verifer_ops array is generated dynamically and may be
> empty depending on configuration, which then causes an out
> of bounds access:
>
> kernel/bpf/verifier.c: In function 'bpf_check':
> kernel/bpf/verifier.c:4320:29: error: array subscript is above array bounds [-Werror=array-bounds]
>
> This adds a check to the start of the function as a workaround.
> I would assume that the function is never called in that configuration,
> so the warning is probably harmless.
>
> Fixes: 00176a34d9e2 ("bpf: remove the verifier ops from program structure")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Daniel Borkmann <daniel@...earbox.net>

LGTM, and bpf_analyzer() already has proper logic to bail out for
such cases (although only used by nfp right now, which is there
when NET is configured anyway).