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

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Message-ID: <20171102155945.vvrrugvhrgdvvkso@ast-mbp>
Date:   Thu, 2 Nov 2017 08:59:47 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "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 Thu, Nov 02, 2017 at 12:05:52PM +0100, 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>
> ---
> Since there hasn't been a linux-next release in two weeks, I'm not
> entirely sure this is still needed, but from looking of the net-next
> contents it seems it is. I did not check any other trees that might
> have a fix already.
> ---
>  kernel/bpf/verifier.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 750aff880ecb..debb60ad08ee 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4447,6 +4447,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
>  	struct bpf_verifer_log *log;
>  	int ret = -EINVAL;
>  
> +	/* no program is valid */
> +	if (ARRAY_SIZE(bpf_verifier_ops) == 0)
> +		return -EINVAL;

sorry I don't see how bpf_verifier_ops can be empty.
Did you mix it up with your previous patch when you made bpf_analyzer_ops empty?