linux-kernel - Re: [PATCH] kernel: bpf: remove dead code

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Message-ID: <20170522095137.Horde.LTr0Ddp7ICoSbO3QDVcrxUX@gator4166.hostgator.com>
Date:   Mon, 22 May 2017 09:51:37 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     David Miller <davem@...emloft.net>
Cc:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel: bpf: remove dead code

Hi David,

Quoting David Miller <davem@...emloft.net>:

> From: "Gustavo A. R. Silva" <garsilva@...eddedor.com>
> Date: Mon, 22 May 2017 09:07:46 -0500
>
>> Execution cannot reach NET_IP_ALIGN inside the following statement:
>> ip_align = strict ? 2 : NET_IP_ALIGN
>>
>> Addresses-Coverity-ID: 1409762
>> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
>> ---
>> NOTE: variable ip_align could also be removed and use value 2 directly.
>
> Incorrect.
>
> Some platforms define NET_IP_ALIGN to zero, so the code must remain
> as is.

The following piece of code at kernel/bpf/verifier.c:798 is preventing  
value NET_IP_ALIGN to be stored in variable ip_align when _strict_ is  
false:

798        if (!strict || size == 1)
799                return 0;


Thanks
--
Gustavo A. R. Silva