netdev - Re: [patch net/stable] ipv6/exthdrs: accept tlv which includes only padding

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Date:	Sat, 7 Sep 2013 14:31:36 +0200 (CEST)
From:	Eldad Zack <eldad@...refinery.com>
To:	Jiri Pirko <jiri@...nulli.us>
cc:	netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru,
	jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net
Subject: Re: [patch net/stable] ipv6/exthdrs: accept tlv which includes only
 padding


Hi Jiri,

On Fri, 6 Sep 2013, Jiri Pirko wrote:

> In rfc4942 and rfc2460 I cannot find anything which would implicate to
> drop packets which have only padding in tlv.

NAK from my side.
Please read RFC4942 2.1.9.5 "Misuse of Pad1 and PadN Options".

While it doesn't specifically discusses this corner case, you can 
understand from "There is no legitimate reason for padding beyond the 
next eight octet..." that there's also no legitimate reason for an 
option header containing only padding.
I can't imagine a sane use-case for this.

> Current behaviour breaks TAHI Test v6LC.1.2.6.

I'm not familiar with this, but IMHO the test should be reversed :)

Cheers,
Eldad

> 
> Problem was intruduced in:
> 9b905fe6843 "ipv6/exthdrs: strict Pad1 and PadN check"
> 
> Signed-off-by: Jiri Pirko <jiri@...nulli.us>
> ---
>  net/ipv6/exthdrs.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> index 07a7d65..8d67900 100644
> --- a/net/ipv6/exthdrs.c
> +++ b/net/ipv6/exthdrs.c
> @@ -162,12 +162,6 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs, struct sk_buff *skb)
>  		off += optlen;
>  		len -= optlen;
>  	}
> -	/* This case will not be caught by above check since its padding
> -	 * length is smaller than 7:
> -	 * 1 byte NH + 1 byte Length + 6 bytes Padding
> -	 */
> -	if ((padlen == 6) && ((off - skb_network_header_len(skb)) == 8))
> -		goto bad;
>  
>  	if (len == 0)
>  		return true;
> -- 
> 1.8.3.1
> 
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