Re: [PATCH net] ipv6: skip __ipv6_select_ident when there is no skb_dst

[Vlad Yasevich <vyasevic@redhat.com>]

On 03/18/2015 10:15 AM, Sabrina Dubroca wrote:
> 2015-03-18, 10:04:10 -0400, Vlad Yasevich wrote:
>> On 03/18/2015 09:52 AM, Sabrina Dubroca wrote:
>>> Matt Grant reported frequent crashes in ipv6_select_ident when
>>> udp6_ufo_fragment is called from openvswitch on a skb that doesn't
>>> have a dst_entry set.
>>>
>>> Skip __ipv6_select_ident in case of a NULL rt.
>>>
>>> Fixes: 0508c07f5e0c ("ipv6: Select fragment id during UFO segmentation if not set.")
>>> Cc: Vladislav Yasevich <vyasevic@redhat.com>
>>> Reported-by: Matt Grant <matt@mattgrant.net.nz>
>>> Tested-by: Matt Grant <matt@mattgrant.net.nz>
>>> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
>>> ---
>> [...]
>>
>> Hi Sabrina
>>
>> This would result in us using id 0 which is not what we want to do.
>>
>> In this case, udp6_ufo_fragment() should be calling ipv6_proxy_select_ident() so that
>> the fragment id is properly generated.
> 
> Hi Vlad,
> 
> So, instead, something like this?  Or do you want to use
> ipv6_proxy_select_ident even when we have a skb_dst?
> 

Yes, this is what I was thinking...

-vlad

> 
> diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
> index ab889bb16b3c..01c41122ddd7 100644
> --- a/net/ipv6/udp_offload.c
> +++ b/net/ipv6/udp_offload.c
> @@ -112,11 +112,17 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
>  		fptr = (struct frag_hdr *)(skb_network_header(skb) + unfrag_ip6hlen);
>  		fptr->nexthdr = nexthdr;
>  		fptr->reserved = 0;
> -		if (skb_shinfo(skb)->ip6_frag_id)
> +		if (skb_shinfo(skb)->ip6_frag_id) {
>  			fptr->identification = skb_shinfo(skb)->ip6_frag_id;
> -		else
> -			ipv6_select_ident(fptr,
> -					  (struct rt6_info *)skb_dst(skb));
> +		} else {
> +			struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);
> +			if (rt) {
> +				ipv6_select_ident(fptr, rt);
> +			} else {
> +				ipv6_proxy_select_ident(skb);
> +				fptr->identification = skb_shinfo(skb)->ip6_frag_id;
> +			}
> +		}
>  
>  		/* Fragment the skb. ipv6 header and the remaining fields of the
>  		 * fragment header are updated in ipv6_gso_segment()
> 
>