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

From: Sabrina Dubroca <[email-masked]>
Date: Wed, 18 Mar 2015 15:15:29 +0100

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 <[email-masked]>
> > Reported-by: Matt Grant <[email-masked]>
> > Tested-by: Matt Grant <[email-masked]>
> > Signed-off-by: Sabrina Dubroca <[email-masked]>
> > ---
> [...]
> 
> 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?

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()

-- 
Sabrina