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

From: Vlad Yasevich <[email-masked]>
Date: Wed, 18 Mar 2015 10:04:10 -0400

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]>
> ---
> David, can you queue it for stable (3.19)?
> 
>  net/ipv6/output_core.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
> index 74581f706c4d..52b1bc76d5c5 100644
> --- a/net/ipv6/output_core.c
> +++ b/net/ipv6/output_core.c
> @@ -62,12 +62,14 @@ EXPORT_SYMBOL_GPL(ipv6_proxy_select_ident);
>  void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
>  {
>  	static u32 ip6_idents_hashrnd __read_mostly;
> -	u32 id;
> +	u32 id = 0;
>  
>  	net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd));
>  
> -	id = __ipv6_select_ident(ip6_idents_hashrnd, &rt->rt6i_dst.addr,
> -				 &rt->rt6i_src.addr);
> +	if (rt)
> +		id = __ipv6_select_ident(ip6_idents_hashrnd, &rt->rt6i_dst.addr,
> +					 &rt->rt6i_src.addr);
> +
>  	fhdr->identification = htonl(id);
>  }
>  EXPORT_SYMBOL(ipv6_select_ident);
> 

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.

-vlad