Re: [PATCH net 1/2] ipv6: reset dst.expires value when clearing expire flag

[Valentijn Sessink <valentyn@blub.net>]

On 24-10-13 07:48, Hannes Frederic Sowa wrote:
> On receiving a packet too big icmp error we update the expire value by
> calling rt6_update_expires. This function uses dst_set_expires which is
> implemented that it can only reduce the expiration value of the dst entry.
> 
> If we insert new routing non-expiry information into the ipv6 fib where
> we already have a matching rt6_info we only clear the RTF_EXPIRES flag
> in rt6i_flags and leave the dst.expires value as is.
> 
> When new mtu information arrives for that cached dst_entry we again
> call dst_set_expires. This time it won't update the dst.expire value
> because we left the dst.expire value intact from the last update. So
> dst_set_expires won't touch dst.expires.
> 
> Fix this by resetting dst.expires when clearing the RTF_EXPIRE flag.
> dst_set_expires checks for a zero expiration and updates the
> dst.expires.
> 
> In the past this (not updating dst.expires) was necessary because
> dst.expire was placed in a union with the dst_entry *from reference. So
> an update on the value would have caused page faults. This split happend
> in ecd9883724b78cc72ed92c98bcb1a46c764fff21 ("ipv6: fix race condition
> regarding dst->expires and dst->from").
> 
> Reported-by: Steinar H. Gunderson <sgunderson@bigfoot.com>
> Reported-by: Valentijn Sessink <valentyn@blub.net>
> Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> ---
> I would propose this patch for -stable.
> 
>  include/net/ip6_fib.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
> index 48ec25a..5e661a9 100644
> --- a/include/net/ip6_fib.h
> +++ b/include/net/ip6_fib.h
> @@ -165,6 +165,7 @@ static inline struct inet6_dev *ip6_dst_idev(struct dst_entry *dst)
>  static inline void rt6_clean_expires(struct rt6_info *rt)
>  {
>  	rt->rt6i_flags &= ~RTF_EXPIRES;
> +	rt->dst.expires = 0;
>  }
>  
>  static inline void rt6_set_expires(struct rt6_info *rt, unsigned long expires)
> 

Tested-by: Valentijn Sessink <valentyn@blub.net>