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

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Message-ID: <20131024054816.GB5973@order.stressinduktion.org>
Date:	Thu, 24 Oct 2013 07:48:16 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	netdev@...r.kernel.org
Cc:	sgunderson@...foot.com, valentyn@...b.net, yoshfuji@...ux-ipv6.org
Subject: [PATCH net 1/2] ipv6: reset dst.expires value when clearing expire flag

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@...foot.com>
Reported-by: Valentijn Sessink <valentyn@...b.net>
Cc: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.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)
-- 
1.8.3.1

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