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Subject[PATCH 3.10 03/24] ipv6: reset dst.expires value when clearing expire flag
3.10-stable review patch.  If anyone has any objections, please let me know.


From: Hannes Frederic Sowa <>

[ Upstream commit 01ba16d6ec85a1ec4669c75513a76b61ec53ee50 ]

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

In the past this (not updating dst.expires) was necessary because
dst.expire was placed in a union with the dst_entry *from reference
and rt6_clean_expires did assign NULL to it. This split happend in
ecd9883724b78cc72ed92c98bcb1a46c764fff21 ("ipv6: fix race condition
regarding dst->expires and dst->from").

Reported-by: Steinar H. Gunderson <>
Reported-by: Valentijn Sessink <>
Cc: YOSHIFUJI Hideaki <>
Acked-by: Eric Dumazet <>
Tested-by: Valentijn Sessink <>
Signed-off-by: Hannes Frederic Sowa <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
include/net/ip6_fib.h | 1 +
1 file changed, 1 insertion(+)

--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -165,6 +165,7 @@ static inline struct inet6_dev *ip6_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)

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