netdev - Re: [PATCH net v2 1/2] ipv6: reset dst.expires value when clearing expire flag

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Message-Id: <20131025.192743.556790819489254616.davem@davemloft.net>
Date:	Fri, 25 Oct 2013 19:27:43 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, sgunderson@...foot.com, valentyn@...b.net,
	yoshfuji@...ux-ipv6.org, edumazet@...gle.com
Subject: Re: [PATCH net v2 1/2] ipv6: reset dst.expires value when clearing
 expire flag

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Thu, 24 Oct 2013 10:14:27 +0200

> 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
> 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 <sgunderson@...foot.com>
> Reported-by: Valentijn Sessink <valentyn@...b.net>
> Cc: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> Tested-by: Valentijn Sessink <valentyn@...b.net>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Applied.
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