linux-kernel - [PATCH 3.16 133/134] ipv6: Should use consistent conditional judgement for ip6 fragment between __ip6_append_data and ip6_finish

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Message-ID: <lsq.1503062000.412180542@decadent.org.uk>
Date:   Fri, 18 Aug 2017 14:13:20 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Zheng Li" <james.z.li@...csson.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 133/134] ipv6: Should use consistent conditional
 judgement for ip6 fragment  between __ip6_append_data and ip6_finish_output

3.16.47-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Zheng Li <james.z.li@...csson.com>

commit e4c5e13aa45c23692e4acf56f0b3533f328199b2 upstream.

There is an inconsistent conditional judgement between __ip6_append_data
and ip6_finish_output functions, the variable length in __ip6_append_data
just include the length of application's payload and udp6 header, don't
include the length of ipv6 header, but in ip6_finish_output use
(skb->len > ip6_skb_dst_mtu(skb)) as judgement, and skb->len include the
length of ipv6 header.

That causes some particular application's udp6 payloads whose length are
between (MTU - IPv6 Header) and MTU were fragmented by ip6_fragment even
though the rst->dev support UFO feature.

Add the length of ipv6 header to length in __ip6_append_data to keep
consistent conditional judgement as ip6_finish_output for ip6 fragment.

Signed-off-by: Zheng Li <james.z.li@...csson.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv6/ip6_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1291,7 +1291,7 @@ emsgsize:

 	skb = skb_peek_tail(&sk->sk_write_queue);
 	cork->length += length;
-	if (((length > mtu) ||
+	if ((((length + fragheaderlen) > mtu) ||
 	     (skb && skb_is_gso(skb))) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->dst.dev->features & NETIF_F_UFO) && !dst_xfrm(&rt->dst) &&