[PATCH 3.16 214/233] ipv4: Should use consistent conditional judgement for ip fragment in __ip_append_data and ip_finish_output

[Ben Hutchings]

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

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

From: zheng li <james.z.li@xxxxxxxxxxxx>

commit 0a28cfd51e17f4f0a056bcf66bfbe492c3b99f38 upstream.

There is an inconsistent conditional judgement in __ip_append_data and
ip_finish_output functions, the variable length in __ip_append_data just
include the length of application's payload and udp header, don't include
the length of ip header, but in ip_finish_output use
(skb->len > ip_skb_dst_mtu(skb)) as judgement, and skb->len include the
length of ip header.

That causes some particular application's udp payload whose length is
between (MTU - IP Header) and MTU were fragmented by ip_fragment even
though the rst->dev support UFO feature.

Add the length of ip header to length in __ip_append_data to keep
consistent conditional judgement as ip_finish_output for ip fragment.

Signed-off-by: Zheng Li <james.z.li@xxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context to apply after "udp: consistently apply
 ufo or fragmentation"]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ipv4/ip_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -886,7 +886,7 @@ static int __ip_append_data(struct sock
 
 	cork->length += length;
 	if ((skb && skb_is_gso(skb)) ||
-	    ((length > mtu) &&
+	    (((length + fragheaderlen) > mtu) &&
 	    (skb_queue_len(queue) <= 1) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->dst.dev->features & NETIF_F_UFO) && !dst_xfrm(&rt->dst) &&