netdev - [PATCH] ipv4: Should use consistent conditional judgement for ip fragment in __ip_append_data and ip_finish

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Date:   Thu,  8 Dec 2016 22:48:51 +0800
From:   Zheng Li <lizheng043@...il.com>
To:     netdev@...r.kernel.org, davem@...emloft.net, kuznet@....inr.ac.ru,
        jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net
Cc:     allen.y.zhao@...csson.com, hua.lv@...csson.com,
        james.z.li@...csson.com
Subject: [PATCH] ipv4: Should use consistent conditional judgement for ip fragment in __ip_append_data and ip_finish_output

From: zheng li <james.z.li@...csson.com>

There is an inconsitent conditional judgement in __ip_append_data and ip_finish_output functions,
the variable length in __ip_append_data just include the length of applicatoin'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 cuase some particular applicatoin's udp payload whose length is between (MTU - IP Header) and MTU
were framented by ip_fragment even though the rst->dev support UFO features.

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@...csson.com>
---
 net/ipv4/ip_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 877bdb0..12a0149 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -936,7 +936,7 @@ static int __ip_append_data(struct sock *sk,
 		csummode = CHECKSUM_PARTIAL;

 	cork->length += length;
-	if (((length > mtu) || (skb && skb_is_gso(skb))) &&
+	if ((((length + fragheaderlen) > mtu) || (skb && skb_is_gso(skb))) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->dst.dev->features & NETIF_F_UFO) && !rt->dst.header_len &&
 	    (sk->sk_type == SOCK_DGRAM) && !sk->sk_no_check_tx) {
-- 
2.7.4