[PATCH 3.8 051/121] net: core: don't account for udp header size when computing seglen

[Kamal Mostafa]

3.8.13.24 -stable review patch.  If anyone has any objections, please let me know.

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

From: Florian Westphal <fw at strlen.de>

[ Upstream commit 6d39d589bb76ee8a1c6cde6822006ae0053decff ]

In case of tcp, gso_size contains the tcpmss.

For UFO (udp fragmentation offloading) skbs, gso_size is the fragment
payload size, i.e. we must not account for udp header size.

Otherwise, when using virtio drivers, a to-be-forwarded UFO GSO packet
will be needlessly fragmented in the forward path, because we think its
individual segments are too large for the outgoing link.

Fixes: fe6cc55f3a9a053 ("net: ip, ipv6: handle gso skbs in forwarding path")
Cc: Eric Dumazet <eric.dumazet at gmail.com>
Reported-by: Tobias Brunner <tobias at strongswan.org>
Signed-off-by: Florian Westphal <fw at strlen.de>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/core/skbuff.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index e255b9c..f97fe58 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3461,12 +3461,14 @@ EXPORT_SYMBOL(skb_try_coalesce);
 unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
 {
 	const struct skb_shared_info *shinfo = skb_shinfo(skb);
-	unsigned int hdr_len;
 
 	if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
-		hdr_len = tcp_hdrlen(skb);
-	else
-		hdr_len = sizeof(struct udphdr);
-	return hdr_len + shinfo->gso_size;
+		return tcp_hdrlen(skb) + shinfo->gso_size;
+
+	/* UFO sets gso_size to the size of the fragmentation
+	 * payload, i.e. the size of the L4 (UDP) header is already
+	 * accounted for.
+	 */
+	return shinfo->gso_size;
 }
 EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);
-- 
1.9.1