net: core: don't account for udp header size when computing seglen

[ 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@gmail.com>
Reported-by: Tobias Brunner <tobias@strongswan.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8ac4a0f..8ae2e43 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3197,12 +3197,14 @@ EXPORT_SYMBOL(__skb_warn_lro_forwarding);
 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);