[PATCH 3.16 134/134] udp: consistently apply ufo or fragmentation

[Ben Hutchings]

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

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

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit 85f1bd9a7b5a79d5baa8bf44af19658f7bf77bfa upstream.

When iteratively building a UDP datagram with MSG_MORE and that
datagram exceeds MTU, consistently choose UFO or fragmentation.

Once skb_is_gso, always apply ufo. Conversely, once a datagram is
split across multiple skbs, do not consider ufo.

Sendpage already maintains the first invariant, only add the second.
IPv6 does not have a sendpage implementation to modify.

A gso skb must have a partial checksum, do not follow sk_no_check_tx
in udp_send_skb.

Found by syzkaller.

Fixes: e89e9cf539a2 ("[IPv4/IPv6]: UFO Scatter-gather approach")
Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - ip6_append_data() doesn't take a queue parameter; use &sk->sk_write_queue
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ipv4/ip_output.c  |    7 +++++--
 net/ipv4/udp.c        |    2 +-
 net/ipv6/ip6_output.c |    7 ++++---
 3 files changed, 10 insertions(+), 6 deletions(-)

--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -885,10 +885,12 @@ static int __ip_append_data(struct sock
 		csummode = CHECKSUM_PARTIAL;
 
 	cork->length += length;
-	if (((length > mtu) || (skb && skb_is_gso(skb))) &&
+	if ((skb && skb_is_gso(skb)) ||
+	    ((length > mtu) &&
+	    (skb_queue_len(queue) <= 1) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->dst.dev->features & NETIF_F_UFO) && !dst_xfrm(&rt->dst) &&
-	    (sk->sk_type == SOCK_DGRAM)) {
+	    (sk->sk_type == SOCK_DGRAM))) {
 		err = ip_ufo_append_data(sk, queue, getfrag, from, length,
 					 hh_len, fragheaderlen, transhdrlen,
 					 maxfraglen, flags);
@@ -1203,6 +1205,7 @@ ssize_t	ip_append_page(struct sock *sk,
 
 	cork->length += size;
 	if ((size + skb->len > mtu) &&
+	    (skb_queue_len(&sk->sk_write_queue) == 1) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->dst.dev->features & NETIF_F_UFO)) {
 		skb_shinfo(skb)->gso_size = mtu - fragheaderlen;
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -824,7 +824,7 @@ static int udp_send_skb(struct sk_buff *
 	if (is_udplite)  				 /*     UDP-Lite      */
 		csum = udplite_csum(skb);
 
-	else if (sk->sk_no_check_tx) {   /* UDP csum disabled */
+	else if (sk->sk_no_check_tx && !skb_is_gso(skb)) {   /* UDP csum off */
 
 		skb->ip_summed = CHECKSUM_NONE;
 		goto send;
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1291,11 +1291,12 @@ emsgsize:
 
 	skb = skb_peek_tail(&sk->sk_write_queue);
 	cork->length += length;
-	if ((((length + fragheaderlen) > mtu) ||
-	     (skb && skb_is_gso(skb))) &&
+	if ((skb && skb_is_gso(skb)) ||
+	    (((length + fragheaderlen) > mtu) &&
+	    (skb_queue_len(&sk->sk_write_queue) <= 1) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->dst.dev->features & NETIF_F_UFO) && !dst_xfrm(&rt->dst) &&
-	    (sk->sk_type == SOCK_DGRAM)) {
+	    (sk->sk_type == SOCK_DGRAM))) {
 		err = ip6_ufo_append_data(sk, getfrag, from, length,
 					  hh_len, fragheaderlen, exthdrlen,
 					  transhdrlen, mtu, flags, rt);