udp: fix GRO reception in case of length mismatch

Currently, the UDP GRO code path does bad things on some edge
conditions - Aggregation can happen even on packet with different
lengths.

Fix the above by rewriting the 'complete' condition for GRO
packets. While at it, note explicitly that we allow merging the
first packet per burst below gso_size.

Reported-by: Sean Tong <seantong114@gmail.com>
Fixes: 52d827791531 ("udp: implement GRO for plain UDP sockets.")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 64f9715173ac8bf3a8d641ae40ef95f67aa7a7a0..d8776b2110c107ea322262d83532cb8c2759a9dc 100644 (file)
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -377,13 +377,14 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
 
                /* Terminate the flow on len mismatch or if it grow "too much".
                 * Under small packet flood GRO count could elsewhere grow a lot
-                * leading to execessive truesize values
+                * leading to execessive truesize values.
+                * On len mismatch merge the first packet shorter than gso_size,
+                * otherwise complete the GRO packet.
                 */
-               if (!skb_gro_receive(p, skb) &&
+               if (uh->len > uh2->len || skb_gro_receive(p, skb) ||
+                   uh->len != uh2->len ||
                    NAPI_GRO_CB(p)->count >= UDP_GRO_CNT_MAX)
                        pp = p;
-               else if (uh->len != uh2->len)
-                       pp = p;
 
                return pp;
        }