udp: prevent local UDP tunnel packets from being GROed

GRO has a fundamental issue with UDP tunnel packets as it can't detect
those in a foolproof way and GRO could happen before they reach the
tunnel endpoint. Previous commits have fixed issues when UDP tunnel
packets come from a remote host, but if those packets are issued locally
they could run into checksum issues.

If the inner packet has a partial checksum the information will be lost
in the GRO logic, either in udp4/6_gro_complete or in
udp_gro_complete_segment and packets will have an invalid checksum when
leaving the host.

Prevent local UDP tunnel packets from ever being GROed at the outer UDP
level.

Due to skb->encapsulation being wrongly used in some drivers this is
actually only preventing UDP tunnel packets with a partial checksum to
be GROed (see iptunnel_handle_offloads) but those were also the packets
triggering issues so in practice this should be sufficient.

Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Fixes: 36707061d6ba ("udp: allow forwarding of plain (non-fraglisted) UDP GRO packets")
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: Willem de Bruijn <willemb@google.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 548476d782371e1a48639fcd34c7b0bdfbc78179..3498dd1d0694dc3ddb984177d2ddffb7b8abd0b9 100644 (file)
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -559,6 +559,12 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
         */
        NAPI_GRO_CB(skb)->is_flist = 0;
        if (!sk || !udp_sk(sk)->gro_receive) {
+               /* If the packet was locally encapsulated in a UDP tunnel that
+                * wasn't detected above, do not GRO.
+                */
+               if (skb->encapsulation)
+                       goto out;
+
                if (skb->dev->features & NETIF_F_GRO_FRAGLIST)
                        NAPI_GRO_CB(skb)->is_flist = sk ? !udp_test_bit(GRO_ENABLED, sk) : 1;