drivers/net: Disable UFO through virtio

IPv6 does not allow fragmentation by routers, so there is no
fragmentation ID in the fixed header.  UFO for IPv6 requires the ID to
be passed separately, but there is no provision for this in the virtio
net protocol.

Until recently our software implementation of UFO/IPv6 generated a new
ID, but this was a bug.  Now we will use ID=0 for any UFO/IPv6 packet
passed through a tap, which is even worse.

Unfortunately there is no distinction between UFO/IPv4 and v6
features, so disable UFO on taps and virtio_net completely until we
have a proper solution.

We cannot depend on VM managers respecting the tap feature flags, so
keep accepting UFO packets but log a warning the first time we do
this.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Fixes: 916e4cf46d02 ("ipv6: reuse ip6_frag_id from ip6_ufo_append_data")
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 8 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 186ce541c657..280d3d2a9792 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -174,7 +174,7 @@ struct tun_struct {
         struct net_device       *dev;
         netdev_features_t       set_features;
 #define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
-                          NETIF_F_TSO6|NETIF_F_UFO)
+                          NETIF_F_TSO6)
 
         int                     vnet_hdr_sz;
         int                     sndbuf;
@@ -1149,8 +1149,18 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
                         skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
                         break;
                 case VIRTIO_NET_HDR_GSO_UDP:
+                {
+                        static bool warned;
+
+                        if (!warned) {
+                                warned = true;
+                                netdev_warn(tun->dev,
+                                            "%s: using disabled UFO feature; please fix this program\n",
+                                            current->comm);
+                        }
                         skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
                         break;
+                }
                 default:
                         tun->dev->stats.rx_frame_errors++;
                         kfree_skb(skb);
@@ -1251,8 +1261,6 @@ static ssize_t tun_put_user(struct tun_struct *tun,
                                 gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
                         else if (sinfo->gso_type & SKB_GSO_TCPV6)
                                 gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
-                        else if (sinfo->gso_type & SKB_GSO_UDP)
-                                gso.gso_type = VIRTIO_NET_HDR_GSO_UDP;
                         else {
                                 pr_err("unexpected GSO type: "
                                        "0x%x, gso_size %d, hdr_len %d\n",
@@ -1762,11 +1770,6 @@ static int set_offload(struct tun_struct *tun, unsigned long arg)
                                 features |= NETIF_F_TSO6;
                         arg &= ~(TUN_F_TSO4|TUN_F_TSO6);
                 }
-
-                if (arg & TUN_F_UFO) {
-                        features |= NETIF_F_UFO;
-                        arg &= ~TUN_F_UFO;
-                }
         }
 
         /* This gives the user a way to test for new features in future by