From: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Date: Fri, 3 Aug 2018 16:58:11 +0900
Subject: veth: Avoid drops by oversized packets when XDP is enabled
Patch-mainline: v4.19-rc1
Git-commit: dc2248220a4aa61560c95aca98d4162095bd7e8a
References: bsc#1109837

Oversized packets including GSO packets can be dropped if XDP is
enabled on receiver side, so don't send such packets from peer.

Drop TSO and SCTP fragmentation features so that veth devices themselves
segment packets with XDP enabled. Also cap MTU accordingly.

v4:
- Don't auto-adjust MTU but cap max MTU.

Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/veth.c |   47 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -543,6 +543,23 @@ static int veth_get_iflink(const struct
 	return iflink;
 }
 
+static netdev_features_t veth_fix_features(struct net_device *dev,
+					   netdev_features_t features)
+{
+	struct veth_priv *priv = netdev_priv(dev);
+	struct net_device *peer;
+
+	peer = rtnl_dereference(priv->peer);
+	if (peer) {
+		struct veth_priv *peer_priv = netdev_priv(peer);
+
+		if (peer_priv->_xdp_prog)
+			features &= ~NETIF_F_GSO_SOFTWARE;
+	}
+
+	return features;
+}
+
 static void veth_set_rx_headroom(struct net_device *dev, int new_hr)
 {
 	struct veth_priv *peer_priv, *priv = netdev_priv(dev);
@@ -572,6 +589,7 @@ static int veth_xdp_set(struct net_devic
 	struct veth_priv *priv = netdev_priv(dev);
 	struct bpf_prog *old_prog;
 	struct net_device *peer;
+	unsigned int max_mtu;
 	int err;
 
 	old_prog = priv->_xdp_prog;
@@ -585,6 +603,15 @@ static int veth_xdp_set(struct net_devic
 			goto err;
 		}
 
+		max_mtu = PAGE_SIZE - VETH_XDP_HEADROOM -
+			  peer->hard_header_len -
+			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+		if (peer->mtu > max_mtu) {
+			NL_SET_ERR_MSG_MOD(extack, "Peer MTU is too large to set XDP");
+			err = -ERANGE;
+			goto err;
+		}
+
 		if (dev->flags & IFF_UP) {
 			err = veth_enable_xdp(dev);
 			if (err) {
@@ -592,14 +619,29 @@ static int veth_xdp_set(struct net_devic
 				goto err;
 			}
 		}
+
+		if (!old_prog) {
+			peer->hw_features &= ~NETIF_F_GSO_SOFTWARE;
+			peer->max_mtu = max_mtu;
+		}
 	}
 
 	if (old_prog) {
-		if (!prog && dev->flags & IFF_UP)
-			veth_disable_xdp(dev);
+		if (!prog) {
+			if (dev->flags & IFF_UP)
+				veth_disable_xdp(dev);
+
+			if (peer) {
+				peer->hw_features |= NETIF_F_GSO_SOFTWARE;
+				peer->max_mtu = ETH_MAX_MTU;
+			}
+		}
 		bpf_prog_put(old_prog);
 	}
 
+	if ((!!old_prog ^ !!prog) && peer)
+		netdev_update_features(peer);
+
 	return 0;
 err:
 	priv->_xdp_prog = old_prog;
@@ -644,6 +686,7 @@ static const struct net_device_ops veth_
 	.ndo_poll_controller	= veth_poll_controller,
 #endif
 	.ndo_get_iflink		= veth_get_iflink,
+	.ndo_fix_features	= veth_fix_features,
 	.ndo_features_check	= passthru_features_check,
 	.ndo_set_rx_headroom	= veth_set_rx_headroom,
 	.ndo_bpf		= veth_xdp,