xdp: XDP_REDIRECT should check IFF_UP and MTU

Otherwise we end up with attempting to send packets from down devices
or to send oversized packets, which may cause unexpected driver/device
behaviour. Generic XDP has already done this check, so reuse the logic
in native XDP.

Fixes: 814abfab ("xdp: add bpf_redirect helper function")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/filter.h

@@ -765,8 +765,8 @@ static inline bool bpf_dump_raw_ok(void)
 struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 				       const struct bpf_insn *patch, u32 len);
 
-static inline int __xdp_generic_ok_fwd_dev(struct sk_buff *skb,
-					   struct net_device *fwd)
+static inline int xdp_ok_fwd_dev(const struct net_device *fwd,
+				 unsigned int pktlen)
 {
 	unsigned int len;
 
@@ -774,7 +774,7 @@ static inline int __xdp_generic_ok_fwd_dev(struct sk_buff *skb,
 		return -ENETDOWN;
 
 	len = fwd->mtu + fwd->hard_header_len + VLAN_HLEN;
-	if (skb->len > len)
+	if (pktlen > len)
 		return -EMSGSIZE;
 
 	return 0;

kernel/bpf/devmap.c

@@ -334,10 +334,15 @@ int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
 {
 	struct net_device *dev = dst->dev;
 	struct xdp_frame *xdpf;
+	int err;
 
 	if (!dev->netdev_ops->ndo_xdp_xmit)
 		return -EOPNOTSUPP;
 
+	err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
+	if (unlikely(err))
+		return err;
+
 	xdpf = convert_to_xdp_frame(xdp);
 	if (unlikely(!xdpf))
 		return -EOVERFLOW;
@@ -350,7 +355,7 @@ int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
 {
 	int err;
 
-	err = __xdp_generic_ok_fwd_dev(skb, dst->dev);
+	err = xdp_ok_fwd_dev(dst->dev, skb->len);
 	if (unlikely(err))
 		return err;
 	skb->dev = dst->dev;

net/core/filter.c

@@ -3128,12 +3128,16 @@ static int __bpf_tx_xdp(struct net_device *dev,
 			u32 index)
 {
 	struct xdp_frame *xdpf;
-	int sent;
+	int err, sent;
 
 	if (!dev->netdev_ops->ndo_xdp_xmit) {
 		return -EOPNOTSUPP;
 	}
 
+	err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
+	if (unlikely(err))
+		return err;
+
 	xdpf = convert_to_xdp_frame(xdp);
 	if (unlikely(!xdpf))
 		return -EOVERFLOW;
@@ -3367,7 +3371,8 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
 		goto err;
 	}
 
-	if (unlikely((err = __xdp_generic_ok_fwd_dev(skb, fwd))))
+	err = xdp_ok_fwd_dev(fwd, skb->len);
+	if (unlikely(err))
 		goto err;
 
 	skb->dev = fwd;