netfilter: bridge: replace physindev with physinif in nf_bridge_info

An skb can be added to a neigh->arp_queue while waiting for an arp
reply. Where original skb's skb->dev can be different to neigh's
neigh->dev. For instance in case of bridging dnated skb from one veth to
another, the skb would be added to a neigh->arp_queue of the bridge.

As skb->dev can be reset back to nf_bridge->physindev and used, and as
there is no explicit mechanism that prevents this physindev from been
freed under us (for instance neigh_flush_dev doesn't cleanup skbs from
different device's neigh queue) we can crash on e.g. this stack:

arp_process
neigh_update
skb = __skb_dequeue(&neigh->arp_queue)
neigh_resolve_output(..., skb)
...
br_nf_dev_xmit
br_nf_pre_routing_finish_bridge_slow
skb->dev = nf_bridge->physindev
br_handle_frame_finish

Let's use plain ifindex instead of net_device link. To peek into the
original net_device we will use dev_get_by_index_rcu(). Thus either we
get device and are safe to use it or we don't get it and drop skb.

Fixes: c4e70a87d975 ("netfilter: bridge: rename br_netfilter.c to br_netfilter_hooks.c")
Suggested-by: Florian Westphal <[e-mail]>
Signed-off-by: Pavel Tikhomirov <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter_bridge.h

···
 	if (!nf_bridge)
 		return 0;
 
-	return nf_bridge->physindev ? nf_bridge->physindev->ifindex : 0;
+	return nf_bridge->physinif;
 }
 
 static inline int nf_bridge_get_physoutif(const struct sk_buff *skb)
···
 {
 	const struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
 
-	return nf_bridge ? nf_bridge->physindev : NULL;
+	return nf_bridge ? dev_get_by_index_rcu(net, nf_bridge->physinif) : NULL;
 }
 
 static inline struct net_device *

include/linux/skbuff.h

···
 	u8			bridged_dnat:1;
 	u8			sabotage_in_done:1;
 	__u16			frag_max_size;
-	struct net_device	*physindev;
+	int			physinif;
 
 	/* always valid & non-NULL from FORWARD on, for physdev match */
 	struct net_device	*physoutdev;

net/bridge/br_netfilter_hooks.c

···
 
 		if ((READ_ONCE(neigh->nud_state) & NUD_CONNECTED) &&
 		    READ_ONCE(neigh->hh.hh_len)) {
+			struct net_device *br_indev;
+
+			br_indev = nf_bridge_get_physindev(skb, net);
+			if (!br_indev) {
+				neigh_release(neigh);
+				goto free_skb;
+			}
+
 			neigh_hh_bridge(&neigh->hh, skb);
-			skb->dev = nf_bridge->physindev;
+			skb->dev = br_indev;
+
 			ret = br_handle_frame_finish(net, sk, skb);
 		} else {
 			/* the neighbour function below overwrites the complete
···
  */
 static int br_nf_pre_routing_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
-	struct net_device *dev = skb->dev;
+	struct net_device *dev = skb->dev, *br_indev;
 	struct iphdr *iph = ip_hdr(skb);
 	struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
 	struct rtable *rt;
 	int err;
+
+	br_indev = nf_bridge_get_physindev(skb, net);
+	if (!br_indev) {
+		kfree_skb(skb);
+		return 0;
+	}
 
 	nf_bridge->frag_max_size = IPCB(skb)->frag_max_size;
 
···
 		} else {
 			if (skb_dst(skb)->dev == dev) {
 bridged_dnat:
-				skb->dev = nf_bridge->physindev;
+				skb->dev = br_indev;
 				nf_bridge_update_protocol(skb);
 				nf_bridge_push_encap_header(skb);
 				br_nf_hook_thresh(NF_BR_PRE_ROUTING,
···
 			skb->pkt_type = PACKET_HOST;
 		}
 	} else {
-		rt = bridge_parent_rtable(nf_bridge->physindev);
+		rt = bridge_parent_rtable(br_indev);
 		if (!rt) {
 			kfree_skb(skb);
 			return 0;
···
 		skb_dst_set_noref(skb, &rt->dst);
 	}
 
-	skb->dev = nf_bridge->physindev;
+	skb->dev = br_indev;
 	nf_bridge_update_protocol(skb);
 	nf_bridge_push_encap_header(skb);
 	br_nf_hook_thresh(NF_BR_PRE_ROUTING, net, sk, skb, skb->dev, NULL,
···
 	}
 
 	nf_bridge->in_prerouting = 1;
-	nf_bridge->physindev = skb->dev;
+	nf_bridge->physinif = skb->dev->ifindex;
 	skb->dev = brnf_get_logical_dev(skb, skb->dev, net);
 
 	if (skb->protocol == htons(ETH_P_8021Q))
···
 		if (skb->protocol == htons(ETH_P_IPV6))
 			nf_bridge->frag_max_size = IP6CB(skb)->frag_max_size;
 
-		in = nf_bridge->physindev;
+		in = nf_bridge_get_physindev(skb, net);
+		if (!in) {
+			kfree_skb(skb);
+			return 0;
+		}
 		if (nf_bridge->pkt_otherhost) {
 			skb->pkt_type = PACKET_OTHERHOST;
 			nf_bridge->pkt_otherhost = false;
···
 static void br_nf_pre_routing_finish_bridge_slow(struct sk_buff *skb)
 {
 	struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
+	struct net_device *br_indev;
+
+	br_indev = nf_bridge_get_physindev(skb, dev_net(skb->dev));
+	if (!br_indev) {
+		kfree_skb(skb);
+		return;
+	}
 
 	skb_pull(skb, ETH_HLEN);
 	nf_bridge->bridged_dnat = 0;
···
 	skb_copy_to_linear_data_offset(skb, -(ETH_HLEN - ETH_ALEN),
 				       nf_bridge->neigh_header,
 				       ETH_HLEN - ETH_ALEN);
-	skb->dev = nf_bridge->physindev;
+	skb->dev = br_indev;
 
 	nf_bridge->physoutdev = NULL;
 	br_handle_frame_finish(dev_net(skb->dev), NULL, skb);

net/bridge/br_netfilter_ipv6.c

···
 {
 	struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
 	struct rtable *rt;
-	struct net_device *dev = skb->dev;
+	struct net_device *dev = skb->dev, *br_indev;
 	const struct nf_ipv6_ops *v6ops = nf_get_ipv6_ops();
+
+	br_indev = nf_bridge_get_physindev(skb, net);
+	if (!br_indev) {
+		kfree_skb(skb);
+		return 0;
+	}
 
 	nf_bridge->frag_max_size = IP6CB(skb)->frag_max_size;
 
···
 		}
 
 		if (skb_dst(skb)->dev == dev) {
-			skb->dev = nf_bridge->physindev;
+			skb->dev = br_indev;
 			nf_bridge_update_protocol(skb);
 			nf_bridge_push_encap_header(skb);
 			br_nf_hook_thresh(NF_BR_PRE_ROUTING,
···
 		ether_addr_copy(eth_hdr(skb)->h_dest, dev->dev_addr);
 		skb->pkt_type = PACKET_HOST;
 	} else {
-		rt = bridge_parent_rtable(nf_bridge->physindev);
+		rt = bridge_parent_rtable(br_indev);
 		if (!rt) {
 			kfree_skb(skb);
 			return 0;
···
 		skb_dst_set_noref(skb, &rt->dst);
 	}
 
-	skb->dev = nf_bridge->physindev;
+	skb->dev = br_indev;
 	nf_bridge_update_protocol(skb);
 	nf_bridge_push_encap_header(skb);
 	br_nf_hook_thresh(NF_BR_PRE_ROUTING, net, sk, skb,

net/ipv4/netfilter/nf_reject_ipv4.c

···
 void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 		   int hook)
 {
-	struct net_device *br_indev __maybe_unused;
 	struct sk_buff *nskb;
 	struct iphdr *niph;
 	const struct tcphdr *oth;
···
 	 * build the eth header using the original destination's MAC as the
 	 * source, and send the RST packet directly.
 	 */
-	br_indev = nf_bridge_get_physindev(oldskb, net);
-	if (br_indev) {
+	if (nf_bridge_info_exists(oldskb)) {
 		struct ethhdr *oeth = eth_hdr(oldskb);
+		struct net_device *br_indev;
+
+		br_indev = nf_bridge_get_physindev(oldskb, net);
+		if (!br_indev)
+			goto free_nskb;
 
 		nskb->dev = br_indev;
 		niph->tot_len = htons(nskb->len);

net/ipv6/netfilter/nf_reject_ipv6.c

···
 void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 		    int hook)
 {
-	struct net_device *br_indev __maybe_unused;
 	struct sk_buff *nskb;
 	struct tcphdr _otcph;
 	const struct tcphdr *otcph;
···
 	 * build the eth header using the original destination's MAC as the
 	 * source, and send the RST packet directly.
 	 */
-	br_indev = nf_bridge_get_physindev(oldskb, net);
-	if (br_indev) {
+	if (nf_bridge_info_exists(oldskb)) {
 		struct ethhdr *oeth = eth_hdr(oldskb);
+		struct net_device *br_indev;
+
+		br_indev = nf_bridge_get_physindev(oldskb, net);
+		if (!br_indev) {
+			kfree_skb(nskb);
+			return;
+		}
 
 		nskb->dev = br_indev;
 		nskb->protocol = htons(ETH_P_IPV6);