netfilter: nf_tables: call skb_valid_dst() before skb_dst()

When fetching the dst_entry from the skb, check if it valid, ie. this is
not a template dst, for extensions that can be used from the netdev
ingress and egress chains.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/nf_reject_ipv4.c

@@ -8,6 +8,7 @@
 #include <net/tcp.h>
 #include <net/route.h>
 #include <net/dst.h>
+#include <net/dst_metadata.h>
 #include <net/netfilter/ipv4/nf_reject.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/netfilter_bridge.h>
@@ -263,6 +264,7 @@ static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
 	if (!dst)
 		return -1;
 
+	skb_dst_drop(skb_in);
 	skb_dst_set(skb_in, dst);
 	return 0;
 }
@@ -279,7 +281,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 	if (!oth)
 		return;
 
-	if (!skb_dst(oldskb) && nf_reject_fill_skb_dst(oldskb) < 0)
+	if (!skb_valid_dst(oldskb) && nf_reject_fill_skb_dst(oldskb) < 0)
 		return;
 
 	if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
@@ -352,7 +354,7 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
 	if (iph->frag_off & htons(IP_OFFSET))
 		return;
 
-	if (!skb_dst(skb_in) && nf_reject_fill_skb_dst(skb_in) < 0)
+	if (!skb_valid_dst(skb_in) && nf_reject_fill_skb_dst(skb_in) < 0)
 		return;
 
 	if (skb_csum_unnecessary(skb_in) ||

net/ipv6/netfilter/nf_reject_ipv6.c

@@ -8,6 +8,7 @@
 #include <net/ip6_route.h>
 #include <net/ip6_fib.h>
 #include <net/ip6_checksum.h>
+#include <net/dst_metadata.h>
 #include <net/netfilter/ipv6/nf_reject.h>
 #include <linux/netfilter_ipv6.h>
 #include <linux/netfilter_bridge.h>
@@ -304,6 +305,7 @@ static int nf_reject6_fill_skb_dst(struct sk_buff *skb_in)
 	if (!dst)
 		return -1;
 
+	skb_dst_drop(skb_in);
 	skb_dst_set(skb_in, dst);
 	return 0;
 }
@@ -336,10 +338,12 @@ void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 	fl6.fl6_sport = otcph->dest;
 	fl6.fl6_dport = otcph->source;
 
-	if (!skb_dst(oldskb)) {
+	if (!skb_valid_dst(oldskb)) {
 		nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false);
 		if (!dst)
 			return;
+
+		skb_dst_drop(oldskb);
 		skb_dst_set(oldskb, dst);
 	}
 
@@ -440,7 +444,7 @@ void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
 	if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
 		skb_in->dev = net->loopback_dev;
 
-	if (!skb_dst(skb_in) && nf_reject6_fill_skb_dst(skb_in) < 0)
+	if (!skb_valid_dst(skb_in) && nf_reject6_fill_skb_dst(skb_in) < 0)
 		return;
 
 	icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);

net/netfilter/nft_meta.c

@@ -20,6 +20,7 @@
 #include <net/dst.h>
 #include <net/ip.h>
 #include <net/sock.h>
+#include <net/dst_metadata.h>
 #include <net/tcp_states.h> /* for TCP_TIME_WAIT */
 #include <net/netfilter/nf_tables.h>
 #include <net/netfilter/nf_tables_core.h>
@@ -279,11 +280,12 @@ static bool nft_meta_get_eval_ifname(enum nft_meta_keys key, u32 *dest,
 static noinline bool
 nft_meta_get_eval_rtclassid(const struct sk_buff *skb, u32 *dest)
 {
-	const struct dst_entry *dst = skb_dst(skb);
+	const struct dst_entry *dst;
 
-	if (!dst)
+	if (!skb_valid_dst(skb))
 		return false;
 
+	dst = skb_dst(skb);
 	*dest = dst->tclassid;
 	return true;
 }

net/netfilter/nft_rt.c

@@ -8,6 +8,7 @@
 #include <linux/netfilter.h>
 #include <linux/netfilter/nf_tables.h>
 #include <net/dst.h>
+#include <net/dst_metadata.h>
 #include <net/ip6_route.h>
 #include <net/route.h>
 #include <net/netfilter/nf_tables.h>
@@ -59,10 +60,11 @@ void nft_rt_get_eval(const struct nft_expr *expr,
 	u32 *dest = &regs->data[priv->dreg];
 	const struct dst_entry *dst;
 
-	dst = skb_dst(skb);
-	if (!dst)
+	if (!skb_valid_dst(skb))
 		goto err;
 
+	dst = skb_dst(skb);
+
 	switch (priv->key) {
 #ifdef CONFIG_IP_ROUTE_CLASSID
 	case NFT_RT_CLASSID:

net/netfilter/nft_xfrm.c

@@ -12,6 +12,7 @@
 #include <linux/netfilter/nf_tables.h>
 #include <net/netfilter/nf_tables_core.h>
 #include <net/netfilter/nf_tables.h>
+#include <net/dst_metadata.h>
 #include <linux/in.h>
 #include <net/xfrm.h>
 
@@ -177,9 +178,15 @@ static void nft_xfrm_get_eval_out(const struct nft_xfrm *priv,
 				  struct nft_regs *regs,
 				  const struct nft_pktinfo *pkt)
 {
-	const struct dst_entry *dst = skb_dst(pkt->skb);
+	const struct dst_entry *dst;
 	int i;
 
+	if (!skb_valid_dst(pkt->skb)) {
+		regs->verdict.code = NFT_BREAK;
+		return;
+	}
+
+	dst = skb_dst(pkt->skb);
 	for (i = 0; dst && dst->xfrm;
 	     dst = ((const struct xfrm_dst *)dst)->child, i++) {
 		if (i < priv->spnum)