ipv6: icmp6: add drop reason support to ndisc_rcv()

Creates three new drop reasons:

SKB_DROP_REASON_IPV6_NDISC_FRAG: invalid frag (suppress_frag_ndisc).

SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT: invalid hop limit.

SKB_DROP_REASON_IPV6_NDISC_BAD_CODE: invalid NDISC icmp6 code.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/dropreason.h

@@ -73,6 +73,9 @@
 	FN(FRAG_TOO_FAR)		\
 	FN(TCP_MINTTL)			\
 	FN(IPV6_BAD_EXTHDR)		\
+	FN(IPV6_NDISC_FRAG)		\
+	FN(IPV6_NDISC_HOP_LIMIT)	\
+	FN(IPV6_NDISC_BAD_CODE)		\
 	FNe(MAX)
 
 /**
@@ -321,6 +324,12 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_MINTTL,
 	/** @SKB_DROP_REASON_IPV6_BAD_EXTHDR: Bad IPv6 extension header. */
 	SKB_DROP_REASON_IPV6_BAD_EXTHDR,
+	/** @SKB_DROP_REASON_IPV6_NDISC_FRAG: invalid frag (suppress_frag_ndisc). */
+	SKB_DROP_REASON_IPV6_NDISC_FRAG,
+	/** @SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT: invalid hop limit. */
+	SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT,
+	/** @SKB_DROP_REASON_IPV6_NDISC_BAD_CODE: invalid NDISC icmp6 code. */
+	SKB_DROP_REASON_IPV6_NDISC_BAD_CODE,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
 	 * used as a real 'reason'

include/net/ndisc.h

@@ -445,7 +445,7 @@ int ndisc_late_init(void);
 void ndisc_late_cleanup(void);
 void ndisc_cleanup(void);
 
-int ndisc_rcv(struct sk_buff *skb);
+enum skb_drop_reason ndisc_rcv(struct sk_buff *skb);
 
 struct sk_buff *ndisc_ns_create(struct net_device *dev, const struct in6_addr *solicit,
 				const struct in6_addr *saddr, u64 nonce);

net/ipv6/icmp.c

@@ -969,7 +969,7 @@ static int icmpv6_rcv(struct sk_buff *skb)
 	case NDISC_NEIGHBOUR_SOLICITATION:
 	case NDISC_NEIGHBOUR_ADVERTISEMENT:
 	case NDISC_REDIRECT:
-		ndisc_rcv(skb);
+		reason = ndisc_rcv(skb);
 		break;
 
 	case ICMPV6_MGM_QUERY:

net/ipv6/ndisc.c

@@ -1804,15 +1804,16 @@ static bool ndisc_suppress_frag_ndisc(struct sk_buff *skb)
 	return false;
 }
 
-int ndisc_rcv(struct sk_buff *skb)
+enum skb_drop_reason ndisc_rcv(struct sk_buff *skb)
 {
 	struct nd_msg *msg;
+	SKB_DR(reason);
 
 	if (ndisc_suppress_frag_ndisc(skb))
-		return 0;
+		return SKB_DROP_REASON_IPV6_NDISC_FRAG;
 
 	if (skb_linearize(skb))
-		return 0;
+		return SKB_DROP_REASON_NOMEM;
 
 	msg = (struct nd_msg *)skb_transport_header(skb);
 
@@ -1821,13 +1822,13 @@ int ndisc_rcv(struct sk_buff *skb)
 	if (ipv6_hdr(skb)->hop_limit != 255) {
 		ND_PRINTK(2, warn, "NDISC: invalid hop-limit: %d\n",
 			  ipv6_hdr(skb)->hop_limit);
-		return 0;
+		return SKB_DROP_REASON_IPV6_NDISC_HOP_LIMIT;
 	}
 
 	if (msg->icmph.icmp6_code != 0) {
 		ND_PRINTK(2, warn, "NDISC: invalid ICMPv6 code: %d\n",
 			  msg->icmph.icmp6_code);
-		return 0;
+		return SKB_DROP_REASON_IPV6_NDISC_BAD_CODE;
 	}
 
 	switch (msg->icmph.icmp6_type) {
@@ -1853,7 +1854,7 @@ int ndisc_rcv(struct sk_buff *skb)
 		break;
 	}
 
-	return 0;
+	return reason;
 }
 
 static int ndisc_netdev_event(struct notifier_block *this, unsigned long event, void *ptr)