ipv6: icmp6: add drop reason support to icmpv6_notify()

Accurately reports what happened in icmpv6_notify() when handling
a packet.

This makes use of the new IPV6_BAD_EXTHDR drop reason.
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/ipv6.h

@@ -436,7 +436,8 @@ static inline void fl6_sock_release(struct ip6_flowlabel *fl)
 		atomic_dec(&fl->users);
 }
 
-void icmpv6_notify(struct sk_buff *skb, u8 type, u8 code, __be32 info);
+enum skb_drop_reason icmpv6_notify(struct sk_buff *skb, u8 type,
+				   u8 code, __be32 info);
 
 void icmpv6_push_pending_frames(struct sock *sk, struct flowi6 *fl6,
 				struct icmp6hdr *thdr, int len);

net/ipv6/icmp.c

@@ -813,16 +813,19 @@ static void icmpv6_echo_reply(struct sk_buff *skb)
 	local_bh_enable();
 }
 
-void icmpv6_notify(struct sk_buff *skb, u8 type, u8 code, __be32 info)
+enum skb_drop_reason icmpv6_notify(struct sk_buff *skb, u8 type,
+				   u8 code, __be32 info)
 {
 	struct inet6_skb_parm *opt = IP6CB(skb);
+	struct net *net = dev_net(skb->dev);
 	const struct inet6_protocol *ipprot;
+	enum skb_drop_reason reason;
 	int inner_offset;
 	__be16 frag_off;
 	u8 nexthdr;
-	struct net *net = dev_net(skb->dev);
 
-	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
+	reason = pskb_may_pull_reason(skb, sizeof(struct ipv6hdr));
+	if (reason != SKB_NOT_DROPPED_YET)
 		goto out;
 
 	seg6_icmp_srh(skb, opt);
@@ -832,14 +835,17 @@ void icmpv6_notify(struct sk_buff *skb, u8 type, u8 code, __be32 info)
 		/* now skip over extension headers */
 		inner_offset = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr),
 						&nexthdr, &frag_off);
-		if (inner_offset < 0)
+		if (inner_offset < 0) {
+			SKB_DR_SET(reason, IPV6_BAD_EXTHDR);
 			goto out;
+		}
 	} else {
 		inner_offset = sizeof(struct ipv6hdr);
 	}
 
 	/* Checkin header including 8 bytes of inner protocol header. */
-	if (!pskb_may_pull(skb, inner_offset+8))
+	reason = pskb_may_pull_reason(skb, inner_offset + 8);
+	if (reason != SKB_NOT_DROPPED_YET)
 		goto out;
 
 	/* BUGGG_FUTURE: we should try to parse exthdrs in this packet.
@@ -854,10 +860,11 @@ void icmpv6_notify(struct sk_buff *skb, u8 type, u8 code, __be32 info)
 		ipprot->err_handler(skb, opt, type, code, inner_offset, info);
 
 	raw6_icmp_error(skb, nexthdr, type, code, inner_offset, info);
-	return;
+	return SKB_CONSUMED;
 
 out:
 	__ICMP6_INC_STATS(net, __in6_dev_get(skb->dev), ICMP6_MIB_INERRORS);
+	return reason;
 }
 
 /*
@@ -953,7 +960,8 @@ static int icmpv6_rcv(struct sk_buff *skb)
 	case ICMPV6_DEST_UNREACH:
 	case ICMPV6_TIME_EXCEED:
 	case ICMPV6_PARAMPROB:
-		icmpv6_notify(skb, type, hdr->icmp6_code, hdr->icmp6_mtu);
+		reason = icmpv6_notify(skb, type, hdr->icmp6_code,
+				       hdr->icmp6_mtu);
 		break;
 
 	case NDISC_ROUTER_SOLICITATION:
@@ -995,7 +1003,8 @@ static int icmpv6_rcv(struct sk_buff *skb)
 		 * must pass to upper level
 		 */
 
-		icmpv6_notify(skb, type, hdr->icmp6_code, hdr->icmp6_mtu);
+		reason = icmpv6_notify(skb, type, hdr->icmp6_code,
+				       hdr->icmp6_mtu);
 	}
 
 	/* until the v6 path can be better sorted assume failure and