[PATCH v2] net-next: improve handling of ICMP_EXT_ECHO icmp type

[Mathias Lark <mathiaslark@gmail.com>]

Introduce a helper for icmp type checking - icmp_is_valid_type.

There is a number of code paths handling ICMP packets. To check
icmp type validity, some of those code paths perform the check
`type <= NR_ICMP_TYPES`. Since the introduction of ICMP_EXT_ECHO
and ICMP_EXT_ECHOREPLY (RFC 8335), this check is no longer correct.

To fix this inconsistency and avoid further problems with future
ICMP types, the patch inserts the icmp_is_valid type helper
wherever it is required. The helper checks if the type is less than
NR_ICMP_TYPES or is equal to ICMP_EXT_ECHO/REPLY.

NR_ICMP_TYPES could theoretically be increased to ICMP_EXT_ECHOREPLY
(43), but that would not make sense as types 19-41 are not used.

Signed-off-by: Mathias Lark <mathias.lark@gmail.com>
---
 include/linux/icmp.h                    | 4 ++++
 net/ipv4/icmp.c                         | 8 +++-----
 net/netfilter/nf_conntrack_proto_icmp.c | 4 +---
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/icmp.h b/include/linux/icmp.h
index 0af4d210ee31..e979c80696b0 100644
--- a/include/linux/icmp.h
+++ b/include/linux/icmp.h
@@ -36,6 +36,11 @@ static inline bool icmp_is_err(int type)
 	return false;
 }
 
+static inline bool icmp_is_valid_type(int type)
+{
+	return type <= NR_ICMP_TYPES || type == ICMP_EXT_ECHO || type == ICMP_EXT_ECHOREPLY;
+}
+
 void ip_icmp_error_rfc4884(const struct sk_buff *skb,
 			   struct sock_ee_data_rfc4884 *out,
 			   int thlen, int off);
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 236debd9fded..686f3133370f 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -273,7 +273,7 @@ EXPORT_SYMBOL(icmp_global_allow);
 
 static bool icmpv4_mask_allow(struct net *net, int type, int code)
 {
-	if (type > NR_ICMP_TYPES)
+	if (!icmp_is_valid_type(type))
 		return true;
 
 	/* Don't limit PMTU discovery. */
@@ -661,7 +661,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
 			 *	Assume any unknown ICMP type is an error. This
 			 *	isn't specified by the RFC, but think about it..
 			 */
-			if (*itp > NR_ICMP_TYPES ||
+			if (!icmp_is_valid_type(*itp) ||
 			    icmp_pointers[*itp].error)
 				goto out;
 		}
@@ -1225,12 +1225,10 @@ int icmp_rcv(struct sk_buff *skb)
 	}
 
 	/*
-	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
-	 *
 	 *	RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently
 	 *		  discarded.
 	 */
-	if (icmph->type > NR_ICMP_TYPES) {
+	if (!icmp_is_valid_type(icmph->type)) {
 		reason = SKB_DROP_REASON_UNHANDLED_PROTO;
 		goto error;
 	}
diff --git a/net/netfilter/nf_conntrack_proto_icmp.c b/net/netfilter/nf_conntrack_proto_icmp.c
index b38b7164acd5..ba4462c393be 100644
--- a/net/netfilter/nf_conntrack_proto_icmp.c
+++ b/net/netfilter/nf_conntrack_proto_icmp.c
@@ -225,12 +225,10 @@ int nf_conntrack_icmpv4_error(struct nf_conn *tmpl,
 	}
 
 	/*
-	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
-	 *
 	 *	RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently
 	 *		  discarded.
 	 */
-	if (icmph->type > NR_ICMP_TYPES) {
+	if (!icmp_is_valid_type(icmph->type)) {
 		icmp_error_log(skb, state, "invalid icmp type");
 		return -NF_ACCEPT;
 	}
-- 
2.36.1