tcp_metrics: use netlink policy for IPv6 addr len validation

Use the netlink policy to validate IPv6 address length.
Destination address currently has policy for max len set,
and source has no policy validation. In both cases
the code does the real check. With correct policy
check the code can be removed.
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20240816212245.467745-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_metrics.c

@@ -617,9 +617,13 @@ static struct genl_family tcp_metrics_nl_family;
 
 static const struct nla_policy tcp_metrics_nl_policy[TCP_METRICS_ATTR_MAX + 1] = {
 	[TCP_METRICS_ATTR_ADDR_IPV4]	= { .type = NLA_U32, },
-	[TCP_METRICS_ATTR_ADDR_IPV6]	= { .type = NLA_BINARY,
-					    .len = sizeof(struct in6_addr), },
+	[TCP_METRICS_ATTR_ADDR_IPV6]	=
+		NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)),
+
 	[TCP_METRICS_ATTR_SADDR_IPV4]	= { .type = NLA_U32, },
+	[TCP_METRICS_ATTR_SADDR_IPV6]	=
+		NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)),
+
 	/* Following attributes are not received for GET/DEL,
 	 * we keep them for reference
 	 */
@@ -811,8 +815,6 @@ static int __parse_nl_addr(struct genl_info *info, struct inetpeer_addr *addr,
 	if (a) {
 		struct in6_addr in6;
 
-		if (nla_len(a) != sizeof(struct in6_addr))
-			return -EINVAL;
 		in6 = nla_get_in6_addr(a);
 		inetpeer_set_addr_v6(addr, &in6);
 		if (hash)