ioam6: improve checks on user data

This patch improves two checks on user data.

The first one prevents bit 23 from being set, as specified by RFC 9197
(Sec 4.4.1):

  Bit 23    Reserved; MUST be set to zero upon transmission and be
            ignored upon receipt.  This bit is reserved to allow for
            future extensions of the IOAM Trace-Type bit field.

The second one checks that the tunnel destination address !=
IPV6_ADDR_ANY, just like we already do for the tunnel source address.

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Link: https://patch.msgid.link/20240830191919.51439-1-justin.iurman@uliege.be
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/ioam6_iptunnel.c

@@ -89,7 +89,7 @@ static bool ioam6_validate_trace_hdr(struct ioam6_trace_hdr *trace)
 	    trace->type.bit12 | trace->type.bit13 | trace->type.bit14 |
 	    trace->type.bit15 | trace->type.bit16 | trace->type.bit17 |
 	    trace->type.bit18 | trace->type.bit19 | trace->type.bit20 |
-	    trace->type.bit21)
+	    trace->type.bit21 | trace->type.bit23)
 		return false;
 
 	trace->nodelen = 0;
@@ -199,9 +199,17 @@ static int ioam6_build_state(struct net *net, struct nlattr *nla,
 		}
 	}
 
-	if (tb[IOAM6_IPTUNNEL_DST])
+	if (tb[IOAM6_IPTUNNEL_DST]) {
 		ilwt->tundst = nla_get_in6_addr(tb[IOAM6_IPTUNNEL_DST]);
 
+		if (ipv6_addr_any(&ilwt->tundst)) {
+			NL_SET_ERR_MSG_ATTR(extack, tb[IOAM6_IPTUNNEL_DST],
+					    "invalid tunnel dest address");
+			err = -EINVAL;
+			goto free_cache;
+		}
+	}
+
 	tuninfo = ioam6_lwt_info(lwt);
 	tuninfo->eh.hdrlen = ((sizeof(*tuninfo) + len_aligned) >> 3) - 1;
 	tuninfo->pad[0] = IPV6_TLV_PADN;