ipv6: Reject routes configurations that specify dsfield (tos)

The ->rtm_tos option is normally used to route packets based on both
the destination address and the DS field. However it's ignored for
IPv6 routes. Setting ->rtm_tos for IPv6 is thus invalid as the route
is going to work only on the destination address anyway, so it won't
behave as specified.
Suggested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -5009,6 +5009,12 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
 	err = -EINVAL;
 	rtm = nlmsg_data(nlh);
 
+	if (rtm->rtm_tos) {
+		NL_SET_ERR_MSG(extack,
+			       "Invalid dsfield (tos): option not available for IPv6");
+		goto errout;
+	}
+
 	*cfg = (struct fib6_config){
 		.fc_table = rtm->rtm_table,
 		.fc_dst_len = rtm->rtm_dst_len,

tools/testing/selftests/net/fib_tests.sh

@@ -988,12 +988,25 @@ ipv6_rt_replace()
 	ipv6_rt_replace_mpath
 }
 
+ipv6_rt_dsfield()
+{
+	echo
+	echo "IPv6 route with dsfield tests"
+
+	run_cmd "$IP -6 route flush 2001:db8:102::/64"
+
+	# IPv6 doesn't support routing based on dsfield
+	run_cmd "$IP -6 route add 2001:db8:102::/64 dsfield 0x04 via 2001:db8:101::2"
+	log_test $? 2 "Reject route with dsfield"
+}
+
 ipv6_route_test()
 {
 	route_setup
 
 	ipv6_rt_add
 	ipv6_rt_replace
+	ipv6_rt_dsfield
 
 	route_cleanup
 }