netdev - [PATCH net-next] ipv6: Reject routes configurations that specify dsfield (tos)

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Date:   Thu, 10 Feb 2022 16:08:08 +0100
From:   Guillaume Nault <gnault@...hat.com>
To:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH net-next] 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@...hat.com>
Signed-off-by: Guillaume Nault <gnault@...hat.com>
---
The same problem exists for ->rtm_scope. I'm working only on ->rtm_tos
here because IPv4 recently started to validate this option too (as part
of the DSCP/ECN clarification effort).
I'll give this patch some soak time, then send another one for
rejecting ->rtm_scope in IPv6 routes if nobody complains.

 net/ipv6/route.c                         |  6 ++++++
 tools/testing/selftests/net/fib_tests.sh | 13 +++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f4884cda13b9..dd98a11fbdb6 100644
--- a/net/ipv6/route.c
+++ b/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,
diff --git a/tools/testing/selftests/net/fib_tests.sh b/tools/testing/selftests/net/fib_tests.sh
index bb73235976b3..e2690cc42da3 100755
--- a/tools/testing/selftests/net/fib_tests.sh
+++ b/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
 }
-- 
2.21.3