ipv4: Reject routes specifying ECN bits in rtm_tos

Use the new dscp_t type to replace the fc_tos field of fib_config, to
ensure IPv4 routes aren't influenced by ECN bits when configured with
non-zero rtm_tos.

Before this patch, IPv4 routes specifying an rtm_tos with some of the
ECN bits set were accepted. However they wouldn't work (never match) as
IPv4 normally clears the ECN bits with IPTOS_RT_MASK before doing a FIB
lookup (although a few buggy code paths don't).

After this patch, IPv4 routes specifying an rtm_tos with any ECN bit
set is rejected.

Note: IPv6 routes ignore rtm_tos altogether, any rtm_tos is accepted,
but treated as if it were 0.
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Acked-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/ip_fib.h

@@ -17,6 +17,7 @@
 #include <linux/rcupdate.h>
 #include <net/fib_notifier.h>
 #include <net/fib_rules.h>
+#include <net/inet_dscp.h>
 #include <net/inetpeer.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
@@ -24,7 +25,7 @@
 
 struct fib_config {
 	u8			fc_dst_len;
-	u8			fc_tos;
+	dscp_t			fc_dscp;
 	u8			fc_protocol;
 	u8			fc_scope;
 	u8			fc_type;

net/ipv4/fib_frontend.c

@@ -32,6 +32,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 
+#include <net/inet_dscp.h>
 #include <net/ip.h>
 #include <net/protocol.h>
 #include <net/route.h>
@@ -735,8 +736,16 @@ static int rtm_to_fib_config(struct net *net, struct sk_buff *skb,
 	memset(cfg, 0, sizeof(*cfg));
 
 	rtm = nlmsg_data(nlh);
+
+	if (!inet_validate_dscp(rtm->rtm_tos)) {
+		NL_SET_ERR_MSG(extack,
+			       "Invalid dsfield (tos): ECN bits must be 0");
+		err = -EINVAL;
+		goto errout;
+	}
+	cfg->fc_dscp = inet_dsfield_to_dscp(rtm->rtm_tos);
+
 	cfg->fc_dst_len = rtm->rtm_dst_len;
-	cfg->fc_tos = rtm->rtm_tos;
 	cfg->fc_table = rtm->rtm_table;
 	cfg->fc_protocol = rtm->rtm_protocol;
 	cfg->fc_scope = rtm->rtm_scope;

net/ipv4/fib_trie.c

@@ -61,6 +61,7 @@
 #include <linux/vmalloc.h>
 #include <linux/notifier.h>
 #include <net/net_namespace.h>
+#include <net/inet_dscp.h>
 #include <net/ip.h>
 #include <net/protocol.h>
 #include <net/route.h>
@@ -1210,9 +1211,9 @@ int fib_table_insert(struct net *net, struct fib_table *tb,
 	struct fib_info *fi;
 	u8 plen = cfg->fc_dst_len;
 	u8 slen = KEYLENGTH - plen;
-	u8 tos = cfg->fc_tos;
 	u32 key;
 	int err;
+	u8 tos;
 
 	key = ntohl(cfg->fc_dst);
 
@@ -1227,6 +1228,7 @@ int fib_table_insert(struct net *net, struct fib_table *tb,
 		goto err;
 	}
 
+	tos = inet_dscp_to_dsfield(cfg->fc_dscp);
 	l = fib_find_node(t, &tp, key);
 	fa = l ? fib_find_alias(&l->leaf, slen, tos, fi->fib_priority,
 				tb->tb_id, false) : NULL;
@@ -1703,8 +1705,8 @@ int fib_table_delete(struct net *net, struct fib_table *tb,
 	struct key_vector *l, *tp;
 	u8 plen = cfg->fc_dst_len;
 	u8 slen = KEYLENGTH - plen;
-	u8 tos = cfg->fc_tos;
 	u32 key;
+	u8 tos;
 
 	key = ntohl(cfg->fc_dst);
 
@@ -1715,6 +1717,7 @@ int fib_table_delete(struct net *net, struct fib_table *tb,
 	if (!l)
 		return -ESRCH;
 
+	tos = inet_dscp_to_dsfield(cfg->fc_dscp);
 	fa = fib_find_alias(&l->leaf, slen, tos, 0, tb->tb_id, false);
 	if (!fa)
 		return -ESRCH;

tools/testing/selftests/net/fib_tests.sh

@@ -1447,6 +1447,81 @@ ipv4_local_rt_cache()
 	log_test $? 0 "Cached route removed from VRF port device"
 }
 
+ipv4_rt_dsfield()
+{
+	echo
+	echo "IPv4 route with dsfield tests"
+
+	run_cmd "$IP route flush 172.16.102.0/24"
+
+	# New routes should reject dsfield options that interfere with ECN
+	run_cmd "$IP route add 172.16.102.0/24 dsfield 0x01 via 172.16.101.2"
+	log_test $? 2 "Reject route with dsfield 0x01"
+
+	run_cmd "$IP route add 172.16.102.0/24 dsfield 0x02 via 172.16.101.2"
+	log_test $? 2 "Reject route with dsfield 0x02"
+
+	run_cmd "$IP route add 172.16.102.0/24 dsfield 0x03 via 172.16.101.2"
+	log_test $? 2 "Reject route with dsfield 0x03"
+
+	# A generic route that doesn't take DSCP into account
+	run_cmd "$IP route add 172.16.102.0/24 via 172.16.101.2"
+
+	# A more specific route for DSCP 0x10
+	run_cmd "$IP route add 172.16.102.0/24 dsfield 0x10 via 172.16.103.2"
+
+	# DSCP 0x10 should match the specific route, no matter the ECN bits
+	$IP route get fibmatch 172.16.102.1 dsfield 0x10 | \
+		grep -q "via 172.16.103.2"
+	log_test $? 0 "IPv4 route with DSCP and ECN:Not-ECT"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x11 | \
+		grep -q "via 172.16.103.2"
+	log_test $? 0 "IPv4 route with DSCP and ECN:ECT(1)"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x12 | \
+		grep -q "via 172.16.103.2"
+	log_test $? 0 "IPv4 route with DSCP and ECN:ECT(0)"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x13 | \
+		grep -q "via 172.16.103.2"
+	log_test $? 0 "IPv4 route with DSCP and ECN:CE"
+
+	# Unknown DSCP should match the generic route, no matter the ECN bits
+	$IP route get fibmatch 172.16.102.1 dsfield 0x14 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with unknown DSCP and ECN:Not-ECT"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x15 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with unknown DSCP and ECN:ECT(1)"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x16 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with unknown DSCP and ECN:ECT(0)"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x17 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with unknown DSCP and ECN:CE"
+
+	# Null DSCP should match the generic route, no matter the ECN bits
+	$IP route get fibmatch 172.16.102.1 dsfield 0x00 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with no DSCP and ECN:Not-ECT"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x01 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with no DSCP and ECN:ECT(1)"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x02 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with no DSCP and ECN:ECT(0)"
+
+	$IP route get fibmatch 172.16.102.1 dsfield 0x03 | \
+		grep -q "via 172.16.101.2"
+	log_test $? 0 "IPv4 route with no DSCP and ECN:CE"
+}
+
 ipv4_route_test()
 {
 	route_setup
@@ -1454,6 +1529,7 @@ ipv4_route_test()
 	ipv4_rt_add
 	ipv4_rt_replace
 	ipv4_local_rt_cache
+	ipv4_rt_dsfield
 
 	route_cleanup
 }