Merge branch 'ipv4-invalidate-broadcast-neigh-upon-address-addition'

Ido Schimmel says:

====================
ipv4: Invalidate neighbour for broadcast address upon address addition

Patch #1 solves a recently reported issue [1]. See detailed description
in the changelog.

Patch #2 adds a matching test case.

Targeting at net-next since as far as I can tell this use case never
worked.

There are no regressions in fib_tests.sh with this change:

 # ./fib_tests.sh
 ...
 Tests passed: 186
 Tests failed:   0

[1] https://lore.kernel.org/netdev/55a04a8f-56f3-f73c-2aea-2195923f09d1@huawei.com/
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/arp.h

@@ -65,6 +65,7 @@ void arp_send(int type, int ptype, __be32 dest_ip,
 	      const unsigned char *src_hw, const unsigned char *th);
 int arp_mc_map(__be32 addr, u8 *haddr, struct net_device *dev, int dir);
 void arp_ifdown(struct net_device *dev);
+int arp_invalidate(struct net_device *dev, __be32 ip, bool force);
 
 struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
 			   struct net_device *dev, __be32 src_ip,

net/ipv4/arp.c

@@ -1116,13 +1116,18 @@ static int arp_req_get(struct arpreq *r, struct net_device *dev)
 	return err;
 }
 
-static int arp_invalidate(struct net_device *dev, __be32 ip)
+int arp_invalidate(struct net_device *dev, __be32 ip, bool force)
 {
 	struct neighbour *neigh = neigh_lookup(&arp_tbl, &ip, dev);
 	int err = -ENXIO;
 	struct neigh_table *tbl = &arp_tbl;
 
 	if (neigh) {
+		if ((neigh->nud_state & NUD_VALID) && !force) {
+			neigh_release(neigh);
+			return 0;
+		}
+
 		if (neigh->nud_state & ~NUD_NOARP)
 			err = neigh_update(neigh, NULL, NUD_FAILED,
 					   NEIGH_UPDATE_F_OVERRIDE|
@@ -1169,7 +1174,7 @@ static int arp_req_delete(struct net *net, struct arpreq *r,
 		if (!dev)
 			return -EINVAL;
 	}
-	return arp_invalidate(dev, ip);
+	return arp_invalidate(dev, ip, true);
 }
 
 /*

net/ipv4/fib_frontend.c

@@ -1124,9 +1124,11 @@ void fib_add_ifaddr(struct in_ifaddr *ifa)
 		return;
 
 	/* Add broadcast address, if it is explicitly assigned. */
-	if (ifa->ifa_broadcast && ifa->ifa_broadcast != htonl(0xFFFFFFFF))
+	if (ifa->ifa_broadcast && ifa->ifa_broadcast != htonl(0xFFFFFFFF)) {
 		fib_magic(RTM_NEWROUTE, RTN_BROADCAST, ifa->ifa_broadcast, 32,
 			  prim, 0);
+		arp_invalidate(dev, ifa->ifa_broadcast, false);
+	}
 
 	if (!ipv4_is_zeronet(prefix) && !(ifa->ifa_flags & IFA_F_SECONDARY) &&
 	    (prefix != addr || ifa->ifa_prefixlen < 32)) {
@@ -1140,6 +1142,7 @@ void fib_add_ifaddr(struct in_ifaddr *ifa)
 		if (ifa->ifa_prefixlen < 31) {
 			fib_magic(RTM_NEWROUTE, RTN_BROADCAST, prefix | ~mask,
 				  32, prim, 0);
+			arp_invalidate(dev, prefix | ~mask, false);
 		}
 	}
 }

tools/testing/selftests/net/fib_tests.sh

@@ -9,7 +9,7 @@ ret=0
 ksft_skip=4
 
 # all tests in this script. Can be overridden with -t option
-TESTS="unregister down carrier nexthop suppress ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw rp_filter ipv4_del_addr ipv4_mangle ipv6_mangle"
+TESTS="unregister down carrier nexthop suppress ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw rp_filter ipv4_del_addr ipv4_mangle ipv6_mangle ipv4_bcast_neigh"
 
 VERBOSE=0
 PAUSE_ON_FAIL=no
@@ -1954,6 +1954,61 @@ ipv6_mangle_test()
 	route_cleanup
 }
 
+ip_neigh_get_check()
+{
+	ip neigh help 2>&1 | grep -q 'ip neigh get'
+	if [ $? -ne 0 ]; then
+		echo "iproute2 command does not support neigh get. Skipping test"
+		return 1
+	fi
+
+	return 0
+}
+
+ipv4_bcast_neigh_test()
+{
+	local rc
+
+	echo
+	echo "IPv4 broadcast neighbour tests"
+
+	ip_neigh_get_check || return 1
+
+	setup
+
+	set -e
+	run_cmd "$IP neigh add 192.0.2.111 lladdr 00:11:22:33:44:55 nud perm dev dummy0"
+	run_cmd "$IP neigh add 192.0.2.255 lladdr 00:11:22:33:44:55 nud perm dev dummy0"
+
+	run_cmd "$IP neigh get 192.0.2.111 dev dummy0"
+	run_cmd "$IP neigh get 192.0.2.255 dev dummy0"
+
+	run_cmd "$IP address add 192.0.2.1/24 broadcast 192.0.2.111 dev dummy0"
+
+	run_cmd "$IP neigh add 203.0.113.111 nud failed dev dummy0"
+	run_cmd "$IP neigh add 203.0.113.255 nud failed dev dummy0"
+
+	run_cmd "$IP neigh get 203.0.113.111 dev dummy0"
+	run_cmd "$IP neigh get 203.0.113.255 dev dummy0"
+
+	run_cmd "$IP address add 203.0.113.1/24 broadcast 203.0.113.111 dev dummy0"
+	set +e
+
+	run_cmd "$IP neigh get 192.0.2.111 dev dummy0"
+	log_test $? 0 "Resolved neighbour for broadcast address"
+
+	run_cmd "$IP neigh get 192.0.2.255 dev dummy0"
+	log_test $? 0 "Resolved neighbour for network broadcast address"
+
+	run_cmd "$IP neigh get 203.0.113.111 dev dummy0"
+	log_test $? 2 "Unresolved neighbour for broadcast address"
+
+	run_cmd "$IP neigh get 203.0.113.255 dev dummy0"
+	log_test $? 2 "Unresolved neighbour for network broadcast address"
+
+	cleanup
+}
+
 ################################################################################
 # usage
 
@@ -2028,6 +2083,7 @@ do
 	ipv4_route_v6_gw)		ipv4_route_v6_gw_test;;
 	ipv4_mangle)			ipv4_mangle_test;;
 	ipv6_mangle)			ipv6_mangle_test;;
+	ipv4_bcast_neigh)		ipv4_bcast_neigh_test;;
 
 	help) echo "Test names: $TESTS"; exit 0;;
 	esac