[PATCHv2 net-next 2/2] ipv4/fib: send notify when delete source address routes

[Hangbin Liu <liuhangbin@gmail.com>]

After deleting an interface address in fib_del_ifaddr(), the function
scans the fib_info list for stray entries and calls fib_flush() and
fib_table_flush(). Then the stray entries will be deleted silently and no
RTM_DELROUTE notification will be sent.

This lack of notification can make routing daemons like NetworkManager,
miss the routing changes. e.g.

+ ip link add dummy1 type dummy
+ ip link add dummy2 type dummy
+ ip link set dummy1 up
+ ip link set dummy2 up
+ ip addr add 192.168.5.5/24 dev dummy1
+ ip route add 7.7.7.0/24 dev dummy2 src 192.168.5.5
+ ip -4 route
7.7.7.0/24 dev dummy2 scope link src 192.168.5.5
192.168.5.0/24 dev dummy1 proto kernel scope link src 192.168.5.5
+ ip monitor route
+ ip addr del 192.168.5.5/24 dev dummy1
Deleted 192.168.5.0/24 dev dummy1 proto kernel scope link src 192.168.5.5
Deleted broadcast 192.168.5.255 dev dummy1 table local proto kernel scope link src 192.168.5.5
Deleted local 192.168.5.5 dev dummy1 table local proto kernel scope host src 192.168.5.5

As Ido reminded, fib_table_flush() isn't only called when an address is
deleted, but also when an interface is deleted or put down. The lack of
notification in these cases is deliberate. And commit 7c6bb7d2faaf
("net/ipv6: Add knob to skip DELROUTE message on device down") introduced
a sysctl to make IPv6 behave like IPv4 in this regard. So we can't send
the route delete notify blindly in fib_table_flush().

To fix this issue, let's add a new bit in "struct fib_info" to track the
deleted prefer source address routes, and only send notify for them.

After update:
+ ip monitor route
+ ip addr del 192.168.5.5/24 dev dummy1
Deleted 192.168.5.0/24 dev dummy1 proto kernel scope link src 192.168.5.5
Deleted broadcast 192.168.5.255 dev dummy1 table local proto kernel scope link src 192.168.5.5
Deleted local 192.168.5.5 dev dummy1 table local proto kernel scope host src 192.168.5.5
Deleted 7.7.7.0/24 dev dummy2 scope link src 192.168.5.5

Suggested-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
---
v2: Add a bit in fib_info to mark the deleted src route.
---
 include/net/ip_fib.h     | 3 ++-
 net/ipv4/fib_semantics.c | 1 +
 net/ipv4/fib_trie.c      | 4 ++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index a91f8a28689a..12dedfa4c9fd 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -153,7 +153,8 @@ struct fib_info {
 #define fib_advmss fib_metrics->metrics[RTAX_ADVMSS-1]
 	int			fib_nhs;
 	u8			fib_nh_is_v6:1,
-				nh_updated:1;
+				nh_updated:1,
+				pfsrc_removed:1;
 	struct nexthop		*nh;
 	struct rcu_head		rcu;
 	struct fib_nh		fib_nh[];
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index ce1c10e408cf..6cd919b442a7 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1884,6 +1884,7 @@ int fib_sync_down_addr(struct net_device *dev, __be32 local)
 			continue;
 		if (fi->fib_prefsrc == local) {
 			fi->fib_flags |= RTNH_F_DEAD;
+			fi->pfsrc_removed = 1;
 			ret++;
 		}
 	}
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 74d403dbd2b4..9cadeeaaa93a 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -2026,6 +2026,7 @@ void fib_table_flush_external(struct fib_table *tb)
 int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all)
 {
 	struct trie *t = (struct trie *)tb->tb_data;
+	struct nl_info info = { .nl_net = net };
 	struct key_vector *pn = t->kv;
 	unsigned long cindex = 1;
 	struct hlist_node *tmp;
@@ -2088,6 +2089,9 @@ int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all)
 
 			fib_notify_alias_delete(net, n->key, &n->leaf, fa,
 						NULL);
+			if (fi->pfsrc_removed)
+				rtmsg_fib(RTM_DELROUTE, htonl(n->key), fa,
+					  KEYLENGTH - fa->fa_slen, tb->tb_id, &info, 0);
 			hlist_del_rcu(&fa->fa_list);
 			fib_release_info(fa->fa_info);
 			alias_free_mem_rcu(fa);
-- 
2.38.1