net/ipv6: remove the old peer route if change it to a new one

When we modify the peer route and changed it to a new one, we should
remove the old route first. Before the fix:

+ ip addr add dev dummy1 2001:db8::1 peer 2001:db8::2
+ ip -6 route show dev dummy1
2001:db8::1 proto kernel metric 256 pref medium
2001:db8::2 proto kernel metric 256 pref medium
+ ip addr change dev dummy1 2001:db8::1 peer 2001:db8::3
+ ip -6 route show dev dummy1
2001:db8::1 proto kernel metric 256 pref medium
2001:db8::2 proto kernel metric 256 pref medium

After the fix:
+ ip addr change dev dummy1 2001:db8::1 peer 2001:db8::3
+ ip -6 route show dev dummy1
2001:db8::1 proto kernel metric 256 pref medium
2001:db8::3 proto kernel metric 256 pref medium

This patch depend on the previous patch "net/ipv6: need update peer route
when modify metric" to update new peer route after delete old one.
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -1226,11 +1226,13 @@ check_cleanup_prefix_route(struct inet6_ifaddr *ifp, unsigned long *expires)
 }
 
 static void
-cleanup_prefix_route(struct inet6_ifaddr *ifp, unsigned long expires, bool del_rt)
+cleanup_prefix_route(struct inet6_ifaddr *ifp, unsigned long expires,
+		     bool del_rt, bool del_peer)
 {
 	struct fib6_info *f6i;
 
-	f6i = addrconf_get_prefix_route(&ifp->addr, ifp->prefix_len,
+	f6i = addrconf_get_prefix_route(del_peer ? &ifp->peer_addr : &ifp->addr,
+					ifp->prefix_len,
 					ifp->idev->dev, 0, RTF_DEFAULT, true);
 	if (f6i) {
 		if (del_rt)
@@ -1293,7 +1295,7 @@ static void ipv6_del_addr(struct inet6_ifaddr *ifp)
 
 	if (action != CLEANUP_PREFIX_RT_NOP) {
 		cleanup_prefix_route(ifp, expires,
-			action == CLEANUP_PREFIX_RT_DEL);
+			action == CLEANUP_PREFIX_RT_DEL, false);
 	}
 
 	/* clean up prefsrc entries */
@@ -4627,6 +4629,7 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, struct ifa6_config *cfg)
 	unsigned long timeout;
 	bool was_managetempaddr;
 	bool had_prefixroute;
+	bool new_peer = false;
 
 	ASSERT_RTNL();
 
@@ -4658,6 +4661,13 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, struct ifa6_config *cfg)
 		cfg->preferred_lft = timeout;
 	}
 
+	if (cfg->peer_pfx &&
+	    memcmp(&ifp->peer_addr, cfg->peer_pfx, sizeof(struct in6_addr))) {
+		if (!ipv6_addr_any(&ifp->peer_addr))
+			cleanup_prefix_route(ifp, expires, true, true);
+		new_peer = true;
+	}
+
 	spin_lock_bh(&ifp->lock);
 	was_managetempaddr = ifp->flags & IFA_F_MANAGETEMPADDR;
 	had_prefixroute = ifp->flags & IFA_F_PERMANENT &&
@@ -4673,6 +4683,9 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, struct ifa6_config *cfg)
 	if (cfg->rt_priority && cfg->rt_priority != ifp->rt_priority)
 		ifp->rt_priority = cfg->rt_priority;
 
+	if (new_peer)
+		ifp->peer_addr = *cfg->peer_pfx;
+
 	spin_unlock_bh(&ifp->lock);
 	if (!(ifp->flags&IFA_F_TENTATIVE))
 		ipv6_ifa_notify(0, ifp);
@@ -4708,7 +4721,7 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, struct ifa6_config *cfg)
 
 		if (action != CLEANUP_PREFIX_RT_NOP) {
 			cleanup_prefix_route(ifp, rt_expires,
-				action == CLEANUP_PREFIX_RT_DEL);
+				action == CLEANUP_PREFIX_RT_DEL, false);
 		}
 	}