ipv6 addrconf: add IFA_F_NOPREFIXROUTE flag to suppress creation of IP6 routes

When adding/modifying an IPv6 address, the userspace application needs
a way to suppress adding a prefix route. This is for example relevant
together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf
generated addresses, but depending on on-link, no route for the
prefix should be added.
Signed-off-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/if_addr.h

@@ -49,6 +49,7 @@ enum {
 #define IFA_F_TENTATIVE		0x40
 #define IFA_F_PERMANENT		0x80
 #define IFA_F_MANAGETEMPADDR	0x100
+#define IFA_F_NOPREFIXROUTE	0x200
 
 struct ifa_cacheinfo {
 	__u32	ifa_prefered;

net/ipv6/addrconf.c

@@ -2434,8 +2434,11 @@ static int inet6_addr_add(struct net *net, int ifindex,
 			    valid_lft, prefered_lft);
 
 	if (!IS_ERR(ifp)) {
-		addrconf_prefix_route(&ifp->addr, ifp->prefix_len, dev,
-				      expires, flags);
+		if (!(ifa_flags & IFA_F_NOPREFIXROUTE)) {
+			addrconf_prefix_route(&ifp->addr, ifp->prefix_len, dev,
+					      expires, flags);
+		}
+
 		/*
 		 * Note that section 3.1 of RFC 4429 indicates
 		 * that the Optimistic flag should not be set for
@@ -3662,7 +3665,8 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, u32 ifa_flags,
 	spin_lock_bh(&ifp->lock);
 	was_managetempaddr = ifp->flags & IFA_F_MANAGETEMPADDR;
 	ifp->flags &= ~(IFA_F_DEPRECATED | IFA_F_PERMANENT | IFA_F_NODAD |
-			IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR);
+			IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR |
+			IFA_F_NOPREFIXROUTE);
 	ifp->flags |= ifa_flags;
 	ifp->tstamp = jiffies;
 	ifp->valid_lft = valid_lft;
@@ -3672,8 +3676,10 @@ static int inet6_addr_modify(struct inet6_ifaddr *ifp, u32 ifa_flags,
 	if (!(ifp->flags&IFA_F_TENTATIVE))
 		ipv6_ifa_notify(0, ifp);
 
-	addrconf_prefix_route(&ifp->addr, ifp->prefix_len, ifp->idev->dev,
-			      expires, flags);
+	if (!(ifa_flags & IFA_F_NOPREFIXROUTE)) {
+		addrconf_prefix_route(&ifp->addr, ifp->prefix_len, ifp->idev->dev,
+				      expires, flags);
+	}
 
 	if (was_managetempaddr || ifp->flags & IFA_F_MANAGETEMPADDR) {
 		if (was_managetempaddr && !(ifp->flags & IFA_F_MANAGETEMPADDR))
@@ -3727,7 +3733,8 @@ inet6_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh)
 	ifa_flags = tb[IFA_FLAGS] ? nla_get_u32(tb[IFA_FLAGS]) : ifm->ifa_flags;
 
 	/* We ignore other flags so far. */
-	ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR;
+	ifa_flags &= IFA_F_NODAD | IFA_F_HOMEADDRESS | IFA_F_MANAGETEMPADDR |
+		     IFA_F_NOPREFIXROUTE;
 
 	ifa = ipv6_get_ifaddr(net, pfx, dev, 1);
 	if (ifa == NULL) {