ipv6: check return value of ipv6_get_lladdr

We should check the return value of ipv6_get_lladdr in inet6_set_iftoken.

A possible situation, which could leave ll_addr unassigned is, when
the user removed her link-local address but a global scoped address was
already set. In this case the interface would still be IF_READY and not
dead. In that case the RS source address is some value from the stack.

v2: Daniel Borkmann noted a small indent inconstancy; no semantic
changes.

Cc: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Reviewed-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -4306,6 +4306,7 @@ static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token)
 	struct inet6_ifaddr *ifp;
 	struct net_device *dev = idev->dev;
 	bool update_rs = false;
+	struct in6_addr ll_addr;
 
 	if (token == NULL)
 		return -EINVAL;
@@ -4325,11 +4326,9 @@ static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token)
 
 	write_unlock_bh(&idev->lock);
 
-	if (!idev->dead && (idev->if_flags & IF_READY)) {
-		struct in6_addr ll_addr;
-
-		ipv6_get_lladdr(dev, &ll_addr, IFA_F_TENTATIVE |
-				IFA_F_OPTIMISTIC);
+	if (!idev->dead && (idev->if_flags & IF_READY) &&
+	    !ipv6_get_lladdr(dev, &ll_addr, IFA_F_TENTATIVE |
+			     IFA_F_OPTIMISTIC)) {
 
 		/* If we're not ready, then normal ifup will take care
 		 * of this. Otherwise, we need to request our rs here.