net: ipv4: remove erroneous advancement of list pointer

Causes crash when lifetime expires on an adress as garbage is
dereferenced soon after.

This used to look like this:

 for (ifap = &ifa->ifa_dev->ifa_list;
      *ifap != NULL; ifap = &(*ifap)->ifa_next) {
          if (*ifap == ifa) ...

but this was changed to:

struct in_ifaddr *tmp;

ifap = &ifa->ifa_dev->ifa_list;
tmp = rtnl_dereference(*ifap);
while (tmp) {
   tmp = rtnl_dereference(tmp->ifa_next); // Bogus
   if (rtnl_dereference(*ifap) == ifa) {
     ...
   ifap = &tmp->ifa_next;		// Can be NULL
   tmp = rtnl_dereference(*ifap);	// Dereference
   }
}

Remove the bogus assigment/list entry skip.

Fixes: 2638eb8b50 ("net: ipv4: provide __rcu annotation for ifa_list")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/devinet.c

@@ -745,8 +745,7 @@ static void check_lifetime(struct work_struct *work)
 				ifap = &ifa->ifa_dev->ifa_list;
 				tmp = rtnl_dereference(*ifap);
 				while (tmp) {
-					tmp = rtnl_dereference(tmp->ifa_next);
-					if (rtnl_dereference(*ifap) == ifa) {
+					if (tmp == ifa) {
 						inet_del_ifa(ifa->ifa_dev,
 							     ifap, 1);
 						break;