ipmr: dont corrupt lists

ipmr_rules_exit() and ip6mr_rules_exit() free a list of items, but
forget to properly remove these items from list. List head is not
changed and still points to freed memory.

This can trigger a fault later when icmpv6_sk_exit() is called.

Fix is to either reinit list, or use list_del() to properly remove items
from list before freeing them.

bugzilla report : https://bugzilla.kernel.org/show_bug.cgi?id=16120

Introduced by commit d1db275dd3f6e4 (ipv6: ip6mr: support multiple
tables) and commit f0ad0860d01e (ipv4: ipmr: support multiple tables)

Reported-by: Alex Zhavnerchik <alex.vizor@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -267,8 +267,10 @@ static void __net_exit ipmr_rules_exit(struct net *net)
 {
 	struct mr_table *mrt, *next;
 
-	list_for_each_entry_safe(mrt, next, &net->ipv4.mr_tables, list)
+	list_for_each_entry_safe(mrt, next, &net->ipv4.mr_tables, list) {
+		list_del(&mrt->list);
 		kfree(mrt);
+	}
 	fib_rules_unregister(net->ipv4.mr_rules_ops);
 }
 #else

net/ipv6/ip6mr.c

@@ -254,8 +254,10 @@ static void __net_exit ip6mr_rules_exit(struct net *net)
 {
 	struct mr6_table *mrt, *next;
 
-	list_for_each_entry_safe(mrt, next, &net->ipv6.mr6_tables, list)
+	list_for_each_entry_safe(mrt, next, &net->ipv6.mr6_tables, list) {
+		list_del(&mrt->list);
 		ip6mr_free_table(mrt);
+	}
 	fib_rules_unregister(net->ipv6.mr6_rules_ops);
 }
 #else