[PATCH net-next] ila: Fix crash caused by rhashtable changes

[Tom Herbert <tom@herbertland.com>]

commit ca26893f05e86 ("rhashtable: Add rhlist interface")
added a field to rhashtable_iter so that length became 56 bytes
and would exceed the size of args in netlink_callback (which is
48 bytes). The netlink diag dump function already has been
allocating a iter structure and storing the pointed to that
in the args of netlink_callback. ila_xlat also uses
rhahstable_iter but is still putting that directly in
the arg block. Now since rhashtable_iter size is increased
we are overwriting beyond the structure. The next field
happens to be cb_mutex pointer in netlink_sock and hence the crash.

Fix is to alloc the rhashtable_iter and save it as pointer
in arg.

Tested:

  modprobe ila
  ./ip ila add loc 3333:0:0:0 loc_match 2222:0:0:1,
  ./ip ila list  # NO crash now

Signed-off-by: Tom Herbert <tom@herbertland.com>
---
 net/ipv6/ila/ila_xlat.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/ila/ila_xlat.c b/net/ipv6/ila/ila_xlat.c
index 628ae6d..af8f52e 100644
--- a/net/ipv6/ila/ila_xlat.c
+++ b/net/ipv6/ila/ila_xlat.c
@@ -474,7 +474,15 @@ static int ila_nl_dump_start(struct netlink_callback *cb)
 {
 	struct net *net = sock_net(cb->skb->sk);
 	struct ila_net *ilan = net_generic(net, ila_net_id);
-	struct ila_dump_iter *iter = (struct ila_dump_iter *)cb->args;
+	struct ila_dump_iter *iter = (struct ila_dump_iter *)cb->args[0];
+
+	if (!iter) {
+		iter = kmalloc(sizeof(*iter), GFP_KERNEL);
+		if (!iter)
+			return -ENOMEM;
+
+		cb->args[0] = (long)iter;
+	}
 
 	return rhashtable_walk_init(&ilan->rhash_table, &iter->rhiter,
 				    GFP_KERNEL);
@@ -482,16 +490,18 @@ static int ila_nl_dump_start(struct netlink_callback *cb)
 
 static int ila_nl_dump_done(struct netlink_callback *cb)
 {
-	struct ila_dump_iter *iter = (struct ila_dump_iter *)cb->args;
+	struct ila_dump_iter *iter = (struct ila_dump_iter *)cb->args[0];
 
 	rhashtable_walk_exit(&iter->rhiter);
 
+	kfree(iter);
+
 	return 0;
 }
 
 static int ila_nl_dump(struct sk_buff *skb, struct netlink_callback *cb)
 {
-	struct ila_dump_iter *iter = (struct ila_dump_iter *)cb->args;
+	struct ila_dump_iter *iter = (struct ila_dump_iter *)cb->args[0];
 	struct rhashtable_iter *rhiter = &iter->rhiter;
 	struct ila_map *ila;
 	int ret;
-- 
2.9.3