[PATCH net] atm: null pointer dereference when both entry and holding_time are NULL.

[pwn9uin@gmail.com]

From: Minjoong Kim <alswnd4123@outlook.kr>

When MPOA_cache_impos_rcvd() receives the msg, it can trigger
Null Pointer Dereference Vulnerability if both entry and
holding_time are NULL. Because there is only for the situation
where entry is NULL and holding_time exists, it can be passed
when both entry and holding_time are NULL. If these are NULL,
the entry will be passd to eg_cache_put() as parameter and
it is referenced by entry->use code in it.

Signed-off-by: Minjoong Kim <alswnd4123@outlook.kr>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
---
 net/atm/mpc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/atm/mpc.c b/net/atm/mpc.c
index 324e3ab96bb3..7fb854ea47dc 100644
--- a/net/atm/mpc.c
+++ b/net/atm/mpc.c
@@ -1314,6 +1314,9 @@ static void MPOA_cache_impos_rcvd(struct k_message *msg,
 	holding_time = msg->content.eg_info.holding_time;
 	dprintk("(%s) entry = %p, holding_time = %u\n",
 		mpc->dev->name, entry, holding_time);
+	if (entry == NULL && !holding_time) {
+		return;
+	}
 	if (entry == NULL && holding_time) {
 		entry = mpc->eg_ops->add_entry(msg, mpc);
 		mpc->eg_ops->put(entry);
-- 
2.34.1