[PATCH] can: Fix kernel panic at security_sock_rcv_skb

[william . c . roberts]

From: Zhang Yanmin <yanmin.zhang@xxxxxxxxx>

The patch is for fix the below kernel panic:
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff81495e25>] selinux_socket_sock_rcv_skb+0x65/0x2a0

Call Trace:
 <IRQ>
 [<ffffffff81485d8c>] security_sock_rcv_skb+0x4c/0x60
 [<ffffffff81d55771>] sk_filter+0x41/0x210
 [<ffffffff81d12913>] sock_queue_rcv_skb+0x53/0x3a0
 [<ffffffff81f0a2b3>] raw_rcv+0x2a3/0x3c0
 [<ffffffff81f06eab>] can_rcv_filter+0x12b/0x370
 [<ffffffff81f07af9>] can_receive+0xd9/0x120
 [<ffffffff81f07beb>] can_rcv+0xab/0x100
 [<ffffffff81d362ac>] __netif_receive_skb_core+0xd8c/0x11f0
 [<ffffffff81d36734>] __netif_receive_skb+0x24/0xb0
 [<ffffffff81d37f67>] process_backlog+0x127/0x280
 [<ffffffff81d36f7b>] net_rx_action+0x33b/0x4f0
 [<ffffffff810c88d4>] __do_softirq+0x184/0x440
 [<ffffffff81f9e86c>] do_softirq_own_stack+0x1c/0x30
 <EOI>
 [<ffffffff810c76fb>] do_softirq.part.18+0x3b/0x40
 [<ffffffff810c8bed>] do_softirq+0x1d/0x20
 [<ffffffff81d30085>] netif_rx_ni+0xe5/0x110
 [<ffffffff8199cc87>] slcan_receive_buf+0x507/0x520
 [<ffffffff8167ef7c>] flush_to_ldisc+0x21c/0x230
 [<ffffffff810e3baf>] process_one_work+0x24f/0x670
 [<ffffffff810e44ed>] worker_thread+0x9d/0x6f0
 [<ffffffff810e4450>] ? rescuer_thread+0x480/0x480
 [<ffffffff810ebafc>] kthread+0x12c/0x150
 [<ffffffff81f9ccef>] ret_from_fork+0x3f/0x70

The sk dereferenced in panic has been released. After the rcu_call in
can_rx_unregister, receiver was protected by RCU but inner data was
not, then later sk will be freed while other CPU is still using it.
We need wait here to make sure sk referenced via receiver was safe.

=> security_sk_free
=> sk_destruct
=> __sk_free
=> sk_free
=> raw_release
=> sock_release
=> sock_close
=> __fput
=> ____fput
=> task_work_run
=> exit_to_usermode_loop
=> syscall_return_slowpath
=> int_ret_from_sys_call

Tracked-On: https://jira01.devtools.intel.com/browse/OAM-40528
Signed-off-by: Zhang Yanmin <yanmin.zhang@xxxxxxxxx>
Signed-off-by: He, Bo <bo.he@xxxxxxxxx>
Signed-off-by: Liu Shuo A <shuo.a.liu@xxxxxxxxx>
Signed-off-by: William Roberts <william.c.roberts@xxxxxxxxx>
---
 net/can/af_can.c | 14 ++++++++------
 net/can/af_can.h |  1 -
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 1108079..fcbe971 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -517,10 +517,8 @@ EXPORT_SYMBOL(can_rx_register);
 /*
  * can_rx_delete_receiver - rcu callback for single receiver entry removal
  */
-static void can_rx_delete_receiver(struct rcu_head *rp)
+static void can_rx_delete_receiver(struct receiver *r)
 {
-	struct receiver *r = container_of(rp, struct receiver, rcu);
-
 	kmem_cache_free(rcv_cache, r);
 }
 
@@ -595,9 +593,13 @@ void can_rx_unregister(struct net_device *dev, canid_t can_id, canid_t mask,
  out:
 	spin_unlock(&can_rcvlists_lock);
 
-	/* schedule the receiver item for deletion */
-	if (r)
-		call_rcu(&r->rcu, can_rx_delete_receiver);
+	/* synchronize_rcu to wait until a grace period has elapsed, to make
+	 * sure all receiver's sk dereferenced by others.
+	 */
+	if (r) {
+		synchronize_rcu();
+		can_rx_delete_receiver(r);
+	}
 }
 EXPORT_SYMBOL(can_rx_unregister);
 
diff --git a/net/can/af_can.h b/net/can/af_can.h
index fca0fe9..a0cbf83 100644
--- a/net/can/af_can.h
+++ b/net/can/af_can.h
@@ -50,7 +50,6 @@
 
 struct receiver {
 	struct hlist_node list;
-	struct rcu_head rcu;
 	canid_t can_id;
 	canid_t mask;
 	unsigned long matches;
-- 
2.7.4