Bluetooth: Check sk is not owned before freeing l2cap_conn

Check that socket sk is not locked in user process before removing
l2cap connection handler.

lock_sock and release_sock do not hold a normal spinlock directly but
instead hold the owner field. This means bh_lock_sock can still execute
even if the socket is "locked". More info can be found here:
http://www.linuxfoundation.org/collaborate/workgroups/networking/socketlocks

krfcommd kernel thread may be preempted with l2cap tasklet which remove
l2cap_conn structure. If krfcommd is in process of sending of RFCOMM reply
(like "RFCOMM UA" reply to "RFCOMM DISC") then kernel crash happens.

...
[  694.175933] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[  694.184936] pgd = c0004000
[  694.187683] [00000000] *pgd=00000000
[  694.191711] Internal error: Oops: 5 [#1] PREEMPT
[  694.196350] last sysfs file: /sys/devices/platform/hci_h4p/firmware/hci_h4p/loading
[  694.260375] CPU: 0    Not tainted  (2.6.32.10 #1)
[  694.265106] PC is at l2cap_sock_sendmsg+0x43c/0x73c [l2cap]
[  694.270721] LR is at 0xd7017303
...
[  694.525085] Backtrace:
[  694.527587] [<bf266be0>] (l2cap_sock_sendmsg+0x0/0x73c [l2cap]) from [<c02f2cc8>] (sock_sendmsg+0xb8/0xd8)
[  694.537292] [<c02f2c10>] (sock_sendmsg+0x0/0xd8) from [<c02f3044>] (kernel_sendmsg+0x48/0x80)

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

1 files changed, 26 insertions, 0 deletions

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index cd8f6ea03841..4ed38272df78 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -3078,6 +3078,14 @@ static inline int l2cap_connect_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hd
                 break;
 
         default:
+                /* don't delete l2cap channel if sk is owned by user */
+                if (sock_owned_by_user(sk)) {
+                        sk->sk_state = BT_DISCONN;
+                        l2cap_sock_clear_timer(sk);
+                        l2cap_sock_set_timer(sk, HZ / 5);
+                        break;
+                }
+
                 l2cap_chan_del(sk, ECONNREFUSED);
                 break;
         }
@@ -3283,6 +3291,15 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd
 
         sk->sk_shutdown = SHUTDOWN_MASK;
 
+        /* don't delete l2cap channel if sk is owned by user */
+        if (sock_owned_by_user(sk)) {
+                sk->sk_state = BT_DISCONN;
+                l2cap_sock_clear_timer(sk);
+                l2cap_sock_set_timer(sk, HZ / 5);
+                bh_unlock_sock(sk);
+                return 0;
+        }
+
         l2cap_chan_del(sk, ECONNRESET);
         bh_unlock_sock(sk);
 
@@ -3305,6 +3322,15 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, struct l2cap_cmd
         if (!sk)
                 return 0;
 
+        /* don't delete l2cap channel if sk is owned by user */
+        if (sock_owned_by_user(sk)) {
+                sk->sk_state = BT_DISCONN;
+                l2cap_sock_clear_timer(sk);
+                l2cap_sock_set_timer(sk, HZ / 5);
+                bh_unlock_sock(sk);
+                return 0;
+        }
+
         l2cap_chan_del(sk, 0);
         bh_unlock_sock(sk);