[PATCH 1/1] Bluetooth: Use chan_list_lock to protect the whole put/destroy invokation

[Lee Jones]

This change prevents a use-after-free caused by one of the worker
threads starting up (see below) *after* the final channel reference
has been put() during sock_close() but *before* the references to the
channel have been destroyed.

  refcount_t: increment on 0; use-after-free.
  BUG: KASAN: use-after-free in refcount_dec_and_test+0x20/0xd0
  Read of size 4 at addr ffffffc114f5bf18 by task kworker/u17:14/705

  CPU: 4 PID: 705 Comm: kworker/u17:14 Tainted: G S      W       4.14.234-00003-g1fb6d0bd49a4-dirty #28
  Hardware name: Qualcomm Technologies, Inc. SM8150 V2 PM8150 Google Inc. MSM sm8150 Flame DVT (DT)
  Workqueue: hci0 hci_rx_work
  Call trace:
   dump_backtrace+0x0/0x378
   show_stack+0x20/0x2c
   dump_stack+0x124/0x148
   print_address_description+0x80/0x2e8
   __kasan_report+0x168/0x188
   kasan_report+0x10/0x18
   __asan_load4+0x84/0x8c
   refcount_dec_and_test+0x20/0xd0
   l2cap_chan_put+0x48/0x12c
   l2cap_recv_frame+0x4770/0x6550
   l2cap_recv_acldata+0x44c/0x7a4
   hci_acldata_packet+0x100/0x188
   hci_rx_work+0x178/0x23c
   process_one_work+0x35c/0x95c
   worker_thread+0x4cc/0x960
   kthread+0x1a8/0x1c4
   ret_from_fork+0x10/0x18

Cc: stable@xxxxxxxxxx
Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
Cc: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: linux-bluetooth@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
---
 net/bluetooth/l2cap_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index ae78490ecd3d4..82279c5919fd8 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -483,9 +483,7 @@ static void l2cap_chan_destroy(struct kref *kref)
 
 	BT_DBG("chan %p", chan);
 
-	write_lock(&chan_list_lock);
 	list_del(&chan->global_l);
-	write_unlock(&chan_list_lock);
 
 	kfree(chan);
 }
@@ -501,7 +499,9 @@ void l2cap_chan_put(struct l2cap_chan *c)
 {
 	BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
 
+	write_lock(&chan_list_lock);
 	kref_put(&c->kref, l2cap_chan_destroy);
+	write_unlock(&chan_list_lock);
 }
 EXPORT_SYMBOL_GPL(l2cap_chan_put);
 
-- 
2.36.1.255.ge46751e96f-goog