[PATCH 5.15.y 1/2] Bluetooth: L2CAP: Fix deadlock

[Karl Mehltretter <kmehltretter@gmail.com>]

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

[ Upstream commit f1a8f402f13f94263cf349216c257b2985100927 ]

This fixes the following deadlock introduced by 39a92a55be13
("bluetooth/l2cap: sync sock recv cb and release")

============================================
WARNING: possible recursive locking detected
6.10.0-rc3-g4029dba6b6f1 #6823 Not tainted
--------------------------------------------
kworker/u5:0/35 is trying to acquire lock:
ffff888002ec2510 (&chan->lock#2/1){+.+.}-{3:3}, at:
l2cap_sock_recv_cb+0x44/0x1e0

but task is already holding lock:
ffff888002ec2510 (&chan->lock#2/1){+.+.}-{3:3}, at:
l2cap_get_chan_by_scid+0xaf/0xd0

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&chan->lock#2/1);
  lock(&chan->lock#2/1);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by kworker/u5:0/35:
 #0: ffff888002b8a940 ((wq_completion)hci0#2){+.+.}-{0:0}, at:
process_one_work+0x750/0x930
 #1: ffff888002c67dd0 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0},
at: process_one_work+0x44e/0x930
 #2: ffff888002ec2510 (&chan->lock#2/1){+.+.}-{3:3}, at:
l2cap_get_chan_by_scid+0xaf/0xd0

To fix the original problem this introduces l2cap_chan_lock at
l2cap_conless_channel to ensure that l2cap_sock_recv_cb is called with
chan->lock held.

Fixes: 89e856e124f9 ("bluetooth/l2cap: sync sock recv cb and release")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
[ Karl Mehltretter: backport only the l2cap_core.c changes. The HCI
  changes are from an unrelated patch accidentally squashed into this
  commit. The l2cap_sock.c change removes locking added by 89e856e124f9,
  which is absent from 5.15.y, so the quoted deadlock cannot occur. The
  core changes are needed because c531e63871c0 was backported without
  the matching lock. ]
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 34f89f7f993b..f1d7a6cdd8aa 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -7992,6 +7992,8 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
 
 	BT_DBG("chan %p, len %d", chan, skb->len);
 
+	l2cap_chan_lock(chan);
+
 	if (chan->state != BT_BOUND && chan->state != BT_CONNECTED)
 		goto drop;
 
@@ -8009,6 +8011,7 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
 	}
 
 drop:
+	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
 free_skb:
 	kfree_skb(skb);
-- 
2.51.0