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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
To:     linux-bluetooth@vger.kernel.org
Subject: [PATCH 2/2] Bluetooth: SCO: Fix possible circular locking dependency sco_sock_getsockopt
Date:   Thu, 30 Mar 2023 15:03:32 -0700
Message-Id: <20230330220332.1035910-3-luiz.dentz@gmail.com>
In-Reply-To: <20230330220332.1035910-1-luiz.dentz@gmail.com>
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From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

This attempts to fix the following trace:

======================================================
WARNING: possible circular locking dependency detected
6.3.0-rc2-g68fcb3a7bf97 #4706 Not tainted
------------------------------------------------------
sco-tester/31 is trying to acquire lock:
ffff8880025b8070 (&hdev->lock){+.+.}-{3:3}, at:
sco_sock_getsockopt+0x1fc/0xa90

but task is already holding lock:
ffff888001eeb130 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at:
sco_sock_getsockopt+0x104/0xa90

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}:
       lock_sock_nested+0x32/0x80
       sco_connect_cfm+0x118/0x4a0
       hci_sync_conn_complete_evt+0x1e6/0x3d0
       hci_event_packet+0x55c/0x7c0
       hci_rx_work+0x34c/0xa00
       process_one_work+0x575/0x910
       worker_thread+0x89/0x6f0
       kthread+0x14e/0x180
       ret_from_fork+0x2b/0x50

-> #1 (hci_cb_list_lock){+.+.}-{3:3}:
       __mutex_lock+0x13b/0xcc0
       hci_sync_conn_complete_evt+0x1ad/0x3d0
       hci_event_packet+0x55c/0x7c0
       hci_rx_work+0x34c/0xa00
       process_one_work+0x575/0x910
       worker_thread+0x89/0x6f0
       kthread+0x14e/0x180
       ret_from_fork+0x2b/0x50

-> #0 (&hdev->lock){+.+.}-{3:3}:
       __lock_acquire+0x18cc/0x3740
       lock_acquire+0x151/0x3a0
       __mutex_lock+0x13b/0xcc0
       sco_sock_getsockopt+0x1fc/0xa90
       __sys_getsockopt+0xe9/0x190
       __x64_sys_getsockopt+0x5b/0x70
       do_syscall_64+0x42/0x90
       entry_SYSCALL_64_after_hwframe+0x70/0xda

other info that might help us debug this:

Chain exists of:
  &hdev->lock --> hci_cb_list_lock --> sk_lock-AF_BLUETOOTH-BTPROTO_SCO

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_BLUETOOTH-BTPROTO_SCO);
                               lock(hci_cb_list_lock);
                               lock(sk_lock-AF_BLUETOOTH-BTPROTO_SCO);
  lock(&hdev->lock);

 *** DEADLOCK ***

1 lock held by sco-tester/31:
 #0: ffff888001eeb130 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0},
 at: sco_sock_getsockopt+0x104/0xa90

Fixes: 248733e87d50 ("Bluetooth: Allow querying of supported offload codecs over SCO socket")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 net/bluetooth/sco.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index f3a5ab9e4fa4..cd1a27ac555d 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -1140,6 +1140,8 @@ static int sco_sock_getsockopt(struct socket *sock, int level, int optname,
 			break;
 		}
 
+		release_sock(sk);
+
 		/* find total buffer size required to copy codec + caps */
 		hci_dev_lock(hdev);
 		list_for_each_entry(c, &hdev->local_codecs, list) {
@@ -1157,15 +1159,13 @@ static int sco_sock_getsockopt(struct socket *sock, int level, int optname,
 		buf_len += sizeof(struct bt_codecs);
 		if (buf_len > len) {
 			hci_dev_put(hdev);
-			err = -ENOBUFS;
-			break;
+			return -ENOBUFS;
 		}
 		ptr = optval;
 
 		if (put_user(num_codecs, ptr)) {
 			hci_dev_put(hdev);
-			err = -EFAULT;
-			break;
+			return -EFAULT;
 		}
 		ptr += sizeof(num_codecs);
 
@@ -1205,12 +1205,14 @@ static int sco_sock_getsockopt(struct socket *sock, int level, int optname,
 			ptr += len;
 		}
 
-		if (!err && put_user(buf_len, optlen))
-			err = -EFAULT;
-
 		hci_dev_unlock(hdev);
 		hci_dev_put(hdev);
 
+		lock_sock(sk);
+
+		if (!err && put_user(buf_len, optlen))
+			err = -EFAULT;
+
 		break;
 
 	default:
-- 
2.39.2