CVE-2021-47038

In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: avoid deadlock between hci_dev->lock and socket lock Commit
eab2404ba798 (“Bluetooth: Add BT_PHY socket option”) added a dependency
between socket lock and hci_dev->lock that could lead to deadlock. It turns
out that hci_conn_get_phy() is not in any way relying on hdev being
immutable during the runtime of this function, neither does it even look at
any of the members of hdev, and as such there is no need to hold that lock.
This fixes the lockdep splat below:
====================================================== WARNING: possible
circular locking dependency detected 5.12.0-rc1-00026-g73d464503354 #10 Not
tainted ------------------------------------------------------
bluetoothd/1118 is trying to acquire lock: ffff8f078383c078
(&hdev->lock){+.+.}-{3:3}, at: hci_conn_get_phy+0x1c/0x150 [bluetooth] but
task is already holding lock: ffff8f07e831d920
(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}-{0:0}, at:
l2cap_sock_getsockopt+0x8b/0x610 which lock already depends on the new
lock. the existing dependency chain (in reverse order) is: -> #3
(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}-{0:0}:
lock_sock_nested+0x72/0xa0 l2cap_sock_ready_cb+0x18/0x70 [bluetooth]
l2cap_config_rsp+0x27a/0x520 [bluetooth] l2cap_sig_channel+0x658/0x1330
[bluetooth] l2cap_recv_frame+0x1ba/0x310 [bluetooth]
hci_rx_work+0x1cc/0x640 [bluetooth] process_one_work+0x244/0x5f0
worker_thread+0x3c/0x380 kthread+0x13e/0x160 ret_from_fork+0x22/0x30 -> #2
(&chan->lock#2/1){+.+.}-{3:3}: __mutex_lock+0xa3/0xa10
l2cap_chan_connect+0x33a/0x940 [bluetooth] l2cap_sock_connect+0x141/0x2a0
[bluetooth] __sys_connect+0x9b/0xc0 __x64_sys_connect+0x16/0x20
do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #1
(&conn->chan_lock){+.+.}-{3:3}: __mutex_lock+0xa3/0xa10
l2cap_chan_connect+0x322/0x940 [bluetooth] l2cap_sock_connect+0x141/0x2a0
[bluetooth] __sys_connect+0x9b/0xc0 __x64_sys_connect+0x16/0x20
do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #0
(&hdev->lock){+.+.}-{3:3}: __lock_acquire+0x147a/0x1a50
lock_acquire+0x277/0x3d0 __mutex_lock+0xa3/0xa10
hci_conn_get_phy+0x1c/0x150 [bluetooth] l2cap_sock_getsockopt+0x5a9/0x610
[bluetooth] __sys_getsockopt+0xcc/0x200 __x64_sys_getsockopt+0x20/0x30
do_syscall_64+0x33/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae other info
that might help us debug this: Chain exists of: &hdev->lock –>
&chan->lock#2/1 –> sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP Possible unsafe
locking scenario: CPU0 CPU1 ---- ----
lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP); lock(&chan->lock#2/1);
lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP); lock(&hdev->lock); *** DEADLOCK*** 1 lock held by bluetoothd/1118: #0: ffff8f07e831d920
(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}-{0:0}, at:
l2cap_sock_getsockopt+0x8b/0x610 [bluetooth] stack backtrace: CPU: 3 PID:
1118 Comm: bluetoothd Not tainted 5.12.0-rc1-00026-g73d464503354 #10
Hardware name: LENOVO 20K5S22R00/20K5S22R00, BIOS R0IET38W (1.16 )
05/31/2017 Call Trace: dump_stack+0x7f/0xa1 check_noncircular+0x105/0x120 ?
__lock_acquire+0x147a/0x1a50 __lock_acquire+0x147a/0x1a50
lock_acquire+0x277/0x3d0 ? hci_conn_get_phy+0x1c/0x150 [bluetooth] ?
__lock_acquire+0x2e1/0x1a50 ? lock_is_held_type+0xb4/0x120 ?
hci_conn_get_phy+0x1c/0x150 [bluetooth] __mutex_lock+0xa3/0xa10 ?
hci_conn_get_phy+0x1c/0x150 [bluetooth] ? lock_acquire+0x277/0x3d0 ?
mark_held_locks+0x49/0x70 ? mark_held_locks+0x49/0x70 ?
hci_conn_get_phy+0x1c/0x150 [bluetooth] hci_conn_get_phy+0x —truncated—