CVE-2021-47038 Bluetooth: avoid deadlock between hci_dev->lock and socket lock
A deadlock in the Linux kernel Bluetooth subsystem can cause a denial of service when specific socket operations are performed.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-47038?
CVE-2021-47038 is a medium-severity vulnerability in Linux kernel, published on 28 Feb 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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---
Weakness: CWE-667
Which versions are affected by CVE-2021-47038?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47038?
Apply the vendor's patch.
Is CVE-2021-47038 being exploited?
There is no known exploitation of CVE-2021-47038 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47038, GHSA-3jvq-9rg9-g8rp, UBUNTU-CVE-2021-47038.