CVE-2021-47038 — Bluetooth: avoid deadlock between hci_dev->lock and socket lock

Affected: Linux

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…

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CVE-2021-47038 — Bluetooth: avoid deadlock between hci_dev->lock and socket lock