Message-ID: <2025061807-CVE-2022-49943-7809@gregkh>
Date: Wed, 18 Jun 2025 13:00:08 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-49943: USB: gadget: Fix obscure lockdep violation for udc_mutex

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

USB: gadget: Fix obscure lockdep violation for udc_mutex

A recent commit expanding the scope of the udc_lock mutex in the
gadget core managed to cause an obscure and slightly bizarre lockdep
violation.  In abbreviated form:

======================================================
WARNING: possible circular locking dependency detected
5.19.0-rc7+ #12510 Not tainted
------------------------------------------------------
udevadm/312 is trying to acquire lock:
ffff80000aae1058 (udc_lock){+.+.}-{3:3}, at: usb_udc_uevent+0x54/0xe0

but task is already holding lock:
ffff000002277548 (kn->active#4){++++}-{0:0}, at: kernfs_seq_start+0x34/0xe0

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (kn->active#4){++++}-{0:0}:
        lock_acquire+0x68/0x84
        __kernfs_remove+0x268/0x380
        kernfs_remove_by_name_ns+0x58/0xac
        sysfs_remove_file_ns+0x18/0x24
        device_del+0x15c/0x440

-> #2 (device_links_lock){+.+.}-{3:3}:
        lock_acquire+0x68/0x84
        __mutex_lock+0x9c/0x430
        mutex_lock_nested+0x38/0x64
        device_link_remove+0x3c/0xa0
        _regulator_put.part.0+0x168/0x190
        regulator_put+0x3c/0x54
        devm_regulator_release+0x14/0x20

-> #1 (regulator_list_mutex){+.+.}-{3:3}:
        lock_acquire+0x68/0x84
        __mutex_lock+0x9c/0x430
        mutex_lock_nested+0x38/0x64
        regulator_lock_dependent+0x54/0x284
        regulator_enable+0x34/0x80
        phy_power_on+0x24/0x130
        __dwc2_lowlevel_hw_enable+0x100/0x130
        dwc2_lowlevel_hw_enable+0x18/0x40
        dwc2_hsotg_udc_start+0x6c/0x2f0
        gadget_bind_driver+0x124/0x1f4

-> #0 (udc_lock){+.+.}-{3:3}:
        __lock_acquire+0x1298/0x20cc
        lock_acquire.part.0+0xe0/0x230
        lock_acquire+0x68/0x84
        __mutex_lock+0x9c/0x430
        mutex_lock_nested+0x38/0x64
        usb_udc_uevent+0x54/0xe0

Evidently this was caused by the scope of udc_mutex being too large.
The mutex is only meant to protect udc->driver along with a few other
things.  As far as I can tell, there's no reason for the mutex to be
held while the gadget core calls a gadget driver's ->bind or ->unbind
routine, or while a UDC is being started or stopped.  (This accounts
for link #1 in the chain above, where the mutex is held while the
dwc2_hsotg_udc is started as part of driver probing.)

Gadget drivers' ->disconnect callbacks are problematic.  Even though
usb_gadget_disconnect() will now acquire the udc_mutex, there's a
window in usb_gadget_bind_driver() between the times when the mutex is
released and the ->bind callback is invoked.  If a disconnect occurred
during that window, we could call the driver's ->disconnect routine
before its ->bind routine.  To prevent this from happening, it will be
necessary to prevent a UDC from connecting while it has no gadget
driver.  This should be done already but it doesn't seem to be;
currently usb_gadget_connect() has no check for this.  Such a check
will have to be added later.

Some degree of mutual exclusion is required in soft_connect_store(),
which can dereference udc->driver at arbitrary times since it is a
sysfs callback.  The solution here is to acquire the gadget's device
lock rather than the udc_mutex.  Since the driver core guarantees that
the device lock is always held during driver binding and unbinding,
this will make the accesses in soft_connect_store() mutually exclusive
with any changes to udc->driver.

Lastly, it turns out there is one place which should hold the
udc_mutex but currently does not: The function_show() routine needs
protection while it dereferences udc->driver.  The missing lock and
unlock calls are added.

The Linux kernel CVE team has assigned CVE-2022-49943 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.19.7 with commit f44b0b95d50fffeca036e1ba36770390e0b519dd and fixed in 5.19.8 with commit 1a065e4673cbdd9f222a05f85e17d78ea50c8d9c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-49943
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/usb/gadget/udc/core.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1a065e4673cbdd9f222a05f85e17d78ea50c8d9c
	https://git.kernel.org/stable/c/1016fc0c096c92dd0e6e0541daac7a7868169903

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