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.
Analysis and contextual insights are available on OpenCVE Cloud.
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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| Source | ID | Title |
|---|---|---|
EUVD |
EUVD-2022-55225 | 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. |
Mon, 11 May 2026 19:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
Fri, 14 Nov 2025 19:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Linux
Linux linux Kernel |
|
| Weaknesses | CWE-667 | |
| CPEs | cpe:2.3:o:linux:linux_kernel:5.19.7:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.0:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.0:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.0:rc3:*:*:*:*:*:* |
|
| Vendors & Products |
Linux
Linux linux Kernel |
|
| Metrics |
cvssV3_1
|
cvssV3_1
|
Fri, 20 Jun 2025 14:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Wed, 18 Jun 2025 11:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | USB: gadget: Fix obscure lockdep violation for udc_mutex | |
| References |
|
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-05-11T19:09:40.620Z
Reserved: 2025-06-18T10:57:27.381Z
Link: CVE-2022-49943
No data.
Status : Analyzed
Published: 2025-06-18T11:15:21.267
Modified: 2025-11-14T19:41:15.223
Link: CVE-2022-49943
OpenCVE Enrichment
No data.
EUVD