CVE-2022-49943 Information

Jun 19, 2025 cve

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->active4)++++-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->active4)++++-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.

Reference

https://git.kernel.org/stable/c/1016fc0c096c92dd0e6e0541daac7a7868169903 https://git.kernel.org/stable/c/1a065e4673cbdd9f222a05f85e17d78ea50c8d9c

CNNVD-202506-2230 (Published: 2025-06-18)

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