CVE-2025-21827

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

Bluetooth: btusb: mediatek: Add locks for usb_driver_claim_interface()

The documentation for usb_driver_claim_interface() says that "the device lock" is needed when the function is called from places other than probe(). This appears to be the lock for the USB interface device. The Mediatek btusb code gets called via this path:

Workqueue: hci0 hci_power_on [bluetooth] Call trace: usb_driver_claim_interface btusb_mtk_claim_iso_intf btusb_mtk_setup hci_dev_open_sync hci_power_on process_scheduled_works worker_thread kthread

With the above call trace the device lock hasn't been claimed. Claim it.

Without this fix, we'd sometimes see the error "Failed to claim iso interface". Sometimes we'd even see worse errors, like a NULL pointer dereference (where intf->dev.driver was NULL) with a trace like:

Call trace: usb_suspend_both usb_runtime_suspend __rpm_callback rpm_suspend pm_runtime_work process_scheduled_works

Both errors appear to be fixed with the proper locking.

A low-impact flaw was found in the Linux kernel's MediaTek USB Bluetooth (btusb) driver. When a MediaTek Bluetooth USB adapter is powered on, the btusb_mtk_claim_iso_intf() function calls usb_driver_claim_interface() from the hci_power_on workqueue without holding the USB interface device lock that this function requires when it is called from outside the probe path. Because of the missing locking, the ISO interface claim can intermittently fail ("Failed to claim iso interface") or a NULL pointer dereference (intf->dev.driver being NULL) can occur during USB runtime suspend, resulting in a denial of service (system crash) or loss of Bluetooth functionality on systems using affected MediaTek Bluetooth USB hardware. Only availability is affected; the Red Hat severity for this flaw is low, with a CVSS 3.1 base score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H). This differs from the upstream CVE record rating of 7.8, which assumes confidentiality and integrity impacts that the technical evidence for this issue does not support.

Red Hat Enterprise Linux 8 and Red Hat In-Vehicle OS are not affected because the vulnerable code is not present in those releases. Red Hat Enterprise Linux 6 and 7 Extended Lifecycle Support streams are out of support scope. For the affected Red Hat Enterprise Linux 9 and 10 kernel and kernel-rt releases, the fix is deferred because this is a local, availability-only race condition of low severity and limited practical impact, and it will be addressed in a future update. The residual risk of the deferred fix is limited to intermittent Bluetooth interface claim failures or a local denial of service on systems using affected MediaTek Bluetooth USB adapters.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.