Linux Kernel Tegra XUSB Unbalanced Regulator Disable Vulnerability

A vulnerability in the Linux kernel's handling of USB role transitions can lead to unbalanced regulator disable operations. This issue occurs in the UTMI PHY mode on Tegra186, when the USB role changes from device to none. The code incorrectly assumes the regulator should be disabled, but if the regulator is always-on, it remains enabled. This mismatch can trigger warnings about unbalanced disables for the VIN_SYS_5V0 regulator. The vulnerability arises because the regulator control logic does not properly account for the ID override state, leading to potential mismanagement of power regulation during USB role transitions.

Impact

The vulnerability can cause power management issues by improperly disabling or failing to disable regulators, leading to unbalanced power states that could affect device functionality.

Reproduction

To reproduce this vulnerability, transition the USB role from DEVICE to NONE while the regulator is set to always-on. This can be done by using a device that supports USB OTG and manually changing the role through the device's settings or by using a script that interacts with the USB subsystem. Monitor the system logs for warnings related to unbalanced regulator disables, which indicate the vulnerability has been triggered.

Remediation

The vulnerability has been addressed in the Linux kernel. Users should upgrade to the latest version where this issue has been fixed.