CVE-2021-47263

What it actually does

Incorrect bit-mask calculation for GPIO pins 0-4 uses BIT(n-1) instead of BIT(n), triggering a shift-out-of-bounds operation in the gpio-wcd934x driver that can cause undefined kernel behavior.

Why it matters to the business

Potential kernel instability or crashes on systems using the affected driver reduces device availability and may require restarts or recovery procedures.

How an attack unfolds

An attacker with local access triggers the driver path that computes an invalid bit shift for pin configuration, leading to UBSAN-detected out-of-bounds behavior.

How to fix it

Update the Linux kernel to a version containing the fix for the bit-mask calculation in drivers/gpio/gpio-wcd934x.c.

How to confirm the fix worked

Confirm the kernel source no longer contains the erroneous BIT(n-1) expression at the cited line and that UBSAN checks pass for the driver.

Typical attack path

1. Obtain local access on a vulnerable Linux system
2. Interact with the gpio-wcd934x GPIO subsystem
3. Trigger pin mask calculation that performs invalid shift

How to detect it

Search kernel logs and dmesg for UBSAN shift-out-of-bounds messages referencing gpio-wcd934x.c.

• UBSAN: shift-out-of-bounds in drivers/gpio/gpio-wcd934x.c:34:14

What your security team should do

• Prioritize kernel updates for systems using wcd934x GPIO hardware
• Enable UBSAN or similar sanitizers in test kernels to catch similar issues
• Review logs for prior shift-out-of-bounds reports after patching