CVE-2023-52456

What it actually does

The flaw leaves the RS485 TX state machine in the SEND state after imx_uart_shutdown disables the Transmission Complete interrupt on TTY close during an ongoing transmission, so imx_uart_stop_tx bails without ever reaching WAIT_AFTER_SEND and TX_EN remains asserted.

Why it matters to the business

Linux systems using i.MX RS485 serial ports can lose all further transmit capability after an application crash or abrupt port close, causing persistent communication outages until reboot.

How an attack unfolds

An attacker with local access starts an RS485 transmission on an affected i.MX UART, then forces the owning process or TTY to close while data is still in flight; the resulting deadlock keeps the transceiver enabled and the port unusable.

How to fix it

Upgrade the Linux kernel to a version containing commit 6e04a9d30509fb53ba6df5d655ed61d607a7cfda or later; rebuild and reboot with the patched kernel. If RS485 is not required, disable the feature in device tree until the update is applied.

How to confirm the fix worked

Confirm the running kernel contains commit 6e04a9d30509fb53ba6df5d655ed61d607a7cfda; exercise repeated open-transmit-close cycles on the RS485 port and verify the state machine reaches WAIT_AFTER_SEND without deadlock.

Typical attack path

1. Obtain local shell or crash a process that holds an RS485 TTY
2. Initiate or trigger an in-progress RS485 transmit
3. Close the TTY or kill the process mid-transmission
4. Observe that subsequent transmissions fail because TX_EN stays low

How to detect it

Review kernel logs for repeated imx_uart state-machine warnings or stalled RS485 transmits; correlate application crash reports with subsequent serial port unavailability; inspect dmesg for imx_uart_shutdown followed by permanent TX_EN assertion.

What your security team should do

• Apply the fixed kernel immediately on any system exposing RS485 via i.MX UARTs
• Prioritize patching in environments where serial reliability affects safety or control systems
• Add kernel version checks to asset inventory for all i.MX-based devices
• Test patched kernels in a lab with simulated application crashes before broad rollout