CVE-2026-74653serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx

Official description

In the Linux kernel, the following vulnerability has been resolved: serial: 8250_of: clear stuck empty-FIFO RX-timeout on LPC32xx The NXP LPC32xx UART (PORT_LPC3220) can latch an RX character-timeout interrupt while the RX FIFO is empty: IIR reports UART_IIR_RX_TIMEOUT (0x0c) but LSR.DR is clear. A character timeout is only cleared by reading RHR, but serial8250_rx_chars() reads RHR only when LSR.DR is set, so nothing ever clears the condition. The interrupt is level-triggered and re-fires immediately, so on a single-core ARM926 the resulting interrupt storm livelocks the CPU. It is reproducible when userspace repeatedly opens the front-panel port (ttyS1): serial8250_do_set_termios() re-enables interrupts on unlock and the handler then spins forever with iir=0xcc lsr=0x60 ier=0x05, tripping the soft-lockup detector in serial8250_handle_irq_locked(). LPC32xx has no dedicated 8250 glue driver, it's driven by the generic 8250_of. Add a hardware specific handle_irq for PORT_LPC3220, wired up in of_platform_serial_setup() the same way fsl8250_handle_irq is installed. The handler follows dw8250_handle_irq(): on an RX timeout with an empty FIFO (LSR.DR and LSR.BI clear) it does one throwaway RHR read to clear the condition, then calls serial8250_handle_irq_locked(). No real received data is ever discarded, and it is a no-op on healthy UARTs which never report a timeout with DR clear. This is the same class of bug already worked around in other 8250 drivers; see commit 424d79183af0 ("serial: 8250_dw: Avoid "too much work" from bogus rx timeout interrupt") which reports the identical iir=0xcc/lsr=0x60. See also UART_RX_TIMEOUT_QUIRK in 8250_omap, and the note in 8250_bcm7271.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/cc325ce1c40a111824827532ac132afb3d1c342b
• https://git.kernel.org/stable/c/c321dc5172c8c66e21ffbeeb7a2ebb88ae6fd4c3
• https://git.kernel.org/stable/c/3ce24bc4d115336218e59b7e286fd3a79f4fc4c6
• https://git.kernel.org/stable/c/7795e8abedc86438cae0454602cbf9038b94bf38
• https://git.kernel.org/stable/c/1423415471274abda87024967d7fe2206ceee0ea