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

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Summary

CVECVE-2026-74653
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-22 16:16:38 UTC
Updated2026-08-22 16:16:38 UTC
DescriptionIn 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.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 3ce24bc4d115336218e59b7e286fd3a79f4fc4c6 git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 7795e8abedc86438cae0454602cbf9038b94bf38 git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 1423415471274abda87024967d7fe2206ceee0ea git Not specified
CNA Linux Linux affected 6.18.45 semver Not specified
CNA Linux Linux affected 7.1.9 semver Not specified
CNA Linux Linux unaffected 6.18.45 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.9 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/7795e8abedc86438cae0454602cbf9038b94bf38 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1423415471274abda87024967d7fe2206ceee0ea 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3ce24bc4d115336218e59b7e286fd3a79f4fc4c6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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