CVE-2026-93123: serial: qcom-geni: do not advance stale DMA completions
In the Linux kernel, the following vulnerability has been resolved:
serial: qcom-geni: do not advance stale DMA completions
The qcom GENI serial DMA TX completion path advances the transmit fifo by the number of bytes recorded in port->txremaining.
If uartflushbuffer() runs after the hardware has completed a DMA transfer but before the DMA completion interrupt has been handled, the serial core resets the transmit fifo while port->txremaining still describes the old DMA transfer.
A previous fix avoided advancing an empty fifo by checking that the fifo length is at least txremaining. That still does not distinguish the old DMA payload from new bytes written after the flush. If userspace writes new data before the stale DMA completion interrupt is handled, the fifo can again contain at least txremaining bytes and the stale completion can advance and discard those new bytes.
Mark an in-flight DMA transfer stale when the transmit fifo is flushed. The later completion still unprepares the original DMA mapping using the saved length, but it no longer advances the transmit fifo.
Affected Software
Event History
Frequently Asked Questions
Under what timing conditions can transmitted data be lost?
Data can be discarded when uart_flush_buffer() runs after hardware has completed a DMA transmit transfer but before its completion interrupt is processed, and userspace writes new data before that stale completion is handled. The stale completion can then advance the reset transmit FIFO using the old transfer length.
What component and traffic path are affected?
The issue affects the qcom GENI serial driver's DMA transmit completion path in the Linux kernel. It concerns transmit FIFO handling rather than receive processing.
What does the fix change?
The fix marks an in-flight DMA transfer as stale when the transmit FIFO is flushed. Its later completion still releases the original DMA mapping using the saved length, but does not advance the transmit FIFO and discard newly written data.