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CVE-2026-74655
serial: qcom-geni: fix TX DMA buffer flush
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem drivers/tty. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74655 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/tty/serial/qcom_geni_serial.c
- What this is
- ARM/QUALCOMM MAILING LISTMAINTAINERS section matched on drivers/*/*/qcom* · linux-arm-msm@vger.kernel.org
Check it on the machine
grep -w CONFIG_SERIAL_QCOM_GENI /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidYnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- bookworm · linux-6.12Ynot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_SERIAL_QCOM_GENI
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-22 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 6.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/tty
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.3 | 6.6.154 | 1606abb7ce8c |
| 6.3 | 6.12.104 | 313ae287442e |
| 6.3 | 6.18.45 | 1c31e2377f4c |
| 6.3 | 7.1.9 | b1801c0d40f6 |
| 6.3 | 7.2 | e3c04834ae1a |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- Exploitation requires local write(2) and tcflush(TCOFLUSH)/tcdrain() ioctls on a Qualcomm GENI DMA UART (/dev/ttyHS*), reachable only through local TTY device-node syscalls, not over a network protocol.
- AC:LAttack complexity, low
- The attacker fully controls timing by issuing a large write during active TX DMA immediately followed by TCOFLUSH; no races or external victim state beyond concurrent DMA completion are required to reproduce the hang and DMA loop.
- PR:LPrivileges required, low
- Triggering the bug needs only permission to open, write, and ioctl an assigned ttyHS serial port (typically dialout-group or embedded-app access on Qualcomm/Android/IoT targets), not init-namespace root or CAP_SYS_ADMIN.
- UI:NUser interaction, none
- No victim interaction is required; the attacker directly drives the vulnerable flush path with their own write and TCOFLUSH/tcdrain calls on the serial device they already control.
- S:CScope, changed
- The flawed stop path unmaps the TX DMA buffer while the GENI engine can still read it and without resetting the TX DMA FSM, crossing the kernel/DMA hardware memory boundary and allowing the device to access host memory outside the intended mapping.
- C:HConfidentiality impact, high
- Stale page-sized DMA retransmissions can leak residual kernel data from the UART xmit buffer and adjacent heap, and post-unmap DMA reads can expose arbitrary remapped physical memory to the serial line or driver state.
- I:HIntegrity impact, high
- Missing flush handling leaves tx_remaining/tx_dma_addr inconsistent with a reset kfifo, enabling kfifo pointer underflow and uncontrolled DMA from wrong offsets that corrupt kernel memory and driver bookkeeping.
- A:HAvailability impact, high
- The UART enters an infinite loop of corrupted TX DMA frames and tcdrain/tty_wait_until_sent never completes, causing permanent hang of processes draining the port and sustained denial of the serial subsystem.