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CVE-2026-80548
s390/vfio_ccw: Selectively expand io_mutex
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem drivers/s390. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-80548 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.105-1 | Update the kernel and reboot. Fixed in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. 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
The io_mutex was defined to serialize the io_regions, but then has also sort of been associated with the I/O themselves because of the close relationship they share. With the handful of races that are possible, the choices are either to: A) expand the scope of io_mutex to close these remaining windows, or B) reduce the scope of io_mutex to just io_region, and introduce a new lock mechanism for the remaining I/O resources This patch implements A, since B brings with it a lot more interactions that would need to be tracked and kept in a correct hierarchy. It also takes advantage of the workqueue element for cp_free() that now gets called out of fsm_notoper(), which could be invoked out of an interrupt context and thus cannot acquire a mutex itself.
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/s390/cio/vfio_ccw_chp.c
drivers/s390/cio/vfio_ccw_cp.c
drivers/s390/cio/vfio_ccw_drv.c
drivers/s390/cio/vfio_ccw_fsm.c
drivers/s390/cio/vfio_ccw_private.h
- What this is
- S390 VFIO-CCW DRIVERMAINTAINERS section matched on drivers/s390/cio/vfio_ccw* · linux-s390@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_S390|CONFIG_VFIO_CCW' /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 does not build this code. In 5 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12n
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_S390, CONFIG_VFIO_CCW
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-08-26 (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
- not yet assignedsource
- Subsystem
- drivers/s390
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.2 | 5.15.218 | dab6a6627b0b |
| 5.2 | 6.1.185 | 56d7488533ce |
| 5.2 | 6.6.153 | f72a51810d49 |
| 5.2 | 6.12.105 | 2ba9efdf9ebe |
| 5.2 | 6.18.46 | b6aecea4b2b2 |
| 5.2 | 7.1.10 | 2a5ac0c0f1f7 |
| 5.2 | 7.2 | 34f4feff3e90 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | 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
- The bug is reached only through local VFIO mediated-device syscalls (read/write/ioctl on vfio-ccw device fds) and deferred work from hardware I/O interrupts and channel-path events; vfio-ccw has no network, Bluetooth, or physical-bus entry point.
- AC:LAttack complexity, low
- The VFIO client controls both sides of each race window: it can submit channel I/O, close or reset the device, and trigger DMA unmap while io_work, notoper_work, or fsm_close concurrently run cp_free, cp_update_scsw, or cp_iova_pinned without full io_mutex protection, and retry to win reliably.
- PR:LPrivileges required, low
- Exploitation requires an opened vfio-ccw mdev device fd (typical QEMU/libvirt VM operator or delegated /dev/vfio holder on IBM Z passthrough hosts), not init-namespace root; mdev creation is admin setup, but triggering the races needs only that delegated VFIO client access.
- UI:NUser interaction, none
- No separate victim action is required; once vfio-ccw passthrough is configured, the attacker issues concurrent channel I/O, region access, device close/reset, or DMA unmap without needing another user to mount media or interact.
- S:CScope, changed
- On IBM Z/LinuxONE, vfio-ccw passes DASD/CCW subchannels into KVM guests; guest-driven channel I/O and path events trigger host interrupt/workqueue activity concurrent with VFIO client teardown, corrupting hypervisor kernel memory outside the VM security boundary.
- C:HConfidentiality impact, high
- cp_free racing with cp_update_scsw, cp_iova_pinned, and io_region access without io_mutex causes use-after-free on ccwchain_list and page_array structures; per kernel UAF guidance this enables attacker-influenced heap reuse and arbitrary kernel read primitives.
- I:HIntegrity impact, high
- Concurrent cp_free during cp_init, page_array_unpin_free, memcpy into io_region, and mutex operations on freed channel_program memory provides heap-sprayable arbitrary write and control-flow hijack potential beyond a simple crash.
- A:HAvailability impact, high
- Use-after-free and double-free of channel program structures during concurrent I/O completion, not-operational cleanup, or device close can immediately oops or panic the host kernel from invalid list/mutex access, and successful exploitation can crash or hang the system.