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CVE-2026-89941
iio: buffer: Make IIO DMA fence release RCU-safe
Published 2026-09-16 (33 days ago) by the Linux kernel CNA. Subsystem drivers/iio. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89941 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-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The `dma_fence` documentation states that if a custom release implementation is provided, the `dma_fence` object must be freed in an RCU-safe way. The current `iio_dma_fence` implementation uses `kfree()`, which might result in a use-after-free. Remove the custom `release` implementation. This makes the DMA fence core fall back to `dma_fence_free()`, which calls `kfree_rcu()` on the fence. This requires that the fence be the first member of `struct iio_dma_fence`. Using the default release method for extended DMA fence structures is a common pattern.
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/iio/industrialio-buffer.c
- What this is
- IIO SUBSYSTEM AND DRIVERSMAINTAINERS section matched on drivers/iio/ · linux-iio@vger.kernel.org · Maintained
- Kernel module
- industrialio
Check it on the machine
grep -wE 'CONFIG_IIO|CONFIG_IIO_BUFFER' /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.
lsmod | grep -w industrialioPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
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.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_IIO, CONFIG_IIO_BUFFER
- 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
- 2026-09-16 (33 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 4.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/iio
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.11 | 6.12.110 | 311595dc0b56 |
| 6.11 | 6.18.51 | 06a9460b8b79 |
| 6.11 | 7.2.5 | 11cef9949111 |
| 6.11 | 7.3 | 8662e56c31cf |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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 use-after-free is reached only through local IIO character-device ioctls (IIO_BUFFER_GET_FD_IOCTL then IIO_BUFFER_DMABUF_ATTACH/ENQUEUE_IOCTL on /dev/iio:deviceN); there is no network, Bluetooth, or USB packet path into the IIO DMA fence release.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by enqueueing IIO DMA-BUF transfers that create and later kfree() the fence while concurrently waiting on or exporting the same dma-buf's reservation fences via DMA_BUF_IOCTL_SYNC/EXPORT_SYNC_FILE, so the missing RCU grace period is attacker-driven.
- PR:LPrivileges required, low
- The IIO open and ioctl path performs no capability check; only filesystem access to /dev/iio:deviceN is required. On Android, automotive, and industrial/SDR systems that ship DMA-capable IIO converters, that node is commonly group-accessible to unprivileged sensor or application users.
- UI:NUser interaction, none
- The attacker opens the IIO device, attaches their own DMA-BUF, and issues enqueue and dma-buf sync/export ioctls themselves; no separate victim action is required.
- S:UScope, unchanged
- The freed iio_dma_fence lives in the host kernel heap and any resulting corruption stays within the same kernel security authority; this is not a VM escape or IOMMU/DMA boundary bypass.
- C:HConfidentiality impact, high
- Immediate kfree() of the dma_fence lets concurrent dma_resv RCU walkers (dma_fence_get_rcu, dma_fence_driver_name) read the reclaimed slab object; per kernel scoring guidance a use-after-free is High confidentiality impact.
- I:HIntegrity impact, high
- The freed dma_fence contains ops function pointers, callback lists, and a spinlock used after free; reclaiming the object with attacker-controlled data yields write and control-flow hijack primitives, so integrity impact is High.
- A:HAvailability impact, high
- Use-after-free of the fence from dma_fence_release or dma_resv iteration causes a kernel oops or panic even without a full exploit, so availability impact is High.