# CVE-2026-63929: iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()

> A memory leak in the Linux kernel IIO buffer subsystem allows local attackers to exhaust kernel memory, causing denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-63929, DEBIAN-CVE-2026-63929, GHSA-7xv7-rch9-q9hw, UBUNTU-CVE-2026-63929

## What is CVE-2026-63929?

CVE-2026-63929 is a memory corruption vulnerability in Linux, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf()

iio_buffer_enqueue_dmabuf() allocates a struct iio_dma_fence (104 bytes,
kmalloc-128) via kmalloc_obj()+dma_fence_init(), which sets the initial
kref to 1.  It then calls dma_resv_add_fence() which takes a second
reference (kref=2), and stores a raw pointer in block->fence.

On the success path the function returns without calling dma_fence_put()
to release the initial reference, so every buffer enqueue permanently
leaks one kmalloc-128 allocation.

The iio_buffer_cleanup() work item only releases the temporary reference
taken during completion signalling by iio_buffer_signal_dmabuf_done();
the initial reference from dma_fence_init() is never released.

With four iio_rwdev instances at 240kHz and 512 samples per buffer,
this produces ~1875 kmalloc-128 allocations per second matching the
observed slab growth exactly. A test with ftrace confirmed that the
dma_fence_destroy event was never triggered.

Fix by calling dma_fence_put() after dma_resv_add_fence(), transferring
ownership of the fence to the DMA reservation object. The DMA fence then
gets properly discarded after being signalled.

## Which versions are affected by CVE-2026-63929?


## How do I fix CVE-2026-63929?

Apply the vendor's patch.

## Is CVE-2026-63929 being exploited?

There is no known exploitation of CVE-2026-63929 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63929 and fix it if it is affected.

What it is: CVE-2026-63929 is a memory corruption vulnerability in Linux, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-63929 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63929/ (Markdown: https://insights.sbomify.com/CVE-2026-63929/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63929
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63929
- OSV: https://osv.dev/vulnerability/CVE-2026-63929

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63929/
Summaries are generated and may contain mistakes; the official description above is the record.