# CVE-2026-99164: spi: imx: fix slab corruption from undersized DMA bounce buffers


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-99164, GHSA-6p78-3986-725v, UBUNTU-CVE-2026-99164

## What is CVE-2026-99164?

CVE-2026-99164 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

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

spi: imx: fix slab corruption from undersized DMA bounce buffers

Since commit faa8e404ad8e ("spi: imx: support dynamic burst length for
ECSPI DMA mode"), the driver allocates its private DMA TX/RX buffers
with kzalloc(dma_len), where dma_len is only rounded up to 4 bytes, but
maps, syncs and unmaps them with DMA_CACHE_ALIGNED_LEN(dma_len), i.e.
rounded up to the cache line size. As a result, the DMA API operates on
memory beyond the end of the allocation.

This was observed on a custom i.MX8MP platform with an mcp251xfd CAN
controller under heavy RPMSG load, as a series of refcount_t warnings
triggered from rpmsg_recv_done() in virtio_rpmsg_bus:

  refcount_t: addition on 0; use-after-free.
  refcount_t: underflow; use-after-free.
  refcount_t: saturated; leaking memory.

Leading finally to an "Unable to handle kernel paging request" oops.
Reproducing this problem took between 30 minutes and roughly 30 hours
under the same workload.

Hardware watchpoints on the refcount of a struct rpmsg_endpoint showed
it was overwritten from 2 to 1 by __pi_memcpy_generic() in the
irq/155-spi2.0 thread. Additionally it was found that a "normal"
rpmsg_recv_done() took 11µs +/-2µs from its kref_get to kref_put. In
the error case the same sequence took about 215µs +/-10µs. Based on
this, an LLM was used to identify the size mismatch fixed here.

Allocate the buffers with DMA_CACHE_ALIGNED_LEN(dma_len) so they cover
the full mapped length, and use the same length for
dma_sync_single_for_cpu() to stay consistent with map and unmap.

With this patch applied, the same workload ran for more than 200 hours
without the problem reproducing.

## Which versions are affected by CVE-2026-99164?


## How do I fix CVE-2026-99164?

Upgrade to a fixed version.

## Is CVE-2026-99164 being exploited?

There is no known exploitation of CVE-2026-99164 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99164 and fix it if it is affected.

What it is: CVE-2026-99164 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99164 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-2026-99164/ (Markdown: https://insights.sbomify.com/CVE-2026-99164/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99164
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99164
- OSV: https://osv.dev/vulnerability/CVE-2026-99164

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99164/
Summaries are generated and may contain mistakes; the official description above is the record.