# CVE-2026-89532: svcrdma: Fix pcl_for_each_segment for empty chunks

> An integer underflow in the Linux kernel's svcrdma module allows remote attackers to cause a denial of service via crafted network packets.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100380, BELL-CVE-2026-89532, DEBIAN-CVE-2026-89532, GHSA-vj46-79mq-hrmq, UBUNTU-CVE-2026-89532

## What is CVE-2026-89532?

CVE-2026-89532 is a critical vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

svcrdma: Fix pcl_for_each_segment for empty chunks

When a parsed chunk list contains a chunk whose ch_segcount is zero,
pcl_for_each_segment computes its inclusive upper bound as
&chunk->ch_segments[ch_segcount - 1]. ch_segcount is u32, so the
subtraction wraps to 0xFFFFFFFF and the bound lands far past the
ch_segments flex array. The loop body then walks unrelated memory at
sizeof(struct svc_rdma_segment) stride until it faults.

A zero-segcount chunk is reachable from the wire:
xdr_check_write_chunk() only rejects segcount values greater than
rc_maxpages, and pcl_alloc_write() links a freshly allocated chunk
onto rc_write_pcl/rc_reply_pcl before its segment-fill loop runs,
so a Write or Reply chunk advertising zero segments leaves
ch_segcount == 0 on the list. When the transport has negotiated
Send-With-Invalidate, svc_rdma_get_inv_rkey() iterates all four
PCLs with pcl_for_each_segment and dereferences segment->rs_handle
on each iteration, turning the underflow into an out-of-bounds read
and a general protection fault.

    xdr_check_write_list / xdr_check_reply_chunk
      pcl_alloc_write()
        chunk = pcl_alloc_chunk(...)  /* ch_segcount = 0 */
        list_add_tail(&chunk->ch_list, &pcl->cl_chunks)
        /* fill loop iterates zero times for wire segcount 0 */

    svc_rdma_get_inv_rkey()
      pcl_for_each_chunk(rc_write_pcl)
        pcl_for_each_segment(segment, chunk)
          pos <= &ch_segments[0u - 1u]  /* 0xFFFFFFFF */
          segment->rs_handle            /* OOB read -> GPF */

Fix by switching the macro to a half-open upper bound that uses
ch_segcount directly. For ch_segcount == 0 the loop start equals the
loop end and the body is skipped; for ch_segcount > 0 the iteration
range is unchanged. All six existing call sites in
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c and
net/sunrpc/xprtrdma/svc_rdma_rw.c remain correct under the new bound,
so no caller changes are needed.

## Which versions are affected by CVE-2026-89532?


## How do I fix CVE-2026-89532?

Apply the vendor's patch.

## Is CVE-2026-89532 being exploited?

There is no known exploitation of CVE-2026-89532 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89532 and fix it if it is affected.

What it is: CVE-2026-89532 is a critical vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89532 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-2026-89532/ (Markdown: https://insights.sbomify.com/CVE-2026-89532/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89532
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89532
- OSV: https://osv.dev/vulnerability/CVE-2026-89532

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89532/
Summaries are generated and may contain mistakes; the official description above is the record.