# CVE-2026-89532

## Summary

- **CVE ID:** CVE-2026-89532
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## 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.

## Affected Products

- Linux — Linux (78147ca8b4a9b6cf0e597ddd6bf17959e08376c2)
- Linux — Linux (5.11)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/9c5a03c3dc505c0295339b0a1b9e4fe36447e482)
- [CNA](https://git.kernel.org/stable/c/a1c954ca4977a4e6ec73ef92fe48073ec54f9fc8)
- [CNA](https://git.kernel.org/stable/c/6d33a7e6bf6c6b293a266a617201285a1ad32c56)
- [CNA](https://git.kernel.org/stable/c/b7713a784c59515d0aba558c8f5df6a0164dd3a9)
- [CNA](https://git.kernel.org/stable/c/1e2e3481e39103a386b86be1c33eaef97cbdf16e)
- [CNA](https://git.kernel.org/stable/c/3a78b841879c2a3243f74edc514236fb2907167f)
- [CNA](https://git.kernel.org/stable/c/06d0390c37fa6714624af771bd72bbf1a7ed9bb1)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.51%
- **EPSS Percentile:** 42.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._