# CVE-2026-89533

## Summary

- **CVE ID:** CVE-2026-89533
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 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.

## Affected Products

- Linux — Linux (d7cc73972661be4a02a1b09f1d9b3283c6c05154)
- 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/6ee4dc7476b3abc92ec1d444533a559f33f59561)
- [CNA](https://git.kernel.org/stable/c/a46b35f213c2426f5d6a0458a8f7e873fc59cdfd)
- [CNA](https://git.kernel.org/stable/c/4493c96bbd0068fadf69cbae8d13426202e34cdc)
- [CNA](https://git.kernel.org/stable/c/4a44c140cc2f3643a39e258bb0c0ab9d0f494f5e)
- [CNA](https://git.kernel.org/stable/c/10873311f91db9454e2fadbf9866bc819e0646d9)
- [CNA](https://git.kernel.org/stable/c/addbf02dfe3b25e7e38e03bbd4e2a6ed86a14be7)
- [CNA](https://git.kernel.org/stable/c/cba8543c18cf42fd80fd63effb6df6ff4f7e73ce)

## 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._