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.
Published: 2026-09-11
Score: 9.8 Critical
EPSS: < 1% Very Low
KEV: No
Impact: Integer Underflow potentially leading to kernel memory corruption
Action: Immediate Patch
AI Analysis

Impact

The Linux kernel contains a defect in the svc_rdma_read_chunk_range function where incorrect arithmetic causes an integer underflow. This results in prompt a massive, erroneous kmalloc_array_node allocation, potentially corrupting kernel memory or causing a denial of service. The vulnerability directly affects the svc_rdma subsystem, which processes Remote Direct Memory Access requests within the kernel space.

Affected Systems

All Linux kernel deployments that use the svc_rdma subsystem are affected, regardless of vendor. The flaw is present in any kernel before the fix incorporated in recent commits; the exact boundary versions are not listed, so any system running a kernel without the patch is vulnerable.

Risk and Exploitability

The CVSS score of 5.9 indicates a medium severity risk. The EPSS score is < 1% and the vulnerability is not listed in CISA KEV. Based on the description, the likely attack vector is through a Remote Direct Memory Access client that can send malformed read requests to the kernel, leading to the integer underflow. Exploit RDMA service, making the threat most acute in environments where RDMA is exposed to untrusted clients.

Generated by OpenCVE AI on September 13, 2026 at 04:04 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade to a Linux kernel version that includes the CVE-2026-89533 fix.
  • Reboot the system to load the patched kernel and ensure the svc_rdma module is updated.
  • If the distribution does not yet provide an updated kernel, apply the official patch from kernel.org and recompile and install the kernel.

Generated by OpenCVE AI on September 13, 2026 at 04:04 UTC.

Tracking

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Advisories

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History

Sun, 13 Sep 2026 06:45:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}

 cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

Sat, 12 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-191
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Important

Fri, 11 Sep 2026 23:45:00 +0000

Type Values Removed Values Added
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.
Title svcrdma: Fix offset arithmetic in read_chunk_range
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-13T06:30:29.669Z

Reserved: 2026-09-11T19:38:34.720Z

Link: CVE-2026-89533

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-11T20:19:36.250

Modified: 2026-09-13T07:17:15.510

Link: CVE-2026-89533

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-11T19:44:12Z

Links: CVE-2026-89533 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-13T04:15:13Z

Weaknesses
  • CWE-191

    Integer Underflow (Wrap or Wraparound)