CVE-2026-89814: Linux Kernel Use-After-Free Vulnerability

CVE-2026-89814 Overview

CVE-2026-89814 is an out-of-bounds array access vulnerability in the Linux kernel's AMD GPU driver (drm/amdgpu). The flaw resides in the ring isolation logic, where adev->isolation[] is indexed using AMDGPU_XCP_NO_PARTITION (a value of ~0) for rings that are not assigned to a partition. SDMA submissions trigger this condition on both the isolation enforcement path and the VM flush path, tripping the Undefined Behavior Sanitizer (UBSAN).

Critical Impact
A local, authenticated user with access to the AMD GPU device can trigger out-of-bounds memory access in kernel space, potentially leading to system instability, information disclosure, or memory corruption.

Affected Products

Linux kernel builds including the drm/amdgpu driver with partition-aware ring isolation support
Systems using AMD GPUs that exercise the SDMA isolation enforcement path
Distributions shipping affected upstream kernel versions prior to the referenced stable commits

Discovery Timeline

2026-09-16 - CVE-2026-89814 published to the National Vulnerability Database (NVD)
2026-09-17 - Last updated in NVD database

Technical Details for CVE-2026-89814

Vulnerability Analysis

The adev->isolation[] array in the AMD GPU driver contains one slot per GPU partition. Rings assigned to a partition use their partition index to access the correct isolation slot. However, rings that are not assigned to any partition retain the sentinel value AMDGPU_XCP_NO_PARTITION, defined as ~0 (all bits set).

When the driver indexes adev->isolation[] with this sentinel value, the access falls far outside the allocated array bounds. The condition is reproducible on SDMA (System DMA) submissions along two distinct code paths: the isolation enforcement path and the VM flush path. Both paths dereference the array before performing the ring type check that would determine whether isolation applies to that ring at all.

The fix aligns the affected code with the existing cleaner shader path by falling back to the first slot (isolation[0]) for rings outside a partition, and defers taking the array address until after the ring type check.

Root Cause

The root cause is missing bounds validation on the partition index prior to array indexing. The driver assumes any value returned for a ring's partition assignment is a valid array index, but the sentinel value AMDGPU_XCP_NO_PARTITION (~0) violates this assumption. This is a classic out-of-bounds read/write [CWE-125/CWE-787] pattern in kernel driver code.

Attack Vector

Exploitation requires local access with permissions to submit work to the AMD GPU device, typically through /dev/dri/renderD* nodes. An attacker submitting SDMA workloads on a system where affected rings are not bound to a partition can trigger the out-of-bounds access. UBSAN-enabled kernels will report the violation; on production kernels without UBSAN, the invalid memory access may cause undefined behavior, kernel memory corruption, or a denial of service.

No verified public exploit code is available for this vulnerability. Refer to the upstream kernel commits for technical details of the fix.

Detection Methods for CVE-2026-89814

Indicators of Compromise

UBSAN reports in dmesg or the kernel log referencing out-of-bounds array indexing within drm/amdgpu isolation or VM flush code paths
Unexpected kernel oops, panics, or GPU hangs correlated with SDMA workload submissions
Unprivileged local processes repeatedly opening /dev/dri/renderD* nodes and submitting unusual SDMA command streams

Detection Strategies

Enable CONFIG_UBSAN on test and staging kernels to surface out-of-bounds accesses during QA and fuzzing
Monitor kernel ring buffer output for amdgpu warnings, GPU resets, or SDMA submission errors
Correlate GPU driver faults with the identity of the local user or container submitting workloads

Monitoring Recommendations

Ingest /var/log/kern.log and journalctl -k output into a centralized logging platform for kernel-level anomaly detection
Alert on repeated GPU driver faults, UBSAN warnings, or kernel panics originating from drm/amdgpu
Track process behavior on multi-tenant systems (containers, virtualization hosts) with shared GPU access

How to Mitigate CVE-2026-89814

Immediate Actions Required

Identify Linux systems running AMD GPUs with kernels predating the fix commits 0bfb938, 964de25, and b309005
Apply the stable kernel update containing the fix as soon as vendor packages are available
Restrict access to /dev/dri/renderD* device nodes to trusted local users and workloads only

Patch Information

The vulnerability is resolved in the following upstream commits: Kernel Git Commit 0bfb938, Kernel Git Commit 964de25, and Kernel Git Commit b309005. The patch clamps the isolation index to the first slot for rings outside a partition and reorders the address computation to occur after the ring type check. Consult your Linux distribution's advisories for backported kernel packages.

Workarounds

Limit local user access to AMD GPU device nodes using group permissions on /dev/dri/renderD*
Avoid running untrusted workloads on multi-tenant hosts with AMD GPUs until the kernel is patched
On non-critical systems, consider unloading or disabling the amdgpu module if GPU acceleration is not required

bash

# Verify the running kernel version and amdgpu module status
uname -r
lsmod | grep amdgpu

# Restrict access to DRI render nodes to the 'render' group only
ls -l /dev/dri/renderD*
sudo chmod 0660 /dev/dri/renderD*
sudo chown root:render /dev/dri/renderD*