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Vulnerability Database/CVE-2026-80870

CVE-2026-80870: Linux Kernel Privilege Escalation Vulnerability

CVE-2026-80870 is a privilege escalation flaw in the Linux kernel drm/amdkfd module that allows invalid userspace IDs to trigger kernel warnings. This post explains its impact, affected versions, and mitigation steps.

Published:

CVE-2026-80870 Overview

CVE-2026-80870 affects the Linux kernel's AMD Kernel Fusion Driver (amdkfd) component. The vulnerability exists in the Checkpoint/Restore in Userspace (CRIU) restore flow for KFD objects. The kernel fails to validate object IDs supplied from userspace before passing them to idr_alloc(). When a restored ID exceeds INT_MAX, the IDR layer triggers a WARN, which prints a warning trace and can cause a panic or reboot on systems configured with panic_on_warn.

Critical Impact

A local user supplying crafted CRIU restore data can trigger a kernel WARN in idr_alloc(), leading to denial of service on systems with panic_on_warn enabled.

Affected Products

  • Linux kernel with AMD KFD (drm/amdkfd) driver enabled
  • Systems using CRIU checkpoint/restore for GPU workloads
  • Distributions shipping vulnerable stable kernel branches referenced in the upstream fix commits

Discovery Timeline

  • 2026-09-04 - CVE-2026-80870 published to NVD
  • 2026-09-04 - Last updated in NVD database

Technical Details for CVE-2026-80870

Vulnerability Analysis

The KFD CRIU restore flow reconstructs kernel objects from state previously saved by userspace. Two restore paths pass userspace-controlled IDs directly to idr_alloc(). In kfd_criu_restore_event(), the code calls create_signal_event() or create_other_event(), which invoke allocate_event_notification_slot() with idr_alloc(..., *restore_id, *restore_id + 1, ...). In criu_restore_memory_of_gpu(), the code passes bo_priv->idr_handle from CRIU data straight into idr_alloc().

The idr_alloc() API requires that ID range values fit within signed integer limits. When a caller supplies a value greater than INT_MAX, the IDR layer emits a WARN. Static analysis with Smatch flagged these paths as reaching idr_alloc() with unchecked userspace values. This maps to improper input validation in a kernel driver [CWE-20].

Root Cause

The root cause is missing bounds validation on IDs deserialized from CRIU restore data. Neither restore path checks whether *restore_id or bo_priv->idr_handle exceeds INT_MAX before invoking idr_alloc(). The IDR layer's internal WARN becomes reachable from an unprivileged user-supplied value.

Attack Vector

A local user with permission to invoke KFD CRIU restore ioctls can craft a restore image containing an event or buffer object ID greater than INT_MAX. When the kernel processes that image, idr_alloc() triggers a WARN. On hardened systems with panic_on_warn=1, this results in a kernel panic and reboot, producing a denial-of-service condition.

No verified exploit code is public. The vulnerability is described in prose in the upstream commit messages; see the referenced kernel git commits for the fix diff.

Detection Methods for CVE-2026-80870

Indicators of Compromise

  • Kernel log entries containing WARN traces originating from idr_alloc() with call stacks referencing kfd_criu_restore_event or criu_restore_memory_of_gpu
  • Unexpected reboots on hosts running AMD GPU workloads with panic_on_warn enabled
  • CRIU restore operations against KFD failing with -EINVAL after patching, which may indicate malformed or tampered checkpoint images

Detection Strategies

  • Monitor dmesg and journal output for kernel WARN messages referencing amdkfd restore paths
  • Baseline expected CRIU workflows and alert on failed KFD restore ioctls from unexpected user contexts
  • Correlate GPU workload restore attempts with kernel taint state changes

Monitoring Recommendations

  • Ingest kernel logs from AMD GPU hosts into a centralized log platform for WARN and panic pattern matching
  • Track kernel version inventory across Linux fleets to identify hosts still running pre-patch builds
  • Alert on repeated CRIU restore failures against the same host, which may indicate probing

How to Mitigate CVE-2026-80870

Immediate Actions Required

  • Apply the upstream stable kernel patches referenced in the CVE record to all AMD GPU hosts using KFD CRIU restore
  • Restrict access to KFD device nodes and CRIU restore capabilities to trusted service accounts only
  • Review whether panic_on_warn is enabled and evaluate the operational risk of unprivileged reboots until patched

Patch Information

The fix adds INT_MAX validation before restored IDs are passed to idr_alloc() in both kfd_criu_restore_event() and criu_restore_memory_of_gpu(). Invalid IDs cause the restore to return -EINVAL, preventing the IDR layer from receiving out-of-range values. The patch is available in the following upstream commits: 085ea93bda71, 543ed0f61d56, 85043dd49c2f, 89a75e3349c4, cb6311f25a09, and f8687018f240.

Workarounds

  • Disable CRIU checkpoint/restore for KFD workloads where the feature is not required
  • Restrict access to /dev/kfd to trusted users via device permissions or Linux capabilities
  • Consider disabling panic_on_warn on non-hardened hosts to prevent reboots from a triggered WARN, accepting the tradeoff of reduced fail-safe behavior

Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.

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