CVE-2026-98079
Received Received - Intake

Race Condition in Linux Kernel Btrfs Zstd Compression

Publication date: 2026-09-25

Last updated on: 2026-09-25

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: btrfs: zstd: fix lost wakeup when waiting for a workspace A writer can sleep forever in zstd_get_workspace() even though a workspace is free. When zstd_alloc_workspace() fails, the task is queued on zwsm->wait and schedules unconditionally, never re-testing the pool. zstd_put_workspace() publishes the workspace and then calls cond_wake_up(), which only wakes when a sleeper is already visible, so a workspace returned between the failed allocation and prepare_to_wait() wakes nobody. The window is wide: zstd_alloc_workspace() goes through kvmalloc() and may enter reclaim. Only a max level workspace triggers the wakeup and one is deliberately kept allocated as the fallback every waiter waits for, so once its wakeup is lost the writer stays in TASK_UNINTERRUPTIBLE until some other task happens to return one. Re-check the pool after prepare_to_wait() has published the waiter, and use the workspace if one turned up.

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Meta Information

Published
2026-09-25
Last Modified
2026-09-25
Generated
2026-09-25
AI Q&A
2026-09-25
EPSS Evaluated
N/A
NVD
CVE-2026-98079
EUVD
EUVD-2026-86909

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

Helpful Resources

Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a Linux kernel vulnerability in the Btrfs filesystem's Zstandard (zstd) compression handling. A writer process can get stuck indefinitely waiting for a workspace to become available, even when one is free. The issue occurs in zstd_get_workspace() where a task sleeps forever after a failed allocation, failing to check if a workspace becomes available later.

Detection Guidance

This vulnerability is specific to the Linux kernel's btrfs filesystem with zstd compression. Detection requires checking kernel logs for stalled zstd workspace allocation attempts or monitoring for processes stuck in TASK_UNINTERRUPTIBLE state during btrfs operations. No direct network detection commands exist as this is a local kernel issue.

Impact Analysis

This could cause system hangs or freezes when processes attempt to write compressed data to Btrfs volumes using zstd compression. Affected systems may become unresponsive until manually rebooted, leading to potential data loss or service disruptions.

Mitigation Strategies

Immediate mitigation requires updating the Linux kernel to a patched version that resolves the btrfs zstd workspace issue. Monitor kernel.org or your distribution's security advisories for kernel updates addressing CVE-2026-98079. No temporary workarounds are recommended as the issue requires kernel-level fixes.

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