Vulnerability Database

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CVE-2025-39759 — linux / linux_kernel

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

In the Linux kernel, the following vulnerability has been resolved:

btrfs: qgroup: fix race between quota disable and quota rescan ioctl

There's a race between a task disabling quotas and another running the rescan ioctl that can result in a use-after-free of qgroup records from the fs_info->qgroup_tree rbtree.

This happens as follows:

  1. Task A enters btrfs_ioctl_quota_rescan() -> btrfs_qgroup_rescan();

  2. Task B enters btrfs_quota_disable() and calls btrfs_qgroup_wait_for_completion(), which does nothing because at that point fs_info->qgroup_rescan_running is false (it wasn't set yet by task A);

  3. Task B calls btrfs_free_qgroup_config() which starts freeing qgroups from fs_info->qgroup_tree without taking the lock fs_info->qgroup_lock;

  4. Task A enters qgroup_rescan_zero_tracking() which starts iterating the fs_info->qgroup_tree tree while holding fs_info->qgroup_lock, but task B is freeing qgroup records from that tree without holding the lock, resulting in a use-after-free.

Fix this by taking fs_info->qgroup_lock at btrfs_free_qgroup_config(). Also at btrfs_qgroup_rescan() don't start the rescan worker if quotas were already disabled.

  • Published: Sep 11, 2025
  • Updated: Jan 10, 2026
  • CVE: CVE-2025-39759
  • Severity: High
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: High
  • Score: 7
  • AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

CWEs:

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