CVE-2026-53050: Linux Kernel Race Condition Vulnerability

CVE-2026-53050 Overview

CVE-2026-53050 is a race condition vulnerability in the Linux kernel's disk quota subsystem. The flaw exists between dquot_scan_active() and quota deactivation logic in quota_release_workfn(). A thread scanning the in-use dquot list can acquire a reference to a dquot that has already been moved to the releasing list. Under memory pressure, the caller of dquot_scan_active() can end up operating on a freed dquot structure, leading to a use-after-free condition.

Critical Impact
The race window allows kernel code to dereference freed quota structures, which can cause memory corruption, kernel panics, or unpredictable filesystem quota behavior on systems with filesystem quotas enabled.

Affected Products

Linux kernel (multiple stable branches receiving backported fixes)
Filesystems with disk quota support enabled (ext4, XFS, and others using the generic quota framework)
Systems running workloads that activate or deactivate quotas dynamically

Discovery Timeline

2026-06-24 - CVE-2026-53050 published to NVD
2026-06-24 - Last updated in NVD database

Technical Details for CVE-2026-53050

Vulnerability Analysis

The vulnerability resides in the kernel's generic disk quota implementation. dquot_scan_active() iterates over the inuse_list of active dquot structures and increments the reference count of any dquot that still has the DQ_ACTIVE_B flag set. Concurrently, quota_release_workfn() moves dquots whose dq_count reached zero to a local rls_head list for release, while leaving DQ_ACTIVE_B set during the window before synchronize_srcu() completes.

During this window, dquot_scan_active() running on another CPU observes the dquot as still active, acquires a reference, and increments dq_count. The release worker then proceeds and triggers WARN_ON_ONCE(atomic_read(&dquot->dq_count)). Beyond the warning, the scanning thread continues to operate on a dquot that the release path may subsequently free.

Root Cause

The root cause is an atomicity violation between list membership and reference acquisition. The release worker removes the dquot from active processing through list_replace_init() but does not clear DQ_ACTIVE_B before dropping dq_list_lock. The patched code ensures the dquot is removed from the releasing list when a new reference is acquired, restoring consistent state between flags and list membership.

Attack Vector

Triggering the race requires local execution with the ability to drive concurrent quota activity. An attacker would need to repeatedly invoke quota operations on a filesystem that uses the generic quota framework while another path scans active dquots. Memory pressure increases the probability of the freed-object path being taken. This is a local kernel concurrency bug rather than a remotely exploitable flaw.

No public proof-of-concept is available, and the issue is documented entirely through upstream kernel commits.

Detection Methods for CVE-2026-53050

Indicators of Compromise

Kernel log entries containing WARN_ON_ONCE traces originating from quota_release_workfn or dquot_scan_active
Unexpected kernel oops or panic messages referencing dquot, dq_count, or the quota subsystem
Filesystem quota inconsistencies appearing after high-load operations involving mount, remount, or quotactl calls

Detection Strategies

Monitor dmesg and /var/log/kern.log for warnings and stack traces involving the dquot release path
Compare installed kernel package versions against vendor advisories that reference the upstream fix commits
Run uname -r against patched stable kernel versions to identify hosts still exposed to the race

Monitoring Recommendations

Forward kernel ring buffer events to a centralized logging or SIEM platform for correlation across fleets
Alert on repeated WARN_ON_ONCE signatures from the quota subsystem, which may indicate the race being hit in production
Track filesystem mount events and quotactl syscall usage on multi-tenant hosts where quotas are enforced

How to Mitigate CVE-2026-53050

Immediate Actions Required

Identify all Linux hosts running kernels predating the fix and that have filesystem quotas enabled
Apply vendor-supplied kernel updates that incorporate the upstream commits referenced in the NVD entry
Reboot patched hosts to load the corrected kernel image, since this fix cannot be applied without kernel replacement on most distributions

Patch Information

The fix is distributed across multiple upstream stable trees. Relevant commits include Kernel Commit 2bdc80f, Kernel Commit 61e25f6, Kernel Commit 6678dde, Kernel Commit 82cbdb4, Kernel Commit ac8a2e0, Kernel Commit e93ab40, Kernel Commit f9438cb8, and Kernel Commit fdd424d. The patch ensures the dquot is removed from the releasing list when a new reference is acquired.

Workarounds

Disable filesystem quotas on affected mounts where the feature is not required, removing the vulnerable code path from execution
Limit local user access to systems that cannot be patched immediately, since the race requires local activity to trigger
Reduce memory pressure on quota-enabled hosts to lower the probability of the use-after-free condition manifesting

bash

# Verify kernel version and quota status on affected hosts
uname -r
mount | grep -E 'usrquota|grpquota|prjquota'
# Disable quotas on a mount point (example for an ext4 mount)
quotaoff -av