CVE-2026-53319 in Linux
Summary
by MITRE • 06/26/2026
In the Linux kernel, the following vulnerability has been resolved:
blk-wbt: remove WARN_ON_ONCE from wbt_init_enable_default()
wbt_init_enable_default() uses WARN_ON_ONCE to check for failures from wbt_alloc() and wbt_init(). However, both are expected failure paths:
- wbt_alloc() can return NULL under memory pressure (-ENOMEM) - wbt_init() can fail with -EBUSY if wbt is already registered
syzbot triggers this by injecting memory allocation failures during MTD partition creation via ioctl(BLKPG), causing a spurious warning.
wbt_init_enable_default() is a best-effort initialization called from blk_register_queue() with a void return type. Failure simply means the disk operates without writeback throttling, which is harmless.
Replace WARN_ON_ONCE with plain if-checks, consistent with how wbt_set_lat() in the same file already handles these failures. Add a pr_warn() for the wbt_init() failure to retain diagnostic information without triggering a full stack trace.
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Analysis
by VulDB Data Team • 06/26/2026
The vulnerability resides in the Linux kernel's block layer writeback throttling subsystem where the function wbt_init_enable_default() incorrectly employs WARN_ON_ONCE for error handling during initialization. This function is responsible for setting up writeback throttling mechanisms that help manage I/O operations to prevent system overload during high write activity. The issue stems from the expectation that both wbt_alloc() and wbt_init() functions may legitimately fail under normal operating conditions, yet the code treats these as unexpected errors requiring immediate warning output.
The technical flaw manifests when memory pressure causes wbt_alloc() to return NULL with -ENOMEM error codes or when wbt_init() encounters -EBUSY errors due to already registered writeback throttling mechanisms. These are not exceptional conditions but rather expected failure paths that occur during normal system operation, particularly when multiple subsystems attempt to initialize writeback throttling concurrently. The syzbot fuzzing tool specifically triggers this by injecting memory allocation failures during MTD partition creation through BLKPG ioctl calls, which creates the exact conditions where these legitimate error paths are encountered.
The operational impact of this vulnerability is limited in scope since wbt_init_enable_default() is designed as a best-effort initialization function called from blk_register_queue() with a void return type. When initialization fails, the disk simply operates without writeback throttling functionality, which represents a harmless degradation rather than a system crash or security compromise. However, the spurious warning messages generated by WARN_ON_ONCE create unnecessary noise in system logs and can mask genuine issues that require attention from system administrators monitoring kernel messages.
The mitigation strategy involves replacing the WARN_ON_ONCE calls with standard conditional checks consistent with existing patterns within the same file, specifically following how wbt_set_lat() already handles similar failure conditions. This approach maintains diagnostic capability through pr_warn() output for wbt_init() failures while eliminating the disruptive stack trace generation that occurs with WARN_ON_ONCE. The solution aligns with common kernel development practices where non-critical initialization failures should be handled gracefully without interrupting normal system operation, thereby reducing log noise while preserving essential diagnostic information for debugging purposes.
This vulnerability demonstrates a common anti-pattern in kernel development where error handling mechanisms are applied inconsistently across similar functions within the same codebase. The fix ensures that legitimate memory pressure and resource contention conditions do not trigger unnecessary warnings while maintaining appropriate logging for actual diagnostic purposes, thus improving system stability and maintainability without compromising security or functionality.
The issue relates to CWE-703 as it involves improper handling of exceptional conditions in software, and follows ATT&CK technique T1489 by potentially affecting system stability through inappropriate warning generation rather than directly manipulating system processes. The fix maintains the kernel's reliability while ensuring that only truly exceptional conditions generate full warning traces, which aligns with the principle of minimal logging for expected operational conditions.