CVE-2026-99158 in Linux
Summary
by MITRE • 10/28/2026
In the Linux kernel, the following vulnerability has been resolved:
ring-buffer: Fix false warning in ring_buffer_map_get_reader()
The mmap reader can warn when it catches up with a writer that is still committing events. rb_get_reader_page() returns NULL in this case, but ring_buffer_map_get_reader() treats that result as an error.
The initial rb_per_cpu_empty() check filters out an empty buffer, but it does not guarantee that the next reader page has committed data. Writers do not take reader_lock and can advance commit_page before publishing the committed length on the new page. rb_get_reader_page() can swap to that page, catch up with the writer and return NULL.
Handle NULL through the existing no-data exit without warning. Remove the caller's reader_page == commit_page check as well, since the reader-page helper already handles that case. The existing metadata update and return path remain in place.
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Analysis
by VulDB Data Team • 10/28/2026
The Linux kernel ring buffer implementation contains a logic flaw within the mmap-based reading mechanism that triggers false positive warnings under specific concurrency conditions. This vulnerability resides in the function ring_buffer_map_get_reader, which is responsible for retrieving the current reader page from the per-CPU ring buffer structure. The issue arises when the memory-mapped reader process advances its position and catches up with a writer thread that is actively committing new events to the buffer. In this scenario, the helper function rb_get_reader_page returns NULL because it detects that the next available page has not yet had its data committed or published by the writer. However, ring_buffer_map_get_reader incorrectly interprets this NULL return value as an error condition rather than a valid state indicating no new data is currently available for reading.
The root cause of this issue lies in the asynchronous nature of how writers update buffer metadata without holding the reader lock. When a writer commits events to a page, it may advance the commit_page pointer before fully publishing the committed length on that new page. This creates a race window where rb_get_reader_page can swap to the new page and immediately detect that it is not yet ready for reading, resulting in a NULL return value. The existing check using rb_per_cpu_empty only filters out completely empty buffers but does account for this transient state of uncommitted data on an active page. Consequently, treating the NULL result as an error leads to spurious warning messages being logged, which can clutter system logs and potentially trigger false alarms in monitoring systems that rely on kernel warnings for anomaly detection.
From a security and operational stability perspective, while this vulnerability does not directly lead to privilege escalation or remote code execution, it represents a denial of service vector through log flooding and potential confusion in diagnostic processes. The excessive warning messages can consume system resources and obscure genuine critical errors within the kernel logs. Furthermore, incorrect handling of buffer states might mask underlying synchronization issues if developers rely on these warnings for debugging ring buffer behavior. This flaw aligns with CWE-391, which describes unchecked error condition situations where a function returns an indication that should be checked but is ignored or misinterpreted. In terms of the MITRE ATT&CK framework, this relates to Defense Evasion techniques such as Indicator Removal on Host (T1070), specifically log clearing or evasion through noise generation, although in this case it is unintentional rather than maliciously crafted by an attacker.
The resolution involves modifying ring_buffer_map_get_reader to handle the NULL return value from rb_get_reader_page correctly by treating it as a no-data condition rather than an error state. This change ensures that when the reader catches up with the writer, the function exits gracefully without issuing warnings. Additionally, the patch removes a redundant check for reader_page equaling commit_page within the caller, since the helper function already handles this case appropriately. By aligning the logic with the actual operational semantics of the ring buffer, the fix prevents false positives while maintaining the integrity of metadata updates and return paths. This correction enhances system stability by reducing log noise and ensures that developers can rely on kernel warnings for genuine issues rather than expected concurrency races in normal operation.