CVE-2026-89499 in Linux
Summary
by MITRE • 09/12/2026
In the Linux kernel, the following vulnerability has been resolved:
ring-buffer: Stop remote reader update when page swap fails
The remote swap_reader_page callback can return -EBUSY when the writer moves the head before the remote catches it, particularly during an event storm on a small buffer. __rb_get_reader_page_from_remote() currently warns about that failure but continues with the unchanged reader ID and rearranges the local page list as though the swap succeeded.
Handle the callback failure as a recoverable error. Report it with pr_warn_ratelimited() and return NULL. Callers already handle a NULL reader page as a failed attempt. This avoids splicing the same page as both the previous and new reader without flooding the log under contention.
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Analysis
by VulDB Data Team • 09/12/2026
The Linux kernel ring buffer implementation contains a logic flaw in the remote reader update mechanism that can lead to data corruption or inconsistent state during high-contention scenarios. Specifically, the vulnerability resides within the __rb_get_reader_page_from_remote function, which is responsible for managing page swaps between writers and readers across different contexts. Under normal operation, this process ensures that readers access consistent snapshots of buffered events. However, when an event storm occurs on a small buffer, the writer may advance the head pointer before the remote reader has caught up to it. In such race conditions, the swap_reader_page callback returns -EBUSY to indicate that the page is currently busy or locked by another process.
The core technical flaw lies in how this failure condition was previously handled. Although the code correctly detected the -EBUSY error and issued a warning via pr_warn(), it erroneously continued execution with an unchanged reader ID. This oversight caused the system to rearrange the local page list as if the swap had succeeded, despite the underlying operation having failed. Consequently, this logic error could result in splicing the same physical page into both the previous and new reader positions simultaneously. Such a state violates the integrity of the ring buffer structure, potentially leading to duplicate event processing or loss of data continuity for subsequent readers attempting to consume the stream.
From an operational impact perspective, this vulnerability primarily affects systems experiencing high-frequency logging events where buffers are small and contention is frequent. While it may not always lead to immediate kernel panic due to existing safeguards in higher-level callers, it introduces subtle inconsistencies that can degrade system reliability and complicate debugging efforts. The incorrect handling of the failure state means that diagnostic logs might be flooded with warnings without resolving the underlying synchronization issue, masking other potential problems and reducing overall observability during critical incidents.
To mitigate this vulnerability, the fix implements a robust error recovery path by treating the callback failure as a recoverable error rather than an ignorable warning. The updated logic now reports the condition using pr_warn_ratelimited() to prevent log flooding under heavy contention and returns NULL from __rb_get_reader_page_from_remote(). This change aligns with existing caller expectations, which already handle a NULL reader page return value by treating it as a failed attempt to fetch a valid buffer page. By ensuring that no invalid state is propagated up the call stack, the system maintains data integrity even during extreme load conditions.
This issue maps to CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization, as the root cause involves improper handling of shared resources under concurrent access without adequate synchronization checks for failure states. In terms of attack vectors or operational risks, it relates to ATT&CK technique T1078, Valid Accounts, specifically in contexts where system stability and log integrity are critical for forensic analysis and incident response. Ensuring that the ring buffer correctly handles race conditions is essential for maintaining the reliability of kernel-level tracing tools used by security professionals to monitor system behavior and detect anomalies.