CVE-2026-99237 in Linux
Summary
by MITRE • 11/02/2026
In the Linux kernel, the following vulnerability has been resolved:
tracing: Hold trace_types_lock when resetting last boot data from readers
update_last_data_if_empty() is called from tracing_open() with O_TRUNC, tracing_read_pipe() and tracing_buffers_read() without trace_types_lock. Two readers can both pass the LAST_BOOT test and free module_delta twice, and a module notifier can update module_delta while it is being freed.
Take trace_types_lock in those paths and keep the callers that already hold it on an unlocked variant.
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Analysis
by VulDB Data Team • 11/03/2026
The Linux kernel tracing subsystem contains a concurrency vulnerability related to race conditions during the reset of last boot data from readers, specifically within functions such as update_last_data_if_empty(). This function is invoked by multiple code paths including tracing_open() when opening files with O_TRUNC flag, tracing_read_pipe(), and tracing_buffers_read(). The core issue arises because these operations are executed without holding trace_types_lock, which serves as a critical synchronization mechanism for managing the state of trace types. When two concurrent readers both pass the LAST_BOOT test simultaneously, they may independently proceed to free module_delta twice in quick succession. This double-free scenario creates a window where memory corruption can occur if one reader frees the resource while another is still accessing or about to access it.
The vulnerability stems from insufficient locking granularity around critical sections that manipulate shared kernel data structures related to tracing buffers and boot-time metrics. Module notifier callbacks, which are triggered during module load and unload events, may update module_delta concurrently with these read operations. Without proper synchronization through trace_types_lock, there is no guarantee of atomicity or mutual exclusion when modifying this shared state variable. This lack of protection allows for potential use-after-free conditions where freed memory might be accessed by subsequent tracing operations, leading to undefined behavior including kernel panics, data corruption, or potentially exploitable code execution paths if an attacker can influence the timing and content of these concurrent accesses.
From a technical perspective, this represents a classic race condition vulnerability classified under CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). The absence of proper locking mechanisms around critical sections that modify shared kernel data structures creates opportunities for attackers to exploit the timing window between checking conditions and performing modifications. In terms of MITRE ATT&CK framework, this vulnerability aligns with techniques involving exploitation of race conditions in system-level components, potentially enabling privilege escalation or denial-of-service attacks against systems relying on accurate tracing functionality for debugging and monitoring purposes.
The operational impact includes potential kernel instability through double-free scenarios that can trigger oops messages or full system crashes depending on memory allocation patterns at the time of exploitation. Attackers with local access could theoretically leverage this race condition to corrupt kernel memory structures, potentially gaining unauthorized code execution capabilities within kernel space if they can precisely control the timing and content of concurrent tracing operations. Even without successful exploitation for privilege escalation, the vulnerability poses significant reliability risks by causing unpredictable system behavior during normal tracing activities such as opening trace files or reading buffer contents.
The resolution involves modifying the affected functions to acquire trace_types_lock before performing any operations that interact with shared boot data structures. Specifically, update_last_data_if_empty() must be called while holding this lock in all invocation paths including those within tracing_open(), tracing_read_pipe(), and tracing_buffers_read(). For callers that already hold trace_types_lock when invoking these functions, the implementation should use an unlocked variant to prevent deadlocks from recursive locking attempts. This approach ensures proper mutual exclusion around critical sections managing module_delta and related boot-time metrics while maintaining performance by avoiding unnecessary lock acquisitions where synchronization is already guaranteed by existing locks held by calling contexts.
Mitigation strategies include applying kernel patches that implement these locking corrections, ensuring all code paths accessing shared tracing state properly synchronize through trace_types_lock. System administrators should monitor for unusual system behavior or crashes during intensive tracing operations and keep systems updated with security patches addressing this vulnerability. For environments where real-time debugging is critical, implementing additional monitoring around module load/unload events can help detect potential exploitation attempts before they cause significant damage to system stability.