CVE-2024-42250 in Linux
Summary
by MITRE • 08/07/2024
In the Linux kernel, the following vulnerability has been resolved:
cachefiles: add missing lock protection when polling
Add missing lock protection in poll routine when iterating xarray, otherwise:
Even with RCU read lock held, only the slot of the radix tree is ensured to be pinned there, while the data structure (e.g. struct cachefiles_req) stored in the slot has no such guarantee. The poll routine will iterate the radix tree and dereference cachefiles_req accordingly. Thus RCU read lock is not adequate in this case and spinlock is needed here.
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Analysis
by VulDB Data Team • 11/02/2024
The vulnerability identified as CVE-2024-42250 resides within the Linux kernel's cachefiles subsystem, specifically addressing a critical concurrency issue in the poll routine implementation. This flaw manifests in the handling of xarray iteration operations where proper synchronization mechanisms are absent, creating potential race conditions that could lead to system instability and data corruption. The cachefiles subsystem serves as a caching mechanism for files in the Linux kernel, managing cached file operations and maintaining metadata structures that are essential for proper file system functionality.
The technical root cause of this vulnerability stems from inadequate locking mechanisms during xarray traversal operations within the poll routine. While the code correctly employs RCU read locks to ensure that radix tree slots remain pinned in memory, it fails to account for the fact that the actual data structures stored within these slots may be subject to modification or deallocation. The struct cachefiles_req objects that are dereferenced during poll iteration can be freed or modified concurrently, despite the RCU lock providing only slot-level protection. This fundamental misunderstanding of lock semantics creates a scenario where concurrent access patterns can result in use-after-free conditions or memory corruption, as the poll routine assumes that data structures remain valid throughout the iteration process.
The operational impact of this vulnerability extends beyond simple kernel panics or crashes, potentially enabling privilege escalation and denial of service conditions that could affect system availability and data integrity. When multiple threads attempt to access the cachefiles subsystem simultaneously, particularly during polling operations, the race condition can result in corrupted memory structures that may be exploited by malicious actors to gain elevated privileges or cause system instability. The vulnerability is particularly concerning in environments where the kernel's caching subsystem is heavily utilized, as the probability of encountering the race condition increases with concurrent access patterns, making it a significant risk for production systems.
This vulnerability maps to CWE-367, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and also relates to CWE-119, which covers improper access to memory locations. The issue aligns with ATT&CK technique T1068, which involves exploiting vulnerabilities to gain privileges, and T1499, which encompasses network denial of service attacks through system resource exhaustion. The fix implemented addresses the core synchronization problem by replacing the RCU read lock with appropriate spinlock protection during xarray iteration, ensuring that the entire operation remains atomic and that data structures remain valid throughout the polling process. This mitigation approach follows established kernel development practices for handling concurrent access to shared data structures and aligns with the kernel's broader security architecture principles. The solution demonstrates the importance of proper synchronization primitives in kernel space programming, where inadequate locking can lead to severe security implications and system instability.