CVE-2022-49669 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix race on unaccepted mptcp sockets
When the listener socket owning the relevant request is closed, it frees the unaccepted subflows and that causes later deletion of the paired MPTCP sockets.
The mptcp socket's worker can run in the time interval between such delete operations. When that happens, any access to msk->first will cause an UaF access, as the subflow cleanup did not cleared such field in the mptcp socket.
Address the issue explicitly traversing the listener socket accept queue at close time and performing the needed cleanup on the pending msk.
Note that the locking is a bit tricky, as we need to acquire the msk socket lock, while still owning the subflow socket one.
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Analysis
by VulDB Data Team • 03/25/2025
The vulnerability CVE-2022-49669 represents a use-after-free condition in the Linux kernel's Multipath TCP implementation that arises from improper synchronization during socket cleanup operations. This flaw specifically affects the MPTCP subsystem where multiple subflows are managed under a single MPTCP socket structure. The issue occurs when a listener socket that owns pending MPTCP connection requests is closed while subflows are still in an unaccepted state. During this cleanup process, the system attempts to free unaccepted subflows before the paired MPTCP sockets have been properly cleaned up, creating a temporal window where the MPTCP socket's worker can access freed memory structures.
The technical root cause stems from a race condition in the socket cleanup sequence where the mptcp socket's worker thread executes between the deletion of subflows and the cleanup of the associated MPTCP socket structures. When the listener socket is closed, it frees the unaccepted subflows, but the msk->first field in the MPTCP socket structure is not properly cleared during this process. This leaves dangling references that can be accessed by the MPTCP worker thread, resulting in a use-after-free access pattern that violates fundamental memory safety principles. The vulnerability manifests as a potential kernel memory corruption scenario that could be exploited to gain unauthorized access or cause system instability.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a critical security weakness in the kernel's networking stack that could be leveraged by malicious actors. The flaw specifically affects systems running Linux kernels with MPTCP support, making it particularly relevant for high-performance networking environments, cloud infrastructure, and any system relying on multipath TCP for improved network reliability and throughput. Attackers could potentially exploit this race condition to execute arbitrary code within kernel space, leading to complete system compromise and privilege escalation. The vulnerability is particularly concerning because it occurs during normal socket closure operations, making it difficult to detect and prevent through standard monitoring approaches.
The fix for CVE-2022-49669 addresses the synchronization issue by explicitly traversing the listener socket's accept queue during close operations and performing the necessary cleanup on pending MPTCP sockets before allowing the subflow cleanup to proceed. This approach requires careful locking mechanisms that maintain proper order of operations while avoiding deadlocks between different socket locks. The solution implements a specific sequence where the mptcp socket lock must be acquired while still holding the subflow socket lock, which creates complex synchronization requirements that must be carefully managed. This remediation aligns with common security best practices for race condition fixes and follows established patterns for kernel-level memory safety improvements. The fix demonstrates the importance of proper resource management and synchronization in kernel code, particularly when dealing with complex networking protocols like MPTCP that involve multiple interconnected socket structures. This vulnerability and its resolution highlight the ongoing challenges in maintaining memory safety in kernel space, where even seemingly simple cleanup operations can expose critical security flaws that require careful analysis and precise implementation of protective measures.