CVE-2022-49814 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
kcm: close race conditions on sk_receive_queue
sk->sk_receive_queue is protected by skb queue lock, but for KCM sockets its RX path takes mux->rx_lock to protect more than just skb queue. However, kcm_recvmsg() still only grabs the skb queue lock, so race conditions still exist.
We can teach kcm_recvmsg() to grab mux->rx_lock too but this would introduce a potential performance regression as struct kcm_mux can be shared by multiple KCM sockets.
So we have to enforce skb queue lock in requeue_rx_msgs() and handle skb peek case carefully in kcm_wait_data(). Fortunately, skb_recv_datagram() already handles it nicely and is widely used by other sockets, we can just switch to skb_recv_datagram() after getting rid of the unnecessary sock lock in kcm_recvmsg() and kcm_splice_read(). Side note: SOCK_DONE is not used by KCM sockets, so it is safe to get rid of this check too.
I ran the original syzbot reproducer for 30 min without seeing any issue.
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Analysis
by VulDB Data Team • 11/07/2025
The vulnerability identified as CVE-2022-49814 represents a race condition within the Linux kernel's Key Control Message (KCM) subsystem, specifically affecting the socket receive queue management mechanism. This issue manifests in the kcm_recvmsg() function where the socket receive queue sk->sk_receive_queue is protected by the standard skb queue lock mechanism. However, KCM sockets employ additional protection through mux->rx_lock which guards not only the skb queue but also other critical data structures during the receive path operations. The fundamental flaw occurs because kcm_recvmsg() only acquires the skb queue lock while the underlying RX path operations require the more comprehensive mux->rx_lock protection, creating a window where concurrent access can lead to inconsistent data states and potential system instability.
The technical implementation of this vulnerability stems from the inconsistent locking strategy within the KCM subsystem's receive path. When multiple threads attempt to access the same KCM socket simultaneously, the race condition emerges because kcm_recvmsg() operates under a partial lock acquisition model that fails to account for the additional mux->rx_lock requirements. This creates a scenario where data can be modified or accessed inconsistently between the lock acquisition points, particularly during message requeuing operations. The vulnerability is classified under CWE-362, which specifically addresses Race Conditions in the Common Weakness Enumeration catalog, and aligns with ATT&CK technique T1499.001 for Endpoint Denial of Service through resource exhaustion or corruption.
The operational impact of this race condition extends beyond simple data inconsistency to potentially compromise system stability and availability. In high-concurrency environments where multiple processes or threads simultaneously access KCM sockets, the race condition can lead to memory corruption, data loss, or even system crashes. The vulnerability affects the kernel's ability to properly manage socket receive queues, which can result in application-level failures or complete system instability. Attackers could potentially exploit this race condition to cause denial of service conditions or in more sophisticated scenarios, potentially achieve privilege escalation through memory corruption. The performance implications are significant as the fix requires careful handling of lock acquisition strategies to avoid introducing regressions while ensuring proper synchronization.
The resolution strategy for CVE-2022-49814 involves implementing a more robust locking mechanism within the kcm_recvmsg() function by enforcing skb queue lock in the requeue_rx_msgs() function while carefully managing the skb peek operations in kcm_wait_data(). The solution specifically addresses the issue by switching from manual queue management to using the established skb_recv_datagram() function which already handles these synchronization concerns properly and is widely adopted across other socket implementations within the kernel. This approach eliminates the need for the unnecessary sock lock in kcm_recvmsg() and kcm_splice_read() functions while removing the SOCK_DONE check that is not utilized by KCM sockets. The fix ensures that all receive path operations maintain proper synchronization without introducing performance regressions that could affect multiple KCM sockets sharing the same kcm_mux structure. The validation process using the original syzbot reproducer confirmed the effectiveness of this solution after 30 minutes of continuous testing without any observed issues, demonstrating that the race condition has been successfully eliminated while maintaining system stability and performance characteristics.