CVE-2026-74666 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
packet: synchronize pressure clearing with ring reconfiguration
packet_set_ring() updates the RX ring state under sk_receive_queue.lock, but used to publish the tpacket receive mode through po->prot_hook.func after releasing that lock. packet_poll() and packet_recvmsg() can then run the pressure clearing path after the ring has been cleared while still seeing tpacket_rcv, causing __packet_rcv_has_room() to dereference stale or NULL ring storage.
Move the existing receive hook assignment into the same sk_receive_queue.lock section as the ring state update. Keep the assignment otherwise unchanged, including on TX ring reconfiguration, to avoid adding behavior changes that are not required for the fix.
Serialize packet_recvmsg() pressure clearing with the same queue lock only after PACKET_SOCK_PRESSURE has been observed. If the flag is clear and the socket has moved away from tpacket_rcv, packet_set_ring() has already detached the socket and waited for synchronize_net(), so no new packet input can set the flag again.
packet_poll() already holds sk_receive_queue.lock, so it uses the new unlocked helper directly.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Linux kernel involves a race condition within the packet socket implementation, specifically affecting how ring buffer state and receive hooks are synchronized during reconfiguration operations. The core issue resides in the function packet_set_ring(), which is responsible for updating the RX (receive) ring state. Historically, this function updated the internal ring structures while holding the sk_receive_queue.lock mutex but published the tpacket receive mode by setting po->prot_hook.func after releasing that lock. This temporal gap between updating the ring state and publishing the hook created a window of vulnerability where concurrent operations could observe an inconsistent system state. Specifically, functions such as packet_poll() and packet_recvmsg(), which handle incoming data processing and pressure clearing mechanisms, could execute their logic while the ring had already been cleared or reconfigured but before the receive hook was properly detached or updated to reflect this change.
This race condition leads to a critical operational impact where __packet_rcv_has_room() may attempt to dereference stale or NULL ring storage pointers. When packet_recvmsg() runs its pressure clearing path, it relies on accurate information about whether there is space in the receive buffer. If the ring has been cleared by another thread but the socket still appears to be using tpacket_rcv due to the delayed hook update, the function may access memory that no longer contains valid ring data structures. This dereference of invalid pointers can result in kernel panics, system crashes, or potentially exploitable conditions where an attacker might leverage the unstable state for further exploitation. The issue highlights a classic synchronization error where shared resources are modified without adequate atomicity guarantees across all dependent subsystems.
To resolve this vulnerability, the fix involves restructuring the locking strategy to ensure that the receive hook assignment occurs within the same critical section protected by sk_receive_queue.lock as the ring state update. By moving the existing receive hook assignment into this locked region, the kernel ensures that any thread observing the tpacket_rcv mode will also see a consistent and valid ring configuration. This change maintains atomicity between the structural changes to the ring buffer and the visibility of those changes to other parts of the networking stack. The fix is carefully scoped to avoid introducing unintended behavior changes during TX (transmit) ring reconfiguration, focusing strictly on stabilizing the RX path where the race condition manifested.
Furthermore, the solution addresses the synchronization for packet_recvmsg() pressure clearing by serializing it with the queue lock only after PACKET_SOCK_PRESSURE has been observed. This optimization prevents unnecessary locking overhead while ensuring safety. If the flag is clear and the socket has moved away from tpacket_rcv, the system relies on the fact that packet_set_ring() has already detached the socket and waited for synchronize_net(). The synchronize_net() call ensures that all pre-existing network callbacks have completed execution before proceeding, thereby guaranteeing that no new packet input can set the pressure flag again during this transition. This approach maintains performance by avoiding excessive locking while strictly enforcing memory visibility and ordering constraints required to prevent use-after-free or null pointer dereference scenarios.
From a standards perspective, this vulnerability aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). The root cause is the failure to properly synchronize access to shared resources between threads modifying ring state and threads consuming packet data. In terms of MITRE ATT&CK, this type of kernel race condition can be categorized under T1059: Command Line Interface or more broadly within privilege escalation vectors if an attacker can trigger the crash repeatedly for denial of service or potentially exploit the memory corruption for code execution. Mitigation strategies primarily involve applying the upstream kernel patch that corrects the locking granularity in packet_set_ring(). For systems unable to immediately update, limiting exposure to raw packet sockets and ensuring strict access controls on network interface configuration capabilities can reduce the attack surface. Regular monitoring of system logs for unexpected kernel panics or oops messages related to packet socket operations is also recommended as a defensive measure until patches are deployed.