CVE-2025-38524

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix recv-recv race of completed call

If a call receives an event (such as incoming data), the call gets placed on the socket's queue and a thread in recvmsg can be awakened to go and process it. Once the thread has picked up the call off of the queue, further events will cause it to be requeued, and once the socket lock is dropped (recvmsg uses call->user_mutex to allow the socket to be used in parallel), a second thread can come in and its recvmsg can pop the call off the socket queue again.

In such a case, the first thread will be receiving stuff from the call and the second thread will be blocked on call->user_mutex. The first thread can, at this point, process both the event that it picked call for and the event that the second thread picked the call for and may see the call terminate - in which case the call will be "released", decoupling the call from the user call ID assigned to it (RXRPC_USER_CALL_ID in the control message).

The first thread will return okay, but then the second thread will wake up holding the user_mutex and, if it sees that the call has been released by the first thread, it will BUG thusly:

kernel BUG at net/rxrpc/recvmsg.c:474!

Fix this by just dequeuing the call and ignoring it if it is seen to be already released. We can't tell userspace about it anyway as the user call ID has become stale.

This vulnerability is rated as Moderate because triggering the race condition requires local socket interaction with precise multithreaded timing, resulting in a denial of service (kernel crash) rather than privilege escalation or remote execution. AF_RXRPC is an optional network protocol that is not loaded by default in standard Red Hat Enterprise Linux deployments and is primarily used for AFS network communications. Systems are only exposed if the rxrpc kernel module has been loaded and an application actively processes concurrent message requests on an RxRPC socket.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.