CVE-2025-38492

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

netfs: Fix race between cache write completion and ALL_QUEUED being set

When netfslib is issuing subrequests, the subrequests start processing immediately and may complete before we reach the end of the issuing function. At the end of the issuing function we set NETFS_RREQ_ALL_QUEUED to indicate to the collector that we arent going to issue any more subreqs and that it can do the final notifications and cleanup.

Now, this isnt a problem if the request is synchronous (NETFS_RREQ_OFFLOAD_COLLECTION is unset) as the result collection will be done in-thread and were guaranteed an opportunity to run the collector.

However, if the request is asynchronous, collection is primarily triggered by the termination of subrequests queuing it on a workqueue. Now, a race can occur here if the app thread sets ALL_QUEUED after the last subrequest terminates.

This can happen most easily with the copy2cache code (as used by Ceph) where, in the collection routine of a read request, an asynchronous write request is spawned to copy data to the cache. Folios are added to the write request as theyre unlocked, but there may be a delay before ALL_QUEUED is set as the write subrequests may complete before we get there.

If all the write subreqs have finished by the ALL_QUEUED point, no further events happen and the collection never happens, leaving the request hanging.

Fix this by queuing the collector after setting ALL_QUEUED. This is a bit heavy-handed and it may be sufficient to do it only if there are no extant subreqs.

Also add a tracepoint to cross-reference both requests in a copy-to-request operation and add a trace to the netfs_rreq tracepoint to indicate the setting of ALL_QUEUED.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/110188a13c4853bd4c342e600ced4dfd26c3feb5
• https://git.kernel.org/stable/c/89635eae076cd8eaa5cb752f66538c9dc6c9fdc3