CVE-2025-38393

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

NFSv4/pNFS: Fix a race to wake on NFS_LAYOUT_DRAIN

We found a few different systems hung up in writeback waiting on the same page lock, and one task waiting on the NFS_LAYOUT_DRAIN bit in pnfs_update_layout(), however the pnfs_layout_hdrs plh_outstanding count was zero.

It seems most likely that this is another race between the waiter and waker similar to commit ed0172af5d6f (SUNRPC: Fix a race to wake a sync task). Fix it up by applying the advised barrier.

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/08287df60bac5b008b6bcdb03053988335d3d282
• https://git.kernel.org/stable/c/1f4da20080718f258e189a2c5f515385fa393da6
• https://git.kernel.org/stable/c/864a54c1243ed3ca60baa4bc492dede1361f4c83
• https://git.kernel.org/stable/c/8846fd02c98da8b79e6343a20e6071be6f372180
• https://git.kernel.org/stable/c/8ca65fa71024a1767a59ffbc6a6e2278af84735e
• https://git.kernel.org/stable/c/c01776287414ca43412d1319d2877cbad65444ac
• https://git.kernel.org/stable/c/e4b13885e7ef1e64e45268feef1e5f0707c47e72
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html