CVE-2025-39697

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

NFS: Fix a race when updating an existing write

After nfs_lock_and_join_requests() tests for whether the request is still attached to the mapping, nothing prevents a call to nfs_inode_remove_request() from succeeding until we actually lock the page group. The reason is that whoever called nfs_inode_remove_request() doesnt necessarily have a lock on the page group head.

So in order to avoid races, lets take the page group lock earlier in nfs_lock_and_join_requests(), and hold it across the removal of the request in nfs_inode_remove_request().

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/0ff42a32784e0f2cb46a46da8e9f473538c13e1b
• https://git.kernel.org/stable/c/181feb41f0b268e6288bf9a7b984624d7fe2031d
• https://git.kernel.org/stable/c/202a3432d21ac060629a760fff3b0a39859da3ea
• https://git.kernel.org/stable/c/76d2e3890fb169168c73f2e4f8375c7cc24a765e
• https://git.kernel.org/stable/c/92278ae36935a54e65fef9f8ea8efe7e80481ace
• https://git.kernel.org/stable/c/c32e3c71aaa1c1ba05da88605e2ddd493c58794f
• https://git.kernel.org/stable/c/f230d40147cc37eb3aef4d50e2e2c06ea73d9a77
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html