Bug 2393481 (CVE-2025-39697)

Summary: CVE-2025-39697 kernel: NFS: Fix a race when updating an existing write
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw use after free in the Linux kernel NFS functionality was found in the way connected user sends malicious data to the server. A remote user could use this flaw to crash the system.
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Description OSIDB Bzimport 2025-09-05 18:01:19 UTC 
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() doesn't
necessarily have a lock on the page group head.

So in order to avoid races, let's 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().
Comment 1 Praise Ogwuche 2025-09-05 21:52:58 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025090548-CVE-2025-39697-5284@gregkh/T