Bug 2422769 (CVE-2025-68242)

Summary: CVE-2025-68242 kernel: NFS: Fix LTP test failures when timestamps are delegated
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A permission checking flaw was found in the NFS client implementation in the Linux kernel. When delegated timestamps are enabled for NFS 4.2, nfs_setattr() fails to verify the inode's UID against the caller's fsuid before allowing timestamp modifications. This allows unprivileged users to modify atime/mtime on files they don't own when timestamp delegation is active.
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Description OSIDB Bzimport 2025-12-16 15:03:38 UTC 
In the Linux kernel, the following vulnerability has been resolved:

NFS: Fix LTP test failures when timestamps are delegated

The utimes01 and utime06 tests fail when delegated timestamps are
enabled, specifically in subtests that modify the atime and mtime
fields using the 'nobody' user ID.

The problem can be reproduced as follow:

# echo "/media *(rw,no_root_squash,sync)" >> /etc/exports
# export -ra
# mount -o rw,nfsvers=4.2 127.0.0.1:/media /tmpdir
# cd /opt/ltp
# ./runltp -d /tmpdir -s utimes01
# ./runltp -d /tmpdir -s utime06

This issue occurs because nfs_setattr does not verify the inode's
UID against the caller's fsuid when delegated timestamps are
permitted for the inode.

This patch adds the UID check and if it does not match then the
request is sent to the server for permission checking.
Comment 1 Alexander B 2025-12-16 21:36:14 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025121632-CVE-2025-68242-45e0@gregkh/T