About vulnerability

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. 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.

Live-patch status from KernelCare for each operating system.