Advisory [CVE-2026-64399] add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE

In the Linux kernel, the following vulnerability has been resolved: ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() overwrites the destination file's data via vfs_clone_file_range() with neither the share-level KSMBD_TREE_CONN_FLAG_WRITABLE check nor a per-handle fp->daccess check that the other write-bearing arms carry.

A client can overwrite destination data on a read-only share, or from a handle opened with only FILE_WRITE_ATTRIBUTES (which still yields an FMODE_WRITE filp). Add both checks, matching the FSCTL_SET_SPARSE permission fix; require FILE_WRITE_DATA since this writes data.

A flaw was found in ksmbd. This vulnerability allows a remote attacker to overwrite data on a shared file system due to insufficient permission checks in the FSCTL_DUPLICATE_EXTENTS_TO_FILE function.

Even if a share is configured as read-only or a client has limited write attributes, an attacker can still modify the destination file's data, leading to unauthorized data alteration. Red Hat severity: not rated.

Weakness: CWE-250. Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9 as not affected.