CVE-2025-40067

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

fs/ntfs3: reject index allocation if $BITMAP is empty but blocks exist

Index allocation requires at least one bit in the $BITMAP attribute to track usage of index entries. If the bitmap is empty while index blocks are already present, this reflects on-disk corruption.

syzbot triggered this condition using a malformed NTFS image. During a rename() operation involving a long filename (which spans multiple index entries), the empty bitmap allowed the name to be added without valid tracking. Subsequent deletion of the original entry failed with -ENOENT, due to unexpected index state.

Reject such cases by verifying that the bitmap is not empty when index blocks exist.