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

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/978aac54e93ea35aab20b32ae393d3d33964e7ae
• https://git.kernel.org/stable/c/be66551da203862c689c12e1d35ce87217c017c1
• https://git.kernel.org/stable/c/039ddf353cc33f6546a87ec1ac3210637d714bec
• https://git.kernel.org/stable/c/0dc7117da8f92dd5fe077d712a756eccbe377d40