CVE-2024-47757

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

nilfs2: fix potential oob read in nilfs_btree_check_delete()

The function nilfs_btree_check_delete(), which checks whether degeneration
to direct mapping occurs before deleting a b-tree entry, causes memory
access outside the block buffer when retrieving the maximum key if the
root node has no entries.

This does not usually happen because b-tree mappings with 0 child nodes
are never created by mkfs.nilfs2 or nilfs2 itself.  However, it can happen
if the b-tree root node read from a device is configured that way, so fix
this potential issue by adding a check for that case.