nilfs2: fix potential oob read in nilfs_btree_check_delete()

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/f3a9859767c7aea758976f5523903d247e585129
• https://git.kernel.org/stable/c/ed76d381dae125b81d09934e365391a656249da8
• https://git.kernel.org/stable/c/d20674f31626e0596ae4c1d9401dfb6739b81b58
• https://git.kernel.org/stable/c/c4f8554996e8ada3be872dfb8f60e93bcf15fb27
• https://git.kernel.org/stable/c/a8abfda768b9f33630cfbc4af6c4214f1e5681b0
• https://git.kernel.org/stable/c/257f9e5185eb6de83377caea686c306e22e871f2
• https://git.kernel.org/stable/c/a33e967b681e088a125b979975c93e3453e686cd
• https://git.kernel.org/stable/c/c4cbcc64bb31e67e02940ce060cc77f7180564cf
• https://git.kernel.org/stable/c/f9c96351aa6718b42a9f42eaf7adce0356bdb5e8