nilfs2: handle errors that nilfs_prepare_chunk() may return

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

nilfs2: handle errors that nilfs_prepare_chunk() may return

Patch series "nilfs2: fix issues with rename operations".

This series fixes BUG_ON check failures reported by syzbot around rename

operations, and a minor behavioral issue where the mtime of a child

directory changes when it is renamed instead of moved.

This patch (of 2):

The directory manipulation routines nilfs_set_link() and

nilfs_delete_entry() rewrite the directory entry in the folio/page

previously read by nilfs_find_entry(), so error handling is omitted on the

assumption that nilfs_prepare_chunk(), which prepares the buffer for

rewriting, will always succeed for these. And if an error is returned, it

triggers the legacy BUG_ON() checks in each routine.

This assumption is wrong, as proven by syzbot: the buffer layer called by

nilfs_prepare_chunk() may call nilfs_get_block() if necessary, which may

fail due to metadata corruption or other reasons. This has been there all

along, but improved sanity checks and error handling may have made it more

reproducible in fuzzing tests.

Fix this issue by adding missing error paths in nilfs_set_link(),

nilfs_delete_entry(), and their caller nilfs_rename().