[PATCH] nilfs2: fix nilfs_empty_dir() misjudgment and long loop on I/O errors

[Ryusuke Konishi <konishi.ryusuke@gmail.com>]

The error handling in nilfs_empty_dir() when a directory folio/page
read fails is incorrect, as in the old ext2 implementation, and if the
folio/page cannot be read or nilfs_check_folio() fails, it will falsely
determine the directory as empty and corrupt the file system.

In addition, since nilfs_empty_dir() does not immediately return on
a failed folio/page read, but continues to loop, this can cause a long
loop with I/O if i_size of the directory's inode is also corrupted,
causing the log writer thread to wait and hang, as reported by syzbot.

Fix these issues by making nilfs_empty_dir() immediately return a false
value (0) if it fails to get a directory folio/page.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+c8166c541d3971bf6c87@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c8166c541d3971bf6c87
Fixes: 2ba466d74ed7 ("nilfs2: directory entry operations")
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: stable@vger.kernel.org
---
Hi Andrew, please apply this as a bug fix.

This fixes a bug in the empty directory function and the resulting
hang issue reported by syzbot.

Thanks,
Ryusuke Konishi

 fs/nilfs2/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nilfs2/dir.c b/fs/nilfs2/dir.c
index a002a44ff161..52e50b1b7f22 100644
--- a/fs/nilfs2/dir.c
+++ b/fs/nilfs2/dir.c
@@ -607,7 +607,7 @@ int nilfs_empty_dir(struct inode *inode)
 
 		kaddr = nilfs_get_folio(inode, i, &folio);
 		if (IS_ERR(kaddr))
-			continue;
+			return 0;
 
 		de = (struct nilfs_dir_entry *)kaddr;
 		kaddr += nilfs_last_byte(inode, i) - NILFS_DIR_REC_LEN(1);
-- 
2.34.1