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

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From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>

commit 7373a51e7998b508af7136530f3a997b286ce81c upstream.

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.

Link: https://lkml.kernel.org/r/20240604134255.7165-1-konishi.ryusuke@xxxxxxxxx
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Reported-by: syzbot+c8166c541d3971bf6c87@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=c8166c541d3971bf6c87
Fixes: 2ba466d74ed7 ("nilfs2: directory entry operations")
Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/nilfs2/dir.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/nilfs2/dir.c
+++ b/fs/nilfs2/dir.c
@@ -608,7 +608,7 @@ 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);


Patches currently in stable-queue which might be from konishi.ryusuke@xxxxxxxxx are

queue-6.9/nilfs2-fix-nilfs_empty_dir-misjudgment-and-long-loop-on-i-o-errors.patch
queue-6.9/nilfs2-fix-potential-kernel-bug-due-to-lack-of-writeback-flag-waiting.patch




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