[PATCH 2/3] ext4: Prevent dangling dentries on casefold directories

Before making a folder a case-insensitive one, this folder could have
been used before and created some negative dentries (given that the
folder needs to be empty before making it case-insensitive, all detries
there are negative ones). During a new file creation, if a d_hash()
collision happens and the name matches a negative dentry, the new file
might have a name different than the specified by user.

To prevent this from happening, remove all negative dentries in a
directory before making it a case-folded one.

Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups")
Signed-off-by: André Almeida <redacted>
---
 fs/ext4/ioctl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index a2cf35066f46..0eede4c93c22 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c

@@ -381,6 +381,9 @@ static int ext4_ioctl_setflags(struct inode *inode,
 			err = -ENOTEMPTY;
 			goto flags_out;
 		}
+
+		if (!(oldflags & EXT4_CASEFOLD_FL) && (flags & EXT4_CASEFOLD_FL))
+			d_clear_dir_neg_dentries(inode);
 	}
 
 	/*

-- 
2.31.0