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

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Message-Id: <20210328144356.12866-3-andrealmeid@collabora.com>
Date:   Sun, 28 Mar 2021 11:43:55 -0300
From:   André Almeida <andrealmeid@...labora.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
Cc:     krisman@...labora.com, kernel@...labora.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        Daniel Rosenberg <drosen@...gle.com>,
        Chao Yu <yuchao0@...wei.com>,
        André Almeida <andrealmeid@...labora.com>
Subject: [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 <andrealmeid@...labora.com>
---
 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