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

From: "André Almeida" <andrealmeid@collabora.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
	Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>
Cc: krisman@collabora.com, kernel@collabora.com,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	"Daniel Rosenberg" <drosen@google.com>,
	"Chao Yu" <yuchao0@huawei.com>,
	"André Almeida" <andrealmeid@collabora.com>
Subject: [PATCH 2/3] ext4: Prevent dangling dentries on casefold directories
Date: Sun, 28 Mar 2021 11:43:55 -0300	[thread overview]
Message-ID: <20210328144356.12866-3-andrealmeid@collabora.com> (raw)
In-Reply-To: <20210328144356.12866-1-andrealmeid@collabora.com>

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@collabora.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

