[PATCH 5.10 31/40] ubifs: prevent creating duplicate encrypted filenames

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Eric Biggers <ebiggers@google.com>

commit 76786a0f083473de31678bdb259a3d4167cf756d upstream.

As described in "fscrypt: add fscrypt_is_nokey_name()", it's possible to
create a duplicate filename in an encrypted directory by creating a file
concurrently with adding the directory's encryption key.

Fix this bug on ubifs by rejecting no-key dentries in ubifs_create(),
ubifs_mkdir(), ubifs_mknod(), and ubifs_symlink().

Note that ubifs doesn't actually report the duplicate filenames from
readdir, but rather it seems to replace the original dentry with a new
one (which is still wrong, just a different effect from ext4).

On ubifs, this fixes xfstest generic/595 as well as the new xfstest I
wrote specifically for this bug.

Fixes: f4f61d2cc6d8 ("ubifs: Implement encrypted filenames")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201118075609.120337-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ubifs/dir.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/fs/ubifs/dir.c
+++ b/fs/ubifs/dir.c
@@ -270,6 +270,15 @@ done:
 	return d_splice_alias(inode, dentry);
 }
 
+static int ubifs_prepare_create(struct inode *dir, struct dentry *dentry,
+				struct fscrypt_name *nm)
+{
+	if (fscrypt_is_nokey_name(dentry))
+		return -ENOKEY;
+
+	return fscrypt_setup_filename(dir, &dentry->d_name, 0, nm);
+}
+
 static int ubifs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
 			bool excl)
 {
@@ -293,7 +302,7 @@ static int ubifs_create(struct inode *di
 	if (err)
 		return err;
 
-	err = fscrypt_setup_filename(dir, &dentry->d_name, 0, &nm);
+	err = ubifs_prepare_create(dir, dentry, &nm);
 	if (err)
 		goto out_budg;
 
@@ -953,7 +962,7 @@ static int ubifs_mkdir(struct inode *dir
 	if (err)
 		return err;
 
-	err = fscrypt_setup_filename(dir, &dentry->d_name, 0, &nm);
+	err = ubifs_prepare_create(dir, dentry, &nm);
 	if (err)
 		goto out_budg;
 
@@ -1038,7 +1047,7 @@ static int ubifs_mknod(struct inode *dir
 		return err;
 	}
 
-	err = fscrypt_setup_filename(dir, &dentry->d_name, 0, &nm);
+	err = ubifs_prepare_create(dir, dentry, &nm);
 	if (err) {
 		kfree(dev);
 		goto out_budg;
@@ -1122,7 +1131,7 @@ static int ubifs_symlink(struct inode *d
 	if (err)
 		return err;
 
-	err = fscrypt_setup_filename(dir, &dentry->d_name, 0, &nm);
+	err = ubifs_prepare_create(dir, dentry, &nm);
 	if (err)
 		goto out_budg;