ext4: fix memory leaks in ext4_fname_{setup_filename,prepare_lookup}

If the filename casefolding fails, we'll be leaking memory from the
fscrypt_name struct, namely from the 'crypto_buf.name' member.

Make sure we free it in the error path on both ext4_fname_setup_filename()
and ext4_fname_prepare_lookup() functions.

Cc: stable@kernel.org
Fixes: 1ae98e29 ("ext4: optimize match for casefolded encrypted dirs")
Signed-off-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230803091713.13239-1-lhenriques@suse.deSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/crypto.c

@@ -33,6 +33,8 @@ int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
 
 #if IS_ENABLED(CONFIG_UNICODE)
 	err = ext4_fname_setup_ci_filename(dir, iname, fname);
+	if (err)
+		ext4_fname_free_filename(fname);
 #endif
 	return err;
 }
@@ -51,6 +53,8 @@ int ext4_fname_prepare_lookup(struct inode *dir, struct dentry *dentry,
 
 #if IS_ENABLED(CONFIG_UNICODE)
 	err = ext4_fname_setup_ci_filename(dir, &dentry->d_name, fname);
+	if (err)
+		ext4_fname_free_filename(fname);
 #endif
 	return err;
 }