[PATCH 02/12] fs_parse: fix fs_param_v_optional handling

[Miklos Szeredi <mszeredi@redhat.com>]

String options always have parameters, hence the check for optional
parameter will never trigger.

Check for param type being a flag first (flag is the only type that does
not have a parameter) and report "Missing value" if the parameter is
mandatory.

Tested with gfs2's "quota" option, which is currently the only user of
fs_param_v_optional.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: Andrew Price <anprice@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Fixes: 31d921c7fb96 ("vfs: Add configuration parser helpers")
Cc: <stable@vger.kernel.org> # v5.4
---
 fs/fs_parser.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/fs_parser.c b/fs/fs_parser.c
index d1930adce68d..5d8833d71b37 100644
--- a/fs/fs_parser.c
+++ b/fs/fs_parser.c
@@ -127,13 +127,15 @@ int fs_parse(struct fs_context *fc,
 	case fs_param_is_u64:
 	case fs_param_is_enum:
 	case fs_param_is_string:
-		if (param->type != fs_value_is_string)
-			goto bad_value;
-		if (!result->has_value) {
+		if (param->type == fs_value_is_flag) {
 			if (p->flags & fs_param_v_optional)
 				goto okay;
-			goto bad_value;
+
+			return invalf(fc, "%s: Missing value for '%s'",
+				      desc->name, param->key);
 		}
+		if (param->type != fs_value_is_string)
+			goto bad_value;
 		/* Fall through */
 	default:
 		break;
-- 
2.21.0