trailer: fix leaking trailer values

Fix leaking trailer values when replacing the value with a command or
when the token value is empty.

This leak is exposed by t7513, but plugging it does not make the whole
test suite pass.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/trailer.c b/trailer.c
index 682d74505b..6bafe92b32 100644
--- a/trailer.c
+++ b/trailer.c
@@ -249,7 +249,9 @@ static char *apply_command(struct conf_info *conf, const char *arg)
 static void apply_item_command(struct trailer_item *in_tok, struct arg_item *arg_tok)
 {
 	if (arg_tok->conf.command || arg_tok->conf.cmd) {
-		const char *arg;
+		char *value_to_free = NULL;
+		char *arg;
+
 		if (arg_tok->value && arg_tok->value[0]) {
 			arg = arg_tok->value;
 		} else {
@@ -257,9 +259,13 @@ static void apply_item_command(struct trailer_item *in_tok, struct arg_item *arg
 				arg = xstrdup(in_tok->value);
 			else
 				arg = xstrdup("");
+			value_to_free = arg_tok->value;
 		}
+
 		arg_tok->value = apply_command(&arg_tok->conf, arg);
-		free((char *)arg);
+
+		free(value_to_free);
+		free(arg);
 	}
 }