config: fix leaking comment character config

When the comment line character has been specified multiple times in the
configuration, then `git_default_core_config()` will cause a memory leak
because it unconditionally copies the string into `comment_line_str`
without free'ing the previous value. In fact, it can't easily free the
value in the first place because it may contain a string constant.

Refactor the code such that we track allocated comment character strings
via a separate non-constant variable `comment_line_str_to_free`. Adapt
sites that set `comment_line_str` to set both and free the old value
that was stored in `comment_line_str_to_free`.

This memory leak is being hit in t3404. As there are still other memory
leaks in that file we cannot yet mark it as passing with leak checking
enabled.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/config.c b/config.c
index 6421894614..205660a8fb 100644
--- a/config.c
+++ b/config.c
@@ -1596,7 +1596,8 @@ static int git_default_core_config(const char *var, const char *value,
 		else if (value[0]) {
 			if (strchr(value, '\n'))
 				return error(_("%s cannot contain newline"), var);
-			comment_line_str = xstrdup(value);
+			comment_line_str = value;
+			FREE_AND_NULL(comment_line_str_to_free);
 			auto_comment_line_char = 0;
 		} else
 			return error(_("%s must have at least one character"), var);