format-patch: don't leak "extra_headers" or "ref_message_ids"

Fix two memory leaks in "struct rev_info" by freeing that memory in
cmd_format_patch(). These two are unusual special-cases in being in
the "struct rev_info", but not being "owned" by the code in
revision.c. I.e. they're members of the struct so that this code in
"builtin/log.c" can conveniently pass information code in
"log-tree.c".

See e.g. the make_cover_letter() caller of log_write_email_headers()
here in "builtin/log.c", and [1] for a demonstration of where the
"extra_headers" and "ref_message_ids" struct members are used.

See 20ff068 (format-patch: resurrect extra headers from config,
2006-06-02) and d1566f7 (git-format-patch: Make the second and
subsequent mails replies to the first, 2006-07-14) for the initial
introduction of "extra_headers" and "ref_message_ids".

We can count on repo_init_revisions() memset()-ing this data to 0
however, so we can count on it being either NULL or something we
allocated. In the case of "extra_headers" let's add a local "char *"
variable to hold it, to avoid the eventual cast from "const char *"
when we free() it.

1. https://lore.kernel.org/git/[email protected]/

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

builtin/log.c

@@ -1747,6 +1747,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	struct commit *commit;
 	struct commit **list = NULL;
 	struct rev_info rev;
+	char *to_free = NULL;
 	struct setup_revision_opt s_r_opt;
 	int nr = 0, total, i;
 	int use_stdout = 0;
@@ -1947,7 +1948,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 		strbuf_addch(&buf, '\n');
 	}
 
-	rev.extra_headers = strbuf_detach(&buf, NULL);
+	rev.extra_headers = to_free = strbuf_detach(&buf, NULL);
 
 	if (from) {
 		if (split_ident_line(&rev.from_ident, from, strlen(from)))
@@ -2284,6 +2285,10 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	strbuf_release(&rdiff1);
 	strbuf_release(&rdiff2);
 	strbuf_release(&rdiff_title);
+	free(to_free);
+	if (rev.ref_message_ids)
+		string_list_clear(rev.ref_message_ids, 0);
+	free(rev.ref_message_ids);
 	UNLEAK(rev);
 	return 0;
 }