builtin/log: fix leaking branch name when creating cover letters

When calling `make_cover_letter()` without a branch name, we try to
derive the branch name by calling `find_branch_name()`. But while this
function returns an allocated string, we never free the result and thus
have a memory leak. Fix this.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

builtin/log.c

@@ -1434,6 +1434,7 @@ static void make_cover_letter(struct rev_info *rev, int use_separate_file,
 	int need_8bit_cte = 0;
 	struct pretty_print_context pp = {0};
 	struct commit *head = list[0];
+	char *to_free = NULL;
 
 	if (!cmit_fmt_is_mail(rev->commit_format))
 		die(_("cover letter needs email format"));
@@ -1455,7 +1456,7 @@ static void make_cover_letter(struct rev_info *rev, int use_separate_file,
 	}
 
 	if (!branch_name)
-		branch_name = find_branch_name(rev);
+		branch_name = to_free = find_branch_name(rev);
 
 	pp.fmt = CMIT_FMT_EMAIL;
 	pp.date_mode.type = DATE_RFC2822;
@@ -1466,6 +1467,7 @@ static void make_cover_letter(struct rev_info *rev, int use_separate_file,
 			   encoding, need_8bit_cte, cfg);
 	fprintf(rev->diffopt.file, "%s\n", sb.buf);
 
+	free(to_free);
 	free(pp.after_subject);
 	strbuf_release(&sb);
 

t/t3206-range-diff.sh

@@ -5,6 +5,7 @@ test_description='range-diff tests'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 # Note that because of the range-diff's heuristics, test_commit does more