Merge branch 'ds/line-log-asan-fix'

Use after free and double freeing at the end in "git log -L... -p"
had been identified and fixed.

* ds/line-log-asan-fix:
  line-log: protect inner strbuf from free

line-log.c

@@ -897,13 +897,13 @@ static void print_line(const char *prefix, char first,
 		fputs("\\ No newline at end of file\n", file);
 }
 
-static char *output_prefix(struct diff_options *opt)
+static const char *output_prefix(struct diff_options *opt)
 {
 	if (opt->output_prefix) {
 		struct strbuf *sb = opt->output_prefix(opt, opt->output_prefix_data);
 		return sb->buf;
 	} else {
-		return xstrdup("");
+		return "";
 	}
 }
 
@@ -916,7 +916,7 @@ static void dump_diff_hacky_one(struct rev_info *rev, struct line_log_data *rang
 	struct diff_ranges *diff = &range->diff;
 
 	struct diff_options *opt = &rev->diffopt;
-	char *prefix = output_prefix(opt);
+	const char *prefix = output_prefix(opt);
 	const char *c_reset = diff_get_color(opt->use_color, DIFF_RESET);
 	const char *c_frag = diff_get_color(opt->use_color, DIFF_FRAGINFO);
 	const char *c_meta = diff_get_color(opt->use_color, DIFF_METAINFO);
@@ -1003,7 +1003,6 @@ static void dump_diff_hacky_one(struct rev_info *rev, struct line_log_data *rang
 out:
 	free(p_ends);
 	free(t_ends);
-	free(prefix);
 }
 
 /*
@@ -1012,10 +1011,9 @@ static void dump_diff_hacky_one(struct rev_info *rev, struct line_log_data *rang
  */
 static void dump_diff_hacky(struct rev_info *rev, struct line_log_data *range)
 {
-	char *prefix = output_prefix(&rev->diffopt);
+	const char *prefix = output_prefix(&rev->diffopt);
 
 	fprintf(rev->diffopt.file, "%s\n", prefix);
-	free(prefix);
 
 	while (range) {
 		dump_diff_hacky_one(rev, range);

t/t4211-line-log.sh

@@ -337,4 +337,32 @@ test_expect_success 'zero-width regex .* matches any function name' '
 	test_cmp expect actual
 '
 
+test_expect_success 'show line-log with graph' '
+	qz_to_tab_space >expect <<-EOF &&
+	* $head_oid Modify func2() in file.c
+	|Z
+	| diff --git a/file.c b/file.c
+	| --- a/file.c
+	| +++ b/file.c
+	| @@ -6,4 +6,4 @@
+	|  int func2()
+	|  {
+	| -    return F2;
+	| +    return F2 + 2;
+	|  }
+	* $root_oid Add func1() and func2() in file.c
+	ZZ
+	  diff --git a/file.c b/file.c
+	  --- /dev/null
+	  +++ b/file.c
+	  @@ -0,0 +6,4 @@
+	  +int func2()
+	  +{
+	  +    return F2;
+	  +}
+	EOF
+	git log --graph --oneline -L:func2:file.c >actual &&
+	test_cmp expect actual
+'
+
 test_done