selftests/bpf: Make a copy of subtest name

test_progs never created a copy of subtest name, rather just stored
pointer to whatever string test provided. This is bad as that string
might be freed or modified by the end of subtest. Fix this by creating
a copy of given subtest name when subtest starts.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191021033902.3856966-6-andriin@fb.com

tools/testing/selftests/bpf/test_progs.c

@@ -20,7 +20,7 @@ struct prog_test_def {
 	bool tested;
 	bool need_cgroup_cleanup;
 
-	const char *subtest_name;
+	char *subtest_name;
 	int subtest_num;
 
 	/* store counts before subtest started */
@@ -81,16 +81,17 @@ void test__end_subtest()
 	fprintf(env.stdout, "#%d/%d %s:%s\n",
 	       test->test_num, test->subtest_num,
 	       test->subtest_name, sub_error_cnt ? "FAIL" : "OK");
+
+	free(test->subtest_name);
+	test->subtest_name = NULL;
 }
 
 bool test__start_subtest(const char *name)
 {
 	struct prog_test_def *test = env.test;
 
-	if (test->subtest_name) {
+	if (test->subtest_name)
 		test__end_subtest();
-		test->subtest_name = NULL;
-	}
 
 	test->subtest_num++;
 
@@ -104,7 +105,13 @@ bool test__start_subtest(const char *name)
 	if (!should_run(&env.subtest_selector, test->subtest_num, name))
 		return false;
 
-	test->subtest_name = name;
+	test->subtest_name = strdup(name);
+	if (!test->subtest_name) {
+		fprintf(env.stderr,
+			"Subtest #%d: failed to copy subtest name!\n",
+			test->subtest_num);
+		return false;
+	}
 	env.test->old_error_cnt = env.test->error_cnt;
 
 	return true;