From: Stanislav Fomichev <sdf@google.com>
Date: Fri, 30 Aug 2019 19:34:26 -0700
Subject: selftests/bpf: test_progs: fix verbose mode garbage
Patch-mainline: v5.4-rc1
Git-commit: d80507d15d45e285fc596d23665c9b88cf0dfec3
References: bsc#1155518

fseeko(.., 0, SEEK_SET) on a memstream just puts the buffer pointer
to the beginning so when we call fflush on it we get some garbage
log data from the previous test. Let's manually set terminating
byte to zero at the reported buffer size.

To show the issue consider the following snippet:

	stream = open_memstream (&buf, &len);

	fprintf(stream, "aaa");
	fflush(stream);
	printf("buf=%s, len=%zu\n", buf, len);
	fseeko(stream, 0, SEEK_SET);

	fprintf(stream, "b");
	fflush(stream);
	printf("buf=%s, len=%zu\n", buf, len);

Output:

	buf=aaa, len=3
	buf=baa, len=1

Fixes: 946152b3c5d6 ("selftests/bpf: test_progs: switch to open_memstream")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Gary Lin <glin@suse.com>
---
 tools/testing/selftests/bpf/test_progs.c |    1 +
 1 file changed, 1 insertion(+)

--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c
@@ -45,6 +45,7 @@ static void dump_test_log(const struct p
 
 	if (env.verbose || test->force_log || failed) {
 		if (env.log_cnt) {
+			env.log_buf[env.log_cnt] = '\0';
 			fprintf(env.stdout, "%s", env.log_buf);
 			if (env.log_buf[env.log_cnt - 1] != '\n')
 				fprintf(env.stdout, "\n");