Re: Re: [PATCH] selftests/bpf: Fix strncpy() fortify warning

From: Rong Tao <rtoax@foxmail.com>
To: andrii.nakryiko@gmail.com
Cc: andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
	daniel@iogearbox.net, haoluo@google.com,
	john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	martin.lau@linux.dev, mykolal@fb.com, rongtao@cestc.cn,
	rtoax@foxmail.com, sdf@google.com, shuah@kernel.org,
	song@kernel.org, yhs@fb.com
Subject: Re: Re: [PATCH] selftests/bpf: Fix strncpy() fortify warning
Date: Fri, 28 Oct 2022 08:26:03 +0800	[thread overview]
Message-ID: <tencent_CD22930180507496CE65B30ACBABC4681506@qq.com> (raw)
In-Reply-To: <CAEf4Bzbq0PSsc6xCGSF=Af-pcysjt8Lv76-4N65AJMpXOOpOcg@mail.gmail.com>

Thanks for your reply, `enable[0] = '\0';` at the beginning and then
strncat() still has the same compile warning

--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -77,7 +77,8 @@ static int __enable_controllers(const char *cgroup_path, const char *controllers
                enable[len] = 0;
                close(fd);
        } else {
-               strncpy(enable, controllers, sizeof(enable));
+               enable[0] = '\0';
+               strncat(enable, controllers, sizeof(enable));
        }

In function ‘__enable_controllers’:
tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-truncation]
   81 |                 strncat(enable, controllers, sizeof(enable));
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/testing/selftests/bpf/cgroup_helpers.c:81:17: warning: ‘strncat’ specified bound 4097 equals destination size [-Wstringop-overflow=]

So, i think just add '-1' for strncpy() is a good way.
