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

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Date:   Fri, 28 Oct 2022 08:26:03 +0800
From:   Rong Tao <rtoax@...mail.com>
To:     andrii.nakryiko@...il.com
Cc:     andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        daniel@...earbox.net, haoluo@...gle.com, john.fastabend@...il.com,
        jolsa@...nel.org, kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, martin.lau@...ux.dev,
        mykolal@...com, rongtao@...tc.cn, rtoax@...mail.com,
        sdf@...gle.com, shuah@...nel.org, song@...nel.org, yhs@...com
Subject: Re: Re: [PATCH] selftests/bpf: Fix strncpy() fortify warning

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.