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From:   Rong Tao <rtoax@foxmail.com>
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Subject: Re: Re: [PATCH] selftests/bpf: Fix strncpy() fortify warning
Date:   Fri, 28 Oct 2022 08:26:03 +0800
In-Reply-To: <CAEf4Bzbq0PSsc6xCGSF=Af-pcysjt8Lv76-4N65AJMpXOOpOcg@mail.gmail.com>
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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.