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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Thu, 27 Oct 2022 13:09:57 -0700
Message-ID: <CAEf4Bzbq0PSsc6xCGSF=Af-pcysjt8Lv76-4N65AJMpXOOpOcg@mail.gmail.com>
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix strncpy() fortify warning
To:     Rong Tao <rtoax@foxmail.com>
Cc:     Rong Tao <rongtao@cestc.cn>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
        "open list:BPF [GENERAL] (Safe Dynamic Programs and Tools)" 
        <bpf@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Thu, Oct 27, 2022 at 4:34 AM Rong Tao <rtoax@foxmail.com> wrote:
>
> From: Rong Tao <rongtao@cestc.cn>
>
> Compile samples/bpf, error:
> $ cd samples/bpf
> $ make
> ...
> In function =E2=80=98__enable_controllers=E2=80=99:
> samples/bpf/../../tools/testing/selftests/bpf/cgroup_helpers.c:80:17: war=
ning: =E2=80=98strncpy=E2=80=99 specified bound 4097 equals destination siz=
e [-Wstringop-truncation]
>    80 |                 strncpy(enable, controllers, sizeof(enable));
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Signed-off-by: Rong Tao <rongtao@cestc.cn>
> ---
>  tools/testing/selftests/bpf/cgroup_helpers.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing=
/selftests/bpf/cgroup_helpers.c
> index e914cc45b766..a70e873b267e 100644
> --- a/tools/testing/selftests/bpf/cgroup_helpers.c
> +++ b/tools/testing/selftests/bpf/cgroup_helpers.c
> @@ -77,7 +77,7 @@ static int __enable_controllers(const char *cgroup_path=
, const char *controllers
>                 enable[len] =3D 0;
>                 close(fd);
>         } else {
> -               strncpy(enable, controllers, sizeof(enable));
> +               strncpy(enable, controllers, sizeof(enable) - 1);

enable is not initialized, so we might end up with non-zero-terminated
string. Let's enable[0] =3D '\0'; at the beginning and then strncat()
here?

>         }
>
>         snprintf(path, sizeof(path), "%s/cgroup.subtree_control", cgroup_=
path);
> --
> 2.31.1
>