netdev - Re: [PATCH bpf-next] selftests/bpf: fix -Wstrict-aliasing in test_sockopt

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Date:   Fri, 28 Jun 2019 13:25:09 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next] selftests/bpf: fix -Wstrict-aliasing in test_sockopt_sk.c

On Thu, Jun 27, 2019 at 6:14 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> Let's use union with u8[4] and u32 members for sockopt buffer,
> that should fix any possible aliasing issues.
>
> test_sockopt_sk.c: In function ‘getsetsockopt’:
> test_sockopt_sk.c:115:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
>   if (*(__u32 *)buf != 0x55AA*2) {
>   ^~
> test_sockopt_sk.c:116:3: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
>    log_err("Unexpected getsockopt(SO_SNDBUF) 0x%x != 0x55AA*2",
>    ^~~~~~~
>
> Fixes: 8a027dc0d8f5 ("selftests/bpf: add sockopt test that exercises sk helpers")
> Reported-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  tools/testing/selftests/bpf/test_sockopt_sk.c | 51 +++++++++----------
>  1 file changed, 24 insertions(+), 27 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/test_sockopt_sk.c b/tools/testing/selftests/bpf/test_sockopt_sk.c
> index 12e79ed075ce..036b652e5ca9 100644
> --- a/tools/testing/selftests/bpf/test_sockopt_sk.c
> +++ b/tools/testing/selftests/bpf/test_sockopt_sk.c
> @@ -22,7 +22,10 @@
>  static int getsetsockopt(void)
>  {
>         int fd, err;
> -       char buf[4] = {};
> +       union {
> +               char u8[4];
> +               __u32 u32;
> +       } buf = {};
>         socklen_t optlen;
>
>         fd = socket(AF_INET, SOCK_STREAM, 0);
> @@ -33,31 +36,31 @@ static int getsetsockopt(void)
>
>         /* IP_TOS - BPF bypass */
>
> -       buf[0] = 0x08;
> -       err = setsockopt(fd, SOL_IP, IP_TOS, buf, 1);
> +       buf.u8[0] = 0x08;
> +       err = setsockopt(fd, SOL_IP, IP_TOS, &buf, 1);
>         if (err) {
>                 log_err("Failed to call setsockopt(IP_TOS)");
>                 goto err;
>         }
>
> -       buf[0] = 0x00;
> +       buf.u8[0] = 0x00;
>         optlen = 1;
> -       err = getsockopt(fd, SOL_IP, IP_TOS, buf, &optlen);
> +       err = getsockopt(fd, SOL_IP, IP_TOS, &buf, &optlen);
>         if (err) {
>                 log_err("Failed to call getsockopt(IP_TOS)");
>                 goto err;
>         }
>
> -       if (buf[0] != 0x08) {
> +       if (buf.u8[0] != 0x08) {
>                 log_err("Unexpected getsockopt(IP_TOS) buf[0] 0x%02x != 0x08",
> -                       buf[0]);
> +                       buf.u8[0]);
>                 goto err;
>         }
>
>         /* IP_TTL - EPERM */
>
> -       buf[0] = 1;
> -       err = setsockopt(fd, SOL_IP, IP_TTL, buf, 1);
> +       buf.u8[0] = 1;
> +       err = setsockopt(fd, SOL_IP, IP_TTL, &buf, 1);
>         if (!err || errno != EPERM) {
>                 log_err("Unexpected success from setsockopt(IP_TTL)");
>                 goto err;
> @@ -65,16 +68,16 @@ static int getsetsockopt(void)
>
>         /* SOL_CUSTOM - handled by BPF */
>
> -       buf[0] = 0x01;
> -       err = setsockopt(fd, SOL_CUSTOM, 0, buf, 1);
> +       buf.u8[0] = 0x01;
> +       err = setsockopt(fd, SOL_CUSTOM, 0, &buf, 1);
>         if (err) {
>                 log_err("Failed to call setsockopt");
>                 goto err;
>         }
>
> -       buf[0] = 0x00;
> +       buf.u32 = 0x00;
>         optlen = 4;
> -       err = getsockopt(fd, SOL_CUSTOM, 0, buf, &optlen);
> +       err = getsockopt(fd, SOL_CUSTOM, 0, &buf, &optlen);
>         if (err) {
>                 log_err("Failed to call getsockopt");
>                 goto err;
> @@ -84,37 +87,31 @@ static int getsetsockopt(void)
>                 log_err("Unexpected optlen %d != 1", optlen);
>                 goto err;
>         }
> -       if (buf[0] != 0x01) {
> -               log_err("Unexpected buf[0] 0x%02x != 0x01", buf[0]);
> +       if (buf.u8[0] != 0x01) {
> +               log_err("Unexpected buf[0] 0x%02x != 0x01", buf.u8[0]);
>                 goto err;
>         }
>
>         /* SO_SNDBUF is overwritten */
>
> -       buf[0] = 0x01;
> -       buf[1] = 0x01;
> -       buf[2] = 0x01;
> -       buf[3] = 0x01;
> -       err = setsockopt(fd, SOL_SOCKET, SO_SNDBUF, buf, 4);
> +       buf.u32 = 0x01010101;
> +       err = setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &buf, 4);
>         if (err) {
>                 log_err("Failed to call setsockopt(SO_SNDBUF)");
>                 goto err;
>         }
>
> -       buf[0] = 0x00;
> -       buf[1] = 0x00;
> -       buf[2] = 0x00;
> -       buf[3] = 0x00;
> +       buf.u32 = 0x00;
>         optlen = 4;
> -       err = getsockopt(fd, SOL_SOCKET, SO_SNDBUF, buf, &optlen);
> +       err = getsockopt(fd, SOL_SOCKET, SO_SNDBUF, &buf, &optlen);
>         if (err) {
>                 log_err("Failed to call getsockopt(SO_SNDBUF)");
>                 goto err;
>         }
>
> -       if (*(__u32 *)buf != 0x55AA*2) {
> +       if (buf.u32 != 0x55AA*2) {
>                 log_err("Unexpected getsockopt(SO_SNDBUF) 0x%x != 0x55AA*2",
> -                       *(__u32 *)buf);
> +                       buf.u32);
>                 goto err;
>         }
>
> --
> 2.22.0.410.gd8fdbe21b5-goog
>