netdev - Re: [PATCH bpf-next 2/2] selftests/bpf: verify that rebinding to port

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Message-ID: <CAEf4BzaOjBN=C=zjmhP-nLJbtm-FKBdpQbJmxtavn6r9VC3eiA@mail.gmail.com>
Date:   Thu, 21 Jan 2021 15:53:37 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: verify that rebinding to port
 < 1024 from BPF works

On Wed, Jan 20, 2021 at 7:16 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> BPF rewrites from 111 to 111, but it still should mark the port as
> "changed".
> We also verify that if port isn't touched by BPF, it's still prohibited.
>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  .../selftests/bpf/prog_tests/bind_perm.c      | 88 +++++++++++++++++++
>  tools/testing/selftests/bpf/progs/bind_perm.c | 36 ++++++++
>  2 files changed, 124 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/bind_perm.c
>  create mode 100644 tools/testing/selftests/bpf/progs/bind_perm.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bind_perm.c b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
> new file mode 100644
> index 000000000000..840a04ac9042
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
> @@ -0,0 +1,88 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include "bind_perm.skel.h"
> +
> +#include <sys/types.h>
> +#include <sys/socket.h>
> +#include <sys/capability.h>
> +
> +static int duration;
> +
> +void try_bind(int port, int expected_errno)
> +{
> +       struct sockaddr_in sin = {};
> +       int fd = -1;
> +
> +       fd = socket(AF_INET, SOCK_STREAM, 0);
> +       if (CHECK(fd < 0, "fd", "errno %d", errno))
> +               goto close_socket;
> +
> +       sin.sin_family = AF_INET;
> +       sin.sin_port = htons(port);
> +
> +       errno = 0;
> +       bind(fd, (struct sockaddr *)&sin, sizeof(sin));
> +       CHECK(errno != expected_errno, "bind", "errno %d, expected %d",
> +             errno, expected_errno);

ASSERT_NEQ() is nicer

> +
> +close_socket:
> +       if (fd >= 0)
> +               close(fd);
> +}
> +
> +void cap_net_bind_service(cap_flag_value_t flag)
> +{
> +       const cap_value_t cap_net_bind_service = CAP_NET_BIND_SERVICE;
> +       cap_t caps;
> +
> +       caps = cap_get_proc();
> +       if (CHECK(!caps, "cap_get_proc", "errno %d", errno))
> +               goto free_caps;
> +
> +       if (CHECK(cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap_net_bind_service,
> +                              CAP_CLEAR),
> +                 "cap_set_flag", "errno %d", errno))
> +               goto free_caps;
> +
> +       if (CHECK(cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap_net_bind_service,
> +                              CAP_CLEAR),
> +                 "cap_set_flag", "errno %d", errno))
> +               goto free_caps;
> +
> +       if (CHECK(cap_set_proc(caps), "cap_set_proc", "errno %d", errno))
> +               goto free_caps;
> +
> +free_caps:
> +       if (CHECK(cap_free(caps), "cap_free", "errno %d", errno))
> +               goto free_caps;
> +}
> +
> +void test_bind_perm(void)
> +{
> +       struct bind_perm *skel;
> +       int cgroup_fd;
> +
> +       cgroup_fd = test__join_cgroup("/bind_perm");
> +       if (CHECK(cgroup_fd < 0, "cg-join", "errno %d", errno))
> +               return;
> +
> +       skel = bind_perm__open_and_load();
> +       if (CHECK(!skel, "skel-load", "errno %d", errno))
> +               goto close_cgroup_fd;

errno is irrelevant; also use ASSERT_PTR_OK() instead

> +
> +       skel->links.bind_v4_prog = bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
> +       if (CHECK(IS_ERR(skel->links.bind_v4_prog),
> +                 "cg-attach", "bind4 %ld",
> +                 PTR_ERR(skel->links.bind_v4_prog)))

try using ASSERT_PTR_OK instead

> +               goto close_skeleton;
> +
> +       cap_net_bind_service(CAP_CLEAR);
> +       try_bind(110, EACCES);
> +       try_bind(111, 0);
> +       cap_net_bind_service(CAP_SET);
> +
> +close_skeleton:
> +       bind_perm__destroy(skel);
> +close_cgroup_fd:
> +       close(cgroup_fd);
> +}

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