Re: [PATCH bpf-next 2/2] selftests/bpf: Test bpf_skc_to_unix_sock()

From: Song Liu <song@kernel.org>
To: Hengqi Chen <hengqi.chen@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: Test bpf_skc_to_unix_sock()
Date: Tue, 5 Oct 2021 22:09:50 -0700	[thread overview]
Message-ID: <CAPhsuW7eK6KA62bcA+pTc8-r5yraN=5H1hocy+TOA3C30KWNDg@mail.gmail.com> (raw)
In-Reply-To: <20211006040623.401527-3-hengqi.chen@gmail.com>

On Tue, Oct 5, 2021 at 9:08 PM Hengqi Chen <hengqi.chen@gmail.com> wrote:
>
> Add a new test which triggers unix_listen kernel function
> to test bpf_skc_to_unix_sock helper.
>
> Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
> ---
>  .../bpf/prog_tests/skc_to_unix_sock.c         | 54 +++++++++++++++++++
>  .../bpf/progs/test_skc_to_unix_sock.c         | 28 ++++++++++
>  2 files changed, 82 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/skc_to_unix_sock.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_skc_to_unix_sock.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/skc_to_unix_sock.c b/tools/testing/selftests/bpf/prog_tests/skc_to_unix_sock.c
> new file mode 100644
> index 000000000000..5d8ed76a71dc
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/skc_to_unix_sock.c
> @@ -0,0 +1,54 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2021 Hengqi Chen */
> +
> +#include <test_progs.h>
> +#include <sys/un.h>
> +#include "test_skc_to_unix_sock.skel.h"
> +
> +static const char *sock_path = "/tmp/test.sock";
> +
> +void test_skc_to_unix_sock(void)
> +{
> +       struct test_skc_to_unix_sock *skel;
> +       struct sockaddr_un sockaddr;
> +       int err, len, sockfd = 0;
> +
> +       skel = test_skc_to_unix_sock__open();
> +       if (!ASSERT_OK_PTR(skel, "could not open BPF object"))
> +               return;
> +
> +       skel->rodata->my_pid = getpid();
> +
> +       err = test_skc_to_unix_sock__load(skel);
> +       if (!ASSERT_OK(err, "could not load BPF object"))
> +               goto cleanup;
> +
> +       err = test_skc_to_unix_sock__attach(skel);
> +       if (!ASSERT_OK(err, "could not attach BPF object"))
> +               goto cleanup;
> +
> +       // trigger unix_listen
> +       sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
> +       if (!ASSERT_GT(sockfd, 0, "socket failed"))
> +               goto cleanup;
> +
> +       sockaddr.sun_family = AF_UNIX;
> +       strcpy(sockaddr.sun_path, sock_path);
> +       len = sizeof(sockaddr);
> +       unlink(sock_path);
> +
> +       err = bind(sockfd, (struct sockaddr *)&sockaddr, len);
> +       if (!ASSERT_OK(err, "bind failed"))
> +               goto cleanup;
> +
> +       err = listen(sockfd, 1);
> +       if (!ASSERT_OK(err, "listen failed"))
> +               goto cleanup;
> +
> +       ASSERT_GT(skel->bss->ret, 0, "bpf_skc_to_unix_sock failed");
> +
> +cleanup:
> +       if (sockfd)
> +               close(sockfd);
> +       test_skc_to_unix_sock__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_skc_to_unix_sock.c b/tools/testing/selftests/bpf/progs/test_skc_to_unix_sock.c
> new file mode 100644
> index 000000000000..544d2ed56d7e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_skc_to_unix_sock.c
> @@ -0,0 +1,28 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2021 Hengqi Chen */
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +const volatile pid_t my_pid = 0;
> +__u64 ret = 0;
> +
> +SEC("fentry/unix_listen")
> +int BPF_PROG(unix_listen, struct socket *sock, int backlog)
> +{
> +       pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +       struct unix_sock *unix_sk;
> +
> +       if (pid != my_pid)
> +               return 0;
> +
> +       unix_sk = (struct unix_sock *)bpf_skc_to_unix_sock(sock->sk);
> +       if (!unix_sk)
> +               return 0;
> +
> +       ret = (__u64)unix_sk;

Other than ret !=0, can we verify unix_sk we get is expected? May we can
verify unix_sock-> path matches /tmp/test.sock?

Thanks,
Song