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

[Hengqi Chen <hengqi.chen@gmail.com>]

On 10/6/21 1:09 PM, Song Liu wrote:
> 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?
> 

Yes, that would be much more precise. Will do.

> Thanks,
> Song
>