netdev - Re: [PATCH bpf-next v4 7/8] selftests/bpf: Fix fd cleanup in sk

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Date:   Wed, 20 Oct 2021 15:19:04 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Jakub Sitnicki <jakub@...udflare.com>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v4 7/8] selftests/bpf: Fix fd cleanup in
 sk_lookup test

On Wed, Oct 20, 2021 at 12:15 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>
> Similar to the fix in commit:
> e31eec77e4ab ("bpf: selftests: Fix fd cleanup in get_branch_snapshot")
>
> We use designated initializer to set fds to -1 without breaking on
> future changes to MAX_SERVER constant denoting the array size.
>
> The particular close(0) occurs on non-reuseport tests, so it can be seen
> with -n 115/{2,3} but not 115/4. This can cause problems with future
> tests if they depend on BTF fd never being acquired as fd 0, breaking
> internal libbpf assumptions.
>
> Fixes: 0ab5539f8584 ("selftests/bpf: Tests for BPF_SK_LOOKUP attach point")
> Reviewed-by: Jakub Sitnicki <jakub@...udflare.com>
> Acked-by: Song Liu <songliubraving@...com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> ---
>  tools/testing/selftests/bpf/prog_tests/sk_lookup.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> index aee41547e7f4..cbee46d2d525 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
> @@ -598,7 +598,7 @@ static void query_lookup_prog(struct test_sk_lookup *skel)
>
>  static void run_lookup_prog(const struct test *t)
>  {
> -       int server_fds[MAX_SERVERS] = { -1 };
> +       int server_fds[] = { [0 ... MAX_SERVERS - 1] = -1 };

if you have this, why do you need early break logic below?

>         int client_fd, reuse_conn_fd = -1;
>         struct bpf_link *lookup_link;
>         int i, err;
> @@ -663,8 +663,9 @@ static void run_lookup_prog(const struct test *t)
>         if (reuse_conn_fd != -1)
>                 close(reuse_conn_fd);
>         for (i = 0; i < ARRAY_SIZE(server_fds); i++) {
> -               if (server_fds[i] != -1)
> -                       close(server_fds[i]);
> +               if (server_fds[i] == -1)
> +                       break;
> +               close(server_fds[i]);
>         }
>         bpf_link__destroy(lookup_link);
>  }
> @@ -1053,7 +1054,7 @@ static void run_sk_assign(struct test_sk_lookup *skel,
>                           struct bpf_program *lookup_prog,
>                           const char *remote_ip, const char *local_ip)
>  {
> -       int server_fds[MAX_SERVERS] = { -1 };
> +       int server_fds[] = { [0 ... MAX_SERVERS - 1] = -1 };
>         struct bpf_sk_lookup ctx;
>         __u64 server_cookie;
>         int i, err;
> @@ -1097,8 +1098,9 @@ static void run_sk_assign(struct test_sk_lookup *skel,
>
>  close_servers:
>         for (i = 0; i < ARRAY_SIZE(server_fds); i++) {
> -               if (server_fds[i] != -1)
> -                       close(server_fds[i]);
> +               if (server_fds[i] == -1)
> +                       break;
> +               close(server_fds[i]);
>         }
>  }
>
> --
> 2.33.1
>