linux-kernel - Re: [PATCH bpf-next v2 4/4] selftests/bpf: Add tests for writing to nf

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Date:   Wed, 17 Aug 2022 21:59:03 +0200
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     Daniel Xu <dxu@...uu.xyz>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, pablo@...filter.org, fw@...len.de,
        toke@...nel.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 4/4] selftests/bpf: Add tests for writing to nf_conn:mark

On Wed, 17 Aug 2022 at 20:43, Daniel Xu <dxu@...uu.xyz> wrote:
>
> Add a simple extension to the existing selftest to write to
> nf_conn:mark. Also add a failure test for writing to unsupported field.
>
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
>  tools/testing/selftests/bpf/prog_tests/bpf_nf.c    |  1 +
>  tools/testing/selftests/bpf/progs/test_bpf_nf.c    |  6 ++++--
>  .../testing/selftests/bpf/progs/test_bpf_nf_fail.c | 14 ++++++++++++++
>  3 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_nf.c b/tools/testing/selftests/bpf/prog_tests/bpf_nf.c
> index 544bf90ac2a7..45389c39f211 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_nf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_nf.c
> @@ -17,6 +17,7 @@ struct {
>         { "set_status_after_insert", "kernel function bpf_ct_set_status args#0 expected pointer to STRUCT nf_conn___init but" },
>         { "change_timeout_after_alloc", "kernel function bpf_ct_change_timeout args#0 expected pointer to STRUCT nf_conn but" },
>         { "change_status_after_alloc", "kernel function bpf_ct_change_status args#0 expected pointer to STRUCT nf_conn but" },
> +       { "write_not_allowlisted_field", "no write support to nf_conn at off" },
>  };
>
>  enum {
> diff --git a/tools/testing/selftests/bpf/progs/test_bpf_nf.c b/tools/testing/selftests/bpf/progs/test_bpf_nf.c
> index 2722441850cc..638b6642d20f 100644
> --- a/tools/testing/selftests/bpf/progs/test_bpf_nf.c
> +++ b/tools/testing/selftests/bpf/progs/test_bpf_nf.c
> @@ -175,8 +175,10 @@ nf_ct_test(struct nf_conn *(*lookup_fn)(void *, struct bpf_sock_tuple *, u32,
>                        sizeof(opts_def));
>         if (ct) {
>                 test_exist_lookup = 0;
> -               if (ct->mark == 42)
> -                       test_exist_lookup_mark = 43;
> +               if (ct->mark == 42) {
> +                       ct->mark++;

Please also include a test for setting ct->mark on allocated but not
inserted nf_conn. For that you might have to add another check in the
btf_struct_access callback to also consider nf_conn___init equivalent
to nf_conn. We use a container type to deny operations that are not
safe for allocated ct, but the layout is same for both (since it just
embeds struct nf_conn inside it), so the rest of the logic should work
the same.

> +                       test_exist_lookup_mark = ct->mark;
> +               }
>                 bpf_ct_release(ct);
>         } else {
>                 test_exist_lookup = opts_def.error;
> diff --git a/tools/testing/selftests/bpf/progs/test_bpf_nf_fail.c b/tools/testing/selftests/bpf/progs/test_bpf_nf_fail.c
> index bf79af15c808..0e4759ab38ff 100644
> --- a/tools/testing/selftests/bpf/progs/test_bpf_nf_fail.c
> +++ b/tools/testing/selftests/bpf/progs/test_bpf_nf_fail.c
> @@ -69,6 +69,20 @@ int lookup_insert(struct __sk_buff *ctx)
>         return 0;
>  }
>
> +SEC("?tc")
> +int write_not_allowlisted_field(struct __sk_buff *ctx)
> +{
> +       struct bpf_ct_opts___local opts = {};
> +       struct bpf_sock_tuple tup = {};
> +       struct nf_conn *ct;
> +
> +       ct = bpf_skb_ct_lookup(ctx, &tup, sizeof(tup.ipv4), &opts, sizeof(opts));
> +       if (!ct)
> +               return 0;
> +       ct->status = 0xF00;
> +       return 0;
> +}
> +
>  SEC("?tc")
>  int set_timeout_after_insert(struct __sk_buff *ctx)
>  {
> --
> 2.37.1
>