netdev - Re: [PATCH bpf-next v7 10/10] selftests: Add selftest for disallowing modify

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Message-ID: <CAEf4BzZnAFtB4Zq8dxee=B=3Z46JR4dn9wA=DOeOURB77N4yRg@mail.gmail.com>
Date:   Mon, 21 Sep 2020 16:25:10 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>,
        KP Singh <kpsingh@...omium.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v7 10/10] selftests: Add selftest for disallowing
 modify_return attachment to freplace

On Sat, Sep 19, 2020 at 4:50 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke@...hat.com>
>
> This adds a selftest that ensures that modify_return tracing programs
> cannot be attached to freplace programs. The security_ prefix is added to
> the freplace program because that would otherwise let it pass the check for
> modify_return.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  .../selftests/bpf/prog_tests/fexit_bpf2bpf.c       |   68 ++++++++++++++++++++
>  .../selftests/bpf/progs/fmod_ret_freplace.c        |   14 ++++
>  .../selftests/bpf/progs/freplace_get_constant.c    |    2 -
>  3 files changed, 83 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/fmod_ret_freplace.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> index 27677e015730..6339d125ef9a 100644
> --- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> @@ -233,6 +233,72 @@ static void test_func_replace_multi(void)
>                                   prog_name, true, test_second_attach);
>  }
>
> +static void test_fmod_ret_freplace(void)
> +{
> +       const char *tgt_name = "./test_pkt_access.o";
> +       const char *freplace_name = "./freplace_get_constant.o";
> +       const char *fmod_ret_name = "./fmod_ret_freplace.o";
> +       struct bpf_link *freplace_link = NULL, *fmod_link = NULL;
> +       struct bpf_object *freplace_obj = NULL, *pkt_obj, *fmod_obj = NULL;
> +       struct bpf_program *prog;
> +       __u32 duration = 0;
> +       int err, pkt_fd;
> +
> +       err = bpf_prog_load(tgt_name, BPF_PROG_TYPE_UNSPEC,
> +                           &pkt_obj, &pkt_fd);
> +       /* the target prog should load fine */
> +       if (CHECK(err, "tgt_prog_load", "file %s err %d errno %d\n",
> +                 tgt_name, err, errno))
> +               return;
> +       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
> +                           .attach_prog_fd = pkt_fd,
> +                          );

this is variable declaration, it has to be together with all the variables above

> +
> +       freplace_obj = bpf_object__open_file(freplace_name, &opts);
> +       if (CHECK(IS_ERR_OR_NULL(freplace_obj), "freplace_obj_open",
> +                 "failed to open %s: %ld\n", freplace_name,
> +                 PTR_ERR(freplace_obj)))
> +               goto out;
> +
> +       err = bpf_object__load(freplace_obj);
> +       if (CHECK(err, "freplace_obj_load", "err %d\n", err))
> +               goto out;
> +
> +       prog = bpf_program__next(NULL, freplace_obj);
> +       freplace_link = bpf_program__attach_trace(prog);
> +       if (CHECK(IS_ERR(freplace_link), "freplace_attach_trace", "failed to link\n"))
> +               goto out;
> +
> +       opts.attach_prog_fd = bpf_program__fd(prog);
> +       fmod_obj = bpf_object__open_file(fmod_ret_name, &opts);
> +       if (CHECK(IS_ERR_OR_NULL(fmod_obj), "fmod_obj_open",
> +                 "failed to open %s: %ld\n", fmod_ret_name,
> +                 PTR_ERR(fmod_obj)))
> +               goto out;
> +
> +       err = bpf_object__load(fmod_obj);
> +       if (CHECK(err, "fmod_obj_load", "err %d\n", err))
> +               goto out;
> +
> +       prog = bpf_program__next(NULL, fmod_obj);
> +       fmod_link = bpf_program__attach_trace(prog);
> +       if (CHECK(!IS_ERR(fmod_link), "fmod_attach_trace",
> +                 "linking fmod_ret to freplace should fail\n"))
> +               goto out;
> +
> +out:
> +       if (!IS_ERR_OR_NULL(freplace_link))
> +               bpf_link__destroy(freplace_link);
> +       if (!IS_ERR_OR_NULL(fmod_link))
> +               bpf_link__destroy(fmod_link);
> +       if (!IS_ERR_OR_NULL(freplace_obj))
> +               bpf_object__close(freplace_obj);
> +       if (!IS_ERR_OR_NULL(fmod_obj))
> +               bpf_object__close(fmod_obj);

no need for all IS_ERR_OR_NULL checks

> +       bpf_object__close(pkt_obj);
> +}
> +
> +

[...]