netdev - Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license

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Message-ID: <CAEf4BzaxmrWFBJ1mzzWzu0yb_iFX528cAFVbXrncPEaJBXrd2A@mail.gmail.com>
Date:   Thu, 25 Mar 2021 21:04:17 -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>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Clark Williams <williams@...hat.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf v2 2/2] bpf/selftests: test that kernel rejects a TCP
 CC with an invalid license

On Thu, Mar 25, 2021 at 2:11 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> This adds a selftest to check that the verifier rejects a TCP CC struct_ops
> with a non-GPL license.
>
> v2:
> - Use a minimal struct_ops BPF program instead of rewriting bpf_dctcp's
>   license in memory.
> - Check for the verifier reject message instead of just the return code.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 44 +++++++++++++++++++
>  .../selftests/bpf/progs/bpf_nogpltcp.c        | 19 ++++++++
>  2 files changed, 63 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> index 37c5494a0381..a09c716528e1 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> @@ -6,6 +6,7 @@
>  #include <test_progs.h>
>  #include "bpf_dctcp.skel.h"
>  #include "bpf_cubic.skel.h"
> +#include "bpf_nogpltcp.skel.h"

total nit, but my eyes can't read "nogpltcp"... wouldn't
"bpf_tcp_nogpl" be a bit easier?

>
>  #define min(a, b) ((a) < (b) ? (a) : (b))
>
> @@ -227,10 +228,53 @@ static void test_dctcp(void)
>         bpf_dctcp__destroy(dctcp_skel);
>  }
>
> +static char *err_str = NULL;
> +static bool found = false;
> +
> +static int libbpf_debug_print(enum libbpf_print_level level,
> +                             const char *format, va_list args)
> +{
> +       char *log_buf;
> +
> +       if (level != LIBBPF_WARN ||
> +           strcmp(format, "libbpf: \n%s\n")) {
> +               vprintf(format, args);
> +               return 0;
> +       }
> +
> +       log_buf = va_arg(args, char *);
> +       if (!log_buf)
> +               goto out;
> +       if (err_str && strstr(log_buf, err_str) != NULL)
> +               found = true;
> +out:
> +       printf(format, log_buf);
> +       return 0;
> +}
> +
> +static void test_invalid_license(void)
> +{
> +       libbpf_print_fn_t old_print_fn = NULL;
> +       struct bpf_nogpltcp *skel;
> +
> +       err_str = "struct ops programs must have a GPL compatible license";
> +       old_print_fn = libbpf_set_print(libbpf_debug_print);
> +
> +       skel = bpf_nogpltcp__open_and_load();
> +       if (CHECK(skel, "bpf_nogplgtcp__open_and_load()", "didn't fail\n"))

ASSERT_OK_PTR()

> +               bpf_nogpltcp__destroy(skel);

you should destroy unconditionally

> +
> +       CHECK(!found, "errmsg check", "expected string '%s'", err_str);

ASSERT_EQ(found, true, "expected_err_msg");

I can never be sure which way CHECK() is checking

> +
> +       libbpf_set_print(old_print_fn);
> +}
> +
>  void test_bpf_tcp_ca(void)
>  {
>         if (test__start_subtest("dctcp"))
>                 test_dctcp();
>         if (test__start_subtest("cubic"))
>                 test_cubic();
> +       if (test__start_subtest("invalid_license"))
> +               test_invalid_license();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c b/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
> new file mode 100644
> index 000000000000..2ecd833dcd41
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_nogpltcp.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <linux/types.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include "bpf_tcp_helpers.h"
> +
> +char _license[] SEC("license") = "X";
> +
> +void BPF_STRUCT_OPS(nogpltcp_init, struct sock *sk)
> +{
> +}
> +
> +SEC(".struct_ops")
> +struct tcp_congestion_ops bpf_nogpltcp = {
> +       .init           = (void *)nogpltcp_init,
> +       .name           = "bpf_nogpltcp",
> +};
> --
> 2.31.0
>