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: <CAEf4BzaucswGy+LiXQC0q_zgQEOTtRJ3GQtaeq7CwJJW9EzGig@mail.gmail.com>
Date:   Fri, 26 Mar 2021 11:14:03 -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

-- Andrii

On Fri, Mar 26, 2021 at 2:43 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
>
> > 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?
>
> Haha, yeah, good point - my eyes also just lump it into a blob...

thanks

>
> >>
> >>  #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
>
> Ah, thanks! I always get confused about CHECK() as well! Maybe it should
> be renamed to ASSERT()? But that would require flipping all the if()
> statements around them as well :/

Exactly, it's the opposite of assert (ASSERT_NOT %-), that
CHECK(!found) is "assert not not found", right?) and it throws me off
every. single. time. Ideally we complete the set of ASSERT_XXX()
macros and convert as much as possible to that. We can also have just
generic ASSERT() for all other complicated cases.

>
> -Toke
>