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

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Fri, 26 Mar 2021 10:43:34 +0100

Andrii Nakryiko <[email-masked]> writes:

> On Thu, Mar 25, 2021 at 2:11 PM Toke Høiland-Jørgensen <[email-masked]> 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 <[email-masked]>
>> ---
>>  .../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...

>>
>>  #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 :/

-Toke