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

Andrii Nakryiko [off-list ref] writes:

On Thu, Mar 25, 2021 at 2:11 PM Toke Høiland-Jørgensen [off-list ref] wrote:

quoted

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 <redacted>
---
 .../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...

quoted

 #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()

quoted

+               bpf_nogpltcp__destroy(skel);

you should destroy unconditionally

quoted

+
+       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