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"

 #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"))

+
+       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