Re: [PATCH bpf 2/2] bpf/selftests: test that kernel rejects a TCP CC with an invalid license
From: Martin KaFai Lau <hidden>
Date: 2021-03-25 18:33:14
Also in:
bpf
On Thu, Mar 25, 2021 at 04:40:34PM +0100, Toke Høiland-Jørgensen wrote:
quoted hunk ↗ jump to hunk
This adds a selftest to check that the verifier rejects a TCP CC struct_ops with a non-GPL license. To save having to add a whole new BPF object just for this, reuse the dctcp CC, but rewrite the license field before loading. Signed-off-by: Toke Høiland-Jørgensen <redacted> --- .../selftests/bpf/prog_tests/bpf_tcp_ca.c | 31 +++++++++++++++++++ 1 file changed, 31 insertions(+)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..613cf8a00b22 100644 --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c@@ -227,10 +227,41 @@ static void test_dctcp(void) bpf_dctcp__destroy(dctcp_skel); } +static void test_invalid_license(void) +{ + /* We want to check that the verifier refuses to load a non-GPL TCP CC. + * Rather than create a whole new file+skeleton, just reuse an existing + * object and rewrite the license in memory after loading. Sine libbpf + * doesn't expose this, we define a struct that includes the first couple + * of internal fields for struct bpf_object so we can overwrite the right + * bits. Yes, this is a bit of a hack, but it makes the test a lot simpler. + */ + struct bpf_object_fragment { + char name[BPF_OBJ_NAME_LEN]; + char license[64]; + } *obj;
It is fragile. A new bpf_nogpltcp.c should be created and it does
not have to be a full tcp-cc. A very minimal implementation with
only .init. Something like this (uncompiled code):
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",
};
libbpf_set_print() can also be used to look for the
the verifier log "struct ops programs must have a GPL compatible license".