selftests/bpf: Add tests for writing to nf_conn:mark

Add a simple extension to the existing selftest to write to
nf_conn:mark. Also add a failure test for writing to unsupported field.

Signed-off-by: Daniel Xu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/prog_tests/bpf_nf.c

···
 	{ "set_status_after_insert", "kernel function bpf_ct_set_status args#0 expected pointer to STRUCT nf_conn___init but" },
 	{ "change_timeout_after_alloc", "kernel function bpf_ct_change_timeout args#0 expected pointer to STRUCT nf_conn but" },
 	{ "change_status_after_alloc", "kernel function bpf_ct_change_status args#0 expected pointer to STRUCT nf_conn but" },
+	{ "write_not_allowlisted_field", "no write support to nf_conn at off" },
 };
 
 enum {
···
 	ASSERT_LE(skel->bss->test_delta_timeout, 10, "Test for max ct timeout update");
 	/* expected status is IPS_SEEN_REPLY */
 	ASSERT_EQ(skel->bss->test_status, 2, "Test for ct status update ");
+	ASSERT_EQ(skel->bss->test_insert_lookup_mark, 77, "Test for insert and lookup mark value");
 	ASSERT_EQ(skel->data->test_exist_lookup, 0, "Test existing connection lookup");
 	ASSERT_EQ(skel->bss->test_exist_lookup_mark, 43, "Test existing connection lookup ctmark");
 end:

tools/testing/selftests/bpf/progs/test_bpf_nf.c

···
 int test_succ_lookup = -ENOENT;
 u32 test_delta_timeout = 0;
 u32 test_status = 0;
+u32 test_insert_lookup_mark = 0;
 __be32 saddr = 0;
 __be16 sport = 0;
 __be32 daddr = 0;
···
 
 		bpf_ct_set_timeout(ct, 10000);
 		bpf_ct_set_status(ct, IPS_CONFIRMED);
+		ct->mark = 77;
 
 		ct_ins = bpf_ct_insert_entry(ct);
 		if (ct_ins) {
···
 				test_delta_timeout = ct_lk->timeout - bpf_jiffies64();
 				test_delta_timeout /= CONFIG_HZ;
 				test_status = IPS_SEEN_REPLY;
+				test_insert_lookup_mark = ct_lk->mark;
 				bpf_ct_change_status(ct_lk, IPS_SEEN_REPLY);
 				bpf_ct_release(ct_lk);
 				test_succ_lookup = 0;
···
 		       sizeof(opts_def));
 	if (ct) {
 		test_exist_lookup = 0;
-		if (ct->mark == 42)
-			test_exist_lookup_mark = 43;
+		if (ct->mark == 42) {
+			ct->mark++;
+			test_exist_lookup_mark = ct->mark;
+		}
 		bpf_ct_release(ct);
 	} else {
 		test_exist_lookup = opts_def.error;

tools/testing/selftests/bpf/progs/test_bpf_nf_fail.c

···
 }
 
 SEC("?tc")
+int write_not_allowlisted_field(struct __sk_buff *ctx)
+{
+	struct bpf_ct_opts___local opts = {};
+	struct bpf_sock_tuple tup = {};
+	struct nf_conn *ct;
+
+	ct = bpf_skb_ct_lookup(ctx, &tup, sizeof(tup.ipv4), &opts, sizeof(opts));
+	if (!ct)
+		return 0;
+	ct->status = 0xF00;
+	return 0;
+}
+
+SEC("?tc")
 int set_timeout_after_insert(struct __sk_buff *ctx)
 {
 	struct bpf_ct_opts___local opts = {};