selftests/bpf: Update xdp_context_test_run test to check maximum metadata size

Update the selftest to check that the metadata size check takes the
xdp_frame size into account in bpf_prog_test_run. The original
check (for meta size 256) was broken because the data frame supplied was
smaller than this, triggering a different EINVAL return. So supply a
larger data frame for this test to make sure we actually exercise the
check we think we are.

Signed-off-by: Toke Høiland-Jørgensen <[e-mail]>
Reviewed-by: Amery Hung <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 	struct test_xdp_context_test_run *skel = NULL;
 	char data[sizeof(pkt_v4) + sizeof(__u32)];
 	char bad_ctx[sizeof(struct xdp_md) + 1];
+	char large_data[256];
 	struct xdp_md ctx_in, ctx_out;
 	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
 			    .data_in = &data,
···
 	test_xdp_context_error(prog_fd, opts, 4, sizeof(__u32), sizeof(data),
 			       0, 0, 0);
 
-	/* Meta data must be 255 bytes or smaller */
-	test_xdp_context_error(prog_fd, opts, 0, 256, sizeof(data), 0, 0, 0);
-
 	/* Total size of data must be data_end - data_meta or larger */
 	test_xdp_context_error(prog_fd, opts, 0, sizeof(__u32),
 			       sizeof(data) + 1, 0, 0, 0);
···
 	/* The egress cannot be specified */
 	test_xdp_context_error(prog_fd, opts, 0, sizeof(__u32), sizeof(data),
 			       0, 0, 1);
+
+	/* Meta data must be 216 bytes or smaller (256 - sizeof(struct
+	 * xdp_frame)). Test both nearest invalid size and nearest invalid
+	 * 4-byte-aligned size, and make sure data_in is large enough that we
+	 * actually hit the check on metadata length
+	 */
+	opts.data_in = large_data;
+	opts.data_size_in = sizeof(large_data);
+	test_xdp_context_error(prog_fd, opts, 0, 217, sizeof(large_data), 0, 0, 0);
+	test_xdp_context_error(prog_fd, opts, 0, 220, sizeof(large_data), 0, 0, 0);
 
 	test_xdp_context_test_run__destroy(skel);
 }