selftests/bpf: Test using slice after invalidating dynptr clone

The parent object of a cloned dynptr is skb not the original dynptr.
Invalidate the original dynptr should not prevent the program from
using the slice derived from the cloned dynptr.

Signed-off-by: Amery Hung <ameryhung@gmail.com>

Author: ameryhung

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

@@ -11,6 +11,7 @@
 #include "bpf_qdisc_fail__invalid_dynptr.skel.h"
 #include "bpf_qdisc_fail__invalid_dynptr_slice.skel.h"
 #include "bpf_qdisc_fail__invalid_dynptr_cross_frame.skel.h"
+#include "bpf_qdisc_dynptr_clone.skel.h"
 
 #define LO_IFINDEX 1
 
@@ -186,6 +187,17 @@ static void test_invalid_dynptr_cross_frame(void)
 		bpf_qdisc_fail__invalid_dynptr_cross_frame__destroy(skel);
 }
 
+static void test_dynptr_clone(void)
+{
+	struct bpf_qdisc_dynptr_clone *skel;
+
+	skel = bpf_qdisc_dynptr_clone__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "bpf_qdisc_dynptr_clone__open_and_load"))
+		return;
+
+	bpf_qdisc_dynptr_clone__destroy(skel);
+}
+
 static int get_default_qdisc(char *qdisc_name)
 {
 	FILE *f;
@@ -259,6 +271,8 @@ void test_ns_bpf_qdisc(void)
 		test_invalid_dynptr_slice();
 	if (test__start_subtest("invalid_dynptr_cross_frame"))
 		test_invalid_dynptr_cross_frame();
+	if (test__start_subtest("dynptr_clone"))
+		test_dynptr_clone();
 }
 
 void serial_test_bpf_qdisc_default(void)

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

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "bpf_experimental.h"
+#include "bpf_qdisc_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+int proto;
+
+SEC("struct_ops")
+int BPF_PROG(bpf_qdisc_test_enqueue, struct sk_buff *skb, struct Qdisc *sch,
+	     struct bpf_sk_buff_ptr *to_free)
+{
+	struct bpf_dynptr ptr, ptr_clone;
+	struct ethhdr *hdr;
+
+	bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+
+	bpf_dynptr_clone(&ptr, &ptr_clone);
+
+	hdr = bpf_dynptr_slice(&ptr_clone, 0, NULL, sizeof(*hdr));
+	if (!hdr) {
+		bpf_qdisc_skb_drop(skb, to_free);
+		return NET_XMIT_DROP;
+	}
+
+	*(int *)&ptr = 0;
+
+	proto = hdr->h_proto;
+
+	bpf_qdisc_skb_drop(skb, to_free);
+
+	return NET_XMIT_DROP;
+}
+
+SEC("struct_ops")
+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)
+{
+	return NULL;
+}
+
+SEC("struct_ops")
+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,
+	     struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+SEC("struct_ops")
+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)
+{
+}
+
+SEC("struct_ops")
+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)
+{
+}
+
+SEC(".struct_ops")
+struct Qdisc_ops test = {
+	.enqueue   = (void *)bpf_qdisc_test_enqueue,
+	.dequeue   = (void *)bpf_qdisc_test_dequeue,
+	.init      = (void *)bpf_qdisc_test_init,
+	.reset     = (void *)bpf_qdisc_test_reset,
+	.destroy   = (void *)bpf_qdisc_test_destroy,
+	.id        = "bpf_qdisc_test",
+};
+