selftests/bpf: Test dynptr teardown on subprog return

Add failure tests for slices that escape a subprogram from a dynptr in the
callee stack. Cover immediate use of a ring buffer clone slice,
release-time invalidation of a caller dynptr slice after it crosses a
subprogram return, and immediate use of an skb dynptr slice in a qdisc
program.

Cover the error path where a subprogram would otherwise lose the last
dynptr capable of releasing a referenced resource.

Also add a success control which derives a slice from a caller-owned dynptr
and creates a separate clone in the callee. Destroying that callee-local
clone on return must not invalidate the caller dynptr's slice.

Signed-off-by: Xu Yunxiang <xyx2021@mail.ustc.edu.cn>
Reviewed-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/bpf/20260927120422.1042107-3-xyx2021@mail.ustc.edu.cn
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

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_fail__invalid_dynptr_returned_slice.skel.h"
 #include "bpf_qdisc_fail__untrusted_write.skel.h"
 #include "bpf_qdisc_dynptr_use_after_invalidate_clone.skel.h"
 
@@ -230,6 +231,7 @@ void test_ns_bpf_qdisc(void)
 		test_incompl_ops();
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr);
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_cross_frame);
+	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_returned_slice);
 	RUN_TESTS(bpf_qdisc_fail__invalid_dynptr_slice);
 	RUN_TESTS(bpf_qdisc_fail__untrusted_write);
 	RUN_TESTS(bpf_qdisc_dynptr_use_after_invalidate_clone);

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

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "bpf_experimental.h"
+#include "bpf_qdisc_common.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+int proto;
+
+static __noinline struct ethhdr *slice_in_subprog(struct sk_buff *skb)
+{
+	struct bpf_dynptr ptr;
+
+	bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+	return bpf_dynptr_slice(&ptr, 0, NULL, sizeof(struct ethhdr));
+}
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_returned_slice, struct sk_buff *skb,
+	     struct Qdisc *sch, struct bpf_sk_buff_ptr *to_free)
+{
+	struct ethhdr *hdr;
+
+	hdr = slice_in_subprog(skb);
+	if (!hdr) {
+		bpf_qdisc_skb_drop(skb, to_free);
+		return NET_XMIT_DROP;
+	}
+
+	/* this should fail */
+	proto = hdr->h_proto;
+
+	bpf_qdisc_skb_drop(skb, to_free);
+
+	return NET_XMIT_DROP;
+}
+
+SEC("struct_ops")
+__auxiliary
+struct sk_buff *BPF_PROG(bpf_qdisc_test_dequeue, struct Qdisc *sch)
+{
+	return NULL;
+}
+
+SEC("struct_ops")
+__auxiliary
+int BPF_PROG(bpf_qdisc_test_init, struct Qdisc *sch, struct nlattr *opt,
+	     struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_reset, struct Qdisc *sch)
+{
+}
+
+SEC("struct_ops")
+__auxiliary
+void BPF_PROG(bpf_qdisc_test_destroy, struct Qdisc *sch)
+{
+}
+
+SEC(".struct_ops")
+struct Qdisc_ops test = {
+	.enqueue   = (void *)invalid_dynptr_returned_slice,
+	.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",
+};

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

@@ -1895,6 +1895,101 @@ int clone_invalidate4(void *ctx)
 	return 0;
 }
 
+static __noinline void clone_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+	struct bpf_dynptr clone;
+
+	bpf_dynptr_clone(ptr, &clone);
+	*data = bpf_dynptr_data(&clone, 0, sizeof(val));
+}
+
+static __noinline void caller_slice_in_subprog(struct bpf_dynptr *ptr, int **data)
+{
+	struct bpf_dynptr clone;
+
+	*data = bpf_dynptr_data(ptr, 0, sizeof(val));
+	bpf_dynptr_clone(ptr, &clone);
+}
+
+static __noinline void reserve_dynptr_in_subprog(void)
+{
+	struct bpf_dynptr ptr;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+}
+
+/* A subprogram cannot lose the last dynptr that can release a resource. */
+SEC("?raw_tp")
+__failure __msg("cannot overwrite referenced dynptr")
+int referenced_dynptr_lost_on_subprog_return(void *ctx)
+{
+	reserve_dynptr_in_subprog();
+
+	return 0;
+}
+
+/*
+ * Destroying a callee-local clone on return must not invalidate a slice whose
+ * source dynptr belongs to the caller.
+ */
+SEC("?raw_tp")
+__success
+int caller_dynptr_slice_across_subprog_valid(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	caller_slice_in_subprog(&ptr, &data);
+	if (data)
+		*data = 123;
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+	return 0;
+}
+
+/*
+ * A slice derived from a callee-local clone is invalid after the subprogram
+ * returns.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int callee_dynptr_slice_invalid_after_return(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	clone_slice_in_subprog(&ptr, &data);
+	if (data)
+		/* this should fail */
+		*data = 123;
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+
+	return 0;
+}
+
+/*
+ * A slice from a caller-owned dynptr survives the subprogram return, but
+ * releasing the shared reservation must invalidate it.
+ */
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int caller_dynptr_slice_release_after_subprog_invalid(void *ctx)
+{
+	struct bpf_dynptr ptr;
+	int *data = NULL;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, val, 0, &ptr);
+	caller_slice_in_subprog(&ptr, &data);
+	bpf_ringbuf_submit_dynptr(&ptr, 0);
+	if (data)
+		/* this should fail */
+		*data = 123;
+
+	return 0;
+}
+
 /* Invalidating a dynptr should invalidate any data slices
  * of its parent
  */