[PATCH bpf-next v3 7/9] selftests/bpf: Test using dynptr after freeing the underlying object

Amery Hung
2026-04-21T22:10:26Z

Make sure the verifier invalidates the dynptr and dynptr slice derived
from an skb after the skb is freed.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
.../selftests/bpf/prog_tests/bpf_qdisc.c | 6 ++
.../progs/bpf_qdisc_fail__invalid_dynptr.c | 68 +++++++++++++++++
...f_qdisc_fail__invalid_dynptr_cross_frame.c | 74 +++++++++++++++++++
.../bpf_qdisc_fail__invalid_dynptr_slice.c | 70 ++++++++++++++++++
4 files changed, 218 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr.c
create mode 100644 tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_cross_frame.c
create mode 100644 tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_slice.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
index 730357cd0c9a..65277c8fc887 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_qdisc.c
@@ -8,6 +8,9 @@
#include "bpf_qdisc_fifo.skel.h"
#include "bpf_qdisc_fq.skel.h"
#include "bpf_qdisc_fail__incompl_ops.skel.h"
+#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"

#define LO_IFINDEX 1

@@ -223,6 +226,9 @@ void test_ns_bpf_qdisc(void)
test_qdisc_attach_to_non_root();
if (test__start_subtest("incompl_ops"))
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_slice);
}

void serial_test_bpf_qdisc_default(void)
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr.c
new file mode 100644
index 000000000000..3a20811e3feb
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr.c
@@ -0,0 +1,68 @@
+// 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;
+
+SEC("struct_ops")
+__failure __msg("Expected an initialized dynptr as arg #")
+int BPF_PROG(invalid_dynptr, struct sk_buff *skb, struct Qdisc *sch,
+ struct bpf_sk_buff_ptr *to_free)
+{
+ struct bpf_dynptr ptr;
+ struct ethhdr *hdr;
+
+ bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+
+ bpf_qdisc_skb_drop(skb, to_free);
+
+ hdr = bpf_dynptr_slice(&ptr, 0, NULL, sizeof(*hdr));
+ if (!hdr)
+ return NET_XMIT_DROP;
+
+ proto = hdr->h_proto;
+
+ 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,
+ .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",
+};
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_cross_frame.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_cross_frame.c
new file mode 100644
index 000000000000..2e23b8593af9
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_cross_frame.c
@@ -0,0 +1,74 @@
+// 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 int free_skb(struct sk_buff *skb)
+{
+ bpf_kfree_skb(skb);
+ return 0;
+}
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_cross_frame, struct sk_buff *skb, struct Qdisc *sch,
+ struct bpf_sk_buff_ptr *to_free)
+{
+ struct bpf_dynptr ptr;
+ struct ethhdr *hdr;
+
+ bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+
+ hdr = bpf_dynptr_slice(&ptr, 0, NULL, sizeof(*hdr));
+ if (!hdr)
+ return NET_XMIT_DROP;
+
+ free_skb(skb);
+
+ proto = hdr->h_proto;
+
+ 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_cross_frame,
+ .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",
+};
diff --git a/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_slice.c b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_slice.c
new file mode 100644
index 000000000000..731216c4e45a
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_qdisc_fail__invalid_dynptr_slice.c
@@ -0,0 +1,70 @@
+// 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;
+
+SEC("struct_ops")
+__failure __msg("invalid mem access 'scalar'")
+int BPF_PROG(invalid_dynptr_slice, struct sk_buff *skb, struct Qdisc *sch,
+ struct bpf_sk_buff_ptr *to_free)
+{
+ struct bpf_dynptr ptr;
+ struct ethhdr *hdr;
+
+ bpf_dynptr_from_skb((struct __sk_buff *)skb, 0, &ptr);
+
+ hdr = bpf_dynptr_slice(&ptr, 0, NULL, sizeof(*hdr));
+ if (!hdr) {
+ bpf_qdisc_skb_drop(skb, to_free);
+ return NET_XMIT_DROP;
+ }
+
+ bpf_qdisc_skb_drop(skb, to_free);
+
+ proto = hdr->h_proto;
+
+ 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_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",
+};
--
2.52.0