The dynptr passed to a bpf_user_ringbuf_drain() callback, and values
derived from it, must not be used after that callback returns.

Exercise escapes through the callback context, slices returned by
bpf_dynptr_data() and bpf_dynptr_slice(), and clones stored in the
caller's frame. Also cover an inner callback's dynptr escaping into an
outer callback.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
 .../selftests/bpf/progs/user_ringbuf_fail.c   | 135 ++++++++++++++++++
 1 file changed, 135 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c b/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c
index c0d0422b8030..80eb1e7802ad 100644
--- a/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c
+++ b/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c
@@ -1,9 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
 
+#include <stdbool.h>
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
+#include "bpf_kfuncs.h"
 
 char _license[] SEC("license") = "GPL";
 
@@ -243,3 +245,136 @@ int user_ringbuf_callback_const_ptr_to_dynptr_reg_off(void *ctx)
 			       callback_adjust_bpf_dynptr_reg_off, NULL, 0);
 	return 0;
 }
+
+/* The sample goes back to the producer as soon as the callback returns. */
+struct dynptr_ctx {
+	struct bpf_dynptr *saved;
+};
+
+static long callback_park_dynptr(struct bpf_dynptr *dynptr, void *context)
+{
+	struct dynptr_ctx *c = context;
+
+	c->saved = dynptr;
+	return 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("R3 type=scalar expected=fp, dynptr_ptr")
+int user_ringbuf_callback_park_dynptr(void *ctx)
+{
+	struct dynptr_ctx c = {};
+	char buf[8] = {};
+
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_dynptr, &c, 0);
+	if (c.saved)
+		bpf_dynptr_read(buf, sizeof(buf), c.saved, 0, 0);
+	return buf[0];
+}
+
+struct slice_ctx {
+	char *p;
+};
+
+static long callback_park_data_slice(struct bpf_dynptr *dynptr, void *context)
+{
+	struct slice_ctx *c = context;
+
+	c->p = bpf_dynptr_data(dynptr, 0, 8);
+	return 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int user_ringbuf_callback_park_data_slice(void *ctx)
+{
+	struct slice_ctx c = {};
+
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_data_slice, &c, 0);
+	if (c.p)
+		return c.p[0];
+	return 0;
+}
+
+static long callback_park_kfunc_slice(struct bpf_dynptr *dynptr, void *context)
+{
+	struct slice_ctx *c = context;
+
+	c->p = bpf_dynptr_slice(dynptr, 0, NULL, 8);
+	return 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("invalid mem access 'scalar'")
+int user_ringbuf_callback_park_kfunc_slice(void *ctx)
+{
+	struct slice_ctx c = {};
+
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_kfunc_slice, &c, 0);
+	if (c.p)
+		return c.p[0];
+	return 0;
+}
+
+struct clone_ctx {
+	struct bpf_dynptr clone;
+	__u64 armed;
+};
+
+static long callback_park_clone(struct bpf_dynptr *dynptr, void *context)
+{
+	struct clone_ctx *c = context;
+
+	bpf_dynptr_clone(dynptr, &c->clone);
+	c->armed = 1;
+	return 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("Expected an initialized dynptr as R3")
+int user_ringbuf_callback_park_clone(void *ctx)
+{
+	struct clone_ctx c = {};
+	char buf[8] = {};
+
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_clone, &c, 0);
+	if (c.armed)
+		bpf_dynptr_read(buf, sizeof(buf), &c.clone, 0, 0);
+	return buf[0];
+}
+
+SEC("?raw_tp")
+__failure __msg("Expected an initialized dynptr as R1")
+int user_ringbuf_callback_park_clone_then_slice(void *ctx)
+{
+	struct clone_ctx c = {};
+	char *p;
+
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_clone, &c, 0);
+	if (c.armed) {
+		p = bpf_dynptr_data(&c.clone, 0, 8);
+		if (p)
+			return p[0];
+	}
+	return 0;
+}
+
+/* An inner drain's dynptr must not escape into the outer callback either. */
+static long callback_park_outer(struct bpf_dynptr *dynptr, void *context)
+{
+	struct dynptr_ctx inner = {};
+	char buf[8] = {};
+
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_dynptr, &inner, 0);
+	if (inner.saved)
+		bpf_dynptr_read(buf, sizeof(buf), inner.saved, 0, 0);
+	return buf[0] ? 1 : 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("R3 type=scalar expected=fp, dynptr_ptr")
+int user_ringbuf_callback_nested_park_inner(void *ctx)
+{
+	bpf_user_ringbuf_drain(&user_ringbuf, callback_park_outer, NULL, 0);
+	return 0;
+}
-- 
2.56.0