selftests/bpf: Add test for dynptr reinit in user_ringbuf callback

The original support for bpf_user_ringbuf_drain callbacks simply
short-circuited checks for the dynptr state, allowing users to pass
PTR_TO_DYNPTR (now CONST_PTR_TO_DYNPTR) to helpers that initialize a
dynptr. This bug would have also surfaced with other dynptr helpers in
the future that changed dynptr view or modified it in some way.

Include test cases for all cases, i.e. both bpf_dynptr_from_mem and
bpf_ringbuf_reserve_dynptr, and ensure verifier rejects both of them.
Without the fix, both of these programs load and pass verification.

While at it, remove sys_nanosleep target from failure cases' SEC
definition, as there is no such tracepoint.

Acked-by: David Vernet <[e-mail]>
Acked-by: Joanne Koong <[e-mail]>
Signed-off-by: Kumar Kartikeya Dwivedi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 	{"user_ringbuf_callback_discard_dynptr", "cannot release unowned const bpf_dynptr"},
 	{"user_ringbuf_callback_submit_dynptr", "cannot release unowned const bpf_dynptr"},
 	{"user_ringbuf_callback_invalid_return", "At callback return the register R0 has value"},
+	{"user_ringbuf_callback_reinit_dynptr_mem", "Dynptr has to be an uninitialized dynptr"},
+	{"user_ringbuf_callback_reinit_dynptr_ringbuf", "Dynptr has to be an uninitialized dynptr"},
 };
 
 #define SUCCESS_TEST(_func) { _func, #_func }

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

···
 	__uint(type, BPF_MAP_TYPE_USER_RINGBUF);
 } user_ringbuf SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	__uint(max_entries, 2);
+} ringbuf SEC(".maps");
+
+static int map_value;
+
 static long
 bad_access1(struct bpf_dynptr *dynptr, void *context)
 {
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to read before the pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_bad_access1(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, bad_access1, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to read past the end of the pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_bad_access2(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, bad_access2, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to write to that pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_write_forbidden(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, write_forbidden, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to write to that pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_null_context_write(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, null_context_write, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to write to that pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_null_context_read(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, null_context_read, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to read past the end of the pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_discard_dynptr(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, try_discard_dynptr, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to read past the end of the pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_submit_dynptr(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, try_submit_dynptr, NULL, 0);
···
 /* A callback that accesses a dynptr in a bpf_user_ringbuf_drain callback should
  * not be able to write to that pointer.
  */
-SEC("?raw_tp/sys_nanosleep")
+SEC("?raw_tp/")
 int user_ringbuf_callback_invalid_return(void *ctx)
 {
 	bpf_user_ringbuf_drain(&user_ringbuf, invalid_drain_callback_return, NULL, 0);
 
+	return 0;
+}
+
+static long
+try_reinit_dynptr_mem(struct bpf_dynptr *dynptr, void *context)
+{
+	bpf_dynptr_from_mem(&map_value, 4, 0, dynptr);
+	return 0;
+}
+
+static long
+try_reinit_dynptr_ringbuf(struct bpf_dynptr *dynptr, void *context)
+{
+	bpf_ringbuf_reserve_dynptr(&ringbuf, 8, 0, dynptr);
+	return 0;
+}
+
+SEC("?raw_tp/")
+int user_ringbuf_callback_reinit_dynptr_mem(void *ctx)
+{
+	bpf_user_ringbuf_drain(&user_ringbuf, try_reinit_dynptr_mem, NULL, 0);
+	return 0;
+}
+
+SEC("?raw_tp/")
+int user_ringbuf_callback_reinit_dynptr_ringbuf(void *ctx)
+{
+	bpf_user_ringbuf_drain(&user_ringbuf, try_reinit_dynptr_ringbuf, NULL, 0);
 	return 0;
 }