selftests/bpf: add extra test for using dynptr data slice after release

Add an additional test, "data_slice_use_after_release2", for ensuring
that data slices are correctly invalidated by the verifier after the
dynptr whose ref obj id they track is released. In particular, this
tests data slice invalidation for dynptrs located at a non-zero offset
from the frame pointer.
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/r/20220809214055.4050604-2-joannelkoong@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -22,7 +22,8 @@ static struct {
 	{"add_dynptr_to_map2", "invalid indirect read from stack"},
 	{"data_slice_out_of_bounds_ringbuf", "value is outside of the allowed memory range"},
 	{"data_slice_out_of_bounds_map_value", "value is outside of the allowed memory range"},
-	{"data_slice_use_after_release", "invalid mem access 'scalar'"},
+	{"data_slice_use_after_release1", "invalid mem access 'scalar'"},
+	{"data_slice_use_after_release2", "invalid mem access 'scalar'"},
 	{"data_slice_missing_null_check1", "invalid mem access 'mem_or_null'"},
 	{"data_slice_missing_null_check2", "invalid mem access 'mem_or_null'"},
 	{"invalid_helper1", "invalid indirect read from stack"},

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

@@ -248,7 +248,7 @@ int data_slice_out_of_bounds_map_value(void *ctx)
 
 /* A data slice can't be used after it has been released */
 SEC("?raw_tp")
-int data_slice_use_after_release(void *ctx)
+int data_slice_use_after_release1(void *ctx)
 {
 	struct bpf_dynptr ptr;
 	struct sample *sample;
@@ -272,6 +272,42 @@ int data_slice_use_after_release(void *ctx)
 	return 0;
 }
 
+/* A data slice can't be used after it has been released.
+ *
+ * This tests the case where the data slice tracks a dynptr (ptr2)
+ * that is at a non-zero offset from the frame pointer (ptr1 is at fp,
+ * ptr2 is at fp - 16).
+ */
+SEC("?raw_tp")
+int data_slice_use_after_release2(void *ctx)
+{
+	struct bpf_dynptr ptr1, ptr2;
+	struct sample *sample;
+
+	bpf_ringbuf_reserve_dynptr(&ringbuf, 64, 0, &ptr1);
+	bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(*sample), 0, &ptr2);
+
+	sample = bpf_dynptr_data(&ptr2, 0, sizeof(*sample));
+	if (!sample)
+		goto done;
+
+	sample->pid = 23;
+
+	bpf_ringbuf_submit_dynptr(&ptr2, 0);
+
+	/* this should fail */
+	sample->pid = 23;
+
+	bpf_ringbuf_submit_dynptr(&ptr1, 0);
+
+	return 0;
+
+done:
+	bpf_ringbuf_discard_dynptr(&ptr2, 0);
+	bpf_ringbuf_discard_dynptr(&ptr1, 0);
+	return 0;
+}
+
 /* A data slice must be first checked for NULL */
 SEC("?raw_tp")
 int data_slice_missing_null_check1(void *ctx)