migration/vmstate: fix array of ptr with nullptrs
Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the
reward for trying to migrate an array with some null pointers in it was
an illegal memory access, that is a swift and painless death of the
process. Let's make vmstate cope with this scenario.
The general approach is, when we encounter a null pointer (element),
instead of following the pointer to save/load the data behind it, we
save/load a placeholder. This way we can detect if we expected a null
pointer at the load side but not null data was saved instead.
Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170222160119.52771-4-pasic@linux.vnet.ibm.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 63e7b02..f2dbf84 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -253,6 +253,10 @@
extern const VMStateInfo vmstate_info_uint32;
extern const VMStateInfo vmstate_info_uint64;
+/** Put this in the stream when migrating a null pointer.*/
+#define VMS_NULLPTR_MARKER (0x30U) /* '0' */
+extern const VMStateInfo vmstate_info_nullptr;
+
extern const VMStateInfo vmstate_info_float64;
extern const VMStateInfo vmstate_info_cpudouble;
diff --git a/migration/vmstate.c b/migration/vmstate.c
index 836a7a4..78b3cd4 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -117,7 +117,11 @@
if (field->flags & VMS_ARRAY_OF_POINTER) {
curr_elem = *(void **)curr_elem;
}
- if (field->flags & VMS_STRUCT) {
+ if (!curr_elem) {
+ /* if null pointer check placeholder and do not follow */
+ assert(field->flags & VMS_ARRAY_OF_POINTER);
+ ret = vmstate_info_nullptr.get(f, curr_elem, size, NULL);
+ } else if (field->flags & VMS_STRUCT) {
ret = vmstate_load_state(f, field->vmsd, curr_elem,
field->vmsd->version_id);
} else {
@@ -332,7 +336,11 @@
assert(curr_elem);
curr_elem = *(void **)curr_elem;
}
- if (field->flags & VMS_STRUCT) {
+ if (!curr_elem) {
+ /* if null pointer write placeholder and do not follow */
+ assert(field->flags & VMS_ARRAY_OF_POINTER);
+ vmstate_info_nullptr.put(f, curr_elem, size, NULL, NULL);
+ } else if (field->flags & VMS_STRUCT) {
vmstate_save_state(f, field->vmsd, curr_elem, vmdesc_loop);
} else {
field->info->put(f, curr_elem, size, field, vmdesc_loop);
@@ -747,6 +755,34 @@
.put = put_uint64,
};
+static int get_nullptr(QEMUFile *f, void *pv, size_t size, VMStateField *field)
+
+{
+ if (qemu_get_byte(f) == VMS_NULLPTR_MARKER) {
+ return 0;
+ }
+ error_report("vmstate: get_nullptr expected VMS_NULLPTR_MARKER");
+ return -EINVAL;
+}
+
+static int put_nullptr(QEMUFile *f, void *pv, size_t size,
+ VMStateField *field, QJSON *vmdesc)
+
+{
+ if (pv == NULL) {
+ qemu_put_byte(f, VMS_NULLPTR_MARKER);
+ return 0;
+ }
+ error_report("vmstate: put_nullptr must be called with pv == NULL");
+ return -EINVAL;
+}
+
+const VMStateInfo vmstate_info_nullptr = {
+ .name = "uint64",
+ .get = get_nullptr,
+ .put = put_nullptr,
+};
+
/* 64 bit unsigned int. See that the received value is the same than the one
in the field */
