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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>
This commit is contained in:
Halil Pasic 2017-02-22 17:01:17 +01:00 committed by Dr. David Alan Gilbert
parent cbfda0e6cf
commit 07d4e69147
2 changed files with 42 additions and 2 deletions
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4
include/migration/vmstate.h
View File

@ -253,6 +253,10 @@ extern const VMStateInfo vmstate_info_uint16;
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;

40
migration/vmstate.c
View File

@ -117,7 +117,11 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
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 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
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 @@ const VMStateInfo vmstate_info_uint64 = {
.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 */