hw/cxl: Check size of input data to dynamic capacity mailbox commands

cxl_cmd_dcd_release_dyn_cap() and cmd_dcd_add_dyn_cap_rsp() are missing
input message size checks.  These must be done in the individual
commands when the command has a variable length input payload.

A buggy or malicious guest might send undersized messages via the mailbox.
As that size is used to take a copy of the mailbox content, each command
must check there is sufficient data. In this case the first check is that
there is enough data to read how many extents there are, and the second
that there is enough for those elements to be accessed.

Reported-by: Esifiel <esifiel@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20241101133917.27634-2-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/cxl/cxl-mailbox-utils.c

@@ -2465,11 +2465,20 @@ static CXLRetCode cmd_dcd_add_dyn_cap_rsp(const struct cxl_cmd *cmd,
     uint64_t dpa, len;
     CXLRetCode ret;
 
+    if (len_in < sizeof(*in)) {
+        return CXL_MBOX_INVALID_PAYLOAD_LENGTH;
+    }
+
     if (in->num_entries_updated == 0) {
         cxl_extent_group_list_delete_front(&ct3d->dc.extents_pending);
         return CXL_MBOX_SUCCESS;
     }
 
+    if (len_in <
+        sizeof(*in) + sizeof(*in->updated_entries) * in->num_entries_updated) {
+        return CXL_MBOX_INVALID_PAYLOAD_LENGTH;
+    }
+
     /* Adding extents causes exceeding device's extent tracking ability. */
     if (in->num_entries_updated + ct3d->dc.total_extent_count >
         CXL_NUM_EXTENTS_SUPPORTED) {
@@ -2624,10 +2633,19 @@ static CXLRetCode cmd_dcd_release_dyn_cap(const struct cxl_cmd *cmd,
     uint32_t updated_list_size;
     CXLRetCode ret;
 
+    if (len_in < sizeof(*in)) {
+        return CXL_MBOX_INVALID_PAYLOAD_LENGTH;
+    }
+
     if (in->num_entries_updated == 0) {
         return CXL_MBOX_INVALID_INPUT;
     }
 
+    if (len_in <
+        sizeof(*in) + sizeof(*in->updated_entries) * in->num_entries_updated) {
+        return CXL_MBOX_INVALID_PAYLOAD_LENGTH;
+    }
+
     ret = cxl_detect_malformed_extent_list(ct3d, in);
     if (ret != CXL_MBOX_SUCCESS) {
         return ret;