hw/display/virtio-gpu: Fix memory leak (CID 1453811)

To avoid leaking memory on the error path, reorder the
code as:
- check the parameters first
- check resource already existing
- finally allocate memory

Reported-by: Coverity (CID 1453811: RESOURCE_LEAK)
Fixes: e0933d91 ("virtio-gpu: Add virtio_gpu_resource_create_blob")
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210531101928.1662732-1-philmd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/virtio-gpu.c

@@ -340,37 +340,31 @@ static void virtio_gpu_resource_create_blob(VirtIOGPU *g,
         return;
     }
 
-    res = virtio_gpu_find_resource(g, cblob.resource_id);
-    if (res) {
-        qemu_log_mask(LOG_GUEST_ERROR, "%s: resource already exists %d\n",
-                      __func__, cblob.resource_id);
-        cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_RESOURCE_ID;
-        return;
-    }
-
-    res = g_new0(struct virtio_gpu_simple_resource, 1);
-    res->resource_id = cblob.resource_id;
-    res->blob_size = cblob.size;
-
     if (cblob.blob_mem != VIRTIO_GPU_BLOB_MEM_GUEST &&
         cblob.blob_flags != VIRTIO_GPU_BLOB_FLAG_USE_SHAREABLE) {
         qemu_log_mask(LOG_GUEST_ERROR, "%s: invalid memory type\n",
                       __func__);
         cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER;
-        g_free(res);
         return;
     }
 
-    if (res->iov) {
-        cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
+    if (virtio_gpu_find_resource(g, cblob.resource_id)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: resource already exists %d\n",
+                      __func__, cblob.resource_id);
+        cmd->error = VIRTIO_GPU_RESP_ERR_INVALID_RESOURCE_ID;
         return;
     }
 
+    res = g_new0(struct virtio_gpu_simple_resource, 1);
+    res->resource_id = cblob.resource_id;
+    res->blob_size = cblob.size;
+
     ret = virtio_gpu_create_mapping_iov(g, cblob.nr_entries, sizeof(cblob),
                                         cmd, &res->addrs, &res->iov,
                                         &res->iov_cnt);
-    if (ret != 0) {
+    if (ret != 0 || res->iov) {
         cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
+        g_free(res);
         return;
     }