HID: Intel-thc-hid: Intel-thc: Add safety check for reading DMA buffer

Add DMA buffer readiness check before reading DMA buffer to avoid
unexpected NULL pointer accessing.

Signed-off-by: Even Xu <even.xu@intel.com>
Tested-by: Rui Zhang <rui1.zhang@intel.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Author: Evenxf

drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c

@@ -575,6 +575,11 @@ static int read_dma_buffer(struct thc_device *dev,
 		return -EINVAL;
 	}
 
+	if (!read_config->prd_tbls || !read_config->sgls[prd_table_index]) {
+		dev_err_once(dev->dev, "PRD tables are not ready yet\n");
+		return -EINVAL;
+	}
+
 	prd_tbl = &read_config->prd_tbls[prd_table_index];
 	mes_len = calc_message_len(prd_tbl, &nent);
 	if (mes_len > read_config->max_packet_size) {