mtk-sd: Prevent memory corruption from DMA map failure

If msdc_prepare_data() fails to map the DMA region, the request is
not prepared for data receiving, but msdc_start_data() proceeds
the DMA with previous setting.
Since this will lead a memory corruption, we have to stop the
request operation soon after the msdc_prepare_data() fails to
prepare it.

Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>
Fixes: 208489032bdd ("mmc: mediatek: Add Mediatek MMC driver")
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/mtk-sd.c

···
 	}
 }
 
+static bool msdc_data_prepared(struct mmc_data *data)
+{
+	return data->host_cookie & MSDC_PREPARE_FLAG;
+}
+
 static void msdc_unprepare_data(struct msdc_host *host, struct mmc_data *data)
 {
 	if (data->host_cookie & MSDC_ASYNC_FLAG)
···
 	WARN_ON(!host->hsq_en && host->mrq);
 	host->mrq = mrq;
 
-	if (mrq->data)
+	if (mrq->data) {
 		msdc_prepare_data(host, mrq->data);
+		if (!msdc_data_prepared(mrq->data)) {
+			/*
+			 * Failed to prepare DMA area, fail fast before
+			 * starting any commands.
+			 */
+			mrq->cmd->error = -ENOSPC;
+			mmc_request_done(mmc_from_priv(host), mrq);
+			return;
+		}
+	}
 
 	/* if SBC is required, we have HW option and SW option.
 	 * if HW option is enabled, and SBC does not have "special" flags,