[PATCH 1/2] spi: spi-mt65xx: Fix NULL pointer access in interrupt handler

[Fei Shao]

The TX buffer in spi_transfer can be a NULL pointer, so the interrupt
handler may end up writing to the invalid memory and cause crashes.

Add a check to xfer->tx_buf before using it.

Fixes: 1ce24864bff4 ("spi: mediatek: Only do dma for 4-byte aligned buffers")
Signed-off-by: Fei Shao <fshao@xxxxxxxxxxxx>
---

 drivers/spi/spi-mt65xx.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
index 8d4633b353ee..86ea822c942b 100644
--- a/drivers/spi/spi-mt65xx.c
+++ b/drivers/spi/spi-mt65xx.c
@@ -788,17 +788,18 @@ static irqreturn_t mtk_spi_interrupt(int irq, void *dev_id)
 		mdata->xfer_len = min(MTK_SPI_MAX_FIFO_SIZE, len);
 		mtk_spi_setup_packet(host);
 
-		cnt = mdata->xfer_len / 4;
-		iowrite32_rep(mdata->base + SPI_TX_DATA_REG,
-				trans->tx_buf + mdata->num_xfered, cnt);
+		if (trans->tx_buf) {
+			cnt = mdata->xfer_len / 4;
+			iowrite32_rep(mdata->base + SPI_TX_DATA_REG,
+					trans->tx_buf + mdata->num_xfered, cnt);
 
-		remainder = mdata->xfer_len % 4;
-		if (remainder > 0) {
-			reg_val = 0;
-			memcpy(&reg_val,
-				trans->tx_buf + (cnt * 4) + mdata->num_xfered,
-				remainder);
-			writel(reg_val, mdata->base + SPI_TX_DATA_REG);
+			remainder = mdata->xfer_len % 4;
+			if (remainder > 0) {
+				reg_val = 0;
+				memcpy(&reg_val,
+					trans->tx_buf + (cnt * 4) + mdata->num_xfered,
+					remainder);
+				writel(reg_val, mdata->base + SPI_TX_DATA_REG);
 		}
 
 		mtk_spi_enable_transfer(host);
-- 
2.44.0.396.g6e790dbe36-goog