spi: spi-zynqmp-gqspi: fix use-after-free in zynqmp_qspi_exec_op

When handling op->addr, it is using the buffer "tmpbuf" which has been
freed. This will trigger a use-after-free KASAN warning. Let's use
temporary variables to store op->addr.val and op->cmd.opcode to fix
this issue.

Fixes: 1c26372e5a ("spi: spi-zynqmp-gqspi: Update driver to use spi-mem framework")
Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Link: https://lore.kernel.org/r/20210416004652.2975446-5-quanyang.wang@windriver.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-zynqmp-gqspi.c

@@ -928,8 +928,9 @@ static int zynqmp_qspi_exec_op(struct spi_mem *mem,
 	struct zynqmp_qspi *xqspi = spi_controller_get_devdata
 				    (mem->spi->master);
 	int err = 0, i;
-	u8 *tmpbuf;
 	u32 genfifoentry = 0;
+	u16 opcode = op->cmd.opcode;
+	u64 opaddr;
 
 	dev_dbg(xqspi->dev, "cmd:%#x mode:%d.%d.%d.%d\n",
 		op->cmd.opcode, op->cmd.buswidth, op->addr.buswidth,
@@ -942,14 +943,8 @@ static int zynqmp_qspi_exec_op(struct spi_mem *mem,
 	genfifoentry |= xqspi->genfifobus;
 
 	if (op->cmd.opcode) {
-		tmpbuf = kzalloc(op->cmd.nbytes, GFP_KERNEL | GFP_DMA);
-		if (!tmpbuf) {
-			mutex_unlock(&xqspi->op_lock);
-			return -ENOMEM;
-		}
-		tmpbuf[0] = op->cmd.opcode;
 		reinit_completion(&xqspi->data_completion);
-		xqspi->txbuf = tmpbuf;
+		xqspi->txbuf = &opcode;
 		xqspi->rxbuf = NULL;
 		xqspi->bytes_to_transfer = op->cmd.nbytes;
 		xqspi->bytes_to_receive = 0;
@@ -963,13 +958,12 @@ static int zynqmp_qspi_exec_op(struct spi_mem *mem,
 		if (!wait_for_completion_timeout
 		    (&xqspi->data_completion, msecs_to_jiffies(1000))) {
 			err = -ETIMEDOUT;
-			kfree(tmpbuf);
 			goto return_err;
 		}
-		kfree(tmpbuf);
 	}
 
 	if (op->addr.nbytes) {
+		xqspi->txbuf = &opaddr;
 		for (i = 0; i < op->addr.nbytes; i++) {
 			*(((u8 *)xqspi->txbuf) + i) = op->addr.val >>
 					(8 * (op->addr.nbytes - i - 1));