spi: bcm2835: bcm2835_spi_handle_err(): fix NULL pointer deref for non DMA transfers

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2071848
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2122415

commit 4ceaa68
Author: Marc Kleine-Budde <mkl@pengutronix.de>
Date: Tue, 19 Jul 2022 09:22:35 +0200

    In case a IRQ based transfer times out the bcm2835_spi_handle_err()
    function is called. Since commit 1513cee ("spi: bcm2835: Drop
    dma_pending flag") the TX and RX DMA transfers are unconditionally
    canceled, leading to NULL pointer derefs if ctlr->dma_tx or
    ctlr->dma_rx are not set.

    Fix the NULL pointer deref by checking that ctlr->dma_tx and
    ctlr->dma_rx are valid pointers before accessing them.

    Fixes: 1513cee ("spi: bcm2835: Drop dma_pending flag")
    Cc: Lukas Wunner <lukas@wunner.de>
    Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
    Link: https://lore.kernel.org/r/20220719072234.2782764-1-mkl@pengutronix.de
    Signed-off-by: Mark Brown <broonie@kernel.org>

Signed-off-by: Mark Salter <msalter@redhat.com>

Author: mosalter

drivers/spi/spi-bcm2835.c

@@ -1138,10 +1138,14 @@ static void bcm2835_spi_handle_err(struct spi_controller *ctlr,
 	struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr);
 
 	/* if an error occurred and we have an active dma, then terminate */
-	dmaengine_terminate_sync(ctlr->dma_tx);
-	bs->tx_dma_active = false;
-	dmaengine_terminate_sync(ctlr->dma_rx);
-	bs->rx_dma_active = false;
+	if (ctlr->dma_tx) {
+		dmaengine_terminate_sync(ctlr->dma_tx);
+		bs->tx_dma_active = false;
+	}
+	if (ctlr->dma_rx) {
+		dmaengine_terminate_sync(ctlr->dma_rx);
+		bs->rx_dma_active = false;
+	}
 	bcm2835_spi_undo_prologue(bs);
 
 	/* and reset */