[PATCH v2] tty: serial: pch_uart: add check for dma_alloc_coherent()

[Zhaoyang Yu <2426767509@qq.com>]

Add a check for dma_alloc_coherent() failure to prevent a potential
NULL pointer dereference in dma_handle_rx(). Properly release DMA
channels and the PCI device reference using a goto ladder if the
allocation fails.

Fixes: 3c6a483275f4 ("Serial: EG20T: add PCH_UART driver")
Cc: stable@vger.kernel.org
Signed-off-by: Zhaoyang Yu <2426767509@qq.com>
---
Changes in v2:
- Added the Fixes tag for the initial PCH_UART driver commit, per Andy's review.

 drivers/tty/serial/pch_uart.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index 6729d8e83c3c..ba1fcd663fe2 100644
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -689,8 +689,7 @@ static void pch_request_dma(struct uart_port *port)
 	if (!chan) {
 		dev_err(priv->port.dev, "%s:dma_request_channel FAILS(Tx)\n",
 			__func__);
-		pci_dev_put(dma_dev);
-		return;
+		goto err_pci_get;
 	}
 	priv->chan_tx = chan;
 
@@ -704,18 +703,26 @@ static void pch_request_dma(struct uart_port *port)
 	if (!chan) {
 		dev_err(priv->port.dev, "%s:dma_request_channel FAILS(Rx)\n",
 			__func__);
-		dma_release_channel(priv->chan_tx);
-		priv->chan_tx = NULL;
-		pci_dev_put(dma_dev);
-		return;
+		goto err_req_tx;
 	}
 
 	/* Get Consistent memory for DMA */
 	priv->rx_buf_virt = dma_alloc_coherent(port->dev, port->fifosize,
 				    &priv->rx_buf_dma, GFP_KERNEL);
+	if (!priv->rx_buf_virt)
+		goto err_req_rx;
 	priv->chan_rx = chan;
 
 	pci_dev_put(dma_dev);
+	return;
+
+err_req_rx:
+	dma_release_channel(chan);
+err_req_tx:
+	dma_release_channel(priv->chan_tx);
+	priv->chan_tx = NULL;
+err_pci_get:
+	pci_dev_put(dma_dev);
 }
 
 static void pch_dma_rx_complete(void *arg)
-- 
2.50.1