[PATCH] tty: serial: qcom-geni-serial: fix slab-out-of-bounds on RX FIFO buffer

[Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>]

Driver's probe allocates memory for RX FIFO (port->rx_fifo) based on
default RX FIFO depth, e.g. 16.  Later during serial startup the
qcom_geni_serial_port_setup() updates the RX FIFO depth
(port->rx_fifo_depth) to match real device capabilities, e.g. to 32.

The RX UART handle code will read "port->rx_fifo_depth" number of words
into "port->rx_fifo" buffer, thus exceeding the bounds.  This can be
observed in certain configurations with Qualcomm Bluetooth HCI UART
device and KASAN:

  Bluetooth: hci0: QCA Product ID   :0x00000010
  Bluetooth: hci0: QCA SOC Version  :0x400a0200
  Bluetooth: hci0: QCA ROM Version  :0x00000200
  Bluetooth: hci0: QCA Patch Version:0x00000d2b
  Bluetooth: hci0: QCA controller version 0x02000200
  Bluetooth: hci0: QCA Downloading qca/htbtfw20.tlv
  bluetooth hci0: Direct firmware load for qca/htbtfw20.tlv failed with error -2
  Bluetooth: hci0: QCA Failed to request file: qca/htbtfw20.tlv (-2)
  Bluetooth: hci0: QCA Failed to download patch (-2)
  ==================================================================
  BUG: KASAN: slab-out-of-bounds in handle_rx_uart+0xa8/0x18c
  Write of size 4 at addr ffff279347d578c0 by task swapper/0/0

  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.1.0-rt5-00350-gb2450b7e00be-dirty #26
  Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
  Call trace:
   dump_backtrace.part.0+0xe0/0xf0
   show_stack+0x18/0x40
   dump_stack_lvl+0x8c/0xb8
   print_report+0x188/0x488
   kasan_report+0xb4/0x100
   __asan_store4+0x80/0xa4
   handle_rx_uart+0xa8/0x18c
   qcom_geni_serial_handle_rx+0x84/0x9c
   qcom_geni_serial_isr+0x24c/0x760
   __handle_irq_event_percpu+0x108/0x500
   handle_irq_event+0x6c/0x110
   handle_fasteoi_irq+0x138/0x2cc
   generic_handle_domain_irq+0x48/0x64

If the RX FIFO depth changes after probe, be sure to resize the buffer.

Fixes: f9d690b6ece7 ("tty: serial: qcom_geni_serial: Allocate port->rx_fifo buffer in probe")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 drivers/tty/serial/qcom_geni_serial.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index b487823f0e61..1568fe69e3e8 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -864,9 +864,10 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
 	return IRQ_HANDLED;
 }
 
-static void get_tx_fifo_size(struct qcom_geni_serial_port *port)
+static int get_tx_fifo_size(struct qcom_geni_serial_port *port)
 {
 	struct uart_port *uport;
+	u32 old_rx_fifo_depth = port->rx_fifo_depth;
 
 	uport = &port->uport;
 	port->tx_fifo_depth = geni_se_get_tx_fifo_depth(&port->se);
@@ -874,6 +875,16 @@ static void get_tx_fifo_size(struct qcom_geni_serial_port *port)
 	port->rx_fifo_depth = geni_se_get_rx_fifo_depth(&port->se);
 	uport->fifosize =
 		(port->tx_fifo_depth * port->tx_fifo_width) / BITS_PER_BYTE;
+
+	if (port->rx_fifo && (old_rx_fifo_depth != port->rx_fifo_depth) && port->rx_fifo_depth) {
+		port->rx_fifo = devm_krealloc(uport->dev, port->rx_fifo,
+					      port->rx_fifo_depth * sizeof(u32),
+					      GFP_KERNEL);
+		if (!port->rx_fifo)
+			return -ENOMEM;
+	}
+
+	return 0;
 }
 
 
@@ -888,6 +899,7 @@ static int qcom_geni_serial_port_setup(struct uart_port *uport)
 	u32 rxstale = DEFAULT_BITS_PER_CHAR * STALE_TIMEOUT;
 	u32 proto;
 	u32 pin_swap;
+	int ret;
 
 	proto = geni_se_read_proto(&port->se);
 	if (proto != GENI_SE_UART) {
@@ -897,7 +909,9 @@ static int qcom_geni_serial_port_setup(struct uart_port *uport)
 
 	qcom_geni_serial_stop_rx(uport);
 
-	get_tx_fifo_size(port);
+	ret = get_tx_fifo_size(port);
+	if (ret)
+		return ret;
 
 	writel(rxstale, uport->membase + SE_UART_RX_STALE_CNT);
 
-- 
2.34.1