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: f9d690b6 ("tty: serial: qcom_geni_serial: Allocate port->rx_fifo buffer in probe")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221221164022.1087814-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>