[PATCH v2] Input: usbtouchscreen - add driver_info sanity check

[Johan Hovold <johan@kernel.org>]

Add a sanity check on the device id-table driver_info field to make sure
we never access a type structure (and function pointers) outside of the
device info array (e.g. if someone fails to ifdef a device-id entry).

Note that this also suppresses a compiler warning with -Warray-bounds
(gcc-11.3.0) when compile-testing the driver without enabling any of
the device type Kconfig options:

    drivers/input/touchscreen/usbtouchscreen.c: In function 'usbtouch_probe':
    drivers/input/touchscreen/usbtouchscreen.c:1668:16:warning: array subscript <unknown> is outside array bounds of 'struct usbtouch_device_info[0]' [-Warray-bounds]
     1668 |         type = &usbtouch_dev_info[id->driver_info];

Signed-off-by: Johan Hovold <johan@kernel.org>
---

Changes in v2
 - use ARRAY_SIZE() for the sanity check (Dmitry)
 - drop the dummy entry and combine the two patches as the sanity check
   itself is enough to suppress the compiler warning (Dmitry)
 - use -ENODEV instead of -EINVAL even if this means no error will be
   logged in the unlikely event of a future driver bug


 drivers/input/touchscreen/usbtouchscreen.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/input/touchscreen/usbtouchscreen.c b/drivers/input/touchscreen/usbtouchscreen.c
index 43c521f50c85..b01d026588c8 100644
--- a/drivers/input/touchscreen/usbtouchscreen.c
+++ b/drivers/input/touchscreen/usbtouchscreen.c
@@ -1654,6 +1654,9 @@ static int usbtouch_probe(struct usb_interface *intf,
 	if (id->driver_info == DEVTYPE_IGNORE)
 		return -ENODEV;
 
+	if (id->driver_info >= ARRAY_SIZE(usbtouch_dev_info))
+                return -ENODEV;
+
 	endpoint = usbtouch_get_input_endpoint(intf->cur_altsetting);
 	if (!endpoint)
 		return -ENXIO;
-- 
2.35.1