[PATCH] HID: multitouch: fix integer overflow in set_abs()

[Qasim Ijaz <qasdev00@gmail.com>]

It is possible for a malicious HID device to trigger a signed integer
overflow (undefined behaviour) in set_abs() in the following expression
by supplying bogus logical maximum and minimum values:
	
	int fuzz = snratio ? (fmax - fmin) / snratio : 0;

For example, if the logical_maximum is INT_MAX and logical_minimum is -1
then (fmax - fmin) resolves to INT_MAX + 1, which does not fit in a 32-bit
signed int, so the subtraction overflows. Fix this by computing the 
difference in a 64 bit context.

Fixes: 5519cab477b6 ("HID: hid-multitouch: support for PixCir-based panels")
Cc: stable@vger.kernel.org
Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
---
 drivers/hid/hid-multitouch.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 22c6314a8843..687638ed6d0f 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -540,7 +540,8 @@ static void set_abs(struct input_dev *input, unsigned int code,
 {
 	int fmin = field->logical_minimum;
 	int fmax = field->logical_maximum;
-	int fuzz = snratio ? (fmax - fmin) / snratio : 0;
+	s64 diff = (s64)fmax - (s64)fmin;
+	int fuzz = snratio ? (int)div_s64(diff, snratio) : 0;
 	input_set_abs_params(input, code, fmin, fmax, fuzz, 0);
 	input_abs_set_res(input, code, hidinput_calc_abs_res(field, code));
 }
-- 
2.39.5