[PATCH 4.4 55/78] staging: comedi: dt3000: Fix signed integer overflow divider * base

[Greg Kroah-Hartman]

From: Ian Abbott <abbo...@mev.co.uk>

commit b4d98bc3fc93ec3a58459948a2c0e0c9b501cd88 upstream.

In `dt3k_ns_to_timer()` the following lines near the end of the function
result in a signed integer overflow:

        prescale = 15;
        base = timer_base * (1 << prescale);
        divider = 65535;
        *nanosec = divider * base;

(`divider`, `base` and `prescale` are type `int`, `timer_base` and
`*nanosec` are type `unsigned int`.  The value of `timer_base` will be
either 50 or 100.)

The main reason for the overflow is that the calculation for `base` is
completely wrong.  It should be:

        base = timer_base * (prescale + 1);

which matches an earlier instance of this calculation in the same
function.

Reported-by: David Binderman <dcb...@hotmail.com>
Cc: <sta...@vger.kernel.org>
Signed-off-by: Ian Abbott <abbo...@mev.co.uk>
Link: https://lore.kernel.org/r/20190812111517.26803-1-abbo...@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/staging/comedi/drivers/dt3000.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/staging/comedi/drivers/dt3000.c
+++ b/drivers/staging/comedi/drivers/dt3000.c
@@ -377,7 +377,7 @@ static int dt3k_ns_to_timer(unsigned int
        }
 
        prescale = 15;
-       base = timer_base * (1 << prescale);
+       base = timer_base * (prescale + 1);
        divider = 65535;
        *nanosec = divider * base;
        return (prescale << 16) | (divider);