linux-5.3-rc4/drivers/staging/comedi/drivers/dt3000.c:373: (error) Signed integer overflow for expression 'divider*base'
abbotti at mev.co.uk
Mon Aug 12 10:14:19 UTC 2019
On 12/08/2019 08:37, David Binderman wrote:
> Hello there,
> Source code is
> prescale = 15;
> base = timer_base * (1 << prescale);
> divider = 65535;
> *nanosec = divider * base;
> timer_base seems to be 500 or 100.
> nanosec is a pointer to int, so it can only hold about 2,000,000,000 nanoseconds, or about 2 seconds.
Thanks for the report.
I couldn't reproduce the error with the compiler version I was using,
but I can see that it is likely to result in an arithmetic overflow.
I think the main problem is that the line (in (dt3k_ns_to_timer()):
base = timer_base * (1 << prescale);
base = timer_base * (prescale + 1);
which matches the earlier instance of this calculation in the same function.
In practice, these lines of code should never be reached due to earlier
range checks in dt3k_ai_cmdtest().
> Suggest rework code to use longs.
It wouldn't do any harm to change the `int` variables to `unsigned int`.
> David Binderman
> time-_Base seems to be 50 or 100.
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