Re: [PATCH] comedi: drivers: ni_tio: Fix arithmetic expression overflow

[Ian Abbott]

On 18/01/2024 09:32, Greg Kroah-Hartman wrote:
> On Thu, Jan 18, 2024 at 10:36:19AM +0300, Denis Arefev wrote:
> > The value of an arithmetic expression period_ns * 1000 is subject
> > to overflow due to a failure to cast operands to a larger data
> > type before performing arithmetic
> >
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >
> > Reviewed-by: Ian Abbott <abbotti@xxxxxxxxx>
> > Signed-off-by: Denis Arefev <arefev@xxxxxxxxx>
> > ---
> >   drivers/comedi/drivers/ni_tio.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/comedi/drivers/ni_tio.c b/drivers/comedi/drivers/ni_tio.c
> > index da6826d77e60..acc914903c70 100644
> > --- a/drivers/comedi/drivers/ni_tio.c
> > +++ b/drivers/comedi/drivers/ni_tio.c
> > @@ -800,7 +800,7 @@ static int ni_tio_set_clock_src(struct ni_gpct *counter,
> >   				GI_PRESCALE_X2(counter_dev->variant) |
> >   				GI_PRESCALE_X8(counter_dev->variant), bits);
> >   	}
> > -	counter->clock_period_ps = period_ns * 1000;
> > +	counter->clock_period_ps = period_ns * 1000UL;
>
> Can period_ns ever be "too big" to cause such an overflow?

The period_ns value comes from user-space and could be any unsigned int 
value.  It's used to let the driver know the period of an external clock 
source.

> And what commit id does this fix?

Fixes: 3e90b1c7ebe9 ("staging: comedi: ni_tio: tidy up 
ni_tio_set_clock_src() and helpers")
Cc: <stable@xxxxxxxxxxxxxxx> # v5.15+

The first affected kernel version is v3.17.  This patch should apply 
cleanly to v5.13 onwards (when comedi was moved out of drivers/staging), 
but earlier stable/longterm kernels would require a backported patch.

@Denis, if you could add the above Fixes: and Cc: lines to a v2 patch, 
that would be great!

> thanks,
>
> greg k-h

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