Re: [PATCH] staging: comedi: dt2811: fix integer overflow in multiply
On Sun, Feb 03, 2019 at 02:29:04PM +0300, Dan Carpenter wrote:
> > diff --git a/drivers/staging/comedi/drivers/dt2811.c
> > b/drivers/staging/comedi/drivers/dt2811.c
> > index 05207a519755..820e75f850ff 100644
> > --- a/drivers/staging/comedi/drivers/dt2811.c
> > +++ b/drivers/staging/comedi/drivers/dt2811.c
> > @@ -323,7 +323,8 @@ static unsigned int dt2811_ns_to_timer(unsigned int
> > *nanosec,
> > for (_mult = 0; _mult <= 7; _mult++) {
> > unsigned int div = dt2811_clk_dividers[_div];
> > unsigned int mult = dt2811_clk_multipliers[_mult];
> > - unsigned long long divider = div * mult;
> > + unsigned long long divider =
> > + (unsigned long long)div * mult;
>
> The max "div" can be is 12. The max "mult" can be is 10,000,000. So
> this is a false positive because there is no overflow. The code is not
> complicated. Unfortunately, Smatch has the exact same problem...
Smatch actually parses this correctly, but I had a power failure over
the weekend that messed up my results.
regards,
dan carpenter
Re: [PATCH] staging: comedi: dt2811: fix integer overflow in multiply
On Sat, Feb 02, 2019 at 09:59:16PM +, Colin King wrote:
> From: Colin Ian King
>
> Multiplying two unsigned ints leads to an unsigned int result. The
> intention is that the result is a unsigned long long, so to fix the
> overflow cast the div to an unsigned long long to ensure that the
> multiplication is on unsigned long longs to avoid overflow.
>
> Detected by CoverityScan, CID#1357597 ("Unintentioal integer overflow")
>
> Fixes: f2975a9b2ab9 ("staging: comedi: dt2811: add async command support for
> AI subdevice")
> Signed-off-by: Colin Ian King
> ---
> drivers/staging/comedi/drivers/dt2811.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/staging/comedi/drivers/dt2811.c
> b/drivers/staging/comedi/drivers/dt2811.c
> index 05207a519755..820e75f850ff 100644
> --- a/drivers/staging/comedi/drivers/dt2811.c
> +++ b/drivers/staging/comedi/drivers/dt2811.c
> @@ -323,7 +323,8 @@ static unsigned int dt2811_ns_to_timer(unsigned int
> *nanosec,
> for (_mult = 0; _mult <= 7; _mult++) {
> unsigned int div = dt2811_clk_dividers[_div];
> unsigned int mult = dt2811_clk_multipliers[_mult];
> - unsigned long long divider = div * mult;
> + unsigned long long divider =
> + (unsigned long long)div * mult;
The max "div" can be is 12. The max "mult" can be is 10,000,000. So
this is a false positive because there is no overflow. The code is not
complicated. Unfortunately, Smatch has the exact same problem...
We should fix the checker instead of the code.
regards,
dan carpenter
[PATCH] staging: comedi: dt2811: fix integer overflow in multiply
From: Colin Ian King
Multiplying two unsigned ints leads to an unsigned int result. The
intention is that the result is a unsigned long long, so to fix the
overflow cast the div to an unsigned long long to ensure that the
multiplication is on unsigned long longs to avoid overflow.
Detected by CoverityScan, CID#1357597 ("Unintentioal integer overflow")
Fixes: f2975a9b2ab9 ("staging: comedi: dt2811: add async command support for AI
subdevice")
Signed-off-by: Colin Ian King
---
drivers/staging/comedi/drivers/dt2811.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/staging/comedi/drivers/dt2811.c
b/drivers/staging/comedi/drivers/dt2811.c
index 05207a519755..820e75f850ff 100644
--- a/drivers/staging/comedi/drivers/dt2811.c
+++ b/drivers/staging/comedi/drivers/dt2811.c
@@ -323,7 +323,8 @@ static unsigned int dt2811_ns_to_timer(unsigned int
*nanosec,
for (_mult = 0; _mult <= 7; _mult++) {
unsigned int div = dt2811_clk_dividers[_div];
unsigned int mult = dt2811_clk_multipliers[_mult];
- unsigned long long divider = div * mult;
+ unsigned long long divider =
+ (unsigned long long)div * mult;
unsigned int divisor = DT2811_TMRCTR_MANTISSA(_div) |
DT2811_TMRCTR_EXPONENT(_mult);
--
2.20.1
