Quoting Hans Verkuil <hverkuil@xxxxxxxxx>:
On 01/30/2018 09:51 AM, Gustavo A. R. Silva wrote:
Hi Hans,
Quoting Hans Verkuil <hverkuil@xxxxxxxxx>:
Hi Gustavo,
On 01/30/2018 01:33 AM, Gustavo A. R. Silva wrote:
Cast len to const u64 in order to avoid a potential integer
overflow. This variable is being used in a context that expects
an expression of type const u64.
Addresses-Coverity-ID: 1454996 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
drivers/media/platform/vivid/vivid-cec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/media/platform/vivid/vivid-cec.c
b/drivers/media/platform/vivid/vivid-cec.c
index b55d278..30240ab 100644
--- a/drivers/media/platform/vivid/vivid-cec.c
+++ b/drivers/media/platform/vivid/vivid-cec.c
@@ -83,7 +83,7 @@ static void vivid_cec_pin_adap_events(struct
cec_adapter *adap, ktime_t ts,
if (adap == NULL)
return;
ts = ktime_sub_us(ts, (CEC_TIM_START_BIT_TOTAL +
- len * 10 * CEC_TIM_DATA_BIT_TOTAL));
+ (const u64)len * 10 * CEC_TIM_DATA_BIT_TOTAL));
This makes no sense. Certainly the const part is pointless. And given that
len is always <= 16 there definitely is no overflow.
Yeah, I understand your point and I know there is no chance of an
overflow in this particular case.
I don't really want this cast in the code.
Sorry,
I'm working through all the Linux kernel Coverity reports, and I
thought of sending a patch for this because IMHO it doesn't hurt to
give the compiler complete information about the arithmetic in which
an expression is intended to be evaluated.
I agree that the _const_ part is a bit odd. What do you think about
the cast to u64 alone?
What happens if you do: ((u64)CEC_TIM_START_BIT_TOTAL +
I think that forces everything else in the expression to be evaluated
as u64.
Well, in this case the operator precedence takes place and the
expression len * 10 * CEC_TIM_DATA_BIT_TOTAL is computed first. So the
issue remains the same.
I can switch the expressions as follows:
(u64)len * 10 * CEC_TIM_DATA_BIT_TOTAL + CEC_TIM_START_BIT_TOTAL
and avoid the cast in the middle.
What do you think?
It definitely needs a comment that this fixes a bogus Coverity report.
I actually added the following line to the message changelog:
Addresses-Coverity-ID: 1454996 ("Unintentional integer overflow")
Certainly, I've run across multiple false positives as in this case,
but I have also fixed many actual bugs thanks to the Coverity reports.
So I think in general it is valuable to take a look into these
reports, either if they spot actual bugs or promote code correctness.
Thanks
--
Gustavo
