Messages in this thread | | | Subject | Re: [PATCH v3 4/8] i2c: ov9650: use 64-bit arithmetic instead of 32-bit | From | "Gustavo A. R. Silva" <> | Date | Thu, 15 Feb 2018 10:12:46 -0600 |
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On 02/15/2018 07:52 AM, Hans Verkuil wrote: > On 08/02/18 17:39, Gustavo A. R. Silva wrote: >> Hi Sakari, >> >> On 02/07/2018 03:59 PM, Sakari Ailus wrote: >>> Hi Gustavo, >>> >>> On Tue, Feb 06, 2018 at 10:47:50AM -0600, Gustavo A. R. Silva wrote: >>>> Add suffix ULL to constants 10000 and 1000000 in order to give the >>>> compiler complete information about the proper arithmetic to use. >>>> Notice that these constants are used in contexts that expect >>>> expressions of type u64 (64 bits, unsigned). >>>> >>>> The following expressions: >>>> >>>> (u64)(fi->interval.numerator * 10000) >>>> (u64)(iv->interval.numerator * 10000) >>>> fiv->interval.numerator * 1000000 / fiv->interval.denominator >>>> >>>> are currently being evaluated using 32-bit arithmetic. >>>> >>>> Notice that those casts to u64 for the first two expressions are only >>>> effective after such expressions are evaluated using 32-bit arithmetic, >>>> which leads to potential integer overflows. So based on those casts, it >>>> seems that the original intention of the code is to actually use 64-bit >>>> arithmetic instead of 32-bit. >>>> >>>> Also, notice that once the suffix ULL is added to the constants, the >>>> outer casts to u64 are no longer needed. >>>> >>>> Addresses-Coverity-ID: 1324146 ("Unintentional integer overflow") >>>> Fixes: 84a15ded76ec ("[media] V4L: Add driver for OV9650/52 image sensors") >>>> Fixes: 79211c8ed19c ("remove abs64()") >>>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> >>>> --- >>>> Changes in v2: >>>> - Update subject and changelog to better reflect the proposed code changes. >>>> - Add suffix ULL to constants instead of casting variables. >>>> - Remove unnecessary casts to u64 as part of the code change. >>>> - Extend the same code change to other similar expressions. >>>> >>>> Changes in v3: >>>> - None. >>>> >>>> drivers/media/i2c/ov9650.c | 9 +++++---- >>>> 1 file changed, 5 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/drivers/media/i2c/ov9650.c b/drivers/media/i2c/ov9650.c >>>> index e519f27..e716e98 100644 >>>> --- a/drivers/media/i2c/ov9650.c >>>> +++ b/drivers/media/i2c/ov9650.c >>>> @@ -1130,7 +1130,7 @@ static int __ov965x_set_frame_interval(struct ov965x *ov965x, >>>> if (fi->interval.denominator == 0) >>>> return -EINVAL; >>>> - req_int = (u64)(fi->interval.numerator * 10000) / >>>> + req_int = fi->interval.numerator * 10000ULL / >>>> fi->interval.denominator; >>> >>> This has been addressed by your earlier patch "i2c: ov9650: fix potential integer overflow in >>> __ov965x_set_frame_interval" I tweaked a little. It's not in media tree >>> master yet. >>> >> >> Yeah. Actually this patch is supposed to be an improved version of the one you mention. That is why this is version 3. >> >> Also, I wonder if the same issue you mention below regarding 32-bit ARM applies in this case too? >> >>>> for (i = 0; i < ARRAY_SIZE(ov965x_intervals); i++) { >>>> @@ -1139,7 +1139,7 @@ static int __ov965x_set_frame_interval(struct ov965x *ov965x, >>>> if (mbus_fmt->width != iv->size.width || >>>> mbus_fmt->height != iv->size.height) >>>> continue; >>>> - err = abs((u64)(iv->interval.numerator * 10000) / >>>> + err = abs(iv->interval.numerator * 10000ULL / >>> >>> This and the chunk below won't work on e.g. 32-bit ARM. do_div(), please. >>> >> >> Thanks for pointing this out. >> >>>> iv->interval.denominator - req_int); >>>> if (err < min_err) { >>>> fiv = iv; >>>> @@ -1148,8 +1148,9 @@ static int __ov965x_set_frame_interval(struct ov965x *ov965x, >>>> } >>>> ov965x->fiv = fiv; >>>> - v4l2_dbg(1, debug, &ov965x->sd, "Changed frame interval to %u us\n", >>>> - fiv->interval.numerator * 1000000 / fiv->interval.denominator); >>>> + v4l2_dbg(1, debug, &ov965x->sd, "Changed frame interval to %llu us\n", >>>> + fiv->interval.numerator * 1000000ULL / >>>> + fiv->interval.denominator); >> >> I wonder if do_div should be used for the code above? > > Yes, do_div should be used. >
I got it.
Thanks, Hans. -- Gustavo
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