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SubjectRe: [PATCH v3 4/8] i2c: ov9650: use 64-bit arithmetic instead of 32-bit
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.

>
> 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.

> 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);
>
> return 0;
> }

--
Regards,

Sakari Ailus
e-mail: sakari.ailus@iki.fi

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