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, 8 Feb 2018 10:39:39 -0600 |
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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?
I appreciate your feedback.
Thank you! -- Gustavo
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