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 <gust...@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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