On 11/26/2014 12:55 PM, Linus Torvalds wrote:
> On Nov 26, 2014 6:00 AM, "Sasha Levin" <sasha.le...@oracle.com
> <mailto:sasha.le...@oracle.com>> wrote:
>>
>> We've used to detect integer overflows by causing an overflow and testing the
>> result. For example, to test for addition overflow we would:
>>
>> if (a + b < a)
>> /* Overflow detected */
>>
>> While it works, this is actually an undefined behaviour and we're not
>> guaranteed to have integers overflowing this way.
>
> Bullshit.
>
> Integer overflow is completely well defined in unsigned types.
>
> Don't make up things like this.
Yes, I messed up and picked case where both types are unsigned in my example
patch. Apologies.
The kernel still has it's share of *signed* integer overflows. Example?
fadvise64_64():
loff_t offset, len;
[...]
loff_t endbyte;
[...]
/* Careful about overflows. Len == 0 means "as much as possible" */
endbyte = offset + len;
if (!len || endbyte < len)
endbyte = -1;
else
endbyte--; /* inclusive */
In essence, it's checking (offset + len < len), all of which are signed.
Thanks,
Sasha
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
