Re: BUG #14722: Segfault in tuplesort_heap_siftup, 32 bit overflow

Sergey Koposov <skoposov(at)cmu(dot)edu> writes:
> On Thu, 2017-06-29 at 10:00 -0700, Peter Geoghegan wrote:
>> This is an oversight in commit 263865a. The fix is to use a variable
>> that won't overflow in tuplesort_heap_siftup() -- this is probably a
>> one-liner, because when the variable overflows today, the correct
>> behavior would be for control to break out of the loop that declares
>> the overflowing variable "j", and, I don't see any similar problem in
>> other heap maintenance routines. It's a very isolated problem.
>>
>> I could write a patch.

> Just to avoid being forgotten, I attach a trivial patch against 9.5
> branch as well as have created a commitfest submission
> https://commitfest.postgresql.org/14/1189/

I don't like s/int/int64/g as a fix for this. That loop is probably
a hot spot, and this fix is going to be expensive on any machine where
int64 isn't the native word width. How about something like this instead:

- int j = 2 * i + 1;
+ int j;

+ if (unlikely(i > INT_MAX / 2))
+ break; /* if j would overflow, we're done */
+ j = 2 * i + 1;
if (j >= n)
break;

regards, tom lane