Georgi Guninski's blog

Controversy and exploitability of gcc issue 30475 |assert(int+100 > int)|

Controversy and exploitability of gcc issue 30475 |assert(int+100 > int)|

There is heated discussion on gcc's bugzilla starting from 2007:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30475
and clang is also affected, depending on optimization flags.

poc is the program at end.

gcc with all optimization flags optimizes away |assert(a+100 > a)|
even if there is no integer overflow, only signed overflow.

clang fires the assertion with -O0, but also optimizes it away
with -O3

The formal verifier CBMC fires the assertion, which might of
interest about formally verified programs.

Signed integer arithmetic is commonly used even without integer
overflows. If |(int) -1 < (unsigned int) 2| holds, this would
be disaster.

Could this compiler issue be security problem?

Any workarounds?

===poc===
#include 

int foo(int a) {
  assert(a+100 > a);
  printf("%d %d\n",a+100,a);
  return a;
}

int main() {
  foo(100);
  foo(0x7fffffff);
}
=========


CV:    https://j.ludost.net/resumegg.pdf
site:  http://www.guninski.com
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