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Date: Fri, 8 Nov 2019 10:03:44 +0200
From: Georgi Guninski <gguninski@...il.com>
To: oss-security@...ts.openwall.com
Subject: 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.
Could this compiler issue be security problem?
Any workarounds?
===poc===
#include <assert.h>
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
blog: https://j.ludost.net/blog
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