https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112635
Bug ID: 112635
Summary: stack smash protection does not work when code is
compiled with -O
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgcc
Assignee: unassigned at gcc dot gnu.org
Reporter: ago at gentoo dot org
Target Milestone: ---
If this is a known thing, please forgive me.
I was playing with the stack-smash protection and this is what I have found.
Please consider the following block of code:
#include <stdio.h>
int main () {
char *buf[1];
buf[1] = "A (stack-based) buffer overflow";
printf("%s \n", buf[1]);
return 0;
}
If compiled with -fsanitize=address I get:
==24180==ERROR: AddressSanitizer: stack-buffer-overflow on address
0x7f54c7600028 at pc 0x000000401210 bp 0x7fff54f73180 sp 0x7fff54f73178
WRITE of size 8 at 0x7f54c7600028 thread T0
If compiled with -fstack-protector-strong I get:
A (stack-based) buffer overflow
*** stack smashing detected ***: terminated
Aborted
But while compiled with -fstack-protector-strong and -O1 (and also -O2/-O3/-Os)
I just get it working without any issue (it prints "A (stack-based) buffer
overflow")
So in the practice it does not work when -O is used.
I'm running gcc 13 on Gentoo, but I have reproduced this issue on ubuntu-22
(gcc-11.4.0), ubuntu-20 (gcc-9.4.0), and also centos-7 (gcc-4.8.5)
A side note:
I used checksec (https://github.com/slimm609/checksec.sh) basically a `readelf
-W -s a.out | grep "stack_chk_fail"` in this case to understand what happens
and I can see:
- when '-fstack-protector-strong' reports canary found (as expected)
- when '-fstack-protector-strong -O2' reports NO canary found
- when '-fstack-protector-all -O2' reports canary found but no 'stack smashing
detected' at runtime
