According to https://man.openbsd.org/NetBSD-8.1/security.7#FORTIFY_SOURCE
OpenBSD implements glibc bounds checking on certain functions. I am
trying to detect FORTIFY_SOURCE without looking up operating system
names and versions.
The following code works for Linux, but fails under OpenBSD (it is
part of an autoconf test):
#include <string.h>
int main(int argc, char** argv)
{
[char msg[16];]
#[strcpy(msg, argv[0]);]
#[return (int)(msg[0] & ~msg[1]);]
[memcpy(msg, argv[0], strlen(argv[0]));]
[return msg[0] != msg[strlen(argv[0])-1];]
}
I then compile it and scan for the fortified function call:
if $CC -D_FORTIFY_SOURCE=2 $CPPFLAGS -O2 $CFLAGS fortify_test.c -o
fortify_test.exe;
then
count=`readelf --relocs fortify_test.exe | grep -i -c '_chk'`
if test "$count" -ne 0; then
AC_MSG_RESULT([yes]); NSD_CPPFLAGS="$NSD_CPPFLAGS -D_FORTIFY_SOURCE=2"
else
AC_MSG_RESULT([no])
fi
fi
The problem is, OpenBSD is not using the fortified function even
though the destination buffer size can be deduced:
$ readelf --relocs fortify_test.exe | grep -i -c '_chk'
0
And:
$ readelf --relocs fortify_test.exe
Relocation section '.rela.dyn' at offset 0x488 contains 2 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000002168 000000000008 R_X86_64_RELATIVE 00000000000013e0
000000002160 000300000006 R_X86_64_GLOB_DAT 0000000000000000
_Jv_RegisterClasses + 0
Relocation section '.rela.plt' at offset 0x4b8 contains 7 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000002188 000100000007 R_X86_64_JUMP_SLO 0000000000000000 _csu_finish + 0
000000002190 000200000007 R_X86_64_JUMP_SLO 0000000000000000 exit + 0
000000002198 000300000007 R_X86_64_JUMP_SLO 0000000000000000
_Jv_RegisterClasses + 0
0000000021a0 000400000007 R_X86_64_JUMP_SLO 0000000000000000 atexit + 0
0000000021a8 000500000007 R_X86_64_JUMP_SLO 0000000000000000 strlen + 0
0000000021b0 000600000007 R_X86_64_JUMP_SLO 0000000000000000 memcpy + 0
0000000021b8 000700000007 R_X86_64_JUMP_SLO 0000000000000000
__stack_smash_handler + 0
I expect to see memcpy_chk or strcpy_chk.
Do I have a misunderstanding of OpenBSD's implementation?
If someone could point out what is wrong I would greatly appreciate it.
