Illustration of buffer overflows for students (linux, C)
- by osgx
Hello
My friend is teacher of first-year CS students. We want to show them buffer overflow exploitation. But modern distribs are protected from simples buffer overflows:
HOME=`perl -e "print 'A'x269"` one_widely_used_utility_is_here --help
on debian (blame it)
Caught signal 11,
on modern commercial redhat
*** buffer overflow detected ***: /usr/bin/one_widely_used_utility_is_here terminated
======= Backtrace: =========
/lib/libc.so.6(__chk_fail+0x41)[0xc321c1]
/lib/libc.so.6(__strcpy_chk+0x43)[0xc315e3]
/usr/bin/one_widely_used_utility_is_here[0x805xxxc]
/usr/bin/one_widely_used_utility_is_here[0x804xxxc]
/lib/libc.so.6(__libc_start_main+0xdc)[0xb61e9c]
/usr/bin/one_widely_used_utility_is_here[0x804xxx1]
======= Memory map: ========
00336000-00341000 r-xp 00000000 08:02
2751047 /lib/libgcc_s-4.1.2-20080825.so.1
00341000-00342000 rwxp 0000a000 08:02
2751047 /lib/libgcc_s-4.1.2-20080825.so.1
008f3000-008f4000 r-xp 008f3000 00:00 0 [vdso]
The same detector fails for more synthetic examples from the internet.
How can we demonstrate buffer overflow with modern non-GPL distribs (there is no debian in classes)
How can we
DISABLE canary word checking in stack ?
DISABLE checking variants of strcpy/strcat ?
write an example (in plain C) with working buffer overrun ?
