I think you will need to more artfully choose your particular byte 253 to match your libc. I think the mail from nexusat_private-way.co.uk is heading the right direction. -----Original Message----- From: Shafik Yaghmour [mailto:subsat_private] Sent: Tuesday, May 13, 2003 3:44 PM To: Cameron Brown Cc: vuln-devat_private Subject: RE: Administrivia: List Announcement On Tue, 13 May 2003, Cameron Brown wrote: > If I supply an argv[1] of > 252 bytes, then byte 253 may (depending on > many factors) overwrite the first byte of buf2. This is going to be > (I > think) part of the size of the malloc'd buf2. What interesting things > can happen when you then free() an incorrectly-sized buf2 (or otherwise > operate on buf2 if this were a real program) is something I am anxious > to learn from others on this list! Hmmm, for me it seg faults on free(buf1). I am running on Linux BTW, here is some output from gdb: [shafik@localhost VULNDEV]$ ./a.out `perl -e 'print "A"x2000'` `perl -e 'print "B"x2000'` Segmentation fault (core dumped) [shafik@localhost VULNDEV]$ gdb ./a.out ./core GNU gdb Red Hat Linux (5.2-2) Copyright 2002 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-redhat-linux"... Core was generated by `./a.out AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA' . Program terminated with signal 11, Segmentation fault. Reading symbols from /lib/libc.so.6...done. Loaded symbols for /lib/libc.so.6 Reading symbols from /lib/ld-linux.so.2...done. Loaded symbols for /lib/ld-linux.so.2 #0 0x400aa1e6 in chunk_free (ar_ptr=0x4015bc80, p=0x8049770) at malloc.c:3242 3242 malloc.c: No such file or directory. in malloc.c (gdb) up #1 0x400a9fc0 in __libc_free (mem=0x8049778) at malloc.c:3154 3154 in malloc.c (gdb) up #2 0x080485b3 in main (argc=3, argv=0xbfffe9d4) at vulndev-1.c:26 26 free(buf1); (gdb) -- Those who dream by day are cognizant of many things which escape those who dream only by night. -Edgar Allan Poe
This archive was generated by hypermail 2b30 : Tue May 13 2003 - 20:14:38 PDT