Hey guys, Thanks for all of the great feedback about assembler and c. I was playing with the code at: http://community.core-sdi.com/~gera/InsecureProgramming/abo1.html (Thanks for the link, Claes) And if it is run, it produces a segmentation fault. After running gdb against the program, I obtain the following data: [rewt@n00bB0x]# gdb abo1 Copyright 2001 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"... (gdb) disass main Dump of assembler code for function main: 0x8048460 <main>: push %ebp 0x8048461 <main+1>: mov %esp,%ebp 0x8048463 <main+3>: sub $0x108,%esp 0x8048469 <main+9>: sub $0x8,%esp 0x804846c <main+12>: mov 0xc(%ebp),%eax 0x804846f <main+15>: add $0x4,%eax 0x8048472 <main+18>: pushl (%eax) 0x8048474 <main+20>: lea 0xfffffef8(%ebp),%eax 0x804847a <main+26>: push %eax 0x804847b <main+27>: call 0x804834c <strcpy> 0x8048480 <main+32>: add $0x10,%esp 0x8048483 <main+35>: leave 0x8048484 <main+36>: ret 0x8048485 <main+37>: lea 0x0(%esi),%esi 0x8048488 <main+40>: nop 0x8048489 <main+41>: nop 0x804848a <main+42>: nop 0x804848b <main+43>: nop 0x804848c <main+44>: nop 0x804848d <main+45>: nop 0x804848e <main+46>: nop 0x804848f <main+47>: nop End of assembler dump. (gdb) quit [rewt@n00bB0x]# I guess I don't really know where to go from here. I see that the buffer has space form 256 bytes. Okay, so I run ./abo1 AAAAAAAA(256 times) and it runs okay, then when I run ./abo1 with AAAA(more than 256X) it returns with a segmentation fault. The part I'm not understanding is, after I've overflowed the buffer, how do I know where the next bytes will be stored? Will they be stored at the next memory address (in this case 0x8048480)? Once you know where they are stored, how can you append your code, do you just do a AAAAAA(howevermanytimesyouneedit) and then append your code to the end of it? Thanks for fielding these beginner questions. They're embarrassing to ask, but everyone's gotta start somewhere. -Jeremy -----Original Message----- From: Kim Reece [mailto:sorelat_private] Sent: Monday, July 15, 2002 4:53 PM To: Knud Erik Højgaard Cc: Jeremy Junginger; vuln-devat_private Subject: Re: Assembler/C References "art of assembly" - i forget the author name, but it's a very good book and a simple google search will turn it up plus just about any 'advanced' c book, i.e. one that doesn't assume you are incapable of understanding an if statement and need kindergarden style graphics to not get bored. --sorel
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