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+---- Thread: [Assembly] Is this considered a BOF? (/showthread.php?tid=614056)
Is this considered a BOF? - GhostSniper - Aug 15, 2010
Code
section .data
msg: db 'Test',0
section .text
global _start
_start:
mov ecx,msg
mov edx,4
call _read
mov ecx,msg
call _print
call _exit
;#################################################
;###################=-Functions-=#################
_read:
mov eax,3
mov ebx,0
mov edx,4
int 0x80
RET
_print:
mov eax,4
mov ebx,1
int 0x80
RET
_exit:
mov eax,1
mov ebx,0
int 0x80
RETCode
[Dean@Fedora-13 asm]$ nasm -f elf template.asm -o temp.o
[Dean@Fedora-13 asm]$ ld -s temp.o -o test
[Dean@Fedora-13 asm]$ ./test
1234echo Buffer overflow?
1234
[Dean@Fedora-13 asm]$ echo Buffer overflow?
Buffer overflow?
[Dean@Fedora-13 asm]$* - g4143 - Aug 15, 2010
(Aug 15, 2010 07:12 PM)GhostSniper Wrote:Example of what happens:Codesection .data
msg: db 'Test',0
section .text
global _start
_start:
mov ecx,msg
mov edx,4
call _read
mov ecx,msg
call _print
call _exit
;##
;##=-Functions-=##
_read:
mov eax,3
mov ebx,0
mov edx,4
int 0x80
RET
_print:
mov eax,4
mov ebx,1
int 0x80
RET
_exit:
mov eax,1
mov ebx,0
int 0x80
RET
I know my buffer is only 4 bytes. But is reading in 24, so is it forcing the terminal to read in the rest of the bytes? Anyone care to clear this up?Code[Dean@Fedora-13 asm]$ nasm -f elf template.asm -o temp.o
[Dean@Fedora-13 asm]$ ld -s temp.o -o test
[Dean@Fedora-13 asm]$ ./test
1234echo Buffer overflow?
1234
[Dean@Fedora-13 asm]$ echo Buffer overflow?
Buffer overflow?
[Dean@Fedora-13 asm]$
The program only reads 4 bytes into the buffer and then dumps the remainder when the program exits..Where are the extra bytes before the program exits? The bytes are maintained by the operating system or kernel and so are not considered a BOF.