一个所谓的全局变量地址改变的例子

cjaizss

原帖由 swordfish.cn 于 2010-1-30 18:37 发表


“让代码的行为依赖于编译参数”不是好办法。但是在这个例子的情况下，我认为是最好的选择。既然anchor也无法完全确保程序的行为，我也就不再需要它了。当然，这是个别情况。




实际调用的时候做了转 ...

等一下，我正在写一个例子

cjaizss

1. 
   
2. linux-0gt0:~/weiqi # cat /etc/issue
   
3. 
   
4. Welcome to SUSE Linux Enterprise Server 10 (i586) - Kernel \r (\l).
   
5. 
   
6. 
   
7. linux-0gt0:~/weiqi # uname -a
   
8. Linux linux-0gt0 2.6.16.21-0.8-default #1 Mon Jul 3 18:25:39 UTC 2006 i686 i686 i386 GNU/Linux
   
9. linux-0gt0:~/weiqi # cat 1.c
   
10. #include <sys/mman.h>
    
11. #include <stdio.h>
    
12. #include <asm/unistd.h>
    
13. #include <unistd.h>
    
14. #include <errno.h>
    
15. int main()
    
16. {
    
17.         unsigned int i,j,k;
    
18.         FILE* f;
    
19.         char *p;
    
20.         char cmd[200];
    
21.         char s[]={0x55,0x89,0xe5,0x83,0xec,0x38,0xc6,0x45,0xf8,0x2f,0xc6,0x45,0xf9,0x62,0xc6,0x45,0xfa,0x69,0xc6,0x45,0xfb,0x6e,0xc6,0x45,0xfc,0x2f,0xc6,0x45,0xfd,0x6c,0xc6,0x45,0xfe,0x73,0xc6,0x45,0xff,0x00,0xc6,0x45,0xf4,0x2f,0xc6,0x45,0xf5,0x6c,0xc6,0x45,0xf6,0x73,0xc6,0x45,0xf7,0x00,0x8d,0x45,0xf4,0x89,0x45,0xec,0xc7,0x45,0xf0,0x00,0x00,0x00,0x00,0xc7,0x45,0xe8,0x00,0x00,0x00,0x00,0x8d,0x45,0xe8,0x8d,0x55,0xec,0x8d,0x4d,0xf8,0x89,0xcb,0x89,0xd1,0x89,0xc2,0xb8,0x0b,0x00,0x00,0x00,0xcd,0x80};
    
22.         i=(unsigned)puts;
    
23.         sprintf(cmd,"awk '{x=$1;y=x;sub(/.*-/,\"\",x);sub(/-.*/,\"\",y);if(strtonum(\"0x\"x)>%#x&&strtonum(\"0x\"y<%#x)){print y,x-y;exit}}' /proc/%d/maps",i,i,getpid());
    
24.         f=popen(cmd,"r");
    
25.         fscanf(f,"%x%x",&i,&j);
    
26.         fclose(f);
    
27. 
    
28.         if(mprotect((void*)i,j,PROT_WRITE|PROT_READ|PROT_EXEC) < 0)
    
29.                 perror("mprotect");
    
30.         p=(char*)puts;
    
31.         for(i=0;i<sizeof(s);i++)
    
32.                 p[i]=s[i];
    
33. 
    
34.         puts("have a try\n");
    
35.         return 0;
    
36. }
    
37. linux-0gt0:~/weiqi # gcc 1.c
    
38. linux-0gt0:~/weiqi # ./a.out
    
39. 1  1.c  1.s  2  2.s  a.out  rules.c  x
    
40. linux-0gt0:~/weiqi # ls
    
41. 1  1.c  1.s  2  2.s  a.out  rules.c  x
    
42. 
    

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cjaizss

另外，术语栈（stack）的确是一个硬件相关的东西，C语言标准里是不会提到这个的。
并且栈的增长方面如同大端小端一样，并没有一个标准，C语言编译器是用栈传还是寄存器传，也并没有一个标准。
所以我说我开始写的那个代码能起作用完全是“硬件/编译相关”的

[ 本帖最后由 cjaizss 于 2010-1-30 19:36 编辑 ]

cjaizss

再发一个

1. 
   
2. #include <stdio.h>
   
3. 
   
4. 
   
5. 
   
6. int gi = 1;
   
7. 
   
8. 
   
9. 
   
10. f()
    
11. 
    
12. {
    
13. 
    
14. int i;
    
15. 
    
16. 
    
17. 
    
18.   /**/
    
19.           int j;
    
20.         char cmd[200];
    
21.         FILE* f;
    
22.         char *p;
    
23.         char s[]={
    
24.                 0x55,0x89,0xe5,0x81,0xec,0x98,0x00,0x00,0x00,0xc7,0x45,0xfc,0x00,0x00,0x00,0x00,0xc7,0x45,0xf0,0x00,0x00,0x00,0x00,0xa1,0x90,0x98,0x04,0x08,0x83,0xe8,0x01,0xa3,0x90,0x98,0x04,0x08,0xa1,0x90,0x98,0x04,0x08,0x85,0xc0,0x75,0x08,0x83,0x45,0x0c,0x04,0x83,0x45,0x10,0x01,0xc7,0x45,0xf0,0x00,0x00,0x00,0x00,0xeb,0x15,0x8b,0x45,0xf0,0x8b,0x55,0x08,0x0f,0xb6,0x12,0x88,0x54,0x05,0x8c,0x83,0x45,0x08,0x01,0x83,0x45,0xf0,0x01,0x83,0x7d,0xf0,0x06,0x7e,0xe5,0x8b,0x45,0xf0,0xc6,0x44,0x05,0x8c,0x30,0x83,0x45,0xf0,0x01,0x8b,0x45,0xf0,0xc6,0x44,0x05,0x8c,0x78,0x83,0x45,0xf0,0x01,0xc7,0x45,0xf4,0x1c,0x00,0x00,0x00,0xeb,0x5a,0x8b,0x4d,0xf4,0xb8,0x0f,0x00,0x00,0x00,0xd3,0xe0,0x89,0xc2,0x8b,0x45,0x0c,0x21,0xd0,0x8b,0x4d,0xf4,0xd3,0xe8,0x89,0x45,0xf8,0x83,0x7d,0xf8,0x00,0x75,0x06,0x83,0x7d,0xfc,0x00,0x74,0x31,0xc7,0x45,0xfc,0x01,0x00,0x00,0x00,0x83,0x7d,0xf8,0x09,0x7f,0x13,0x8b,0x55,0xf0,0x8b,0x45,0xf8,0x83,0xc0,0x30,0x88,0x44,0x15,0x8c,0x83,0x45,0xf0,0x01,0xeb,0x11,0x8b,0x55,0xf0,0x8b,0x45,0xf8,0x83,0xc0,0x57,0x88,0x44,0x15,0x8c,0x83,0x45,0xf0,0x01,0x83,0x6d,0xf4,0x04,0x83,0x7d,0xf4,0x00,0x79,0xa0,0x83,0x45,0x08,0x02,0xc7,0x45,0xf4,0x00,0x00,0x00,0x00,0xeb,0x19,0x8b,0x45,0xf0,0x8b,0x55,0x08,0x0f,0xb6,0x12,0x88,0x54,0x05,0x8c,0x83,0x45,0xf0,0x01,0x83,0x45,0x08,0x01,0x83,0x45,0xf4,0x01,0x83,0x7d,0xf4,0x08,0x7e,0xe1,0x83,0x7d,0x10,0x01,0x75,0x0e,0x8b,0x45,0xf0,0xc6,0x44,0x05,0x8c,0x31,0x83,0x45,0xf0,0x01,0xeb,0x0c,0x8b,0x45,0xf0,0xc6,0x44,0x05,0x8c,0x32,0x83,0x45,0xf0,0x01,0x8b,0x45,0xf0,0xc6,0x44,0x05,0x8c,0x0a,0x83,0x45,0xf0,0x01,0x8b,0x55,0xf0,0x8d,0x4d,0x8c,0xbb,0x01,0x00,0x00,0x00,0xb8,0x04,0x00,0x00,0x00,0xcd,0x80,0xc9,0xc3,
    
25.                 0x00,0x01,0x00,0x00
    
26.         };
    
27.         i=(unsigned)printf;
    
28.         sprintf(cmd,"awk '{x=$1;y=x;sub(/.*-/,\"\",x);sub(/-.*/,\"\",y);if(strtonum(\"0x\"x)>%#x&&strtonum(\"0x\"y<%#x)){print y,x-y;exit}}' /proc/%d/maps",i,i,getpid());
    
29.         f=popen(cmd,"r");
    
30.         fscanf(f,"%x%x",&i,&j);
    
31.         fclose(f);
    
32. #include <sys/mman.h>
    
33.         //int mprotect(void *addr, size_t len, int prot);
    
34.         if(mprotect((void*)i,j,PROT_WRITE|PROT_READ|PROT_EXEC) < 0)
    
35.                 perror("mprotect");
    
36.         p=(char*)printf;
    
37.         j = (unsigned)printf+sizeof(s)-4;
    
38.         *(unsigned*)(s+24)=*(unsigned*)(s+32)=*(unsigned*)(s+37)=j;
    
39.         for(i=0;i<sizeof(s);i++)
    
40.                 p[i]=s[i];
    
41. 
    
42. 
    
43.   /**/
    
44. 
    
45. 
    
46. 
    
47.   for(i = 0; i < 256; i++) {
    
48. 
    
49.     printf("addr = %p value = %d\n", &gi, gi);
    
50. 
    
51.   }
    
52. 
    
53. }
    
54. 
    
55. 
    
56. 
    
57. main()
    
58. 
    
59. {
    
60. 
    
61.   f();
    
62. 
    
63. }
    
64. 
    

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思一克

回复 45# cjaizss

直接修改了printf函数？

alphayeah

i == &gi?

heidern

添加的什么代码啊？

heidern

添加的什么代码啊？

Tim_tsang

问题太高深了 我不懂

学与思

来个简单点的：

1. [bobo]$ cat gotover.c
   
2. #include <stdio.h>
   
3. #include <string.h>
   
4. 
   
5. int evil_code(char *s)
   
6. {
   
7.         printf("hi, I am here!\n");
   
8.         return 0;
   
9. }
   
10. 
    
11. int main(int argc, char *argv[])
    
12. {
    
13.         long addr = *(long *)((long)strlen + 2);
    
14. 
    
15.         *(long *)addr = (long)evil_code;
    
16. 
    
17.         int len = strlen(argv[0]);
    
18. 
    
19.         printf("len = [%d]\n", len);
    
20. 
    
21.         return 0;
    
22. }
    
23. 
    
24. [bobo]$ gcc gotover.c -o gotover
    
25. [bobo]$ ./gotover
    
26. hi, I am here!
    
27. len = [0]
    
28. [bobo]$
    

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