我正在编写“HACKING Art Of Exploitation”一书练习 Convert2.c 第 61 页。
这是我的代码。下面是我的问题。
#include <stdio.h>
void usage(char *program_name) {
printf("Usage: %s <message> <# of times to repeat>\n", program_name);
exit(1);
}
int main(int argc, char *argv[]) {
int i, count;
// if(argc < 3) //if fewer than 3 arguments is used
// usage(argv[0]); // display usage message and exit
count = atoi(argv[2]); //convert the second arg into an interger
printf("Repeating %d times\n", count);
for(i=0; i < count; i++)
printf("%3d - %s\n", i, argv[1]); // print the first arg
}
GDB 输出...
➜ git:(master) ✗ 👽 gdb -q a.out
Reading symbols from a.out...done.
(gdb) run test
Starting program: /home/fruitdealer/clones/C_zombie/hacking/a.out test
Program received signal SIGSEGV, Segmentation fault.
__GI_____strtol_l_internal (nptr=0x0, endptr=endptr@entry=0x0, base=base@entry=10, group=group@entry=0,
loc=0x7ffff7dd0560 <_nl_global_locale>) at ../stdlib/strtol_l.c:292
292 ../stdlib/strtol_l.c: No such file or directory.
(gdb) break main
Breakpoint 1 at 0x555555554707: file convert.c, line 14.
(gdb) where
#0 __GI_____strtol_l_internal (nptr=0x0, endptr=endptr@entry=0x0, base=base@entry=10, group=group@entry=0,
loc=0x7ffff7dd0560 <_nl_global_locale>) at ../stdlib/strtol_l.c:292
#1 0x00007ffff7a29122 in __strtol (nptr=<optimized out>, endptr=endptr@entry=0x0, base=base@entry=10)
at ../stdlib/strtol.c:106
#2 0x00007ffff7a24690 in atoi (nptr=<optimized out>) at atoi.c:27
#3 0x000055555555471f in main (argc=2, argv=0x7fffffffdeb8) at convert.c:14
(gdb) run test
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/fruitdealer/clones/C_zombie/hacking/a.out test
Breakpoint 1, main (argc=2, argv=0x7fffffffdeb8) at convert.c:14
14 count = atoi(argv[2]); //convert the second arg into an interger
(gdb) cont
Continuing.
Program received signal SIGSEGV, Segmentation fault.
__GI_____strtol_l_internal (nptr=0x0, endptr=endptr@entry=0x0, base=base@entry=10, group=group@entry=0,
loc=0x7ffff7dd0560 <_nl_global_locale>) at ../stdlib/strtol_l.c:292
292 ../stdlib/strtol_l.c: No such file or directory.
(gdb) x/3xw 0x7fffffffdeb8
0x7fffffffdeb8: 0xffffe220 0x00007fff 0xffffe250
(gdb) x/s 0xffffe220
0xffffe220: <error: Cannot access memory at address 0xffffe220>
(gdb) x/s 0xffffe250
0xffffe250: <error: Cannot access memory at address 0xffffe250>
(gdb) x/sw 0xffffe250
0xffffe250: <error: Cannot access memory at address 0xffffe250>
(gdb)
我发布了所有 gdb 输出，因为我不确定您需要多少。当我在 gdb 上运行“x/s”并获得 <error: Cannot access memory at address 0xffffe250> 时，我的问题出在我的 GDB 输出的底部错误。
Jon Erickson 可以访问这本书 0xffffe220和 0x00007fff然后他在 0xffffe250 上出错这部分内存。
我错过了什么？
为什么我无法访问 0x7fffffffdeb8 中的三个地址中的任何一个？ ？
最佳答案
地址的前半部分被截断。如果您注意到，存储地址需要 8 个字节，因为您使用的是 64 位计算机，而不是 32 位计算机。您正在尝试访问截断的地址。
0x7fffffffdeb8 不是三个地址，而是一个半。尝试访问以 0x00007fff... 开头的字节
关于无法访问特定的内存地址。在 C 程序中，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53235027/