[linux] 명령행 인자를 이용한 프로그램 실행

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LAB> c 언어에서 명령행 인자를 이용한 프로그램 실행

# vi argc.c
-- argc.c --
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  char cmd[100];   

// 디버그 모드이면 argc 변수의 값을 출력해라.
#ifdef DEBUG
  printf("argc = %d \n", argc); 
#endif

  if(argc != 2)
  {
    fprintf(stderr, "Usage : %s username\n", argv[0]);
    exit(1);
  }

  // 명령어 문자열을 완성한다.
  // e.g. useradd linux
  sprintf(cmd, "useradd %s", argv[1]);
  system(cmd);

  // 명령어 문자열을 완성한다.
  // e.g. passwd linux
  sprintf(cmd, "passwd %s", argv[1]);
  system(cmd);

  return 0;
}
-- argc.c --

# ./argc bbb
Changing password for user bbb.
New UNIX password: 
Retype new UNIX password: 
passwd: all authentication tokens updated successfully.

# ssh bbb@localhost
bbb@localhost's password: 

$ id
uid=510(bbb) gid=510(bbb) groups=510(bbb) context=user_u:system_r:unconfined_t:s0

# gcc -g -o argc argc.c 
[root@fw c]# gdb -q argc
Reading symbols from /root/programming/c/argc...done.
(gdb) b main
Breakpoint 1 at 0x804846b: file argc.c, line 13.
(gdb) r 
Starting program: /root/programming/c/argc 

Breakpoint 1, main (argc=1, argv=0xbfffea94) at argc.c:13
13	  if(argc != 2)
(gdb) n
15	    fprintf(stderr, "Usage : %s username\n", argv[0]);
(gdb) n
Usage : /root/programming/c/argc username
16	    exit(1);
(gdb) n

Program exited with code 01.
(gdb) n
The program is not being run.
(gdb) n
The program is not being run.
(gdb) n
The program is not being run.
(gdb) r
Starting program: /root/programming/c/argc 
warning: .dynamic section for "/lib/libc.so.6" is not at the expected address
warning: difference appears to be caused by prelink, adjusting expectations

Breakpoint 1, main (argc=1, argv=0xbfffea94) at argc.c:13
13	  if(argc != 2)
(gdb) 
(gdb) 
(gdb) 
(gdb) r ccc
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /root/programming/c/argc ccc

Breakpoint 1, main (argc=2, argv=0xbfffea94) at argc.c:13
13	  if(argc != 2)
(gdb) info registers 
eax            0xbfffea94	-1073747308
ecx            0xbfffea10	-1073747440
edx            0x2	2
ebx            0x87dff4	8904692
esp            0xbfffe970	0xbfffe970
ebp            0xbfffe9f8	0xbfffe9f8
esi            0x721ca0	7478432
edi            0x0	0
eip            0x804846b	0x804846b <main+23>
eflags         0x200282	[ SF IF ID ]
cs             0x73	115
ss             0x7b	123
ds             0x7b	123
es             0x7b	123
fs             0x0	0
gs             0x33	51
(gdb) x/16xw $ebp
0xbfffe9f8:	0xbfffea68	0x0073aebc	0x00721ca0	0x08048520
0xbfffea08:	0xbfffea68	0x0073aebc	0x00000002	0xbfffea94
0xbfffea18:	0xbfffeaa0	0x00722828	0x00000000	0x00000001
0xbfffea28:	0x00000001	0x00000000	0x0087dff4	0x00721ca0
(gdb) x/s 0xbfffea94
0xbfffea94:	 "\252\353\377\277\303\353\377\277"
(gdb) x/x 0xbfffea94
0xbfffea94:	0xbfffebaa
(gdb) x/16xw 0xbfffea94
0xbfffea94:	0xbfffebaa	0xbfffebc3	0x00000000	0xbfffebc7
0xbfffeaa4:	0xbfffebe1	0xbfffebf1	0xbfffebfc	0xbfffec0a
0xbfffeab4:	0xbfffec2c	0xbfffec3f	0xbfffec49	0xbfffee0c
0xbfffeac4:	0xbfffee18	0xbfffee9d	0xbfffeeb7	0xbfffeec6
(gdb) x/s 0xbfffebaa
0xbfffebaa:	 "/root/programming/c/argc"
(gdb) x/s 0xbfffebc3
0xbfffebc3:	 "ccc"
(gdb) 
(gdb) n
21	  sprintf(cmd, "useradd %s", argv[1]);
(gdb) display cmd
1: cmd = "h\202\004\b", '\000' <repeats 12 times>, ".N=\366", '\000' <repeats 24 times>"\260, \203\004\b\000\000\000\000`\227\004\b\330\351\377\277\r\203\004\b\364\337\207\000\f\302\207\000\b\352\377\277\071\205\004\b\205\017u\000\240\352\377\277\b\352\377\277\364\337\207\000\200Hq"
(gdb) print argv[1]
$1 = 0xbfffebc3 "ccc"
(gdb) n
22	  system(cmd);
1: cmd = "useradd ccc\000\000\000\000\000.N=\366", '\000' <repeats 24 times>"\260, \203\004\b\000\000\000\000`\227\004\b\330\351\377\277\r\203\004\b\364\337\207\000\f\302\207\000\b\352\377\277\071\205\004\b\205\017u\000\240\352\377\277\b\352\377\277\364\337\207\000\200Hq"
(gdb) n
Detaching after fork from child process 9544.
26	  sprintf(cmd, "passwd %s", argv[1]);
1: cmd = "useradd ccc\000\000\000\000\000.N=\366", '\000' <repeats 24 times>"\260, \203\004\b\000\000\000\000`\227\004\b\330\351\377\277\r\203\004\b\364\337\207\000\f\302\207\000\b\352\377\277\071\205\004\b\205\017u\000\240\352\377\277\b\352\377\277\364\337\207\000\200Hq"
(gdb) n
27	  system(cmd);
1: cmd = "passwd ccc\000\000\000\000\000\000.N=\366", '\000' <repeats 24 times>"\260, \203\004\b\000\000\000\000`\227\004\b\330\351\377\277\r\203\004\b\364\337\207\000\f\302\207\000\b\352\377\277\071\205\004\b\205\017u\000\240\352\377\277\b\352\377\277\364\337\207\000\200Hq"
(gdb) n
Detaching after fork from child process 9549.
Changing password for user ccc.
New UNIX password: 
Retype new UNIX password: 
passwd: all authentication tokens updated successfully.
29	  return 0;
1: cmd = "passwd ccc\000\000\000\000\000\000.N=\366", '\000' <repeats 24 times>"\260, \203\004\b\000\000\000\000`\227\004\b\330\351\377\277\r\203\004\b\364\337\207\000\f\302\207\000\b\352\377\277\071\205\004\b\205\017u\000\240\352\377\277\b\352\377\277\364\337\207\000\200Hq"
(gdb) c
Continuing.
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