/
pretend.c
74 lines (61 loc) · 1.78 KB
/
pretend.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
/**********************************************************************
*
* pretend : 2013-03-20
* emptymonkey's tool for altering identity.
*
* This is a simple program for changing uids, primary gids, and the
* supplimentary gid lists, regardless of if those ids exist on
* this system. (E.g. uids for users that don't appear in /etc/passwd.)
* This program just calls the underlying syscalls that are responsible
* for this kind of management. Nothing fancy.
*
* Example usage:
*
* empty@monkey:~$ id
* uid=1000(empty) gid=1000(empty) groups=1000(empty),24(cdrom),25(floppy),29(audio)
* empty@monkey:~$ sudo ./pretend 23:19:555:1037 id
* uid=23 gid=19 groups=555,1037
*
**********************************************************************/
#define _GNU_SOURCE
#include <errno.h>
#include <error.h>
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define MAX_SUPPLEMENTAL_GROUPS 128
int main(int argc, char **argv){
uid_t uid;
gid_t gid, gid_list[MAX_SUPPLEMENTAL_GROUPS];
int i;
char *end_ptr;
if(argc < 3){
fprintf(stderr, "Usage: %s uid:gid[:gid1:gid2:...] COMMAND [ARGS]\n", argv[0]);
exit(-1);
}
memset(gid_list, 0, sizeof(gid_list));
uid = (uid_t) strtol(argv[1], &end_ptr, 10);
gid = (gid_t) strtol(end_ptr + 1, &end_ptr, 10);
if(errno){
fprintf(stderr, "Usage: %s uid:gid[:gid1:gid2:...] COMMAND [ARGS]\n", argv[0]);
exit(-1);
}
i = 0;
while(*end_ptr != 0){
gid_list[i++] = (gid_t) strtol(end_ptr + 1, &end_ptr, 10);
}
if(setgroups((size_t) i, gid_list)){
error(-1, errno, "setgroups()");
}
if(setresgid(gid, gid, gid)){
error(-1, errno, "setresgid()");
}
if(setresuid(uid, uid, uid)){
error(-1, errno, "setresuid()");
}
execvp(argv[2], argv + 2);
error(-1, errno, "execv()");
return(-1);
}