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
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
|
/* IVLE - Informatics Virtual Learning Environment
* Copyright (C) 2007-2008 The University of Melbourne
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* Program: Trampoline
* Author: Tom Conway, Matt Giuca
* Date: 20/12/2007
*
* This program runs a given program in a given working dir.
* First, it chroots to a jail path and setuids to a given user ID.
* This is intented to provide a safe execution environment for arbitrary
* programs and scripts.
*
* Scripts (such as Python programs) should be executed by supplying
* "/usr/bin/python" as the program, and the script as the first argument.
*
* Usage: trampoline uid jail-path working-path program [args...]
* Must run as root. Will safely setuid to the supplied uid, checking that it
* is not root. Recommended that the file is set up as follows:
* sudo chown root:root trampoline; sudo chroot +s trampoline
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* conf.h is admin-configured by the setup process.
* It defines jail_base.
*/
#include "conf.h"
/* Argument names */
#define ARG_UID 1
#define ARG_JAILPATH 2
#define ARG_CWD 3
#define ARG_PROG 4
#define MIN_ARGC 5
#define UID_ROOT 0
/* Returns TRUE if the given uid is allowed to execute trampoline.
* Only root or the web server should be allowed to execute.
* This is determined by the whitelist allowed_uids in conf.h.
*/
int uid_allowed(int uid)
{
int i;
/* root is always allowed to execute trampoline */
if (uid == 0)
return 1;
/* loop over all allowed_uids */
for (i=(sizeof(allowed_uids)/sizeof(*allowed_uids))-1; i>=0; i--)
{
if (allowed_uids[i] == uid)
return 1;
}
/* default to disallowing */
return 0;
}
int main(int argc, char* const argv[])
{
char* jailpath;
int uid;
/* Disallow execution from all users but the whitelisted ones, and root */
if (!uid_allowed(getuid()))
{
fprintf(stderr, "only the web server may execute trampoline\n");
exit(1);
}
/* Args check and usage */
if (argc < MIN_ARGC)
{
fprintf(stderr, "usage: %s <uid> <jail> <cwd> <program> [args...]\n",
argv[0]);
exit(EXIT_FAILURE);
}
/* Disallow suiding to the root user */
uid = atoi(argv[ARG_UID]);
if (uid == UID_ROOT)
{
fprintf(stderr, "cannot set up a jail as root\n");
exit(1);
}
/* Jail path must:
* Be non-empty
* Start with a '/'
* Not contain "/.."
* Begin with jail_base
*/
jailpath = argv[ARG_JAILPATH];
if (strlen(jailpath) < 1 || jailpath[0] != '/'
|| strstr(jailpath, "/..")
|| strncmp(jailpath, jail_base, strlen(jail_base)))
{
fprintf(stderr, "bad jail path: %s\n", jailpath);
exit(1);
}
/* chroot into the jail.
* Henceforth this process, and its children, cannot see anything above
* jailpath. */
if (chroot(jailpath))
{
perror("could not chroot");
exit(1);
}
/* chdir into the specified working directory */
if (chdir(argv[ARG_CWD]))
{
perror("could not chdir");
exit(1);
}
/* setuid to the given user ID.
* Henceforth we will be running as this user instead of root.
*/
if (setuid(uid))
{
perror("could not setuid");
exit(1);
}
/* exec (replace this process with the a new instance of the target
* program). Pass along all the arguments.
* Note that for script execution, the "program" will be the interpreter,
* and the first argument will be the script. */
execv(argv[ARG_PROG], argv + ARG_PROG);
/* nb exec won't return unless there was an error */
perror("could not exec");
return EXIT_FAILURE;
}
|