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12938118 MT |
1 | /* This file is part of the IPCop Firewall. |
2 | * | |
3 | * IPCop is free software; you can redistribute it and/or modify | |
4 | * it under the terms of the GNU General Public License as published by | |
5 | * the Free Software Foundation; either version 2 of the License, or | |
6 | * (at your option) any later version. | |
7 | * | |
8 | * IPCop is distributed in the hope that it will be useful, | |
9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
11 | * GNU General Public License for more details. | |
12 | * | |
13 | * You should have received a copy of the GNU General Public License | |
14 | * along with IPCop; if not, write to the Free Software | |
15 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
16 | * | |
17 | * Copyright (C) 2003-04-22 Robert Kerr <rkerr@go.to> | |
18 | * | |
19 | * $Id: setuid.c,v 1.2.2.1 2005/11/18 14:51:43 franck78 Exp $ | |
20 | * | |
21 | */ | |
22 | ||
23 | #include <stdio.h> | |
24 | #include <string.h> | |
25 | #include <errno.h> | |
26 | #include <unistd.h> | |
27 | #include <stdlib.h> | |
28 | #include <sys/types.h> | |
29 | #include <limits.h> | |
30 | #include <sys/time.h> | |
31 | #include <sys/resource.h> | |
32 | #include <sys/stat.h> | |
33 | #include <fcntl.h> | |
34 | #include <grp.h> | |
35 | #include <signal.h> | |
36 | #include <sys/wait.h> | |
37 | #include <glob.h> | |
38 | #include "setuid.h" | |
39 | ||
40 | #ifndef OPEN_MAX | |
41 | #define OPEN_MAX 256 | |
42 | #endif | |
43 | ||
44 | /* Trusted environment for executing commands */ | |
45 | char * trusted_env[4] = { | |
46 | "PATH=/usr/bin:/usr/sbin:/sbin:/bin", | |
47 | "SHELL=/bin/sh", | |
48 | "TERM=dumb", | |
49 | NULL | |
50 | }; | |
51 | ||
52 | /* Spawns a child process that uses /bin/sh to interpret a command. | |
53 | * This is much the same in use and purpose as system(), yet as it uses execve | |
54 | * to pass a trusted environment it's immune to attacks based upon changing | |
55 | * IFS, ENV, BASH_ENV and other such variables. | |
56 | * Note this does NOT guard against any other attacks, inparticular you MUST | |
57 | * validate the command you are passing. If the command is formed from user | |
58 | * input be sure to check this input is what you expect. Nasty things can | |
59 | * happen if a user can inject ; or `` into your command for example */ | |
2dcea58c MT |
60 | int safe_system(char* command) { |
61 | return system_core(command, 0, 0, "safe_system"); | |
12938118 MT |
62 | } |
63 | ||
64 | /* Much like safe_system but lets you specify a non-root uid and gid to run | |
65 | * the command as */ | |
2dcea58c MT |
66 | int unpriv_system(char* command, uid_t uid, gid_t gid) { |
67 | return system_core(command, uid, gid, "unpriv_system"); | |
12938118 MT |
68 | } |
69 | ||
2dcea58c | 70 | int system_core(char* command, uid_t uid, gid_t gid, char *error) { |
12938118 MT |
71 | int pid, status; |
72 | ||
73 | if(!command) | |
74 | return 1; | |
75 | ||
2dcea58c | 76 | switch(pid = fork()) { |
12938118 MT |
77 | case -1: |
78 | return -1; | |
2dcea58c MT |
79 | |
80 | case 0: /* child */ { | |
81 | char *argv[4]; | |
82 | ||
83 | if (gid && setgid(gid)) { | |
12938118 MT |
84 | fprintf(stderr, "%s: ", error); |
85 | perror("Couldn't setgid"); | |
86 | exit(127); | |
87 | } | |
2dcea58c MT |
88 | |
89 | if (uid && setuid(uid)) { | |
12938118 MT |
90 | fprintf(stderr, "%s: ", error); |
91 | perror("Couldn't setuid"); | |
92 | exit(127); | |
93 | } | |
2dcea58c | 94 | |
12938118 MT |
95 | argv[0] = "sh"; |
96 | argv[1] = "-c"; | |
97 | argv[2] = command; | |
98 | argv[3] = NULL; | |
99 | execve("/bin/sh", argv, trusted_env); | |
100 | fprintf(stderr, "%s: ", error); | |
101 | perror("execve failed"); | |
102 | exit(127); | |
103 | } | |
2dcea58c | 104 | |
12938118 MT |
105 | default: /* parent */ |
106 | do { | |
2dcea58c MT |
107 | if (waitpid(pid, &status, 0) == -1) { |
108 | if (errno != EINTR) | |
12938118 | 109 | return -1; |
2dcea58c | 110 | } else { |
12938118 | 111 | return status; |
2dcea58c | 112 | } |
12938118 MT |
113 | } while (1); |
114 | } | |
115 | ||
116 | } | |
117 | ||
118 | /* General routine to initialise a setuid root program, and put the | |
119 | * environment in a known state. Returns 1 on success, if initsetuid() returns | |
120 | * 0 then you should exit(1) immediately, DON'T attempt to recover from the | |
121 | * error */ | |
2dcea58c MT |
122 | int initsetuid(void) { |
123 | int fds, i; | |
12938118 MT |
124 | struct stat st; |
125 | struct rlimit rlim; | |
126 | ||
127 | /* Prevent signal tricks by ignoring all except SIGKILL and SIGCHILD */ | |
2dcea58c MT |
128 | for (i = 0; i < NSIG; i++) { |
129 | if (i != SIGKILL && i != SIGCHLD) | |
130 | signal(i, SIG_IGN); | |
12938118 MT |
131 | } |
132 | ||
133 | /* dump all non-standard file descriptors (a full descriptor table could | |
134 | * lead to DoS by preventing us opening files) */ | |
2dcea58c MT |
135 | if ((fds = getdtablesize()) == -1) |
136 | fds = OPEN_MAX; | |
137 | for (i = 3; i < fds; i++) | |
138 | close(i); | |
12938118 MT |
139 | |
140 | /* check stdin, stdout & stderr are open before going any further */ | |
2dcea58c MT |
141 | for (i = 0; i < 3; i++) |
142 | if( fstat(i, &st) == -1 && ((errno != EBADF) || (close(i), open("/dev/null", O_RDWR, 0)) != i)) | |
12938118 MT |
143 | return 0; |
144 | ||
145 | /* disable core dumps in case we're processing sensitive information */ | |
146 | rlim.rlim_cur = rlim.rlim_max = 0; | |
2dcea58c MT |
147 | if (setrlimit(RLIMIT_CORE, &rlim)) { |
148 | perror("Couldn't disable core dumps"); | |
149 | return 0; | |
150 | } | |
12938118 MT |
151 | |
152 | /* drop any supplementary groups, set uid & gid to root */ | |
2dcea58c MT |
153 | if (setgroups(0, NULL)) { |
154 | perror("Couldn't clear group list"); | |
155 | return 0; | |
156 | } | |
157 | ||
158 | if (setgid(0)) { | |
159 | perror("Couldn't setgid(0)"); | |
160 | return 0; | |
161 | } | |
162 | ||
163 | if (setuid(0)) { | |
164 | perror("Couldn't setuid(0)"); | |
165 | return 0; | |
166 | } | |
12938118 MT |
167 | |
168 | return 1; | |
169 | } |