1 /*
2 **
3 ** Copyright 2010, The Android Open Source Project
4 **
5 ** Licensed under the Apache License, Version 2.0 (the "License");
6 ** you may not use this file except in compliance with the License.
7 ** You may obtain a copy of the License at
8 **
9 ** http://www.apache.org/licenses/LICENSE-2.0
10 **
11 ** Unless required by applicable law or agreed to in writing, software
12 ** distributed under the License is distributed on an "AS IS" BASIS,
13 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 ** See the License for the specific language governing permissions and
15 ** limitations under the License.
16 */
17
18 #define PROGNAME "run-as"
19 #define LOG_TAG PROGNAME
20
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <sys/types.h>
25 #include <sys/stat.h>
26 #include <dirent.h>
27 #include <errno.h>
28 #include <unistd.h>
29 #include <time.h>
30 #include <stdarg.h>
31
32 #include <private/android_filesystem_config.h>
33 #include "package.h"
34
35 /*
36 * WARNING WARNING WARNING WARNING
37 *
38 * This program runs as set-uid root on Android production devices.
39 * Be very conservative when modifying it to avoid any serious
40 * security issue. Keep in mind the following:
41 *
42 * - This program should only run for the 'root' or 'shell' users
43 *
44 * - Avoid anything that is more complex than simple system calls
45 * until the uid/gid has been dropped to that of a normal user
46 * or you are sure to exit.
47 *
48 * This avoids depending on environment variables, system properties
49 * and other external factors that may affect the C library in
50 * unpredictable ways.
51 *
52 * - Do not trust user input and/or the filesystem whenever possible.
53 *
54 * Read README.TXT for more details.
55 *
56 *
57 *
58 * The purpose of this program is to run a command as a specific
59 * application user-id. Typical usage is:
60 *
61 * run-as <package-name> <command> <args>
62 *
63 * The 'run-as' binary is setuid, but will check the following:
64 *
65 * - that it is invoked from the 'shell' or 'root' user (abort otherwise)
66 * - that '<package-name>' is the name of an installed and debuggable package
67 * - that the package's data directory is well-formed (see package.c)
68 *
69 * If so, it will cd to the package's data directory, drop to the application's
70 * user id / group id then run the command there.
71 *
72 * This can be useful for a number of different things on production devices:
73 *
74 * - Allow application developers to look at their own applicative data
75 * during development.
76 *
77 * - Run the 'gdbserver' binary executable to allow native debugging
78 */
79
80 static void
usage(void)81 usage(void)
82 {
83 const char* str = "Usage: " PROGNAME " <package-name> <command> [<args>]\n\n";
84 write(1, str, strlen(str));
85 exit(1);
86 }
87
88
89 static void
panic(const char * format,...)90 panic(const char* format, ...)
91 {
92 va_list args;
93
94 fprintf(stderr, "%s: ", PROGNAME);
95 va_start(args, format);
96 vfprintf(stderr, format, args);
97 va_end(args);
98 exit(1);
99 }
100
101
main(int argc,char ** argv)102 int main(int argc, char **argv)
103 {
104 const char* pkgname;
105 int myuid, uid, gid;
106 PackageInfo info;
107
108 /* check arguments */
109 if (argc < 2)
110 usage();
111
112 /* check userid of caller - must be 'shell' or 'root' */
113 myuid = getuid();
114 if (myuid != AID_SHELL && myuid != AID_ROOT) {
115 panic("only 'shell' or 'root' users can run this program\n");
116 }
117
118 /* retrieve package information from system */
119 pkgname = argv[1];
120 if (get_package_info(pkgname, &info) < 0) {
121 panic("Package '%s' is unknown\n", pkgname);
122 return 1;
123 }
124
125 /* reject system packages */
126 if (info.uid < AID_APP) {
127 panic("Package '%s' is not an application\n", pkgname);
128 return 1;
129 }
130
131 /* reject any non-debuggable package */
132 if (!info.isDebuggable) {
133 panic("Package '%s' is not debuggable\n", pkgname);
134 return 1;
135 }
136
137 /* check that the data directory path is valid */
138 if (check_data_path(info.dataDir, info.uid) < 0) {
139 panic("Package '%s' has corrupt installation\n", pkgname);
140 return 1;
141 }
142
143 /* then move to it */
144 {
145 int ret;
146 do {
147 ret = chdir(info.dataDir);
148 } while (ret < 0 && errno == EINTR);
149
150 if (ret < 0) {
151 panic("Could not cd to package's data directory: %s\n", strerror(errno));
152 return 1;
153 }
154 }
155
156 /* Ensure that we change all real/effective/saved IDs at the
157 * same time to avoid nasty surprises.
158 */
159 uid = gid = info.uid;
160 if(setresgid(gid,gid,gid) || setresuid(uid,uid,uid)) {
161 panic("Permission denied\n");
162 return 1;
163 }
164
165 /* User specified command for exec. */
166 if (argc >= 3 ) {
167 if (execvp(argv[2], argv+2) < 0) {
168 panic("exec failed for %s Error:%s\n", argv[2], strerror(errno));
169 return -errno;
170 }
171 }
172
173 /* Default exec shell. */
174 execlp("/system/bin/sh", "sh", NULL);
175
176 panic("exec failed\n");
177 return 1;
178 }
179