1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include <errno.h>
18 #include <error.h>
19 #include <getopt.h>
20 #include <paths.h>
21 #include <pwd.h>
22 #include <stdbool.h>
23 #include <stdio.h>
24 #include <stdlib.h>
25 #include <string.h>
26 #include <unistd.h>
27
28 #include <private/android_filesystem_config.h>
29
pwtoid(const char * tok,uid_t * uid,gid_t * gid)30 void pwtoid(const char* tok, uid_t* uid, gid_t* gid) {
31 struct passwd* pw = getpwnam(tok);
32 if (pw) {
33 if (uid) *uid = pw->pw_uid;
34 if (gid) *gid = pw->pw_gid;
35 } else {
36 char* end;
37 errno = 0;
38 uid_t tmpid = strtoul(tok, &end, 10);
39 if (errno != 0 || end == tok) error(1, errno, "invalid uid/gid '%s'", tok);
40 if (uid) *uid = tmpid;
41 if (gid) *gid = tmpid;
42 }
43 }
44
extract_uidgids(const char * uidgids,uid_t * uid,gid_t * gid,gid_t * gids,int * gids_count)45 void extract_uidgids(const char* uidgids, uid_t* uid, gid_t* gid, gid_t* gids, int* gids_count) {
46 char *clobberablegids;
47 char *nexttok;
48 char *tok;
49 int gids_found;
50
51 if (!uidgids || !*uidgids) {
52 *gid = *uid = 0;
53 *gids_count = 0;
54 return;
55 }
56
57 clobberablegids = strdup(uidgids);
58 strcpy(clobberablegids, uidgids);
59 nexttok = clobberablegids;
60 tok = strsep(&nexttok, ",");
61 pwtoid(tok, uid, gid);
62 tok = strsep(&nexttok, ",");
63 if (!tok) {
64 /* gid is already set above */
65 *gids_count = 0;
66 free(clobberablegids);
67 return;
68 }
69 pwtoid(tok, NULL, gid);
70 gids_found = 0;
71 while ((gids_found < *gids_count) && (tok = strsep(&nexttok, ","))) {
72 pwtoid(tok, NULL, gids);
73 gids_found++;
74 gids++;
75 }
76 if (nexttok && gids_found == *gids_count) {
77 fprintf(stderr, "too many group ids\n");
78 }
79 *gids_count = gids_found;
80 free(clobberablegids);
81 }
82
main(int argc,char ** argv)83 int main(int argc, char** argv) {
84 uid_t current_uid = getuid();
85 if (current_uid != AID_ROOT && current_uid != AID_SHELL) error(1, 0, "not allowed");
86
87 // Handle -h and --help.
88 ++argv;
89 if (*argv && (strcmp(*argv, "--help") == 0 || strcmp(*argv, "-h") == 0)) {
90 fprintf(stderr,
91 "usage: su [UID[,GID[,GID2]...]] [COMMAND [ARG...]]\n"
92 "\n"
93 "Switch to WHO (default 'root') and run the given command (default sh).\n"
94 "\n"
95 "where WHO is a comma-separated list of user, group,\n"
96 "and supplementary groups in that order.\n"
97 "\n");
98 return 0;
99 }
100
101 // The default user is root.
102 uid_t uid = 0;
103 gid_t gid = 0;
104
105 // If there are any arguments, the first argument is the uid/gid/supplementary groups.
106 if (*argv) {
107 gid_t gids[10];
108 int gids_count = sizeof(gids)/sizeof(gids[0]);
109 extract_uidgids(*argv, &uid, &gid, gids, &gids_count);
110 if (gids_count) {
111 if (setgroups(gids_count, gids)) {
112 error(1, errno, "setgroups failed");
113 }
114 }
115 ++argv;
116 }
117
118 if (setgid(gid)) error(1, errno, "setgid failed");
119 if (setuid(uid)) error(1, errno, "setuid failed");
120
121 // Reset parts of the environment.
122 setenv("PATH", _PATH_DEFPATH, 1);
123 unsetenv("IFS");
124 struct passwd* pw = getpwuid(uid);
125 if (pw) {
126 setenv("LOGNAME", pw->pw_name, 1);
127 setenv("USER", pw->pw_name, 1);
128 } else {
129 unsetenv("LOGNAME");
130 unsetenv("USER");
131 }
132
133 // Set up the arguments for exec.
134 char* exec_args[argc + 1]; // Having too much space is fine.
135 size_t i = 0;
136 for (; *argv != NULL; ++i) {
137 exec_args[i] = *argv++;
138 }
139 // Default to the standard shell.
140 if (i == 0) exec_args[i++] = "/system/bin/sh";
141 exec_args[i] = NULL;
142
143 execvp(exec_args[0], exec_args);
144 error(1, errno, "failed to exec %s", exec_args[0]);
145 }
146