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 <stdio.h>
23#include <stdlib.h>
24#include <string.h>
25#include <unistd.h>
26
27#include <private/android_filesystem_config.h>
28
29void pwtoid(const char* tok, uid_t* uid, gid_t* gid) {
30    struct passwd* pw = getpwnam(tok);
31    if (pw) {
32        if (uid) *uid = pw->pw_uid;
33        if (gid) *gid = pw->pw_gid;
34    } else {
35        char* end;
36        errno = 0;
37        uid_t tmpid = strtoul(tok, &end, 10);
38        if (errno != 0 || end == tok) error(1, errno, "invalid uid/gid '%s'", tok);
39        if (uid) *uid = tmpid;
40        if (gid) *gid = tmpid;
41    }
42}
43
44void extract_uidgids(const char* uidgids, uid_t* uid, gid_t* gid, gid_t* gids, int* gids_count) {
45    char *clobberablegids;
46    char *nexttok;
47    char *tok;
48    int gids_found;
49
50    if (!uidgids || !*uidgids) {
51        *gid = *uid = 0;
52        *gids_count = 0;
53        return;
54    }
55
56    clobberablegids = strdup(uidgids);
57    strcpy(clobberablegids, uidgids);
58    nexttok = clobberablegids;
59    tok = strsep(&nexttok, ",");
60    pwtoid(tok, uid, gid);
61    tok = strsep(&nexttok, ",");
62    if (!tok) {
63        /* gid is already set above */
64        *gids_count = 0;
65        free(clobberablegids);
66        return;
67    }
68    pwtoid(tok, NULL, gid);
69    gids_found = 0;
70    while ((gids_found < *gids_count) && (tok = strsep(&nexttok, ","))) {
71        pwtoid(tok, NULL, gids);
72        gids_found++;
73        gids++;
74    }
75    if (nexttok && gids_found == *gids_count) {
76        fprintf(stderr, "too many group ids\n");
77    }
78    *gids_count = gids_found;
79    free(clobberablegids);
80}
81
82int main(int argc, char** argv) {
83    uid_t current_uid = getuid();
84    if (current_uid != AID_ROOT && current_uid != AID_SHELL) error(1, 0, "not allowed");
85
86    // Handle -h and --help.
87    ++argv;
88    if (*argv && (strcmp(*argv, "--help") == 0 || strcmp(*argv, "-h") == 0)) {
89        fprintf(stderr,
90                "usage: su [UID[,GID[,GID2]...]] [COMMAND [ARG...]]\n"
91                "\n"
92                "Switch to WHO (default 'root') and run the given command (default sh).\n"
93                "\n"
94                "where WHO is a comma-separated list of user, group,\n"
95                "and supplementary groups in that order.\n"
96                "\n");
97        return 0;
98    }
99
100    // The default user is root.
101    uid_t uid = 0;
102    gid_t gid = 0;
103
104    // If there are any arguments, the first argument is the uid/gid/supplementary groups.
105    if (*argv) {
106        gid_t gids[10];
107        int gids_count = sizeof(gids)/sizeof(gids[0]);
108        extract_uidgids(*argv, &uid, &gid, gids, &gids_count);
109        if (gids_count) {
110            if (setgroups(gids_count, gids)) {
111                error(1, errno, "setgroups failed");
112            }
113        }
114        ++argv;
115    }
116
117    if (setgid(gid)) error(1, errno, "setgid failed");
118    if (setuid(uid)) error(1, errno, "setuid failed");
119
120    // Reset parts of the environment.
121    setenv("PATH", _PATH_DEFPATH, 1);
122    unsetenv("IFS");
123    struct passwd* pw = getpwuid(uid);
124    if (pw) {
125        setenv("LOGNAME", pw->pw_name, 1);
126        setenv("USER", pw->pw_name, 1);
127    } else {
128        unsetenv("LOGNAME");
129        unsetenv("USER");
130    }
131
132    // Set up the arguments for exec.
133    char* exec_args[argc + 1];  // Having too much space is fine.
134    size_t i = 0;
135    for (; *argv != NULL; ++i) {
136      exec_args[i] = *argv++;
137    }
138    // Default to the standard shell.
139    if (i == 0) exec_args[i++] = const_cast<char*>("/system/bin/sh");
140    exec_args[i] = NULL;
141
142    execvp(exec_args[0], exec_args);
143    error(1, errno, "failed to exec %s", exec_args[0]);
144}
145