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
30void 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
45void 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
83int 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    setenv("LOGNAME", pw->pw_name, 1);
126    setenv("USER", pw->pw_name, 1);
127
128    // Set up the arguments for exec.
129    char* exec_args[argc + 1];  // Having too much space is fine.
130    size_t i = 0;
131    for (; *argv != NULL; ++i) {
132      exec_args[i] = *argv++;
133    }
134    // Default to the standard shell.
135    if (i == 0) exec_args[i++] = "/system/bin/sh";
136    exec_args[i] = NULL;
137
138    execvp(exec_args[0], exec_args);
139    error(1, errno, "failed to exec %s", exec_args[0]);
140}
141