remount_service.cpp revision 9aa4fda4e64c1882faf019cc2a483ee4917e0c85 
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#define TRACE_TAG TRACE_ADB
18
19#include "sysdeps.h"
20
21#include <errno.h>
22#include <fcntl.h>
23#include <mntent.h>
24#include <stdio.h>
25#include <stdlib.h>
26#include <string.h>
27#include <sys/mount.h>
28#include <unistd.h>
29
30#include <string>
31
32#include "adb.h"
33#include "adb_io.h"
34#include "adb_utils.h"
35#include "cutils/properties.h"
36
37// Returns the device used to mount a directory in /proc/mounts.
38static std::string find_mount(const char* dir) {
39    std::unique_ptr<FILE, int(*)(FILE*)> fp(setmntent("/proc/mounts", "r"), endmntent);
40    if (!fp) {
41        return "";
42    }
43
44    mntent* e;
45    while ((e = getmntent(fp.get())) != nullptr) {
46        if (strcmp(dir, e->mnt_dir) == 0) {
47            return e->mnt_fsname;
48        }
49    }
50    return "";
51}
52
53bool make_block_device_writable(const std::string& dev) {
54    int fd = unix_open(dev.c_str(), O_RDONLY | O_CLOEXEC);
55    if (fd == -1) {
56        return false;
57    }
58
59    int OFF = 0;
60    bool result = (ioctl(fd, BLKROSET, &OFF) != -1);
61    adb_close(fd);
62    return result;
63}
64
65static bool remount_partition(int fd, const char* dir) {
66    if (!directory_exists(dir)) {
67        return true;
68    }
69    std::string dev = find_mount(dir);
70    if (dev.empty()) {
71        return true;
72    }
73    if (!make_block_device_writable(dev)) {
74        WriteFdFmt(fd, "remount of %s failed; couldn't make block device %s writable: %s\n",
75                   dir, dev.c_str(), strerror(errno));
76        return false;
77    }
78    if (mount(dev.c_str(), dir, "none", MS_REMOUNT, nullptr) == -1) {
79        WriteFdFmt(fd, "remount of %s failed: %s\n", dir, strerror(errno));
80        return false;
81    }
82    return true;
83}
84
85void remount_service(int fd, void* cookie) {
86    if (getuid() != 0) {
87        WriteFdExactly(fd, "Not running as root. Try \"adb root\" first.\n");
88        adb_close(fd);
89        return;
90    }
91
92    char prop_buf[PROPERTY_VALUE_MAX];
93    property_get("partition.system.verified", prop_buf, "");
94    bool system_verified = (strlen(prop_buf) > 0);
95
96    property_get("partition.vendor.verified", prop_buf, "");
97    bool vendor_verified = (strlen(prop_buf) > 0);
98
99    if (system_verified || vendor_verified) {
100        // Allow remount but warn of likely bad effects
101        bool both = system_verified && vendor_verified;
102        WriteFdFmt(fd,
103                   "dm_verity is enabled on the %s%s%s partition%s.\n",
104                   system_verified ? "system" : "",
105                   both ? " and " : "",
106                   vendor_verified ? "vendor" : "",
107                   both ? "s" : "");
108        WriteFdExactly(fd,
109                       "Use \"adb disable-verity\" to disable verity.\n"
110                       "If you do not, remount may succeed, however, you will still "
111                       "not be able to write to these volumes.\n");
112    }
113
114    bool success = true;
115    success &= remount_partition(fd, "/system");
116    success &= remount_partition(fd, "/vendor");
117    success &= remount_partition(fd, "/oem");
118
119    WriteFdExactly(fd, success ? "remount succeeded\n" : "remount failed\n");
120
121    adb_close(fd);
122}
123