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 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 <android-base/properties.h>
33
34 #include "adb.h"
35 #include "adb_io.h"
36 #include "adb_utils.h"
37 #include "fs_mgr.h"
38
39 // Returns the device used to mount a directory in /proc/mounts.
find_proc_mount(const char * dir)40 static std::string find_proc_mount(const char* dir) {
41 std::unique_ptr<FILE, int(*)(FILE*)> fp(setmntent("/proc/mounts", "r"), endmntent);
42 if (!fp) {
43 return "";
44 }
45
46 mntent* e;
47 while ((e = getmntent(fp.get())) != nullptr) {
48 if (strcmp(dir, e->mnt_dir) == 0) {
49 return e->mnt_fsname;
50 }
51 }
52 return "";
53 }
54
55 // Returns the device used to mount a directory in the fstab.
find_fstab_mount(const char * dir)56 static std::string find_fstab_mount(const char* dir) {
57 std::unique_ptr<fstab, decltype(&fs_mgr_free_fstab)> fstab(fs_mgr_read_fstab_default(),
58 fs_mgr_free_fstab);
59 struct fstab_rec* rec = fs_mgr_get_entry_for_mount_point(fstab.get(), dir);
60 return rec ? rec->blk_device : "";
61 }
62
63 // The proc entry for / is full of lies, so check fstab instead.
64 // /proc/mounts lists rootfs and /dev/root, neither of which is what we want.
find_mount(const char * dir,bool is_root)65 static std::string find_mount(const char* dir, bool is_root) {
66 if (is_root) {
67 return find_fstab_mount(dir);
68 } else {
69 return find_proc_mount(dir);
70 }
71 }
72
make_block_device_writable(const std::string & dev)73 bool make_block_device_writable(const std::string& dev) {
74 int fd = unix_open(dev.c_str(), O_RDONLY | O_CLOEXEC);
75 if (fd == -1) {
76 return false;
77 }
78
79 int OFF = 0;
80 bool result = (ioctl(fd, BLKROSET, &OFF) != -1);
81 unix_close(fd);
82 return result;
83 }
84
remount_partition(int fd,const char * dir)85 static bool remount_partition(int fd, const char* dir) {
86 if (!directory_exists(dir)) {
87 return true;
88 }
89 bool is_root = strcmp(dir, "/") == 0;
90 std::string dev = find_mount(dir, is_root);
91 // Even if the device for the root is not found, we still try to remount it
92 // as rw. This typically only happens when running Android in a container:
93 // the root will almost always be in a loop device, which is dynamic, so
94 // it's not convenient to put in the fstab.
95 if (dev.empty() && !is_root) {
96 return true;
97 }
98 if (!dev.empty() && !make_block_device_writable(dev)) {
99 WriteFdFmt(fd, "remount of %s failed; couldn't make block device %s writable: %s\n",
100 dir, dev.c_str(), strerror(errno));
101 return false;
102 }
103 if (mount(dev.c_str(), dir, "none", MS_REMOUNT | MS_BIND, nullptr) == -1) {
104 // This is useful for cases where the superblock is already marked as
105 // read-write, but the mount itself is read-only, such as containers
106 // where the remount with just MS_REMOUNT is forbidden by the kernel.
107 WriteFdFmt(fd, "remount of the %s mount failed: %s.\n", dir, strerror(errno));
108 return false;
109 }
110 if (mount(dev.c_str(), dir, "none", MS_REMOUNT, nullptr) == -1) {
111 WriteFdFmt(fd, "remount of the %s superblock failed: %s\n", dir, strerror(errno));
112 return false;
113 }
114 return true;
115 }
116
remount_service(int fd,void * cookie)117 void remount_service(int fd, void* cookie) {
118 if (getuid() != 0) {
119 WriteFdExactly(fd, "Not running as root. Try \"adb root\" first.\n");
120 adb_close(fd);
121 return;
122 }
123
124 bool system_verified = !(android::base::GetProperty("partition.system.verified", "").empty());
125 bool vendor_verified = !(android::base::GetProperty("partition.vendor.verified", "").empty());
126
127 if (system_verified || vendor_verified) {
128 // Allow remount but warn of likely bad effects
129 bool both = system_verified && vendor_verified;
130 WriteFdFmt(fd,
131 "dm_verity is enabled on the %s%s%s partition%s.\n",
132 system_verified ? "system" : "",
133 both ? " and " : "",
134 vendor_verified ? "vendor" : "",
135 both ? "s" : "");
136 WriteFdExactly(fd,
137 "Use \"adb disable-verity\" to disable verity.\n"
138 "If you do not, remount may succeed, however, you will still "
139 "not be able to write to these volumes.\n");
140 }
141
142 bool success = true;
143 if (android::base::GetBoolProperty("ro.build.system_root_image", false)) {
144 success &= remount_partition(fd, "/");
145 } else {
146 success &= remount_partition(fd, "/system");
147 }
148 success &= remount_partition(fd, "/odm");
149 success &= remount_partition(fd, "/oem");
150 success &= remount_partition(fd, "/product");
151 success &= remount_partition(fd, "/vendor");
152
153 WriteFdExactly(fd, success ? "remount succeeded\n" : "remount failed\n");
154
155 adb_close(fd);
156 }
157