1 /*
2 * Copyright (C) 2019 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 "mount_namespace.h"
18
19 #include <sys/mount.h>
20
21 #include <string>
22 #include <vector>
23
24 #include <ApexProperties.sysprop.h>
25 #include <android-base/file.h>
26 #include <android-base/logging.h>
27 #include <android-base/properties.h>
28 #include <android-base/result.h>
29 #include <android-base/unique_fd.h>
30
31 #include "util.h"
32
33 #ifndef RECOVERY
34 #define ACTIVATE_FLATTENED_APEX 1
35 #endif
36
37 #ifdef ACTIVATE_FLATTENED_APEX
38 #include <apex_manifest.pb.h>
39 #include <com_android_apex.h>
40 #include <selinux/android.h>
41 #endif // ACTIVATE_FLATTENED_APEX
42
43 namespace android {
44 namespace init {
45 namespace {
46
BindMount(const std::string & source,const std::string & mount_point)47 static bool BindMount(const std::string& source, const std::string& mount_point) {
48 if (mount(source.c_str(), mount_point.c_str(), nullptr, MS_BIND | MS_REC, nullptr) == -1) {
49 PLOG(ERROR) << "Failed to bind mount " << source;
50 return false;
51 }
52 return true;
53 }
54
ChangeMount(const std::string & mount_point,unsigned long mountflags)55 static bool ChangeMount(const std::string& mount_point, unsigned long mountflags) {
56 if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
57 PLOG(ERROR) << "Failed to remount " << mount_point << " as " << std::hex << mountflags;
58 return false;
59 }
60 return true;
61 }
62
OpenMountNamespace()63 static int OpenMountNamespace() {
64 int fd = open("/proc/self/ns/mnt", O_RDONLY | O_CLOEXEC);
65 if (fd < 0) {
66 PLOG(ERROR) << "Cannot open fd for current mount namespace";
67 }
68 return fd;
69 }
70
GetMountNamespaceId()71 static std::string GetMountNamespaceId() {
72 std::string ret;
73 if (!android::base::Readlink("/proc/self/ns/mnt", &ret)) {
74 PLOG(ERROR) << "Failed to read namespace ID";
75 return "";
76 }
77 return ret;
78 }
79
IsApexUpdatable()80 static bool IsApexUpdatable() {
81 static bool updatable = android::sysprop::ApexProperties::updatable().value_or(false);
82 return updatable;
83 }
84
85 // In case we have two sets of APEXes (non-updatable, updatable), we need two separate mount
86 // namespaces.
NeedsTwoMountNamespaces()87 static bool NeedsTwoMountNamespaces() {
88 if (!IsApexUpdatable()) return false;
89 if (IsRecoveryMode()) return false;
90 // In microdroid, there's only one set of APEXes in built-in directories include block devices.
91 if (IsMicrodroid()) return false;
92 return true;
93 }
94
95 static android::base::unique_fd bootstrap_ns_fd;
96 static android::base::unique_fd default_ns_fd;
97
98 static std::string bootstrap_ns_id;
99 static std::string default_ns_id;
100
101 } // namespace
102
SetupMountNamespaces()103 bool SetupMountNamespaces() {
104 // Set the propagation type of / as shared so that any mounting event (e.g.
105 // /data) is by default visible to all processes. When private mounting is
106 // needed for /foo/bar, then we will make /foo/bar as a mount point (by
107 // bind-mounting by to itself) and set the propagation type of the mount
108 // point to private.
109 if (!ChangeMount("/", MS_SHARED | MS_REC)) return false;
110
111 // /apex is a private mountpoint to give different sets of APEXes for
112 // the bootstrap and default mount namespaces. The processes running with
113 // the bootstrap namespace get APEXes from the read-only partition.
114 if (!(ChangeMount("/apex", MS_PRIVATE))) return false;
115
116 // /linkerconfig is a private mountpoint to give a different linker configuration
117 // based on the mount namespace. Subdirectory will be bind-mounted based on current mount
118 // namespace
119 if (!(ChangeMount("/linkerconfig", MS_PRIVATE))) return false;
120
121 // The two mount namespaces present challenges for scoped storage, because
122 // vold, which is responsible for most of the mounting, lives in the
123 // bootstrap mount namespace, whereas most other daemons and all apps live
124 // in the default namespace. Scoped storage has a need for a
125 // /mnt/installer view that is a slave bind mount of /mnt/user - in other
126 // words, all mounts under /mnt/user should automatically show up under
127 // /mnt/installer. However, additional mounts done under /mnt/installer
128 // should not propagate back to /mnt/user. In a single mount namespace
129 // this is easy to achieve, by simply marking the /mnt/installer a slave
130 // bind mount. Unfortunately, if /mnt/installer is only created and
131 // bind mounted after the two namespaces are created below, we end up
132 // with the following situation:
133 // /mnt/user and /mnt/installer share the same peer group in both the
134 // bootstrap and default namespaces. Marking /mnt/installer slave in either
135 // namespace means that it won't propagate events to the /mnt/installer in
136 // the other namespace, which is still something we require - vold is the
137 // one doing the mounting under /mnt/installer, and those mounts should
138 // show up in the default namespace as well.
139 //
140 // The simplest solution is to do the bind mount before the two namespaces
141 // are created: the effect is that in both namespaces, /mnt/installer is a
142 // slave to the /mnt/user mount, and at the same time /mnt/installer in the
143 // bootstrap namespace shares a peer group with /mnt/installer in the
144 // default namespace.
145 // /mnt/androidwritable is similar to /mnt/installer but serves for
146 // MOUNT_EXTERNAL_ANDROID_WRITABLE apps.
147 if (!mkdir_recursive("/mnt/user", 0755)) return false;
148 if (!mkdir_recursive("/mnt/installer", 0755)) return false;
149 if (!mkdir_recursive("/mnt/androidwritable", 0755)) return false;
150 if (!(BindMount("/mnt/user", "/mnt/installer"))) return false;
151 if (!(BindMount("/mnt/user", "/mnt/androidwritable"))) return false;
152 // First, make /mnt/installer and /mnt/androidwritable a slave bind mount
153 if (!(ChangeMount("/mnt/installer", MS_SLAVE))) return false;
154 if (!(ChangeMount("/mnt/androidwritable", MS_SLAVE))) return false;
155 // Then, make it shared again - effectively creating a new peer group, that
156 // will be inherited by new mount namespaces.
157 if (!(ChangeMount("/mnt/installer", MS_SHARED))) return false;
158 if (!(ChangeMount("/mnt/androidwritable", MS_SHARED))) return false;
159
160 bootstrap_ns_fd.reset(OpenMountNamespace());
161 bootstrap_ns_id = GetMountNamespaceId();
162
163 // When APEXes are updatable (e.g. not-flattened), we create separate mount
164 // namespaces for processes that are started before and after the APEX is
165 // activated by apexd. In the namespace for pre-apexd processes, small
166 // number of essential APEXes (e.g. com.android.runtime) are activated.
167 // In the namespace for post-apexd processes, all APEXes are activated.
168 bool success = true;
169 if (NeedsTwoMountNamespaces()) {
170 // Creating a new namespace by cloning, saving, and switching back to
171 // the original namespace.
172 if (unshare(CLONE_NEWNS) == -1) {
173 PLOG(ERROR) << "Cannot create mount namespace";
174 return false;
175 }
176 default_ns_fd.reset(OpenMountNamespace());
177 default_ns_id = GetMountNamespaceId();
178
179 if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
180 PLOG(ERROR) << "Cannot switch back to bootstrap mount namespace";
181 return false;
182 }
183 } else {
184 // Otherwise, default == bootstrap
185 default_ns_fd.reset(OpenMountNamespace());
186 default_ns_id = GetMountNamespaceId();
187 }
188
189 LOG(INFO) << "SetupMountNamespaces done";
190 return success;
191 }
192
193 // Switch the mount namespace of the current process from bootstrap to default OR from default to
194 // bootstrap. If the current mount namespace is neither bootstrap nor default, keep it that way.
SwitchToMountNamespaceIfNeeded(MountNamespace target_mount_namespace)195 Result<void> SwitchToMountNamespaceIfNeeded(MountNamespace target_mount_namespace) {
196 if (IsRecoveryMode() || !IsApexUpdatable()) {
197 // we don't have multiple namespaces in recovery mode or if apex is not updatable
198 return {};
199 }
200
201 const std::string current_namespace_id = GetMountNamespaceId();
202 MountNamespace current_mount_namespace;
203 if (current_namespace_id == bootstrap_ns_id) {
204 current_mount_namespace = NS_BOOTSTRAP;
205 } else if (current_namespace_id == default_ns_id) {
206 current_mount_namespace = NS_DEFAULT;
207 } else {
208 // services with `namespace mnt` start in its own mount namespace. So we need to keep it.
209 return {};
210 }
211
212 // We're already in the target mount namespace.
213 if (current_mount_namespace == target_mount_namespace) {
214 return {};
215 }
216
217 const auto& ns_fd = target_mount_namespace == NS_BOOTSTRAP ? bootstrap_ns_fd : default_ns_fd;
218 const auto& ns_name = target_mount_namespace == NS_BOOTSTRAP ? "bootstrap" : "default";
219 if (ns_fd.get() != -1) {
220 if (setns(ns_fd.get(), CLONE_NEWNS) == -1) {
221 return ErrnoError() << "Failed to switch to " << ns_name << " mount namespace.";
222 }
223 }
224 return {};
225 }
226
GetCurrentMountNamespace()227 base::Result<MountNamespace> GetCurrentMountNamespace() {
228 std::string current_namespace_id = GetMountNamespaceId();
229 if (current_namespace_id == "") {
230 return Error() << "Failed to get current mount namespace ID";
231 }
232
233 if (current_namespace_id == bootstrap_ns_id) {
234 return NS_BOOTSTRAP;
235 } else if (current_namespace_id == default_ns_id) {
236 return NS_DEFAULT;
237 }
238
239 return Error() << "Failed to find current mount namespace";
240 }
241
242 } // namespace init
243 } // namespace android
244