1 /*
2  * Copyright (C) 2018 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 "AppFuseUtil.h"
18 
19 #include <sys/mount.h>
20 #include <utils/Errors.h>
21 
22 #include <android-base/logging.h>
23 #include <android-base/stringprintf.h>
24 
25 #include "Utils.h"
26 
27 using android::base::StringPrintf;
28 
29 namespace android {
30 namespace vold {
31 
32 namespace {
33 
34 static size_t kAppFuseMaxMountPointName = 32;
35 
GetMountPath(uid_t uid,const std::string & name,std::string * path)36 static android::status_t GetMountPath(uid_t uid, const std::string& name, std::string* path) {
37     if (name.size() > kAppFuseMaxMountPointName) {
38         LOG(ERROR) << "AppFuse mount name is too long.";
39         return -EINVAL;
40     }
41     for (size_t i = 0; i < name.size(); i++) {
42         if (!isalnum(name[i])) {
43             LOG(ERROR) << "AppFuse mount name contains invalid character.";
44             return -EINVAL;
45         }
46     }
47     *path = StringPrintf("/mnt/appfuse/%d_%s", uid, name.c_str());
48     return android::OK;
49 }
50 
Mount(int device_fd,const std::string & path)51 static android::status_t Mount(int device_fd, const std::string& path) {
52     const auto opts = StringPrintf(
53         "fd=%i,"
54         "rootmode=40000,"
55         "default_permissions,"
56         "allow_other,"
57         "user_id=0,group_id=0,"
58         "context=\"u:object_r:app_fuse_file:s0\","
59         "fscontext=u:object_r:app_fusefs:s0",
60         device_fd);
61 
62     const int result =
63         TEMP_FAILURE_RETRY(mount("/dev/fuse", path.c_str(), "fuse",
64                                  MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_NOATIME, opts.c_str()));
65     if (result != 0) {
66         PLOG(ERROR) << "Failed to mount " << path;
67         return -errno;
68     }
69 
70     return android::OK;
71 }
72 
RunCommand(const std::string & command,uid_t uid,const std::string & path,int device_fd)73 static android::status_t RunCommand(const std::string& command, uid_t uid, const std::string& path,
74                                     int device_fd) {
75     if (DEBUG_APPFUSE) {
76         LOG(DEBUG) << "Run app fuse command " << command << " for the path " << path << " and uid "
77                    << uid;
78     }
79 
80     if (command == "mount") {
81         return Mount(device_fd, path);
82     } else if (command == "unmount") {
83         // If it's just after all FD opened on mount point are closed, umount2 can fail with
84         // EBUSY. To avoid the case, specify MNT_DETACH.
85         if (umount2(path.c_str(), UMOUNT_NOFOLLOW | MNT_DETACH) != 0 && errno != EINVAL &&
86             errno != ENOENT) {
87             PLOG(ERROR) << "Failed to unmount directory.";
88             return -errno;
89         }
90         if (rmdir(path.c_str()) != 0) {
91             PLOG(ERROR) << "Failed to remove the mount directory.";
92             return -errno;
93         }
94         return android::OK;
95     } else {
96         LOG(ERROR) << "Unknown appfuse command " << command;
97         return -EPERM;
98     }
99 
100     return android::OK;
101 }
102 
103 }  // namespace
104 
MountAppFuse(uid_t uid,int mountId,android::base::unique_fd * device_fd)105 int MountAppFuse(uid_t uid, int mountId, android::base::unique_fd* device_fd) {
106     std::string name = std::to_string(mountId);
107 
108     // Check mount point name.
109     std::string path;
110     if (GetMountPath(uid, name, &path) != android::OK) {
111         LOG(ERROR) << "Invalid mount point name";
112         return -1;
113     }
114 
115     // Forcibly remove the existing mount before we attempt to prepare the
116     // directory. If we have a dangling mount, then PrepareDir may fail if the
117     // indirection to FUSE doesn't work.
118     android::vold::ForceUnmount(path);
119 
120     // Create directories.
121     const android::status_t result = android::vold::PrepareDir(path, 0700, 0, 0);
122     if (result != android::OK) {
123         PLOG(ERROR) << "Failed to prepare directory " << path;
124         return -1;
125     }
126 
127     // Open device FD.
128     // NOLINTNEXTLINE(android-cloexec-open): Deliberately not O_CLOEXEC
129     device_fd->reset(open("/dev/fuse", O_RDWR));
130     if (device_fd->get() == -1) {
131         PLOG(ERROR) << "Failed to open /dev/fuse";
132         return -1;
133     }
134 
135     // Mount.
136     return RunCommand("mount", uid, path, device_fd->get());
137 }
138 
UnmountAppFuse(uid_t uid,int mountId)139 int UnmountAppFuse(uid_t uid, int mountId) {
140     std::string name = std::to_string(mountId);
141 
142     // Check mount point name.
143     std::string path;
144     if (GetMountPath(uid, name, &path) != android::OK) {
145         LOG(ERROR) << "Invalid mount point name";
146         return -1;
147     }
148 
149     return RunCommand("unmount", uid, path, -1 /* device_fd */);
150 }
151 
OpenAppFuseFile(uid_t uid,int mountId,int fileId,int flags)152 int OpenAppFuseFile(uid_t uid, int mountId, int fileId, int flags) {
153     std::string name = std::to_string(mountId);
154 
155     // Check mount point name.
156     std::string mountPoint;
157     if (GetMountPath(uid, name, &mountPoint) != android::OK) {
158         LOG(ERROR) << "Invalid mount point name";
159         return -1;
160     }
161 
162     std::string path = StringPrintf("%s/%d", mountPoint.c_str(), fileId);
163     return TEMP_FAILURE_RETRY(open(path.c_str(), flags));
164 }
165 
166 }  // namespace vold
167 }  // namespace android
168