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      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.
     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.
     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.
     65 static std::string find_mount(const char* dir) {
     66     if (strcmp(dir, "/") == 0) {
     67        return find_fstab_mount(dir);
     68     } else {
     69        return find_proc_mount(dir);
     70     }
     71 }
     72 
     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 
     85 static bool remount_partition(int fd, const char* dir) {
     86     if (!directory_exists(dir)) {
     87         return true;
     88     }
     89     std::string dev = find_mount(dir);
     90     if (dev.empty()) {
     91         return true;
     92     }
     93     if (!make_block_device_writable(dev)) {
     94         WriteFdFmt(fd, "remount of %s failed; couldn't make block device %s writable: %s\n",
     95                    dir, dev.c_str(), strerror(errno));
     96         return false;
     97     }
     98     if (mount(dev.c_str(), dir, "none", MS_REMOUNT, nullptr) == -1) {
     99         WriteFdFmt(fd, "remount of %s failed: %s\n", dir, strerror(errno));
    100         return false;
    101     }
    102     return true;
    103 }
    104 
    105 void remount_service(int fd, void* cookie) {
    106     if (getuid() != 0) {
    107         WriteFdExactly(fd, "Not running as root. Try \"adb root\" first.\n");
    108         adb_close(fd);
    109         return;
    110     }
    111 
    112     bool system_verified = !(android::base::GetProperty("partition.system.verified", "").empty());
    113     bool vendor_verified = !(android::base::GetProperty("partition.vendor.verified", "").empty());
    114 
    115     if (system_verified || vendor_verified) {
    116         // Allow remount but warn of likely bad effects
    117         bool both = system_verified && vendor_verified;
    118         WriteFdFmt(fd,
    119                    "dm_verity is enabled on the %s%s%s partition%s.\n",
    120                    system_verified ? "system" : "",
    121                    both ? " and " : "",
    122                    vendor_verified ? "vendor" : "",
    123                    both ? "s" : "");
    124         WriteFdExactly(fd,
    125                        "Use \"adb disable-verity\" to disable verity.\n"
    126                        "If you do not, remount may succeed, however, you will still "
    127                        "not be able to write to these volumes.\n");
    128     }
    129 
    130     bool success = true;
    131     if (android::base::GetBoolProperty("ro.build.system_root_image", false)) {
    132         success &= remount_partition(fd, "/");
    133     } else {
    134         success &= remount_partition(fd, "/system");
    135     }
    136     success &= remount_partition(fd, "/vendor");
    137     success &= remount_partition(fd, "/oem");
    138 
    139     WriteFdExactly(fd, success ? "remount succeeded\n" : "remount failed\n");
    140 
    141     adb_close(fd);
    142 }
    143