libfstools/mount.c

   1 /*
   2  * Copyright (C) 2014 John Crispin <blogic@openwrt.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License version 2.1
   6  * as published by the Free Software Foundation
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  */
  13
  14 #include <sys/types.h>
  15 #include <sys/stat.h>
  16 #include <sys/mount.h>
  17 #include <sys/wait.h>
  18
  19 #include <errno.h>
  20 #include <stdio.h>
  21 #include <unistd.h>
  22 #include <string.h>
  23
  24 #include "libfstools.h"
  25
  26 /* this is a raw syscall - man 2 pivot_root */
  27 extern int pivot_root(const char *new_root, const char *put_old);
  28
  29 /**
  30  * mount_move - move mounted point to the new location
  31  *
  32  * @oldroot: directory that is current location of mount point
  33  * @newroot: new directory for the mount point
  34  */
  35 int
  36 mount_move(const char *oldroot, const char *newroot, const char *dir)
  37 {
  38 #ifndef MS_MOVE
  39 #define MS_MOVE (1 << 13)
  40 #endif
  41         struct stat s;
  42         char olddir[64];
  43         char newdir[64];
  44         int ret;
  45
  46         snprintf(olddir, sizeof(olddir), "%s%s", oldroot, dir);
  47         snprintf(newdir, sizeof(newdir), "%s%s", newroot, dir);
  48
  49         if (stat(olddir, &s) || !S_ISDIR(s.st_mode))
  50                 return -1;
  51
  52         if (stat(newdir, &s) || !S_ISDIR(s.st_mode))
  53                 return -1;
  54
  55         ret = mount(olddir, newdir, NULL, MS_NOATIME | MS_MOVE, NULL);
  56
  57 /*      if (ret)
  58                 ULOG_ERR("failed %s %s: %m\n", olddir, newdir);*/
  59
  60         return ret;
  61 }
  62
  63 int
  64 pivot(char *new, char *old)
  65 {
  66         char pivotdir[64];
  67         int ret;
  68
  69         if (mount_move("", new, "/proc"))
  70                 return -1;
  71
  72         snprintf(pivotdir, sizeof(pivotdir), "%s%s", new, old);
  73
  74         ret = pivot_root(new, pivotdir);
  75
  76         if (ret < 0) {
  77                 ULOG_ERR("pivot_root failed %s %s: %m\n", new, pivotdir);
  78                 return -1;
  79         }
  80
  81         mount_move(old, "", "/dev");
  82         mount_move(old, "", "/tmp");
  83         mount_move(old, "", "/sys");
  84         mount_move(old, "", "/overlay");
  85
  86         return 0;
  87 }
  88
  89 void
  90 selinux_restorecon(char *overlaydir)
  91 {
  92         struct stat s;
  93         pid_t restorecon_pid;
  94         int status;
  95
  96         /* on non-SELinux system we don't have /sbin/restorecon, return */
  97         if (stat("/sbin/restorecon", &s))
  98                 return;
  99
 100         restorecon_pid = fork();
 101         if (!restorecon_pid)
 102                 execl("/sbin/restorecon", "restorecon", overlaydir, (char *) NULL);
 103         else if (restorecon_pid > 0)
 104                 waitpid(restorecon_pid, &status, 0);
 105 }
 106
 107 /**
 108  * fopivot - switch to overlay using passed dir as upper one
 109  *
 110  * @rw_root: writable directory that will be used as upper dir
 111  * @ro_root: directory where old root will be put
 112  */
 113 int
 114 fopivot(char *rw_root, char *ro_root)
 115 {
 116         char overlay[64], mount_options[64], upperdir[64], workdir[64], upgrade[64], upgrade_dest[64];
 117         struct stat st;
 118
 119         if (find_filesystem("overlay")) {
 120                 ULOG_ERR("BUG: no suitable fs found\n");
 121                 return -1;
 122         }
 123
 124         snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root);
 125         snprintf(upperdir, sizeof(upperdir), "%s/upper", rw_root);
 126         snprintf(workdir, sizeof(workdir), "%s/work", rw_root);
 127         snprintf(upgrade, sizeof(upgrade), "%s/sysupgrade.tgz", rw_root);
 128         snprintf(upgrade_dest, sizeof(upgrade_dest), "%s/sysupgrade.tgz", upperdir);
 129         snprintf(mount_options, sizeof(mount_options), "lowerdir=/,upperdir=%s,workdir=%s",
 130                  upperdir, workdir);
 131
 132         /*
 133          * Initialize SELinux security label on newly created overlay
 134          * filesystem where /upper doesn't yet exist
 135          */
 136         if (stat(upperdir, &st))
 137                 selinux_restorecon(rw_root);
 138
 139         /*
 140          * Overlay FS v23 and later requires both a upper and
 141          * a work directory, both on the same filesystem, but
 142          * not part of the same subtree.
 143          * We can't really deal with these constraints without
 144          * creating two new subdirectories in /overlay.
 145          */
 146         mkdir(upperdir, 0755);
 147         mkdir(workdir, 0755);
 148
 149         if (stat(upgrade, &st) == 0)
 150                 rename(upgrade, upgrade_dest);
 151
 152         if (mount(overlay, "/mnt", "overlay", MS_NOATIME, mount_options)) {
 153                 ULOG_ERR("mount failed: %m, options %s\n", mount_options);
 154                 return -1;
 155         }
 156
 157         return pivot("/mnt", ro_root);
 158 }
 159
 160 /**
 161  * ramoverlay - use RAM to store filesystem changes on top of RO root
 162  */
 163 int
 164 ramoverlay(void)
 165 {
 166         mkdir("/tmp/root", 0755);
 167         mount("tmpfs", "/tmp/root", "tmpfs", MS_NOATIME, "mode=0755");
 168
 169         return fopivot("/tmp/root", "/rom");
 170 }