libfstools/extroot.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 <unistd.h>
  15 #include <stdlib.h>
  16 #include <stdio.h>
  17 #include <string.h>
  18 #include <sys/mount.h>
  19 #include <sys/types.h>
  20 #include <sys/stat.h>
  21 #include <sys/wait.h>
  22 #include <libgen.h>
  23
  24 #include "libfstools.h"
  25
  26 char const *extroot_prefix = NULL;
  27
  28 /*
  29  * This will execute "block extroot" and make use of mounted extroot or return
  30  * an error.
  31  */
  32 int mount_extroot(void)
  33 {
  34         char ldlib_path[32];
  35         char block_path[32];
  36         char kmod_loader[64];
  37         struct stat s;
  38         pid_t pid;
  39
  40         if (!extroot_prefix)
  41                 return -1;
  42
  43         /* try finding the library directory */
  44         snprintf(ldlib_path, sizeof(ldlib_path), "%s/upper/lib", extroot_prefix);
  45
  46         if (stat(ldlib_path, &s) || !S_ISDIR(s.st_mode))
  47                 snprintf(ldlib_path, sizeof(ldlib_path), "%s/lib", extroot_prefix);
  48
  49         /* try finding the block executable */
  50         snprintf(block_path, sizeof(block_path), "%s/upper/sbin/block", extroot_prefix);
  51
  52         if (stat(block_path, &s) || !S_ISREG(s.st_mode))
  53                 snprintf(block_path, sizeof(block_path), "%s/sbin/block", extroot_prefix);
  54
  55         if (stat(block_path, &s) || !S_ISREG(s.st_mode))
  56                 snprintf(block_path, sizeof(block_path), "/sbin/block");
  57
  58         if (stat(block_path, &s) || !S_ISREG(s.st_mode))
  59                 return -1;
  60
  61         /* set LD_LIBRARY_PATH env var and load kmods from overlay if we found a lib directory there */
  62         if (!stat(ldlib_path, &s) && S_ISDIR(s.st_mode)) {
  63                 setenv("LD_LIBRARY_PATH", ldlib_path, 1);
  64                 snprintf(kmod_loader, sizeof(kmod_loader),
  65                          "/sbin/kmodloader %s/etc/modules-boot.d/", dirname(ldlib_path));
  66                 system(kmod_loader);
  67         }
  68
  69         pid = fork();
  70         if (!pid) {
  71                 mkdir("/tmp/extroot", 0755);
  72                 execl(block_path, block_path, "extroot", NULL);
  73                 exit(-1);
  74         } else if (pid > 0) {
  75                 int status;
  76
  77                 waitpid(pid, &status, 0);
  78                 if (!WEXITSTATUS(status)) {
  79                         if (find_mount("/tmp/extroot/mnt")) {
  80                                 mount("/dev/root", "/", NULL, MS_NOATIME | MS_REMOUNT | MS_RDONLY, 0);
  81
  82                                 mkdir("/tmp/extroot/mnt/proc", 0755);
  83                                 mkdir("/tmp/extroot/mnt/dev", 0755);
  84                                 mkdir("/tmp/extroot/mnt/sys", 0755);
  85                                 mkdir("/tmp/extroot/mnt/tmp", 0755);
  86                                 mkdir("/tmp/extroot/mnt/rom", 0755);
  87
  88                                 if (mount_move("/tmp/extroot", "", "/mnt")) {
  89                                         fprintf(stderr, "moving pivotroot failed - continue normal boot\n");
  90                                         umount("/tmp/extroot/mnt");
  91                                 } else if (pivot("/mnt", "/rom")) {
  92                                         fprintf(stderr, "switching to pivotroot failed - continue normal boot\n");
  93                                         umount("/mnt");
  94                                 } else {
  95                                         umount("/tmp/overlay");
  96                                         rmdir("/tmp/overlay");
  97                                         rmdir("/tmp/extroot/mnt");
  98                                         rmdir("/tmp/extroot");
  99                                         return 0;
 100                                 }
 101                         } else if (find_mount("/tmp/extroot/overlay")) {
 102                                 if (mount_move("/tmp/extroot", "", "/overlay")) {
 103                                         fprintf(stderr, "moving extroot failed - continue normal boot\n");
 104                                         umount("/tmp/extroot/overlay");
 105                                 } else if (fopivot("/overlay", "/rom")) {
 106                                         fprintf(stderr, "switching to extroot failed - continue normal boot\n");
 107                                         umount("/overlay");
 108                                 } else {
 109                                         umount("/tmp/overlay");
 110                                         rmdir("/tmp/overlay");
 111                                         rmdir("/tmp/extroot/overlay");
 112                                         rmdir("/tmp/extroot");
 113                                         return 0;
 114                                 }
 115                         }
 116                 }
 117         }
 118         return -1;
 119 }