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Зашифрованный загрузочный USB-диск с Linux

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Короткая ссылка: [1]
Оригинал: http://feraga.com/node/94


This howto is an update of Howto install a Debian/GNU Linux system onto a USB flash thumbdrive with the root partition encrypted (using Yaird & DM-Crypt).

Improvements:

  • Using Initramfs-tools instead of Yaird so its no longer restricted to only installing on the device it will boot from (i.e. /dev/sda).
  • Uses UUIDs for partitions labels to eliminate device conflicts.

So open your favorite root login shell and follow these steps! Notes:

  1. This howto has only been tested to work with Debian Sid and Etch.
  2. This howto works with the USB thumbdrive detected as any device. Within these notes, you will find /dev/sda and /dev/sdc used interchangeably.
  3. This howto roughly follows the process used by the Automated Installer as of 01/27/2007.

Содержание

[править] Загрузка требуемых модулей ядра (при необходимости)

Загрузите некоторые/все необходимые модули ядра (это примерный список, настоящий зависит от вашей конфигурации):

root@hostname# modprobe ehci_hcd
root@hostname# modprobe ohci_hcd 
root@hostname# modprobe usbhid
root@hostname# modprobe usb_storage
root@hostname# modprobe dm-crypt
root@hostname# modprobe aes (or aes_686 or aes_x86_64 as appropriate for your system)

[править] Инсталляция необходимых приложений

В системе, где готовится флэшка, проинсталлируйте необходимое программное обеспечение.

   %# apt-get install cryptsetup dmsetup parted debootstrap grub

[править] Поиск носителя

Определите, как в системе виден носитель, на который будет устанавливаться система. Для этого нужно просто воткнуть носитель в систему и посмотреть, что делается в логах.

%# tail -n 14 /var/log/messages
Jan  1 12:00:00 hostname kernel: ohci_hcd 0000:00:02.1: wakeup
Jan  1 12:00:00 hostname kernel: usb 2-3: new full speed USB device using ohci_hcd 
                                 and address 2
Jan  1 12:00:00 hostname kernel: Initializing USB Mass Storage driver...
Jan  1 12:00:00 hostname kernel: scsi2 : SCSI emulation for USB Mass Storage devices
Jan  1 12:00:00 hostname kernel: usbcore: registered new driver usb-storage
Jan  1 12:00:00 hostname kernel: USB Mass Storage support registered.
Jan  1 12:00:00 hostname kernel:   Vendor:           Model: TS256MJFLASHA     Rev: 1.00
Jan  1 12:00:00 hostname kernel:   Type:   Direct-Access                      ANSI SCSI 
                                   revision: 02
Jan  1 12:00:00 hostname kernel: SCSI device sda: 506400 512-byte hdwr sectors (259 MB)
Jan  1 12:00:00 hostname kernel: sda: Write Protect is off
Jan  1 12:00:00 hostname kernel: SCSI device sda: 506400 512-byte hdwr sectors (259 MB)
Jan  1 12:00:00 hostname kernel: sda: Write Protect is off
Jan  1 12:00:00 hostname kernel:  sda: sda1 sda2
Jan  1 12:00:00 hostname kernel: sd 2:0:0:0: Attached scsi removable disk sda

Флэшка увиделась как /dev/sda.

[править] Создание разделов

Далее нам необходимо разбить диск. Для того, чтобы мы могли загружаться с флешки, мы должны иметь загрузочный раздел (boot) и основной раздел (root). Раздела подкачки здесь не будет, так как он займет много места на нашей флешке.

Нам необходимо создать небольшой незашифрованный загрузочный раздел, а остальное разметить как основной раздел.

%# parted /dev/sda "mklabel msdos mkpart primary 0.0 25.0 mkpart primary 25.0 -0 set 1 boot on"

[править] Форматирование под LUKS

Отформатируйте раздел, который должен быть зашифрован, под LUKS.

%# cryptsetup luksFormat /dev/sda2

WARNING!
========
This will overwrite data on /dev/sda2 irrevocably.

Are you sure? (Type uppercase yes): YES
Enter LUKS passphrase:
Verify passphrase:
Command successful.

[править] Подключение зашифрованного раздела

root@hostname# cryptsetup luksOpen /dev/sda2 rootfs
Enter LUKS passphrase:
key slot 0 unlocked.
Command successful.
root@hostname#

[править] Форматирование зашифрованного раздела

root@hostname# mkfs.ext2 /dev/mapper/rootfs
mke2fs 1.39-WIP (29-Mar-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
123392 inodes, 246383 blocks
12319 blocks (5.00%) reserved for the super user
First data block=0
8 block groups
32768 blocks per group, 32768 fragments per group
15424 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376

Writing inode tables: done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 35 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

[править] Форматирование загрузочного раздела

%# mkfs.ext2 /dev/sda1
mke2fs 1.39-WIP (29-Mar-2006)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
5208 inodes, 20800 blocks
1040 blocks (5.00%) reserved for the super user
First data block=1
3 block groups
8192 blocks per group, 8192 fragments per group
1736 inodes per group
Superblock backups stored on blocks:
        8193

Writing inode tables: done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 35 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

[править] Определение UUID (универсальный уникальный идентификатор)

Итак, на этом шаге мы должны узнать UUID наших разделов (загрузочного и зашифрованного) для того, чтобы прописать их в /etc/crypttab и /etc/fstab.

root@hostname# /lib/udev/vol_id -u /dev/sda1
72ea8e0a-256e-47bd-bfc6-6ba33c2ecd48
root@hostname# /lib/udev/vol_id -u /dev/sda2 or cryptsetup luksUUID /dev/sda2
6278aae2-cad0-437d-affa-02277a0cca52
root@hostname#

Note-icon.gif

Программа /sbin/blkid возвращает неверный UUID для разделов LUKS.

[править] Монтирование разделов

После того как разделы готовы, нужно создать временную точки монтирования и подмонтировать к ним созданные разделы.

%# mkdir /mnt/buildroot
%# mount -t ext2 /dev/mapper/rootfs /mnt/buildroot
%# mkdir /mnt/buildroot/boot
%# mount /dev/sda1 /mnt/buildroot/boot


[править] Инсталляция базовой системы

После того как файловая система подмонтирована, внутрь можно установить Debian.

%# debootstrap --arch i386 sid /mnt/buildroot
I: Retrieving Release
I: Retrieving Packages
I: Validating Packages
I: Resolving dependencies of required packages...
I: Resolving dependencies of base packages...
I: Found additional base dependencies: libdb4.2 libgnutls12 libreadline5
   libsigc++-2.0-0c2a openbsd-inetd readline-common
I: Checking component main on http://ftp.debian.org/debian...
I: Retrieving adduser
...
I: Configuring gnupg...
I: Configuring sysklogd...
I: Configuring klogd...
I: Configuring netbase...
I: Configuring openbsd-inetd...
I: Base system installed successfully.

[править] Временное подключения /dev, /sys и /proc

Some applications that we will install while need access to the system devices and files. To allow that we need to bind certain directories.

%# mount -o bind /dev/ /mnt/buildroot/dev
%# mount -o bind /sys /mnt/buildroot/sys

[править] chroot внутрь новой системы

%# chroot /mnt/buildroot /bin/su -l

[править] Конфигурирование системы

[править] FILE: /etc/fstab

Use vi to create the /etc/fstab file and add these contents to it:

#/etc/fstab: static file system information.
#
/dev/mapper/rootfs  /          ext2    defaults,errors=remount-ro,noatime 0 1
UUID=72ea8e0a-256e-47bd-bfc6-6ba33c2ecd48 /boot ext2 defaults,noatime,ro  0 1
none            /proc          proc    defaults                           0 0
tmpfs           /tmp           tmpfs   defaults,noatime                   0 0
tmpfs           /var/lock      tmpfs   defaults,noatime                   0 0
tmpfs           /var/log       tmpfs   defaults,noatime                   0 0
tmpfs           /var/run       tmpfs   defaults,noatime                   0 0

Note: /var/tmp should not be mounted as tmpfs as the files stored here are often expected to survive a reboot.

Since we're mounting /boot as read-only, we need to add a hook for apt to remount it as read-write for updates. Create /etc/apt/apt.conf.d/30remount_readwrite like so:

DPkg
{
    Pre-Invoke {
        "mount -o remount,rw /boot;" }
    Post-Invoke {
        "mount -o remount,ro /boot;" }
}

Then mount all the filesystems:

hostname:~# mount -a (may need to be run twice)
hostname:~# 

[править] Set Hostname

Set the hostname by editing /etc/hostname, and then add the base configuration to /etc/hosts:

127.0.0.1 localhost.localdoman localhost <hostname>

[править] FILE: /etc/apt/sources.list

Next we have to add some sources to the Apt configuration.

deb http://ftp.debian.org/debian sid main non-free contrib
deb-src http://ftp.debian.org/debian sid main non-free contrib
deb http://mirrors.kernel.org/debian/ sid main non-free contrib
deb-src http://mirrors.kernel.org/debian/ sid main non-free contrib

[править] Recreate subdirectories for tmpfs mounted directories

Using Tmpfs to save space has one side effect, and that is since it deletes everything when you unmount it, it causes some applications to lose their log directories. So we need to recreate them when the system boots. The easiest way to do that is to create a initialization file in /etc/rcS.d/S37feraga-init.sh.

#!/bin/sh

case "$1" in
    start)
        echo
        echo "Feraga"
        echo "-Recreating required subdirectories on /var/log (tmpfs)"

        # /var/log subdirectories.
        mkdir -p /var/log/fsck
        mkdir -p /var/log/ksymoops
        mkdir -p /var/log/news

        # Example for the mixmaster anonymous remailer
        if [ -f /usr/bin/mixmaster ] ; then
            mkdir -p /var/log/mixmaster
        fi

        # Example for the Tor proxy
        if [ -f /usr/sbin/tor ] ; then
            mkdir -p /var/log/tor
        fi

        # Example for Privoxy
        if [ -f /usr/sbin/privoxy ] ; then
            mkdir -p /var/log/privoxy
        fi

        # Apt archive subdirectories.
        mkdir -p /var/cache/apt/archives/partial

        echo "-done."
        echo
        ;;
    stop)
        echo "Feraga shutting down."
        # Add anything that needs to happen at shutdown here.
        echo
        ;;
    *)
        echo "Usage: cryptdisks {start|stop}"
        exit 1
        ;;
esac

[править] Установка дополнительных пакетов

Сначала нужно обновить базу apt.

%# apt-get update
Get:1 http://mirrors.kernel.org sid Release.gpg [189B]
Get:2 http://mirrors.kernel.org sid Release [38.3kB]
Get:3 http://mirrors.kernel.org sid/main Packages [4079kB]
Get:4 http://ftp.debian.org sid Release.gpg [189B]
Hit http://ftp.debian.org sid Release
Hit http://ftp.debian.org sid/main Packages
Get:5 http://ftp.debian.org sid/non-free Packages [74.6kB]
Get:6 http://ftp.debian.org sid/contrib Packages [57.1kB]
Get:7 http://ftp.debian.org sid/main Sources [1559kB]
Get:8 http://ftp.debian.org sid/non-free Sources [30.3kB]
Get:9 http://ftp.debian.org sid/contrib Sources [24.3kB]
Get:10 http://mirrors.kernel.org sid/non-free Packages [74.6kB]
Get:11 http://mirrors.kernel.org sid/contrib Packages [57.1kB]
Get:12 http://mirrors.kernel.org sid/main Sources [1559kB]
Get:13 http://mirrors.kernel.org sid/non-free Sources [30.3kB]
Get:14 http://mirrors.kernel.org sid/contrib Sources [24.3kB]
Fetched 7608kB in 48s (158kB/s)
Reading package lists... Done

Поскольку места на диске не очень много, лучше почаще стирать закэшированные deb-пакеты.

%# apt-get clean

Установить initramfs-tools:

%#  apt-get install initramfs-tools
Reading package lists... Done
Building dependency tree... Done
The following extra packages will be installed:
  busybox klibc-utils libklibc libvolume-id0 udev
The following NEW packages will be installed:
  busybox initramfs-tools klibc-utils libklibc libvolume-id0 udev
0 upgraded, 6 newly installed, 0 to remove and 0 not upgraded.
Need to get 873kB of archives.
After unpacking 2564kB of additional disk space will be used.
Do you want to continue [Y/n]? y
<SNIP>             
Fetched 873kB in 1s (711kB/s)
Preconfiguring packages ...
Selecting previously deselected package libvolume-id0.
(Reading database ... 9071 files and directories currently installed.)
Unpacking libvolume-id0 (from .../libvolume-id0_0.103-2_i386.deb) ...
Selecting previously deselected package udev.
Unpacking udev (from .../archives/udev_0.103-2_i386.deb) ...
Selecting previously deselected package busybox.
Unpacking busybox (from .../busybox_1%3a1.1.3-4_i386.deb) ...
Selecting previously deselected package libklibc.
Unpacking libklibc (from .../libklibc_1.4.31-1_i386.deb) ...
Selecting previously deselected package klibc-utils.
Unpacking klibc-utils (from .../klibc-utils_1.4.31-1_i386.deb) ...
Selecting previously deselected package initramfs-tools.
Unpacking initramfs-tools (from .../initramfs-tools_0.85e_all.deb) ...
Setting up libvolume-id0 (0.103-2) ...

Setting up udev (0.103-2) ...
A chroot environment has been detected, udev not started.

Setting up busybox (1.1.3-4) ...
Setting up libklibc (1.4.31-1) ...
Setting up klibc-utils (1.4.31-1) ...
Setting up initramfs-tools (0.85e) ...

Отредактируйте /etc/initramfs-tools/modules:

usbcore
ehci-hcd
ohci-hcd
uhci-hcd
usbhid
ide-core
scsi_mod
usb-storage
mbcache
ext2
ide-cd
ide-disk
ide-generic
sd_mod

Configure /etc/initramfs-tools/initramfs.conf

# initramfs.conf
# Configuration file for mkinitramfs(8). See initramfs.conf(5).
MODULES=most
BUSYBOX=y
BOOT=local
DEVICE=eth0
NFSROOT=auto

Install Cryptsetup:

hostname#  apt-get install cryptsetup dmsetup hashalot
Reading package lists... Done
Building dependency tree... Done
Suggested packages:
  dosfstools
The following NEW packages will be installed:
  cryptsetup dmsetup hashalot
0 upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 318kB of archives.
After unpacking 942kB of additional disk space will be used.
Do you want to continue [Y/n]? y
<SNIP>
Fetched 318kB in 0s (1400kB/s)
Selecting previously deselected package dmsetup.
(Reading database ... 9299 files and directories currently installed.)
Unpacking dmsetup (from .../dmsetup_2%3a1.02.12-1_i386.deb) ...
Selecting previously deselected package cryptsetup.
Unpacking cryptsetup (from .../cryptsetup_2%3a1.0.4+svn26-1_i386.deb) ...
Selecting previously deselected package hashalot.
Unpacking hashalot (from .../hashalot_0.3-4_i386.deb) ...
Setting up dmsetup (1.02.12-1) ...
Setting up cryptsetup (1.0.4+svn26-1) ...

Setting up hashalot (0.3-4) ...

localepurge: Disk space freed in /usr/share/locale: 4K
hostname# 

Now that cryptsetup is installed, add the required mounting information to /etc/crypttab:

# <target name> <source device> <key file> <options>
rootfs /dev/disk/by-uuid/6278aae2-cad0-437d-affa-02277a0cca52 none luks

Install cryptroot scripts for initramfs.

hostname# cp /usr/share/initramfs-tools/hooks/cryptroot /etc/initramfs-tools/hooks/
hostname:~# cp /usr/share/initramfs-tools/scripts/local-top/cryptroot /etc/initramfs-tools/scripts/local-top/
hostname:~#

Now we need to add a small delay in /etc/initramfs-tools/scripts/local-top/cryptroot to allow for USB detection.

<SNIP>
    modprobe -q dm_crypt  ## After this line add the following.

    # Add delay
    echo "Sleeping for 5 seconds to allow USB detection."
    sleep 5
    echo "Awake, attempting to mount encrypted partitions."

<SNIP>

[править] Установка GRUB

Установим GRUB до того как приступим к инсталляции ядра. Если так сделать, при установке ядра соответствующие строки в конфигурационный файл GRUB добавятся автоматически.

Во-первых, находясь в chroot, нужно перемонтировать /boot в режиме rw:

%# mount -o remount,rw /boot
%# apt-get install grub

После этого выйти из chroot и дать команду:

%# grub-install --recheck --root-directory=/mnt/buildroot /dev/sda 
Probing devices to guess BIOS drives. This may take a long time.
Installation finished. No error reported.
This is the contents of the device map /mnt/buildroot//boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

(fd0)   /dev/fd0
(hd0)   /dev/hda
(hd1)   /dev/sda

После этого можно вернуться в chroot, открыть там /boot/grub/menu.lst и записать в него такую конфигурацию:

# default num
default         0

# timeout sec
timeout         5

# pretty colours
color green/black black/green

### BEGIN AUTOMAGIC KERNELS LIST

## ## Start Default Options ##

# kopt=root=/dev/mapper/rootfs ro\n")
# groot=(hd0,0)
# alternative=true
# lockalternative=false
# defoptions=
# lockold=false
# howmany=all
# memtest86=true
# updatedefaultentry=false

## ## End Default Options ##

### END DEBIAN AUTOMAGIC KERNELS LIST

После этого нужно снова вызвать GRUB (для этого нужно выйти из chroot).

%# grub
Probing devices to guess BIOS drives. This may take a long time.


    GNU GRUB  version 0.97  (640K lower / 3072K upper memory)

       [ Minimal BASH-like line editing is supported.   For
         the   first   word,  TAB  lists  possible  command
         completions.  Anywhere else TAB lists the possible
         completions of a device/filename. ]
grub> root (hd1,0)
root (hd1,0)
 Filesystem type is ext2fs, partition type 0x83
grub> setup (hd1)
setup (hd1)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd1)"... 
          failed (this is not fatal)
 Running "embed /boot/grub/e2fs_stage1_5 (hd1,0)"... 
          failed (this is not fatal)
 Running "install /boot/grub/stage1 (hd1) /boot/grub/stage2 
          p /boot/grub/menu.lst "... succeeded
Done.
grub> quit 

Удалите файл с картой устройств device.map для того чтобы при перезагрузке выполнилось повторное сканирование.

%# rm -f /boot/grub/device.map

[править] Установка ядра

Install Kernel

Before we can install the kernel, we need to set its configuration. Edit /etc/kernel-img.conf so that it looks like this:

do_symlinks = yes
relative_links = yes
do_bootloader = no
do_bootfloppy = no
do_initrd = yes        ## <--- Verify this line
link_in_boot = yes
postinst_hook = /sbin/update-grub
postrm_hook   = /sbin/update-grub

Next we install the kernel. The package linux-image-686 is a dummy package that requires the current kernel image as a dependency. Remove the linux-image-686 dummy package immediately afterwards or it will force you to update kernels every time a new one is published.

hostname:~# apt-get install linux-image-686
<SNIP>
hostname:~# apt-get remove linux-image-686
<SNIP>
hostname:~# apt-get clean
hostname:~# 

After the kernel is installed, remount /boot as read-only.

hostname:~# mount -o remount,ro /boot
hostname:~# 

[править] Добавление учётных записей пользователей

Either:

Copy an existing /etc/group, /etc/passwd, and /etc/shadow file over from another system (this has to be done from outside the chroot directory).

root@hostname# cp /etc/passwd /etc/group /etc/shadow /mnt/buildroot/etc/
root@hostname# 

Then chroot in and create their homedirectories

root@hostname# chroot /mnt/buildroot /bin/su -
hostname:~# mkdir /home/<username>
hostname:~# chown <username>.<username> /home/<username>
<Repeat as necessary>
hostname:~# exit
root@hostname# 

Or:

Set root password and add users in the chroot

hostname# chroot /mnt/buildroot /bin/su -
hostname:~# passwd
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
hostname:~# adduser test
Adding user `test'...
Adding new group `test' (1001).
Adding new user `test' (1001) with group `test'.
Creating home directory `/home/test'.
Copying files from `/etc/skel'
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for test
Enter the new value, or press ENTER for the default
        Full Name []: test
        Room Number []:
        Work Phone []:
        Home Phone []:
        Other []:
Is the information correct? [y/N] y
hostname:~#

<Repeat as necessary for more users>

[править] Выход из chroot

%# umount -a
%# umount /proc
%# exit

[править] Размонтирование носителя

Time to unmount everything we've mounted and prepare for reboot.

root@hostname# umount /mnt/buildroot/dev/mapper
root@hostname# umount /mnt/buildroot/sys
root@hostname# umount /mnt/buildroot
root@hostname# cryptsetup luksClose rootfs

[править] Проверка

Можно перезагрузиться и проверить, что получилось.