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appnotes:authmenus [2009/02/17 20:14]
mcb30
appnotes:authmenus [2013/03/04 15:34] (current)
genec Fix cmd.c32 -> gpxecmd.c32
Line 2: Line 2:
  
 This page outlines the steps I took to implement a proof of concept comprising user authentication at preboot time and dynamically generated boot menus. ​ The user is first presented with a login screen. ​ The user's credentials are passed via an SSL-encrypted link to a server, which authenticates the user and then provides a boot menu containing a list of authorised boot selections. ​ The list of boot selections can vary according to the user. This page outlines the steps I took to implement a proof of concept comprising user authentication at preboot time and dynamically generated boot menus. ​ The user is first presented with a login screen. ​ The user's credentials are passed via an SSL-encrypted link to a server, which authenticates the user and then provides a boot menu containing a list of authorised boot selections. ​ The list of boot selections can vary according to the user.
 +
 +{{ :​screenshots:​gpxe_ssl_menu.png?​320x240|Sample menu screen}}
  
 ===== Setup (boring part) ===== ===== Setup (boring part) =====
Line 11: Line 13:
     SSLRequireSSL     SSLRequireSSL
  
-and a file "menu.gpxe" ​containing+You must choose between being able to load vesamenu.c32 directly ​and loading the current version of vesamenu.c32. 
 +==== vesamenu.c32 current ==== 
 +The current version of vesamenu.c32 can not be loaded directly from gPXE and requires PXELINUX as an intermediate layer. ​ You will need two PHP files, ​boot.php containing
  
-    ​#!gpxe +  <?php 
-     +   
-    ​imgfree +  header ( "​Content-type:​ text/​plain"​ ); 
-    ​login +  echo "#!gpxe\n"; 
-    ​kernel -menu https://​${username:​uristring}:​${password:​uristring}@my.web.server/​boot/​vesamenu.c32 menu.php +   
-    boot menu+  $proto = "​https";​ 
 +  // Comment out/remove the following if strictly using HTTPS 
 +  if (!isset($_SERVER["​HTTPS"​])) 
 +    ​$proto = "​http";​ 
 +   
 +  // This assigns the host that gPXE should use using the most logical variables 
 +  if ( $_SERVER["​HTTP_HOST"​] != ""​ ) { 
 +    ​$host=$_SERVER["​HTTP_HOST"​];​ 
 +  } else { 
 +    ​if ( $_SERVER["​SERVER_NAME"​] != 0) { 
 +  $host=$_SERVER["​SERVER_NAME"​];​ 
 +    ​} else { 
 +  $host=$_SERVER["​SERVER_ADDR"​];​ 
 +    } 
 +  } 
 +   
 +  // Comment out/remove the following if you are running on a standard port 
 +  if (!((! isset($_SERVER["​HTTPS"​]) ) && ($_SERVER["​SERVER_PORT"​] == 80)) 
 +    && !(isset($_SERVER["​HTTPS"​]) && ($_SERVER["​SERVER_PORT"​] == 443)) ){ 
 +      if (strrpos($host,​ ":"​) == FALSE) 
 +        $host=$host.":"​.$_SERVER["​SERVER_PORT"​];​ 
 +  } 
 +   
 +  $uri=$_SERVER["​REQUEST_URI"​];​ 
 +  $dir=substr ( $uri, 0, strrpos ($uri, "/"​) + 1); 
 +   
 +  echo "#​!gpxe\n"; 
 +  echo "​imgfree\n";​ 
 +  echo "​login\n";​ 
 +  echo "set 209:string bootcfg.php\n";​ 
 +  echo "set 210:string ". 
 +       ​$proto."​://\${username:​uristring}:​\${password:​uristring}@". 
 +       $host.$dir."​\n";​ 
 +  echo "chain \${210:​string}pxelinux.0\n";​ 
 +  ?> 
 + 
 +and a bootcfg.php containing 
 + 
 +  <?php 
 +   
 +  header ( "​Content-type:​ text/plain" ); 
 +   
 +  echo "UI runmenu\n\n";​ 
 +  echo "LABEL runmenu\n";​ 
 +  echo "COM32 vesamenu.c32\n";​ 
 +  echo "​APPEND menu.php\n";​ 
 +  ?> 
 + 
 +Selecting this method will require that you use gpxecmd.c32 to execute gPXE commands and scripts. 
 +==== vesamenu.c32 directly ==== 
 +You will need a file "boot.php" containing 
 + 
 +  <?php 
 +   
 +  header ( "​Content-type:​ text/plain" ); 
 +   
 +  $uri=$_SERVER["​REQUEST_URI"​];​ 
 +  $dir=substr ( $uri, 0, strrpos ($uri, "/"​) + 1); 
 +   
 +  echo "#​!gpxe\n";​ 
 +  echo "​imgfree\n";​ 
 +  echo "​login\n";​ 
 +  echo "chain ". 
 +       "​https://​\${username:​uristring}:​\${password:​uristring}@"​. 
 +       ​$_SERVER["​HTTP_HOST"​].$dir. 
 +       "​vesamenu.c32 menu.php\n"; 
 +  ?>​ 
 + 
 +In order to use vesamenu.c32 directly from gPXE, you must use Syslinux-3.86 from [[http://​www.kernel.org/​pub/​linux/​utils/​boot/​syslinux/​3.xx/​]] and not the latest version.
  
-Configure your DHCP server to hand out //menu.gpxe// as the boot file, using something like (for ISC dhcpd)((If you are using PXE-chaining,​ you may want to investigate the various methods for avoiding infinite loops described in the [[:​pxechaining|PXE chainloading]] HowTo.)):+==== Setup part 1 continued ==== 
 +Configure your DHCP server to hand out //boot.php// as the boot file, using something like (for ISC dhcpd)((If you are using PXE-chaining,​ you may want to investigate the various methods for avoiding infinite loops described in the [[:​pxechaining|PXE chainloading]] HowTo.)):
  
-    filename "​https://​my.web.server/​boot/​menu.gpxe";+    filename "​https://​my.web.server/​boot/​boot.php";
  
-Download the latest //​syslinux//​ tarball from [[http://​www.kernel.org/​pub/​linux/​utils/​boot/​syslinux/​]] and build it.  Copy the files //​com32/​menu/​vesamenu.c32//​ and //​com32/​modules/​cmd.c32//((At the time of writing, //cmd.c32// is not yet integrated into a //​syslinux//​ release; you will need to apply the patch from [[http://​rom.etherboot.org/​share/​mcb30/​syslinux-cmd.patch]] before building //​syslinux//,​ or just grab the prebuild //cmd.c32// binary from [[http://​rom.etherboot.org/​share/​mcb30/​cmd.c32]].)) ​into the "​boot"​ directory.+Download the latest //​syslinux//​ tarball from [[http://​www.kernel.org/​pub/​linux/​utils/​boot/​syslinux/​]] and extract ​it.  Copy the files //​com32/​menu/​vesamenu.c32//​ and //​com32/​modules/​gpxecmd.c32// into the "​boot"​ directory ​on the web server.
  
 ===== Setup (interesting part) ===== ===== Setup (interesting part) =====
  
-In the "​boot"​ directory, you can now create a file called "​menu.php"​. ​ This PHP script needs to generate a standard syslinux menu configuration file; the resulting menu will be displayed to the user.+In the "​boot"​ directory, you can now create a file called "​menu.php"​. ​ This PHP script needs to generate a standard ​//syslinux// menu configuration file; the resulting menu will be displayed to the user.
  
 The PHP script will have access to the plaintext of the username and password (in the variables ''​%%$_SERVER["​PHP_AUTH_USER"​]%%''​ and ''​%%$_SERVER["​PHP_AUTH_PW"​]%%''​). ​ Although the script has access to the plaintext, the traffic over the wire was encrypted with SSL and so is (nominally) not vulnerable to eavesdropping. The PHP script will have access to the plaintext of the username and password (in the variables ''​%%$_SERVER["​PHP_AUTH_USER"​]%%''​ and ''​%%$_SERVER["​PHP_AUTH_PW"​]%%''​). ​ Although the script has access to the plaintext, the traffic over the wire was encrypted with SSL and so is (nominally) not vulnerable to eavesdropping.
Line 36: Line 109:
     <?php     <?php
     ​     ​
-    header ( 'Content-type:​ text/plain' ​);+    header ( "Content-type:​ text/plain" ​);
     ​     ​
     $username = $_SERVER["​PHP_AUTH_USER"​];​     $username = $_SERVER["​PHP_AUTH_USER"​];​
Line 61: Line 134:
     function sanboot ( $label, $root_path ) {     function sanboot ( $label, $root_path ) {
       label ( $label );       label ( $label );
-      echo " ​ kernel ​cmd.c32\n";​+      echo " ​ kernel ​gpxecmd.c32\n";​
       echo " ​ append sanboot "​.$root_path."​\n";​       echo " ​ append sanboot "​.$root_path."​\n";​
       echo "​\n";​       echo "​\n";​
Line 77: Line 150:
       echo " ​ menu label Authentication Failed\n";​       echo " ​ menu label Authentication Failed\n";​
       echo " ​ menu disable\n";​       echo " ​ menu disable\n";​
-      uriboot ( "Try again",​ "menu.gpxe", ""​ );+      uriboot ( "Try again",​ "boot.php", ""​ );
     }     }
     ​     ​
Line 136: Line 209:
 ===== Screenshots ===== ===== Screenshots =====
  
 +When first booting, the user sees this login screen:
  
 +{{ :​screenshots:​gpxe_login.png?​720x400 |Login screen}}
 +
 +After authenticating correctly as //mcb30//, the user sees this menu screen:
 +
 +{{ :​screenshots:​gpxe_ssl_menu.png?​640x480 |Menu screen}}
 +
 +This was generated by //​menu.php//​ as:
 +
 +    menu background atlantis.png
 +    prompt 0
 +    timeout 100
 +    allowoptions 0
 +    menu timeoutrow 29
 +    menu vshift 2
 +    menu rows 8
 +    menu color title  1;​36;​44 ​  #​ff8bc2ff #00000000 std
 +    menu color unsel  37;44     #​ff1069c5 #00000000 std
 +    menu color sel    7;​37;​40 ​  #​ff000000 #ffff7518 all
 +    menu color hotkey 1;​37;​44 ​  #​ffffffff #00000000 std
 +    menu color hotsel 1;7;37;40 #ff000431 #ffff7518 all
 +    ​
 +    menu title Secure Network Boot for mcb30
 +    label item1
 +      menu label ^1 MS-DOS 6.22
 +      kernel gpxecmd.c32
 +      append sanboot iscsi:​chipmunk.tuntap::::​iqn.2007-07.chipmunk:​msdos622
 +    ​
 +    label item2
 +      menu label ^2 Windows 2k3
 +      kernel gpxecmd.c32
 +      append sanboot iscsi:​chipmunk.tuntap::::​iqn.2007-07.chipmunk:​win2k3
 +    ​
 +    label item3
 +      menu label ^3 Linux rescue shell
 +      kernel http://​chipmunk.tuntap/​images/​uniboot/​uniboot.php
  
 ===== Further reading ===== ===== Further reading =====
Line 142: Line 251:
 The syntax of the generated menu files is documented within the //​syslinux//​ project at [[http://​syslinux.zytor.com/​wiki/​index.php/​Comboot/​menu.c32]] and [[http://​syslinux.zytor.com/​wiki/​index.php/​SYSLINUX]]. The syntax of the generated menu files is documented within the //​syslinux//​ project at [[http://​syslinux.zytor.com/​wiki/​index.php/​Comboot/​menu.c32]] and [[http://​syslinux.zytor.com/​wiki/​index.php/​SYSLINUX]].
  
 +===== Future ideas =====
 +
 +==== Pass-through authentication to iSCSI ====
 +
 +If the user eventually ends up performing an iSCSI boot, gPXE will still have the user's credentials available for iSCSI authentication. ​ If the iSCSI target could be made to authenticate against the same user database as the PHP script, this would allow for single sign-on right through to the iSCSI boot stage.
 +
 +The credentials do get passed to the loaded OS via the iBFT, so we get single sign-on through to the iSCSI runtime stage for free.
 +
 +For extra bonus points, it would be possible to write a Windows driver (very similar in structure to [[:​sanbootconf|sanbootconf]]) that would pick up the username and password from the iBFT, and store them in the registry as the autologon credentials;​ this would give you single sign-on right through to the desktop. ​ The relevant registry entries are all found in //​HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon//,​ and should be set as follows:
 +
 +  * //​DefaultUserName//​ - set to user name from iBFT
 +
 +  * //​DefaultPassword//​ - set to password from iBFT
 +
 +  * //​AutoAdminLogon//​ - set to 1
 +
 +  * //​AutoLogonCount//​ - set to 1, so that Windows erases((Hopefully Windows will erase the credentials. ​ If it doesn'​t then this single sign-on approach would be a really bad idea, since the //​Winlogon//​ key is by default readable by all users on the system.)) the credentials from the registry as soon as they have been used.
 +
 +Note that Windows imposes a minimum password length of 12 characters, and a maximum of 16 characters, for iSCSI authentication;​ this scheme will silently break unless your password policy enforces an appropriate min/max password length of 12<​-->​16 characters.

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