suEXEC Support - Make apache runs under a real user ID

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The suEXEC feature provides    Apache users the ability    to run CGI and SSI programs    under user IDs different from the user ID of the calling    web server. Normally, when a CGI or SSI program executes, it    runs as the same user who is running the web server.
    Used properly, this feature can reduce    considerably the security risks involved with allowing users to    develop and run private CGI or SSI programs. However, if suEXEC    is improperly configured, it can cause any number of problems    and possibly create new holes in your computer's security. If    you aren't familiar with managing setuid root programs    and the security issues they present, we highly recommend that    you not consider using suEXEC.
  

• Before we begin
• suEXEC Security Model
• Configuring & Installing    suEXEC
• Enabling & Disabling    suEXEC
• Using suEXEC
• Debugging suEXEC
• Beware the Jabberwock:    Warnings & Examples
  

Before we begin    Before jumping head-first into this document,    you should be aware of the assumptions made on the part of the    Apache Group and this document.
    First, it is assumed that you are using a UNIX    derivative operating system that is capable of    setuid and setgid operations.    All command examples are given in this regard. Other platforms,    if they are capable of supporting suEXEC, may differ in their    configuration.
    Second, it is assumed you are familiar with    some basic concepts of your computer's security and its    administration. This involves an understanding of    setuid/setgid operations and the various    effects they may have on your system and its level of    security.
    Third, it is assumed that you are using an    unmodified version of suEXEC code. All code    for suEXEC has been carefully scrutinized and tested by the    developers as well as numerous beta testers. Every precaution    has been taken to ensure a simple yet solidly safe base of    code. Altering this code can cause unexpected problems and new    security risks. It is highly recommended you    not alter the suEXEC code unless you are well versed in the    particulars of security programming and are willing to share    your work with the Apache Group for consideration.
    Fourth, and last, it has been the decision of    the Apache Group to NOT make suEXEC part of    the default installation of Apache. To this end, suEXEC    configuration requires of the administrator careful attention    to details. After due consideration has been given to the    various settings for suEXEC, the administrator may install    suEXEC through normal installation methods. The values for    these settings need to be carefully determined and specified by    the administrator to properly maintain system security during    the use of suEXEC functionality. It is through this detailed    process that the Apache Group hopes to limit suEXEC    installation only to those who are careful and determined    enough to use it.
    Still with us? Yes? Good. Let's move on!

http://httpd.apache.org/docs/2.2/suexec.html
http://httpd.apache.org/docs/2.2/suexec.html
http://httpd.apache.org/docs/2.2/suexec.html

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Configuring & Installing    suEXEC   

Here's where we begin the fun.


    suEXEC configuration options

--enable-suexec

This option enables the suEXEC feature which is never      installed or activated by default. At least one      --with-suexec-xxxxx option has to be provided      together with the --enable-suexec option to let      APACI accept your request for using the suEXEC feature.

--with-suexec-bin=PATH

The path to the suexec binary must be hard-coded      in the server for security reasons. Use this option to override      the default path. e.g.      --with-suexec-bin=/usr/sbin/suexec

--with-suexec-caller=UID

The username under which      Apache normally runs. This is the only user allowed to      execute this program.

--with-suexec-userdir=DIR

Define to be the subdirectory under users' home      directories where suEXEC access should be allowed. All      executables under this directory will be executable by suEXEC      as the user so they should be "safe" programs. If you are      using a "simple" UserDir      directive (ie. one without a "*" in it) this should be set to the same      value. suEXEC will not work properly in cases where the UserDir directive points to      a location that is not the same as the user's home directory      as referenced in the passwd file. Default value is      "public_html".
      If you have virtual hosts with a different UserDir for each,      you will need to define them to all reside in one parent      directory; then name that parent directory here. If      this is not defined properly, "~userdir" cgi requests will      not work!

--with-suexec-docroot=DIR

Define as the DocumentRoot set for Apache. This will be      the only hierarchy (aside from UserDirs) that can be used for suEXEC behavior. The      default directory is the --datadir value with the suffix      "/htdocs", e.g. if you configure with      "--datadir=/home/apache" the directory      "/home/apache/htdocs" is used as document root for the      suEXEC wrapper.

--with-suexec-uidmin=UID

Define this as the lowest UID allowed to be a target user      for suEXEC. For most systems, 500 or 100 is common. Default      value is 100.

--with-suexec-gidmin=GID

Define this as the lowest GID allowed to be a target      group for suEXEC. For most systems, 100 is common and      therefore used as default value.

--with-suexec-logfile=FILE

This defines the filename to which all suEXEC      transactions and errors are logged (useful for auditing and      debugging purposes). By default the logfile is named      "suexec_log" and located in your standard logfile      directory (--logfiledir).

--with-suexec-safepath=PATH

Define a safe PATH environment to pass to CGI      executables. Default value is      "/usr/local/bin:/usr/bin:/bin".

    Compiling and installing the suEXEC wrapper

            If you have enabled the suEXEC feature with the      --enable-suexec option the suexec binary      (together with Apache itself) is automatically built if you execute      the make command.
      After all components have been built you can execute the      command make install to install them. The binary image      suexec is installed in the directory defined by the      --sbindir option. The default location is      "/usr/local/apache2/bin/suexec".
      Please note that you need root      privileges for the installation step. In order      for the wrapper to set the user ID, it must be installed as      owner root and must have the setuserid      execution bit set for file modes.

        Setting paranoid permissions

            Although the suEXEC wrapper will check to ensure that its      caller is the correct user as specified with the      --with-suexec-caller configure      option, there is      always the possibility that a system or library call suEXEC uses      before this check may be exploitable on your system. To counter      this, and because it is best-practise in general, you should use      filesystem permissions to ensure that only the group Apache      runs as may execute suEXEC.
      If for example, your web server is configured to run as:
          User    www
          Group webgroup
      

      and suexec is installed at      "/usr/local/apache2/bin/suexec", you should run:
                chgrp webgroup /usr/local/apache2/bin/suexec
          chmod 4750 /usr/local/apache2/bin/suexec
      

      This will ensure that only the group Apache runs as can even      execute the suEXEC wrapper.
   
Enabling & Disabling    suEXEC   
Upon startup of Apache, it looks for the file    suexec in the directory defined by the    --sbindir option (default is    "/usr/local/apache/sbin/suexec"). If Apache finds a properly    configured suEXEC wrapper, it will print the following message    to the error log:
    [notice] suEXEC mechanism enabled (wrapper: /path/to/suexec)

    If you don't see this message at server startup, the server is    most likely not finding the wrapper program where it expects    it, or the executable is not installed setuid root.
     If you want to enable the suEXEC mechanism for the first time    and an Apache server is already running you must kill and    restart Apache. Restarting it with a simple HUP or USR1 signal    will not be enough.
     If you want to disable suEXEC you should kill and restart    Apache after you have removed the suexec file.


Using suEXEC   
Requests for CGI programs will call the suEXEC wrapper only if    they are for a virtual host containing a SuexecUserGroup directive or if    they are processed by mod_userdir.
   
Virtual Hosts:
One way to use the suEXEC    wrapper is through the SuexecUserGroup directive in    VirtualHost definitions.  By    setting this directive to values different from the main server    user ID, all requests for CGI resources will be executed as the    User and Group defined for that <VirtualHost>. If this    directive is not specified for a <VirtualHost> then the main server userid    is assumed.
   
User directories:
Requests that are     processed by mod_userdir will call the suEXEC     wrapper to execute CGI programs under the userid of the requested     user directory.  The only requirement needed for this feature to     work is for CGI execution to be enabled for the user and that the     script must meet the scrutiny of the security     checks above.  See also the     --with-suexec-userdir compile     time option.


Debugging suEXEC   
The suEXEC wrapper will write log information    to the file defined with the --with-suexec-logfile    option as indicated above. If you feel you have configured and    installed the wrapper properly, have a look at this log and the    error_log for the server to see where you may have gone astray.


http://httpd.apache.org/docs/2.2/suexec.html

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Beware the Jabberwock:    Warnings & Examples   
NOTE! This section may not be    complete. For the latest revision of this section of the    documentation, see the Apache Group's Online    Documentation version.
    There are a few points of interest regarding    the wrapper that can cause limitations on server setup. Please    review these before submitting any "bugs" regarding suEXEC.
   

• suEXEC Points Of Interest
•         Hierarchy limitations        
            For security and efficiency reasons, all suEXEC requests          must remain within either a top-level document root for          virtual host requests, or one top-level personal document          root for userdir requests. For example, if you have four          VirtualHosts configured, you would need to structure all          of your VHosts' document roots off of one main Apache          document hierarchy to take advantage of suEXEC for          VirtualHosts. (Example forthcoming.)        
•         suEXEC's PATH environment variable        
            This can be a dangerous thing to change. Make certain          every path you include in this define is a          trusted directory. You don't want to          open people up to having someone from across the world          running a trojan horse on them.        
•         Altering the suEXEC code        
            Again, this can cause Big Trouble if you          try this without knowing what you are doing. Stay away          from it if at all possible.  
  
  

低调的爱

谢谢您阿，我非常高兴












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