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Sun Java System Web Server 6.1 SP12 Programmer's Guide

Creating Custom Execution Environments for CGI Programs (UNIX only)

Before you can create a custom execution environment, you must install the suid Cgistub and run it as root:

ProcedureTo create custom execution environments for CGI programs

  1. Log in as the superuser.

    su

  2. Create the private directory for Cgistub:

    cd server_root/https-instance

    mkdir private

  3. Copy Cgistub to the private directory:

    cd private

    cp ../../bin/https/bin/Cgistub .

  4. Set the owner of private to the server user:

    chown user .

  5. Set the permissions on private:

    chmod 500 .

  6. Set the owner of Cgistub to root:

    chown root Cgistub

  7. Set the permissions on Cgistub:

    chmod 4711 Cgistub

  8. You can give each reference to the send-cgi SAF in obj.conf a user parameter. For example:

    Service fn="send-cgi" user="user"

    You can use variable substitution. For example, in server.xml add a VARS subelement to VS (virtual server) element.

    <VARS user="user"/>

    This lets you write the send-cgi SAF line in obj.conf as follows:

    Service fn="send-cgi" user="$user"

    For more information about send-cgi in the obj.conf file and server.xml, see the Sun Java System Web Server 6.1 SP12 Administrator’s Configuration File Reference.

  9. Restart the server to update the changes into effect.

    Note –

    Installing Cgistub in the server_root/https-instance/private directory is recommended. If you install it anywhere else, you must specify the path to Cgistub in the init-cgi function in magnus.conf. For details, see the Sun Java System Web Server 6.1 SP12 NSAPI Programmer’s Guide.

    Note –

    It is not possible to install the suid Cgistub program on an NFS mount, you install your server instance to a local file system.

    Cgistub enforces the following security restrictions:

    • The user the CGI program executes as must have a uid of 100 or greater. This prevents anyone from using Cgistub to obtain root access.

    • The CGI program must be owned by the user it is executed as and must not be writable by anyone other than its owner. This makes it difficult for anyone to remotely execute programs.

    • Cgistub creates its UNIX listen socket with 0700 permissions.

    Note –

    Socket permissions are not respected on a number of UNIX variants, including current versions of SunOS/Solaris. To prevent a malicious user from exploiting Cgistub, change the server’s temporary directory (using the magnus.conf TempDir directive) to a directory accessible only to the server user.

    After you have installed Cgistub you can create custom execution environments by doing the following, as described in this section:

Specifying a Unique CGI Directory and UNIX User and Group for a Virtual Server

To prevent CGI programs of the virtual server from interfering with other users, these programs should be stored in a unique directory and executed with the permissions of a unique UNIX user and group.

First, create the UNIX user and group. The exact steps required to create a user and group vary by operating system. For instructions, consult your operating system's documentation.

ProcedureTo create a cgi-bin directory for the virtual server

  1. Log in as the superuser.

    su

  2. Change to the virtual server directory.

    cd vs_dir

  3. Create the cgi-bin directory.

    mkdir cgi-bin

    chown user:group cgi-bin

    chmod 755 cgi-bin

    Now you can set the virtual server’s CGI directory, user, and group in one of these ways:

Specifying a Chroot Directory for a Virtual Server

To further improve security, these CGI scripts should be prevented from accessing data outside the virtual server directory.

First, set up the chroot environment. The exact steps required to set up the chroot environment vary by operating system. For instructions, consult your operating system’s documentation. The man pages for ftpd and chroot are good place to start.

These are the steps required for Solaris versions 2.6 through 8

ProcedureTo specify a Chroot Directory for a Virtual Server

  1. Log in as the superuser.

    su

  2. Change to the chroot directory. This is typically the vs_dir directory mentioned in the previous section.

    cd chroot

  3. Create tmp in the chroot directory:

    mkdir tmp

    chmod 1777 tmp

  4. Create dev in the chroot directory:

    mkdir dev

    chmod 755 dev

  5. List /dev/tcp, and note the major and minor numbers of the resulting output. In this example, the major number is 11 and the minor number is 42:

    ls -lL /dev/tcp

    crw-rw-rw- 1 root sys 11, 42 Apr 9 1998 /dev/tcp

  6. Create the tcp device using the major and minor numbers:

    mknod dev/tcp c 11 42

    chmod 666 dev/tcp

  7. Repeat steps 5 and 6 for each of the following devices each device will have a different major and minor combination:

    /dev/udp /dev/ip /dev/kmem /dev/kstat /dev/ksyms /dev/mem /dev/null /dev/stderr /dev/stdin /dev/stdout /dev/ticotsord /dev/zero

  8. Set permissions on the devices in dev in the chroot directory:

    chmod 666 dev/*

  9. Create and populate lib and usr/lib in the chroot directory:

    mkdir usr

    mkdir usr/lib

    ln -s /usr/lib

    ln /usr/lib/* usr/lib

    You can ignore the messages this command generates.

    If the /usr/lib directory is on a different file system, replace the last command with the following:

    cp -rf /usr/lib/* usr/lib

  10. Create and populate bin and usr/bin in the chroot directory:

    mkdir usr/bin

    ln -s /usr/bin

    ln /usr/bin/* usr/bin

    You can ignore the messages this command generates.

    If the /usr/bin directory is on a different file system, replace the last command with the following:

    cp -rf /usr/bin/* usr/bin

  11. Create and populate etc in the chroot directory:

    mkdir etc

    ln /etc/passwd /etc/group /etc/netconfig etc

  12. Test the chroot environment:

    chroot chroot bin/ls -l

    The output should look something like this:

    lrwxrwxrwx   1 root   other   8 Jan 13 03:32 bin -> /usr/bin
drwxr-xr-x   2 user    group   512 Jan 13 03:42 cgi-bin
drwxr-xr-x   2 root   other   512 Jan 13 03:28 dev
drwxr-xr-x   2 user    group   512 Jan 13 03:26 docs
drwxr-xr-x   2 root   other   512 Jan 13 03:33 etc
lrwxrwxrwx   1 root   other   8 Jan 13 03:30 lib -> /usr/lib
drwxr-xr-x   4 root   other   512 Jan 13 03:32 usr

    Now you can set the chroot directory of the virtual server in one of these ways: