Lighttpd

Apache suEXEC

[http://cyanite.org/execwrap/ ExecWrap] (previously
linked from the front page) seems to be a piece of cake to install. This
page deals specifically with the suEXEC code distributed with the Apache web
server, and with PHP: we want PHP executed as the target user.

=== Background about suEXEC ===

See the [http://httpd.apache.org/docs/1.3/suexec.html documentation of suEXEC].
In a nutshell, suEXEC will take care that all things are fine, cleanup the
environment and be sure some conditions are met, and then setuid. Among the
things suEXEC checks are that:

• the script you will execute belongs to the target user/group and that nobody
  else can modify it;
• the directory where this script is belongs to the target user/group, and that
  nobody can write anything there;
• suEXEC is launched from this target directory.

as a consequence, there's quite a bit of wrapping involved: at some point
you need to change your current directory to the target directory to launch
suEXEC, and it's simpler to launch a script (belonging to the target) user
that will eventually launch the php executable.

So there are two script in the way, which is rather clumsy. On the bright
side it's quite flexible.

=== Lighttpd Configuration ===

lighttpd.conf contains this piece:

{{{
$HTTP["host"] =~ "^mywebsite.org$" {
fastcgi.server = ( ".php" =>
( "localhost" =>
( "socket" => "/var/run/fastcgi/myuser.socket",
"bin-path" => "/usr/local/etc/suexec/myuser.sh",
"idle-timeout" => 30,
"min-procs" => 3,
"max-procs" => 10,
"max-load-per-proc" => 4
) ) )
}
}}}

'''/usr/local/etc/suexec/myuser.sh''' is the script that will launch suEXEC (see
bellow). '''/var/run/fastcgi/''' is the directory what will contains the UNIX
sockets used by lighttpd to communicate with the FastCGI backends. It is
important that only the '''www''' user can write in that directory.

=== Wrapping suEXEC ===

So, lighttpd runs '''/usr/local/etc/suexec/myuser.sh every now and then'''. lighttpd
must be able to execute this script. This script takes care of what's needed
to launch suEXEC: cd'ing to the target directory.

'''/usr/local/etc/suexec/myuser.sh''': {{{
#!sh
#!/bin/sh

user=myuser
group=mygroup

cd /usr/local/www/data/$user
/usr/local/sbin/suexec $user $group php.sh
}}}

Please note: '''/usr/local/www/data/''' is not chosen at random - suEXEC will only
accept to run scripts in a specific directory that is configured at run time.
Depending on the distribution you run, it may be something different. Run
'''suexec -V''' as root to be sure:

{{{
#!ShellExample
$ sudo suexec -V
-D DOC_ROOT="/usr/local/www/data"
-D GID_MIN=1000
-D HTTPD_USER="www"
-D LOG_EXEC="/var/log/httpd-suexec.log"
-D LOGIN_CAP
-D SAFE_PATH="/bin:/usr/bin:/usr/local/bin"
-D UID_MIN=1000
-D USERDIR_SUFFIX="public_html"
}}}

The script must be in the DOC_ROOT directory you see here.

==== The user's script: php.sh ====

This script and the directory it's in must belong to the target user/group (here,
myuser and mygroup).

'''/usr/local/www/data/myuser/php.sh''': {{{
#!sh
#!/bin/sh

exec /usr/local/bin/php
}}}

to be on the safe side, you probably want to: {{{
#!ShellExample

1. chown -R myuser:mygroup /usr/local/www/data/myuser/
   }}}

=== Troubleshooting ===

Apart from the lighttpd log files, pieces of information about what's going on
are available in the /var/log/httpd-suexec.log file (see the output of '''suexec -V''',
it may be different for you). Usually problems are related to permissions and ownership
of the files.