mod_cgi/3784: CGI scripts not executed if gid not equal to server's gid

[Nigel Cole <N....@sc98c.demon.co.uk>]

>Number:         3784
>Category:       mod_cgi
>Synopsis:       CGI scripts not executed if gid not equal to server's gid
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Wed Jan 27 07:50:00 PST 1999
>Last-Modified:
>Originator:     N.Cole@sc98c.demon.co.uk
>Organization:
apache
>Release:        1.3.4
>Environment:
Solaris 2.6, Generic_105181-05

gcc 2.8.0
>Description:
This is an expansion of PR 2580: I have a cgi-bin script which is executable
by a group the webserver belongs to, but which is different to the group the
server is running as. Apache won't execute it. I'm not using suexec.

MULTIPLE_GROUPS isn't being set by default, so Apache only checks permissions
using its own group id, decides it can't run it (in ap_can_exec in util.c, 
called from cgi_handler in mod_cgi.c), and gives a confusing error message
("file permissions deny server execution" even though, as far as the OS is
concerned, the server is permitted to execute it).

I tried recompiling with MULTIPLE_GROUPS set (though I'm uncomfortable about
doing this since I can't find any references to it), and Apache still
refused to run the script. A look at http_main.c revealed that the array 
group_id_list is only set when geteuid() returns 0 (ie running as root).
>How-To-Repeat:
No example URL, but it's easy to repeat: just change the permissions on a
cgi-bin script to 750 and put it in a group that the server belongs to but
doesn't run as.
>Fix:
Set MULTIPLE_GROUPS?

Also, move the "#ifdef MULTIPLE_GROUPS" block of code in set_group_privs (in
http_main.c) outside the "if (!geteuid())" block.

(These changes appear to work, but I haven't searched the code to find any
unwanted side-effects.)

Not a fix, but the error message would be a lot clearer if it reported
something like "cannot execute: not in server's group".

A work-round for those of us who need scripts restricted to a different group
is to use the directory permissions to limit access, since Apache only 
considers the file permissions.
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