threaded MPM on focal selects cgid instead of cgi but doesn't work

[Steve Langasek]

apache2 2.4.41-4ubuntu3.14 on focal. With mpm_worker selected, 'a2enmod cgi' redirects to cgid:

# a2enmod cgi
Your MPM seems to be threaded. Selecting cgid instead of cgi.
Enabling module cgid.
To activate the new configuration, you need to run:
  systemctl restart apache2
#

However, after restarting apache2, attempting to access a CGI returns a 503.

access log:

10.131.50.215 - - [18/Mar/2023:20:34:54 +0000] "GET /madison.cgi HTTP/1.1" 503 568 "-" "Wget/1.20.3 (linux-gnu)"

error log:

[Sat Mar 18 20:34:54.428705 2023] [cgid:error] [pid 3571669:tid 140058430510848] (13)Permission denied: [client 10.131.50.215:34668] AH01257: unable to connect to cgi daemon after multiple tries: /srv/ubuntu-archive/madison.cgi

/run/apache2/ contains:

srwx------ 1 www-data root 0 Mar 18 21:45 cgisock.3576630

Permissions on /run/apache2 were for some reason 0600 root root. Changing this to 0700 www-data root doesn't change anything.

# fuser -v /run/apache2/cgisock.3576630
                     USER PID ACCESS COMMAND
/run/apache2/cgisock.3576630:
                     www-data 3576631 F.... apache2
#

Not sure what's wrong here, but I do think that 'a2enmod cgi' if it's going to redirect to cgid should somehow manage to make cgid work.

[Sergio Durigan Junior (sergiodj)]

Maybe I'm missing some step when trying to reproduce the problem, but:

$ lxc launch ubuntu:focal apache2
$ lxc shell apache2
# apt update && apt install -y apache2
# a2dismod mpm_event
Module mpm_event disabled.
To activate the new configuration, you need to run:
  systemctl restart apache2
# a2enmod mpm_worker
Enabling module mpm_worker.
To activate the new configuration, you need to run:
  systemctl restart apache2
# a2enmod cgi
Enabling module cgid.
To activate the new configuration, you need to run:
  systemctl restart apache2
# systemctl restart apache2
# ls -la /run/apache2/
total 4
drwxr-xr-x 2 root root 80 Mar 21 02:28 .
drwxr-xr-x 24 root root 760 Mar 21 02:20 ..
-rw-r--r-- 1 root root 6 Mar 21 02:28 apache2.pid
srwx------ 1 www-data root 0 Mar 21 02:28 cgisock.16732
# cat > /var/www/html/foo.cgi << _EOF_
#!/usr/bin/perl
print "Content-type: text/html\n\n";
print "Hello, World.";
_EOF_
# chmod +x /var/www/html/foo.cgi
# vim /etc/apache2/sites-enabled/000-default.conf
...
        <Directory "/var/www/html">
                Options +ExecCgi
                AddHandler cgi-script .cgi
        </Directory>
...
:wq
# systemctl restart apache2

Then, in another terminal:

$ curl 10.96.142.106/foo.cgi
Hello, World.

I'm running:

# apt policy apache2
apache2:
  Installed: 2.4.41-4ubuntu3.14
  Candidate: 2.4.41-4ubuntu3.14
  Version table:
 *** 2.4.41-4ubuntu3.14 500
        500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.4.41-4ubuntu3 500
        500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

Maybe there's something weird going with the CGI script?