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I have a webserver running CentOS 6.2 and the latest Apache from repositories. Todey I encountered a problem when running an executable program via CGI on Apache. The program is supposed to connect to some site, download something and then returns it to user (normal port-80 request, nothing fishy).

The problem is, that the CGI programs returns Permission denied on socket_open command.

Other simpler CGI programs that do not require network connectivity work fine and this program works just as well when invoked from command line, so I suspected some permissions issue and since setting a setuid on the executable didn't resolve a problem, I came to a conclusion that it is something that SELinux has control over.

I have never really worked with SELinux, but getsebool -a | grep httpd returns

allow_httpd_anon_write --> off
allow_httpd_mod_auth_ntlm_winbind --> off
allow_httpd_mod_auth_pam --> off
allow_httpd_sys_script_anon_write --> off
httpd_builtin_scripting --> on
httpd_can_check_spam --> off
httpd_can_network_connect --> off
httpd_can_network_connect_cobbler --> off
httpd_can_network_connect_db --> off
httpd_can_network_memcache --> off
httpd_can_network_relay --> off
httpd_can_sendmail --> off
httpd_dbus_avahi --> on
httpd_enable_cgi --> on
httpd_enable_ftp_server --> off
httpd_enable_homedirs --> off
httpd_execmem --> off
httpd_read_user_content --> off
httpd_setrlimit --> off
httpd_ssi_exec --> off
httpd_tmp_exec --> off
httpd_tty_comm --> on
httpd_unified --> on
httpd_use_cifs --> off
httpd_use_gpg --> off
httpd_use_nfs --> off

I suspect that httpd_can_network_connect --> off is the problematic one here, but this is a permision for the httpd, not the actual executable. Are SELinux permissions inherited from parent process? How would I set it to be enabled for the script only and not for the whole httpd? Or is there a whole different problem and not a SELinux related one?

Thank you for help.

Edit: I tried setenforce 0 and the script is working then, so it is a SELinux thing.

Edit 2: ausearch -ts recent -m avc returns

time->Thu May  3 23:52:29 2012
type=SYSCALL msg=audit(1336081949.221:18563): arch=c000003e syscall=42 success=no exit=-13 a0=8 a1=7fff21161cb0 a2=10 a3=7fff21161a30 items=0 ppid=6813 pid=6814 auid=4294967295 uid=48 gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=4294967295 comm=".stutsk" exe="/var/www/html/stutsk-cgi/.stutsk" subj=system_u:system_r:httpd_sys_script_t:s0 key=(null)
type=AVC msg=audit(1336081949.221:18563): avc:  denied  { name_connect } for  pid=6814 comm=".stutsk" dest=80 scontext=system_u:system_r:httpd_sys_script_t:s0 tcontext=system_u:object_r:http_port_t:s0 tclass=tcp_socket
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As a starting point: a) Prove you have a SELinux problem by setting SELinux to permissive (echo 0 >/selinux/enforce) and retest. b) Check your audit log for denied errors (auditd needs to be running) c) use audit2allow -a -w (from the policycoreutils-python package) to generate the necessary rules based on your audit log. –  cyberx86 May 3 '12 at 1:25
If your running the cgi script from a cgi-bin directory then I am pretty certain that the script does a domain transition of its own into httpd_cgi_script_t (I believe). Can you re-run the script and produce the output of "ausearch -ts recent -m avc" –  Matthew Ife May 3 '12 at 20:53
This is probably true. See my edit. –  Tibor May 3 '12 at 21:53

2 Answers 2

up vote 1 down vote accepted

Personally, would have reservations of permitting CGI processing being able to fetch stuff from the network (just makes me feel uncomfortable) but you can enable this with the following policy:

policy_module(localhttpd_script_t, 1.0.0)

        type httpd_sys_script_t;
        type http_port_t;

gen_tunable(`httpd_script_can_http_connect', `false')

tunable_policy(`httpd_script_can_http_connect', `
        allow httpd_sys_script_t self:tcp_socket rw_socket_perms;

You'll need to install the policycoreutils-python stuff if its not done already.

To make this, run

make -f /usr/share/selinux/devel/Makefile load

This will compile and install the module. I compiled on Fedora 15, but I dont think theres any special policy thats unique to that system.

To turn this on (temporarily) run the command *setsebool httpd_script_can_http_connect 1* and to make permanent *setsebool -P httpd_script_can_http_connect 1* .

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I don't think that CGI that has access to the network is something special. It needs to connect to the database server, for example. Anyway, thank you for your answer! –  Tibor May 4 '12 at 20:00

Are SELinux permissions inherited from parent process?

Yes, unless a rule causes a transition to a new domain.

How would I set it to be enabled for the script only and not for the whole httpd?

You'd need to create a new domain that allows network access, and write a rule that causes a domain transition when the script interpreter is invoked. Note that this will cause any script invoked by this interpreter when invoked by httpd to follow this transition; it is much less trivial to cause a script-specific domain transition.

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