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How do I tell what would be allowed by a boolean?
danwalsh

I received and Email today that asked the following question:

I still fail to understand the difference between  httpd_can_network_connect_db and httpd_can_network_connect. Some people say the former allows connections to known database ports. My question are:

What are these ports? Where are the corresponding policy defined? I found many  .pp files deeply under /etc/selinux, and I feel sorry that they are binary which are almost impossible to interpret, so where can I find the the source files for the compiled policy, and what is the language to define policies?


You could use the semanage command for how the booleans are described.

> semanage boolean -l | grep httpd_can_network_connect
httpd_can_network_connect_db   (off  ,  off)  Allow HTTPD scripts and modules to connect to databases over the network.
httpd_can_network_connect      (off  ,  off)  Allow HTTPD scripts and modules to connect to the network using TCP.


The best answer to this is to look at the sesearch and seinfo tools and on newer (Fedora/RHEL7) systems sepolicy command.  Also look at the man pages that have been generated.

man httpd_selinux

sesearch and seinfo are available in the setools-cmdline package.  sepolicy is in policycoreutils-python package.

httpd_can_network_connect_db

sesearch -A -s httpd_t -b httpd_can_network_connect_db -p name_connect
   allow httpd_t postgresql_port_t : tcp_socket { recv_msg send_msg name_connect } ;
   allow httpd_t mssql_port_t : tcp_socket name_connect ;
   allow httpd_t oracle_port_t : tcp_socket name_connect ;
   allow httpd_t mysqld_port_t : tcp_socket { recv_msg send_msg name_connect } ;
   allow httpd_t gds_db_port_t : tcp_socket name_connect ;


The command above reads in the policy and prints out what happens when you enable the httpd_can_network_connect_db boolean.  We further restrict the search to see how it affects the httpd_t, apache, process type with the name_connect access.     sesearch tells us that turning on httpd_can_network_connect_db would allow the httpd_t domain to connect to tcp ports labeled postgresql_port_t, mssql_port_t, oracle_port_t, mysqld_port_t, gds_db_port_t.  You can use seinfo to turn these port types into port definitions. semanage port -l would also work.

> seinfo  --port | grep -e postgresql_port_t -e mysqld_port_t -e oracle_port_t -e gds_db_port_t | grep tcp
    portcon tcp 3050 system_u:object_r:gds_db_port_t:s0
    portcon tcp 1186 system_u:object_r:mysqld_port_t:s0
    portcon tcp 3306 system_u:object_r:mysqld_port_t:s0
    portcon tcp 63132-63164 system_u:object_r:mysqld_port_t:s0
    portcon tcp 1521 system_u:object_r:oracle_port_t:s0
    portcon tcp 2483 system_u:object_r:oracle_port_t:s0
    portcon tcp 2484 system_u:object_r:oracle_port_t:s0
    portcon tcp 5432 system_u:object_r:postgresql_port_t:s0


> sepolicy network -t postgresql_port_t
postgresql_port_t: tcp: 5432


httpd_can_network_connect

> sesearch -A -s httpd_t -b httpd_can_network_connect -p name_connect
Found 1 semantic av rules:
   allow httpd_t port_type : tcp_socket name_connect ;


The above command shows that httpd_can_network_connect allows httpd_t to connect to all tcp socket types that have the port_type attribute.

> seinfo -aport_type -x | wc -l
245


Using seinfo above would show you that port_type is the attribute of all port types, meaning that turning on the httpd_can_network_connect boolean, allows the httpd_t domain to connect to ALL tcp network ports.

Bottom Line httpd_can_network_connect_db allows httpd_t to connect to an additional 10 ports while httpd_can_network_connect adds thousands.


Many thanks, Dan, for thorough explanation. I followed your instructions and verified in my CentOS 6.4 release, although the output in my box differs from yours a little, I have amlost clear understanding, except a few minor points:

1) say in this rule,

allow httpd_t postgresql_port_t : tcp_socket { recv_msg send_msg name_connect } ;

httpd_selinux(8) says httpd_t type is entered via the httpd_exec_t file type whose label rules can be found in /etc/selinux/targeted/modules/active/file_contexts. And by either seinfo or semanage the postgresql_port_t port type can be verified as tcp/5432.

I read tcp_sockt as resource class and those in curly brackets are permissions, but there is still a minor gap between them and my old understanding of Linux system APIs. How can I resolve the gap?

2) I read the 'allow source_type target_type: resoure_class { permissions }' as kind of policy language syntax. And I recall you mentioned in an old post that it is m4, and Brindle's blog mentioned there will be a new policy language. So where can I find the source of the existing policies, and when will the new language take over?

3) there's a minor mind leap I saw this command

seinfo -aport_type -x | wc -l

where port_type is an attribute. What's an attribute? I guess it is kind of aggregation of types?

PS: I read almost 80 recent posts last night, I wish I have read your blog many years ago.

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