SELinux - VPP Custom SELinux Policy

Overview

Security-enhanced Linux (SELinux) is a security feature in the Linux kernel. At a very high level, SELinux implements mandatory access controls (MAC), as opposed to discretionary access control (DAC) implemented in standard Linux. MAC defines how processes can interact with other system components (Files, Directories, Other Processes, Pipes, Sockets, Network Ports). Each system component is assigned a label, and then the SELinux Policy defines which labels and which actions on each label a process is able to perform. The VPP Custom SELinux Policy defines the actions VPP is allowed to perform on which labels.

The VPP Custom SELinux Policy is intended to be installed on RPM based platforms (tested on CentOS 7 and RHEL 7). Though SELinux can run on Debian platforms, it typically is not and therefore is not currently being built for Debian.

The VPP Custom SELinux Policy does not enable or disable SELinux, only allows VPP to run when SELinux is enabled. A fresh install of either Fedora, CentOS or RHEL will have SELinux enabled by default. To determine if SELinux is enabled on a given system and enable it if needed, run:

$ getenforce
Permissive

$ sudo setenforce 1

$ getenforce
Enforcing

To make the change persistent, modify the following file to set SELINUX=enforcing:

$ sudo vi /etc/selinux/config
:
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=enforcing
:

Installation

To install VPP, see the installation instructions on the VPP Wiki (https://wiki.fd.io/view/VPP/Installing_VPP_binaries_from_packages). The VPP Custom SELinux Policy is packaged in its own RPM starting in 18.04, vpp-selinux-policy-<VERSION>-<RELEASE>.rpm. It is packaged and installed along with the other VPP RPMs.

Fresh Install of VPP

If VPP has never been installed on a system, then starting in 18.04, the VPP Custom SELinux Policy will be installed with the other RPMs and all the system components managed by VPP will be labeled properly.

Fix SELinux Labels for VPP

In the case where the VPP Custom Policy is being installed for the first time, either because VPP has been upgraded or packages were removed and then reinstalled, several directories and files will not not be properly labeled. The labels on these files will need to be fixed for VPP to run properly with SELinux enabled. After the VPP Custom SELinux Policy is installed, run the following commands to fix the labels. If VPP is already running, make sure to restart VPP after the labels are fixed. This change is persistent for the life of the file. Once the VPP Custom Policy is installed on the system, subsequent files created by VPP will be labeled properly. This is only to fix files created by VPP prior to the VPP Custom Policy being installed.

$ sudo restorecon -Rv /etc/vpp/
$ sudo restorecon -Rv /usr/lib/vpp_api_test_plugins/
$ sudo restorecon -Rv /usr/lib/vpp_plugins/
$ sudo restorecon -Rv /usr/share/vpp/
$ sudo restorecon -Rv /var/run/vpp/

$ sudo chcon -t vpp_tmp_t /tmp/vpp_*
$ sudo chcon -t vpp_var_run_t /var/run/.vpp_*

NOTE: Because the VPP APIs allow custom filenames in certain scenarios, the above commands may not handle all files. Inspect your system and correct any files that are mislabeled. For example, to verify all VPP files in /tmp/ are labeled properly, run:

$ sudo ls -alZ /tmp/

Any files not properly labeled with vpp_tmp_t, run:

$ sudo chcon -t vpp_tmp_t /tmp/<filename>

VPP Files

Use of Non-default File Directories

VPP installs multiple files on the system. Some files have fixed directory and file names: - /etc/bash_completion.d/vppctl_completion - /etc/sysctl.d/80-vpp.conf - /usr/lib/systemd/system/vpp.service

Others files have default directory and file names but the default can be overwritten: - /etc/vpp/startup.conf - Can be changed via the /usr/lib/systemd/system/vpp.service file by changing the -c option on the VPP command line:

ExecStart=/usr/bin/vpp -c /etc/vpp/startup.conf

  • /run/vpp/cli.sock

    • Can be changed via the /etc/vpp/startup.conf file by changing the cli-listen setting:

unix {
:
  cli-listen /run/vpp/cli.sock
:
}

  • /var/log/vpp/vpp.log

    • Can be changed via the /etc/vpp/startup.conf file by changing the log setting:

unix {
  :
  log /var/log/vpp/vpp.log
  :
}

If the directory of any VPP installed files is changed from the default, ensure that the proper SELiunx label is applied. The SELinux label can be determined by passing the -Z option to many common Linux commands:

ls -alZ /run/vpp/
drwxr-xr-x. root vpp  system_u:object_r:vpp_var_run_t:s0 .
drwxr-xr-x. root root system_u:object_r:var_run_t:s0     ..
srwxrwxr-x. root vpp  system_u:object_r:vpp_var_run_t:s0 cli.sock

VPP SELinux Types

The following SELinux types are created by the VPP Custom SELinux Policy: - vpp_t - Applied to: - VPP process and spawned threads.

  • vpp_config_rw_t - Applied to:

    • /etc/vpp/*

  • vpp_tmp_t - Applied to:

    • /tmp/*

  • vpp_exec_t - Applied to:

    • /usr/bin/*

  • vpp_lib_t - Applied to:

    • /usr/lib/vpp_api_test_plugins/*

    • /usr/lib/vpp_plugins/*

  • vpp_unit_file_t - Applied to:

    • /usr/lib/systemd/system/vpp.*

  • vpp_log_t - Applied to:

    • /var/log/vpp/*

  • vpp_var_run_t - Applied to:

    • /var/run/vpp/*

Debug SELinux Issues

If SELinux issues are suspected, there are a few steps that can be taken to debug the issue. This section provides a few pointers on on those steps. Any SELinux JIRAs will need this information to properly address the issue.

Additional SELinux Packages and Setup

First, install the SELinux troubleshooting packages:

$ sudo yum -y install setroubleshoot setroubleshoot-server setools-console
-- OR --
$ sudo dnf -y install setroubleshoot setroubleshoot-server setools-console

To enable proper logging, restart auditd:

$ sudo service auditd restart

While debugging issues, it is best to set SELinux to Permissive mode. In Permissive mode, SELinux will still detect and flag errors, but will allow processes to continue normal operation. This allows multiple errors to be collected at once as opposed to breaking on each individual error. To set SELinux to Permissive mode (until next reboot or it is set back), use:

$ sudo setenforce 0

$ getenforce
Permissive

After debugging, to set SELinux back to Enforcing mode, use:

$ sudo setenforce 1

$ getenforce
Enforcing

Debugging

Once the SELinux troubleshooting packages are installed, perform the actions that are suspected to be blocked by SELinux. Either tail the log during these actions or grep the log for additional SELinux logs:

sudo tail -f /var/log/messages
-- OR --
sudo journalctl -f

Below are some examples of SELinux logs that are generated:

May 14 11:28:34 svr-22 setroubleshoot: SELinux is preventing /usr/bin/vpp from read access on the file hostCreate.txt. For complete SELinux messages run: sealert -l a418f869-f470-4c8a-b8e9-bdd41f2dd60b
May 14 11:28:34 svr-22 python: SELinux is preventing /usr/bin/vpp from read access on the file hostCreate.txt.#012#012*****  Plugin catchall (100. confidence) suggests   **************************#012#012If you believe that vpp should be allowed read access on the hostCreate.txt file by default.#012Then you should report this as a bug.#012You can generate a local policy module to allow this access.#012Do#012allow this access for now by executing:#012# ausearch -c 'vpp_main' --raw | audit2allow -M my-vppmain#012# semodule -i my-vppmain.pp#012
May 14 11:28:34 svr-22 setroubleshoot: SELinux is preventing /usr/bin/vpp from read access on the file hostCreate.txt. For complete SELinux messages run: sealert -l a418f869-f470-4c8a-b8e9-bdd41f2dd60b
May 14 11:28:34 svr-22 python: SELinux is preventing /usr/bin/vpp from read access on the file hostCreate.txt.#012#012*****  Plugin catchall (100. confidence) suggests   **************************#012#012If you believe that vpp should be allowed read access on the hostCreate.txt file by default.#012Then you should report this as a bug.#012You can generate a local policy module to allow this access.#012Do#012allow this access for now by executing:#012# ausearch -c 'vpp_main' --raw | audit2allow -M my-vppmain#012# semodule -i my-vppmain.pp#012
May 14 11:28:37 svr-22 setroubleshoot: SELinux is preventing vpp_main from map access on the packet_socket packet_socket. For complete SELinux messages run: sealert -l ab6667d9-3f14-4dbd-96a0-7a655f7b4eb1
May 14 11:28:37 svr-22 python: SELinux is preventing vpp_main from map access on the packet_socket packet_socket.#012#012*****  Plugin catchall (100. confidence) suggests   **************************#012#012If you believe that vpp_main should be allowed map access on the packet_socket packet_socket by default.#012Then you should report this as a bug.#012You can generate a local policy module to allow this access.#012Do#012allow this access for now by executing:#012# ausearch -c 'vpp_main' --raw | audit2allow -M my-vppmain#012# semodule -i my-vppmain.pp#012
May 14 11:28:51 svr-22 setroubleshoot: SELinux is preventing vpp_main from map access on the packet_socket packet_socket. For complete SELinux messages run: sealert -l ab6667d9-3f14-4dbd-96a0-7a655f7b4eb1
May 14 11:28:51 svr-22 python: SELinux is preventing vpp_main from map access on the packet_socket packet_socket.#012#012*****  Plugin catchall (100. confidence) suggests   **************************#012#012If you believe that vpp_main should be allowed map access on the packet_socket packet_socket by default.#012Then you should report this as a bug.#012You can generate a local policy module to allow this access.#012Do#012allow this access for now by executing:#012# ausearch -c 'vpp_main' --raw | audit2allow -M my-vppmain#012# semodule -i my-vppmain.pp#012

From the logs above, there are two sets of commands that are recommended to be run. The first is to run the sealert command. The second is to run the ausearch | audit2allow commands and the semodule command.

sealert Command

This sealert command provides a more detailed output for the given issue detected.

$ sealert -l a418f869-f470-4c8a-b8e9-bdd41f2dd60b
SELinux is preventing /usr/bin/vpp from 'read, write' accesses on the chr_file noiommu-0.

*****  Plugin device (91.4 confidence) suggests   ****************************

If you want to allow vpp to have read write access on the noiommu-0 chr_file
Then you need to change the label on noiommu-0 to a type of a similar device.
Do
# semanage fcontext -a -t SIMILAR_TYPE 'noiommu-0'
# restorecon -v 'noiommu-0'

*****  Plugin catchall (9.59 confidence) suggests   **************************

If you believe that vpp should be allowed read write access on the noiommu-0 chr_file by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# ausearch -c 'vpp' --raw | audit2allow -M my-vpp
# semodule -i my-vpp.pp


Additional Information:
Source Context                system_u:system_r:vpp_t:s0
Target Context                system_u:object_r:device_t:s0
Target Objects                noiommu-0 [ chr_file ]
Source                        vpp
Source Path                   /usr/bin/vpp
Port                          <Unknown>
Host                          vpp_centos7_selinux
Source RPM Packages           vpp-19.01.2-rc0~17_gcfd3086.x86_64
Target RPM Packages
Policy RPM                    selinux-policy-3.13.1-229.el7_6.12.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Permissive
Host Name                     vpp_centos7_selinux
Platform                      Linux vpp_centos7_selinux
                              3.10.0-957.12.1.el7.x86_64 #1 SMP Mon Apr 29
                              14:59:59 UTC 2019 x86_64 x86_64
Alert Count                   1
First Seen                    2019-05-13 18:10:50 EDT
Last Seen                     2019-05-13 18:10:50 EDT
Local ID                      a418f869-f470-4c8a-b8e9-bdd41f2dd60b

Raw Audit Messages
type=AVC msg=audit(1557785450.964:257): avc:  denied  { read write } for  pid=5273 comm="vpp" name="noiommu-0" dev="devtmpfs" ino=36022 scontext=system_u:system_r:vpp_t:s0 tcontext=system_u:object_r:device_t:s0 tclass=chr_file permissive=1


type=AVC msg=audit(1557785450.964:257): avc:  denied  { open } for  pid=5273 comm="vpp" path="/dev/vfio/noiommu-0" dev="devtmpfs" ino=36022 scontext=system_u:system_r:vpp_t:s0 tcontext=system_u:object_r:device_t:s0 tclass=chr_file permissive=1


type=SYSCALL msg=audit(1557785450.964:257): arch=x86_64 syscall=open success=yes exit=ENOTBLK a0=7fb395ffd7f0 a1=2 a2=7fb395ffd803 a3=7fb395ffe2a0 items=0 ppid=1 pid=5273 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=993 sgid=0 fsgid=993 tty=(none) ses=4294967295 comm=vpp exe=/usr/bin/vpp subj=system_u:system_r:vpp_t:s0 key=(null)

Hash: vpp,vpp_t,device_t,chr_file,read,write

In general, this command pumps out too much info and is only needed for additional debugging for tougher issues. Also note that once the process being tested is restarted, this command loses it’s context and will not provide any information:

$ sealert -l a418f869-f470-4c8a-b8e9-bdd41f2dd60b
Error
query_alerts error (1003): id (a418f869-f470-4c8a-b8e9-bdd41f2dd60b) not found

ausearch | audit2allow and semodule Commands

These set of commands are more useful for basic debugging. The ausearch | audit2allow commands generate a set files. It may be worthwhile to run the commands in a temporary subdirectory:

$ mkdir test-01/; cd test-01/

$ sudo ausearch -c 'vpp_main' --raw | audit2allow -M my-vppmain

$ ls
my-vpp.pp  my-vpp.te

$ cat my-vpp.te
module my-vpp 1.0;

require {
        type user_home_t;
        type vpp_t;
        class packet_socket map;
        class file { open read };
}

#============= vpp_t ==============
allow vpp_t self:packet_socket map;
allow vpp_t user_home_t:file { open read };

As shown above, the file my-vpp.te has been generated. This file shows possible changes to the SELinux policy that may fix the issue. If an SELinux policy was being created from scratch, this policy could be applied using the semodule -i my-vpp.pp command. HOWEVER, VPP already has a policy in place. So these changes need to be incorporated into the existing policy. The VPP SELinux policy is located in the following files:

$ ls extras/selinux/
selinux_doc.md  vpp-custom.fc  vpp-custom.if  vpp-custom.te

In this example, map needs to be added to the packet_socket class. If the vpp-custom.te is examined (prior to this fix), then one would see that the packet_socket class is already defined and just needs to be updated:

$ vi extras/selinux/vpp-custom.te
:
allow vpp_t self:process { execmem execstack setsched signal }; # too benevolent
allow vpp_t self:packet_socket { bind create setopt ioctl };  <---
allow vpp_t self:tun_socket { create relabelto relabelfrom };
:

Before blindly applying the changes proposed by the ausearch | audit2allow commands, try to determine what is being allowed by the policy and determine if this is desired, or if the code can be reworked to no longer require the suggested permission. In the my-vpp.te file from above, it is suggested to allow vpp_t (i.e. the VPP process) access to all files in the home directory (allow vpp_t user_home_t:file { open read };). This was because a vppctl exec command was executed calling a script located in the /home/<user>/ directory. Once this script was run from the /usr/share/vpp/ directory as described in a section above, these permissions were no longer needed.