Linux / grsecurity kernel patch

Grsecurity is an innovative approach to security utilizing a multi-layered detection, prevention, and containment model. It is licensed under the GPL. It offers among many other features:

• An intelligent and robust Role-Based Access Control (RBAC) system that can generate least privilege policies for your entire system with no configuration
• Change root (chroot) hardening
• /tmp race prevention
• Extensive auditing
• Prevention of entire classes of exploits related to address space bugs (from the PaX project)
• Additional randomness in the TCP/IP stack
• A restriction that allows a user to only view his/her processes
• Every security alert or audit contains the IP address of the person that caused the event

taken from GrSecHomepage :)

• GrSecurity homepage
• Great article about GrSec on SecurityFocus.com
• PAX Homepage

dowload grsecurity patch for your kernel (2.6.x / 2.4.x) from the site. You might need to wait a bit for a grsecurity patch for latest kernel.

server@/usr/src/linux# zcat ../grsecurity-2.XXX.patch.gz |patch -p1

# gradm-xxxx.tar.gz
# cd gradm
# ./configure
# make && make install
...
Setting up grsecurity ACL password
Password:
Re-enter Password:
Password written to /etc/grsec/pw.

putting all Grsec sysctl options into sysctl.conf

sysctl -a |grep grsec >> /etc/sysctl.conf

kernel.grsecurity.destroy_unused_shm = 1
kernel.grsecurity.chroot_findtask = 1
kernel.grsecurity.dmesg = 0
kernel.grsecurity.audit_ipc = 1
kernel.grsecurity.audit_mount = 0
kernel.grsecurity.audit_chdir = 0
kernel.grsecurity.audit_gid = 33
kernel.grsecurity.audit_group = 1
kernel.grsecurity.rand_tcp_src_ports = 1
kernel.grsecurity.rand_pids = 1
kernel.grsecurity.tpe_restrict_all = 0
kernel.grsecurity.tpe_gid = 0
kernel.grsecurity.tpe = 0
kernel.grsecurity.chroot_deny_sysctl = 1
kernel.grsecurity.chroot_caps = 1
kernel.grsecurity.chroot_execlog = 1
kernel.grsecurity.chroot_restrict_nice = 1
kernel.grsecurity.chroot_deny_mknod = 1
kernel.grsecurity.chroot_deny_chmod = 1
kernel.grsecurity.chroot_enforce_chdir = 1
kernel.grsecurity.chroot_deny_pivot = 1
kernel.grsecurity.chroot_deny_chroot = 1
kernel.grsecurity.chroot_deny_fchdir = 1
kernel.grsecurity.chroot_deny_mount = 1
kernel.grsecurity.chroot_deny_unix = 1
kernel.grsecurity.chroot_deny_shmat = 1
kernel.grsecurity.timechange_logging = 1
kernel.grsecurity.forkfail_logging = 1
kernel.grsecurity.signal_logging = 1
kernel.grsecurity.exec_logging = 0
kernel.grsecurity.execve_limiting = 1
kernel.grsecurity.fifo_restrictions = 1
kernel.grsecurity.linking_restrictions = 1
kernel.pax.softmode = 1
kernel.grsecurity.grsec_lock = 0

• PAX Homepage

The gradm utility controls only grsecurity's RBAC system; it cannot alter the behavior of grsecurity's there features. In a grsecurity-enabled kernel, gradm installs with a simple make; make install. You can set an admin password for gradm, which is a good idea, as once RBAC is enabled, even root's power will be restricted, and to get it back, you need to assume the admin role. You also need a password to shut down RBAC. Set the admin password with the command:

 gradm -P admin

Once you've set up a password, you can log into gradm as admin with the command:

 gradm -a

An innovative way to set up RBAC is to use grsecurity's learning mode. In learning mode, grsecurity watches for processes that run with root privileges, access the Internet, or write to key system files or directories. Grsecurity then generates an access control list (ACL) that instructs grsecurity to run these processes using the least privilege approach mentioned earlier. To enable learning mode, run:

 gradm -F -L /etc/grsec/learning.log

Let this mode run for a day or two to catch any time-sensitive processes. Avoid any administrative tasks during this time – remember, the root account is no longer trusted. After grsecurity has had enough time to recognize normal system usage, shut down learning mode and log into gradm as admin. Shutting down learning mode is necessary because grsecurity hides its configuration files when RBAC is running, as it is during learning mode. This means that the system will display an error message about not being able to find learning.log. In fact, the directory /etc/grsec will not appear to exist, even to root.

To write the ACL to disk, run the command:

 gradm -F -L /etc/grsec/learning.log -O /etc/grsec/acl

To start RBAC with your new ACL, run:

gradm -E

You can now enjoy the security advantages of processes running with the least amount of privileges necessary.

If you encounter any problems, disable RBAC by first logging in with the admin password and then running:

 gradm -D 

TODO