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|Developer(s)||Brad Spengler (Spender)|
|Stable release||3.1 for Linux Kernels 3.2.72 and 3.14.54
(15 October 2015 ) [±]
|Preview release||3.1 for Linux Kernel 4.3.5
(3 February 2016 ) [±]
grsecurity is a set of patches for the Linux kernel which emphasizes security enhancements. It is typically used by computer systems which accept remote connections from untrusted locations, such as web servers and systems offering shell access to its users.
Work on grsecurity began in February 2001 as a port of Openwall Project's security-enhancing patches for version 2.4 of the Linux kernel mainline. The first release of grsecurity was for the Linux kernel 2.4.1.
Since September 9, 2015, the availability of stable grsecurity patches has become limited to the commercial customers of grsecurity. The testing versions of grsecurity patches, as well as the source code and patches for related userspace utilities, remain publicly available.
grsecurity provides a collection of security features to the Linux kernel, ranging from address space protection to process control.
A major component bundled with grsecurity is PaX. Among other features, the patch flags data memory, the stack, for example, as non-executable and program memory as non-writable. The aim is to prevent memory from being overwritten, which can help to prevent many types of security vulnerabilities, such as buffer overflows. PaX also provides address space layout randomization (ASLR), which randomizes important memory addresses to reduce the probability of attacks that rely on easily predicted memory addresses. PaX is not developed by the grsecurity developers. It is available in other Linux distributions such as Gentoo or IPFire, and directly from grsecurity.
Role-based access control
Another notable component of grsecurity is that it provides a full role-based access control (RBAC) system. RBAC is intended to restrict access to the system further than what is normally provided by Unix access control lists, with the aim of creating a fully least-privilege system, where users and processes have the absolute minimum privileges to work correctly and nothing more. This way, if the system is compromised, the ability of the attacker to damage or gain sensitive information on the system can be drastically reduced. RBAC works through a collection of roles. Each role can have individual restrictions on what they can or cannot do, and these roles and restrictions form an access policy, which can be amended as needed.
A list of RBAC features:
- Domain support for users and groups
- Role transition tables
- IP-based roles
- Non-root access to special roles
- Special roles that require no authentication
- Nested subjects
- Support for variables in the configuration
- And, or, and difference set operations on variables in configuration
- Object mode that controls the creation of setuid and setgid files
- Create and delete object modes
- Kernel interpretation of inheritance
- Real-time regular expression resolution
- Ability to deny ptraces to specific processes
- User and group transition checking and enforcement on an inclusive or exclusive basis
- /dev/grsec entry for kernel authentication and learning logs
- Next-generation code that produces least-privilege policies for the entire system with no configuration
- Policy statistics for gradm
- Inheritance-based learning
- Learning configuration file that allows the administrator to enable inheritance-based learning or disable learning on specific paths
- Full path names for offending process and parent process
- RBAC status function for gradm
- /proc/<pid>/ipaddr gives the remote address of the person who started a given process
- Secure policy enforcement
- Supports read, write, append, execute, view, and read-only ptrace object permissions
- Supports hide, protect, and override subject flags
- Supports the PaX flags
- Shared memory protection feature
- Integrated local attack response on all alerts
- Subject flag that ensures a process can never execute trojaned code
- Full-featured, fine-grained auditing
- Resource, socket, and capability support
- Protection against exploit bruteforcing
- /proc/pid filedescriptor/memory protection
- Rules can be placed on non-existent files/processes
- Policy regeneration on subjects and objects
- Configurable log suppression
- Configurable process accounting
- Human-readable configuration
- Not filesystem or architecture dependent
- Scales well: supports as many policies as memory can handle with the same performance hit
- No run-time memory allocation
- SMP safe
- O(1) time efficiency for most operations
- Include directive for specifying additional policies
- Enable, disable, reload capabilities
- Option to hide kernel processes
- No attaching shared memory outside chroot
- No sending of signals by
- No viewing of any process outside chroot, even if /proc is mounted
- No mounting or remounting
- No double chroot
fchdirout of chroot
- No raising of scheduler priority
- No connecting to abstract unix domain sockets outside chroot
- Removal of harmful privileges via cap
grsecurity also adds enhanced auditing to the Linux kernel. Among other things, it can be configured to audit a specific group of users, mounting/unmounting of devices, changes to the system time and date, and
chdir logging. Some of the other audit types allow the administrator to also log denied resource attempts, failed
fork attempts, IPC creation and removal, and
exec logging together with its arguments.
Trusted path execution is another optional feature that can be used to prevent users from executing binaries not owned by the root user, or world-writable binaries. This is useful to prevent users from executing their own malicious binaries or accidentally executing world-writable system binaries that could have been modified by a malicious user.
grsecurity also hardens the way chroot "jails" work. A chroot jail can be used to isolate a particular process from the rest of the system, which can be used to minimise the potential for damage should the service be compromised. There are ways to "break out" of a chroot jail, which grsecurity attempts to prevent.
List of additional features and security improvements:
/procrestrictions that do not leak information about process owners
- Symlink/hardlink restrictions to prevent
- FIFO restrictions
- Enhanced implementation of trusted path execution
- GID-based socket restrictions
- Nearly all options are
sysctl-tunable, with a locking mechanism
- All alerts and audits support a feature that logs the IP address of the attacker with the log
- Stream connections across Unix domain sockets carry the attacker's IP address with them (on 2.4 only)
- Detection of local connections: copies attacker's IP address to the other task
- Automatic deterrence of exploit brute-forcing
- Low, medium, high, and custom security levels
- Tunable flood-time and burst for logging
- Application firewall
- Exec Shield
- Intel MPX
- Linux Security Modules
- Security-Enhanced Linux
- "grsecurity license".
- "Linux Kernel Security (SELinux vs AppArmor vs Grsecurity)".
- Silviu Stahie (2015-08-28). "Grsecurity Forced by Multi-Billion Dollar Company to Release Patches Only to Sponsors". softpedia.com. Retrieved 2016-06-21.
- Brad Spengler; The PaX Team (2015-08-26). "Important Notice Regarding Public Availability of Stable Patches". grsecurity.net. Retrieved 2016-06-21.
- "grsecurity downloads page". grsecurity.net. Retrieved 2016-06-21.
- "Homepage of PaX". Pax.grsecurity.net. Retrieved 2010-08-12.
- "grsecurity". grsecurity.net. Retrieved 2010-08-12.
|Wikibooks has a book on the topic of: Grsecurity|
- Official website
- Academic Research Publications Mentioning grsecurity/PaX
- Edge, Jake (January 7, 2009). "The future for grsecurity". LWN.net.