Version 7 (2.6.23) Smack: Simplified Mandatory Access Control Kernel

diff -uprN -X linux-2.6.23-base/Documentation/dontdiff linux-2.6.23-base/Documentation/Smack.txt linux-2.6.23-smack/Documentation/Smack.txt
@@ -0,0 +1,485 @@
+
+
+    "Good for you, you've decided to clean the elevator!"
+    - The Elevator, from Dark Star
+
+Smack is the the Simplified Mandatory Access Control Kernel.
+Smack is a kernel based implementation of mandatory access
+control that includes simplicity in its primary design goals.
+
+Smack does not implement Domain Type Enforcement (DTE). If
+you want DTE Linux has an implementation called SELinux.
+Those who really want DTE are encouraged to use SELinux.
+Those who don't know what DTE is are encouraged to compare
+SELinux with Smack to determine which mechanisms are best
+suited to the problem at hand.
+
+Smack consists of three major components:
+    - The kernel
+    - A start-up script and a few modified applications
+    - Configuration data
+
+The kernel component of Smack is implemented as a Linux
+Security Modules (LSM) module. It requires netlabel and
+works best with file systems that support extended attributes,
+although xattr support is not strictly required. The Smack
+patch is (currently) self contained, except for Kconfig
+and Makefile changes in the security directory. It is safe
+to run a Smack kernel under a "vanilla" distribution.
+Smack kernels use the CIPSO IP option. Some network
+configurations are intolerant of IP options and can impede
+access to systems that use them as Smack does.
+
+The startup script etc-init.d-smack should be installed
+in /etc/init.d/smack and should be invoked early in the
+start-up process. On Fedora rc5.d/S02smack is recommended.
+This script ensures that certain devices have the correct
+Smack attributes and loads the Smack configuration if
+any is defined.
+
+A version of "ls" that provides a "-M" option to display
+Smack labels on long listing is available.
+
+A hacked version of sshd that allows network logins by users
+with specific Smack labels is available. This version does
+not work for scp. You must set the /etc/ssh/sshd_config
+line:
+   UsePrivilegeSeparation no
+
+The format of /etc/smack/usr is:
+
+   username smack
+
+In keeping with the intent of Smack, configuration data is
+minimal and not strictly required. The most important
+configuration step is mounting the smackfs pseudo filesystem.
+
+Add this line to /etc/fstab:
+
+    smackfs /smack smackfs smackfsdef=* 0 0
+
+and create the /smack directory for mounting.
+
+Smack uses extended attributes (xattrs) to store file labels.
+The command to set a Smack label on a file is:
+
+    # attr -S -s SMACK64 -V "value" path
+
+NOTE: Smack labels are limited to 23 characters. The attr command
+      does not enforce this restriction and can be used to set
+      invalid Smack labels on files.
+
+If you don't do anything special all users will get the floor ("_")
+label when they log in. If you do want to log in via the hacked ssh
+at other labels use the attr command to set the smack value on the
+home directory and it's contents.
+
+You can add access rules in /etc/smack/accesses. They take the form:
+
+    subjectlabel objectlabel access
+
+access is a combination of the letters rwxa which specify the
+kind of access permitted a subject with subjectlabel on an
+object with objectlabel. If there is no rule no access is allowed.
+
+A process can see the smack label it is running with by
+reading /proc/self/attr/current. A privileged process can
+set the process smack by writing there.
+
+From the Smack Whitepaper:
+
+The Simplified Mandatory Access Control Kernel
+
+Casey Schaufler
[email protected]
+
+Mandatory Access Control
+
+Computer systems employ a variety of schemes to constrain how information is
+shared among the people and services using the machine. Some of these schemes
+allow the program or user to decide what other programs or users are allowed
+access to pieces of data. These schemes are called discretionary access
+control mechanisms because the access control is specified at the discretion
+of the user. Other schemes do not leave the decision regarding what a user or
+program can access up to users or programs. These schemes are called mandatory
+access control mechanisms because you don't have a choice regarding the users
+or programs that have access to pieces of data.
+
+Bell & LaPadula
+
+From the middle of the 1980's until the turn of the century Mandatory Access
+Control (MAC) was very closely associated with the Bell & LaPadula security
+model, a mathematical description of the United States Department of Defense
+policy for marking paper documents. MAC in this form enjoyed a following
+within the Capital Beltway and Scandinavian supercomputer centers but was
+often sited as failing to address general needs.
+
+Domain Type Enforcement
+
+Around the turn of the century Domain Type Enforcement (DTE) became popular.
+This scheme organizes users, programs, and data into domains that are
+protected from each other. This scheme has been widely deployed as a component
+of popular Linux distributions. The administrative overhead required to
+maintain this scheme and the detailed understanding of the whole system
+necessary to provide a secure domain mapping leads to the scheme being
+disabled or used in limited ways in the majority of cases.
+
+Smack
+
+Smack is a Mandatory Access Control mechanism designed to provide useful MAC
+while avoiding the pitfalls of its predecessors. The limitations of Bell &
+LaPadula are addressed by providing a scheme whereby access can be controlled
+according to the requirements of the system and its purpose rather than those
+imposed by an arcane government policy. The complexity of Domain Type
+Enforcement and avoided by defining access controls in terms of the access
+modes already in use.
+
+Smack Terminology
+
+The jargon used to talk about Smack will be familiar to those who have dealt
+with other MAC systems and shouldn't be too difficult for the uninitiated to
+pick up. There are four terms that are used in a specific way and that are
+especially important:
+
+	Subject: A subject is an active entity on the computer system.
+	On Smack a subject is a task, which is in turn the basic unit
+	of execution.
+
+	Object: An object is a passive entity on the computer system.
+	On Smack files of all types, IPC, and tasks can be objects.
+
+	Access: Any attempt by a subject to put information into or get
+	information from an object is an access.
+
+	Label: Data that identifies the Mandatory Access Control
+	characteristics of a subject or an object. 
+
+These definitions are consistent with the traditional use in the security
+community. There are also some terms from Linux that are likely to crop up:
+
+	Capability: A task that possesses a capability has permission to
+	violate an aspect of the system security policy, as identified by
+	the specific capability. A task that possesses one or more
+	capabilities is a privileged task, whereas a task with no
+	capabilities is an unprivileged task.
+
+	Privilege: A task that is allowed to violate the system security
+	policy is said to have privilege. As of this writing a task can
+	have privilege either by possessing capabilities or by having an
+	effective user of root.
+
+Smack Basics
+
+Smack is an extension to a Linux system. It enforces additional restrictions
+on what subjects can access which objects, based on the labels attached to
+each of the subject and the object.
+
+Labels
+
+Smack labels are ASCII character strings, one to twenty-three characters in
+length. Single character labels using special characters, that being anything
+other than a letter or digit, are reserved for use by the Smack development
+team. Smack labels are unstructured, case sensitive, and the only operation
+ever performed on them is comparison for equality. Smack labels cannot
+contain unprintable characters or the "/" (slash) character.
+
+There are some predefined labels:
+
+	_ Pronounced "floor", a single underscore character.
+	^ Pronounced "hat", a single circumflex character.
+	* Pronounced "star", a single asterisk character.
+	? Pronounced "huh", a single question mark character.
+
+Every task on a Smack system is assigned a label. System tasks, such as
+init(8) and systems daemons, are run with the floor ("_") label. User tasks
+are assigned labels according to the specification found in the
+/etc/smack/user configuration file.
+
+Access Rules
+
+Smack uses the traditional access modes of Linux. These modes are read,
+execute, write, and occasionally append. There are a few cases where the
+access mode may not be obvious. These include:
+
+	Signals: A signal is a write operation from the subject task to
+	the object task.
+	Internet Domain IPC: Transmission of a packet is considered a
+	write operation from the source task to the destination task.
+
+Smack restricts access based on the label attached to a subject and the label
+attached to the object it is trying to access. The rules enforced are, in
+order:
+
+	1. Any access requested by a task labeled "*" is denied.
+	2. A read or execute access requested by a task labeled "^"
+	   is permitted.
+	3. A read or execute access requested on an object labeled "_"
+	   is permitted.
+	4. Any access requested on an object labeled "*" is permitted.
+	5. Any access requested by a task on an object with the same
+	   label is permitted.
+	6. Any access requested that is explicitly defined in the loaded
+	   rule set is permitted.
+	7. Any other access is denied.
+
+Smack Access Rules
+
+With the isolation provided by Smack access separation is simple. There are
+many interesting cases where limited access by subjects to objects with
+different labels is desired. One example is the familiar spy model of
+sensitivity, where a scientist working on a highly classified project would be
+able to read documents of lower classifications and anything she writes will
+be "born" highly classified. To accommodate such schemes Smack includes a
+mechanism for specifying rules allowing access between labels.
+
+Access Rule Format
+
+The format of an access rule is:
+
+	subject-label object-label access
+
+Where subject-label is the Smack label of the task, object-label is the Smack
+label of the thing being accessed, and access is a string specifying the sort
+of access allowed. The Smack labels are limited to 23 characters. The access
+specification is searched for letters that describe access modes:
+
+	a: indicates that append access should be granted.
+	r: indicates that read access should be granted.
+	w: indicates that write access should be granted.
+	x: indicates that execute access should be granted.
+
+Access mode specifications can be in any order. Examples of acceptable rules
+are:
+
+	TopSecret Secret  rx
+	Secret    Unclass r
+	Manager   Game    x
+	User      HR      w
+	Odd       spells  waxbeans
+	New       Old     rrrrr
+	Closed    Off     none
+
+Order does matter and letters that do not specify an access mode are ignored.
+Examples of unacceptable rules are:
+
+	Top Secret Secret     rx
+	Ace        Ace        r
+
+Spaces are not allowed in labels. Since a subject always has access to files
+with the same label specifying a rule for that case is pointless.
+
+Applying Access Rules
+
+The developers of Linux rarely define new sorts of things, usually importing
+schemes and concepts from other systems. Most often, the other systems are
+variants of Unix. Unix has many endearing properties, but consistency of
+access control models is not one of them. Smack strives to treat accesses as
+uniformly as is sensible while keeping with the spirit of the underlying
+mechanism.
+
+File system objects including files, directories, named pipes, symbolic links,
+and devices require access permissions that closely match those used by mode
+bit access. To open a file for reading read access is required on the file. To
+search a directory requires execute access. Creating a file with write access
+requires both read and write access on the containing directory. Deleting a
+file requires read and write access to the file and to the containing
+directory. It is possible that a user may be able to see that a file exists
+but not any of its attributes by the circumstance of having read access to the
+containing directory but not to the differently labeled file. This is an
+artifact of the file name being data in the directory, not a part of the file.
+
+IPC objects, message queues, semaphore sets, and memory segments exist in flat
+namespaces and access requests are only required to match the object in
+question.
+
+Process objects reflect tasks on the system and the Smack label used to access
+them is the same Smack label that the task would use for its own access
+attempts. Sending a signal via the kill() system call is a write operation
+from the signaler to the recipient. Debugging a process requires both reading
+and writing. Creating a new task is an internal operation that results in two
+tasks with identical Smack labels and requires no access checks.
+
+Sockets are data structures attached to processes and sending a packet from
+one process to another requires that the sender have write access to the
+receiver. The receiver is not required to have read access to the sender.
+
+Setting Access Rules
+
+The configuration file /etc/smack/accesses contains the rules to be set at
+system startup. The contents are written to the special file /smack/load.
+Rules can be written to /smack/load at any time and take effect immediately.
+For any pair of subject and object labels there can be only one rule, with the
+most recently specified overriding any earlier specification. 
+
+Task Attribute
+
+The Smack label of a process can be read from /proc/<pid>/attr/current. A
+process can read its own Smack label from /proc/self/attr/current. A
+privileged process can change its own Smack label by writing to
+/proc/self/attr/current but not the label of another process.
+
+File Attribute
+
+The Smack label of a filesystem object is stored as an extended attribute
+named SMACK64 on the file. This attribute is in the security namespace. It can
+only be changed by a process with privilege.
+
+Privilege
+
+A process with CAP_MAC_OVERRIDE is privileged. 
+
+Smack Networking
+
+As mentioned before, Smack enforces access control on network protocol
+transmissions. Every packet sent by a Smack process is tagged with its Smack
+label. This is done by adding a CIPSO tag to the header of the IP packet. Each
+packet received is expected to have a CIPSO tag that identifies the label and
+if it lacks such a tag the network ambient label is assumed. Before the packet
+is delivered a check is made to determine that a subject with the label on the
+packet has write access to the receiving process and if that is not the case
+the packet is dropped.
+
+CIPSO Configuration
+
+It is normally unnecessary to specify the CIPSO configuration. The default
+values used by the system handle all internal cases. Smack will compose CIPSO
+label values to match the Smack labels being used without administrative
+intervention. Unlabeled packets that come into the system will be given the
+ambient label.
+
+Smack requires configuration in the case where packets from a system that is
+not smack that speaks CIPSO may be encountered. Usually this will be a Trusted
+Solaris system, but there are other, less widely deployed systems out there.
+CIPSO provides 3 important values, a Domain Of Interpretation (DOI), a level,
+and a category set with each packet. The DOI is intended to identify a group
+of systems that use compatible labeling schemes, and the DOI specified on the
+smack system must match that of the remote system or packets will be
+discarded. The DOI is 3 by default. The value can be read from /smack/doi and
+can be changed by writing to /smack/doi.
+
+The label and category set are mapped to a Smack label as defined in
+/etc/smack/cipso.
+
+A Smack/CIPSO mapping has the form:
+
+	smack level[/category[,category]*]
+
+Smack does not expect the level or category sets to be related in any
+particular way and does not assume or assign accesses based on them. Some
+examples of mappings:
+
+	TopSecret 7
+	TS:A,B    7/1,2
+	SecBDE    5/2,4,6
+	RAFTERS   7/12,26
+
+The ":" and "," characters are permitted in a Smack label but have no special
+meaning.
+
+The mapping of Smack labels to CIPSO values is defined by writing to
+/smack/cipso.
+
+In addition to explicit mappings Smack supports direct CIPSO mappings. One
+CIPSO level is used to indicate that the category set passed in the packet is
+in fact an encoding of the Smack label. The level used is 250 by default. The
+value can be read from /smack/direct and changed by writing to /smack/direct.
+
+Socket Attributes
+
+There are three attributes that are associated with sockets. These attributes
+can only be set by privileged tasks, but any task can read them for their own
+sockets.
+
+	SMACK64IPIN: The Smack label of the task object. A privileged
+	program that will enforce policy may set this to the star label.
+
+	SMACK64IPOUT: The Smack label transmitted with outgoing packets.
+	A privileged program may set this to match the label of another
+	task with which it hopes to communicate.
+
+	SMACK64PACKET: The Smack label of the last received packet, but
+	only if it can be provided reliably. If a reliable value is not
+	available an attempt to retrieve this attribute will fail.
+
+Writing Applications for Smack
+
+There are three sorts of applications that will run on a Smack system. How an
+application interacts with Smack will determine what it will have to do to
+work properly under Smack.
+
+Smack Ignorant Applications
+
+By far the majority of applications have no reason whatever to care about the
+unique properties of Smack. Since invoking a program has no impact on the
+Smack label associated with the process the only concern likely to arise is
+whether the process has execute access to the program.
+
+Smack Relevant Applications
+
+Some programs can be improved by teaching them about Smack, but do not make
+any security decisions themselves. The utility ls(1) is one example of such a
+program. 
+
+Smack Enforcing Applications
+
+These are special programs that not only know about Smack, but participate in
+the enforcement of system policy. In most cases these are the programs that
+set up user sessions. There are also network services that provide information
+to processes running with various labels.
+
+File System Interfaces
+
+Smack maintains labels on file system objects using extended attributes. The
+Smack label of a file, directory, or other file system object can be obtained
+using getxattr(2).
+
+	len = getxattr("/", "security.SMACK64", value, sizeof (value));
+
+will put the Smack label of the root directory into value. A privileged
+process can set the Smack label of a file system object with setxattr(2).
+
+	len = strlen("Rubble");
+	rc = setxattr("/foo", "security.SMACK64", "Rubble", len, 0);
+
+will set the Smack label of /foo to "Rubble" if the program has appropriate
+privilege.
+
+Socket Interfaces
+
+The socket attributes can be read using fgetxattr(2).
+
+	len = fgetxattr(fd, "security.SMACK64PACKET", value, sizeof (value));
+
+will put the Smack label of the most recently received packet if it is
+available into value. A privileged process can set the Smack label of outgoing
+packets with fsetxattr(2).
+
+	len = strlen("Rubble");
+	rc = fsetxattr(fd, "security.SMACK64IPOUT", "Rubble", len, 0);
+
+will set the Smack label "Rubble" on packets going out from the socket if the
+program has appropriate privilege. 
+
+	rc = fsetxattr(fd, "security.SMACK64IPIN, "*", strlen("*"), 0);
+
+will set the Smack label "*" as the object label against which incoming
+packets will be checked if the program has appropriate privilege. 
+
+Administration
+
+Smack supports some mount options:
+
+	smackfsdef=label: specifies the label to give files that lack
+	the Smack label extended attribute.
+
+	smackfsroot=label: specifies the label to assign the root of the
+	file system if it lacks the Smack extended attribute.
+
+	smackfshat=label: specifies a label that must have read access to
+	all labels set on the filesystem. Not yet enforced.
+
+	smackfsfloor=label: specifies a label to which all labels set on the
+	filesystem must have read access. Not yet enforced.
+
+These mount options apply to all file system types.
+

diff -uprN -X linux-2.6.23-base/Documentation/dontdiff linux-2.6.23-base/security/Kconfig linux-2.6.23-smack/security/Kconfig
@@ -94,6 +94,7 @@ config SECURITY_ROOTPLUG
 	  If you are unsure how to answer this question, answer N.
 
 source security/selinux/Kconfig
+source security/smack/Kconfig
 
 endmenu
 

diff -uprN -X linux-2.6.23-base/Documentation/dontdiff linux-2.6.23-base/security/Makefile linux-2.6.23-smack/security/Makefile
@@ -4,6 +4,7 @@
 
 obj-$(CONFIG_KEYS)			+= keys/
 subdir-$(CONFIG_SECURITY_SELINUX)	+= selinux
+subdir-$(CONFIG_SECURITY_SMACK)		+= smack
 
 # if we don't select a security model, use the default capabilities
 ifneq ($(CONFIG_SECURITY),y)

@@ -14,5 +15,6 @@ endif
 obj-$(CONFIG_SECURITY)			+= security.o dummy.o inode.o
 # Must precede capability.o in order to stack properly.
 obj-$(CONFIG_SECURITY_SELINUX)		+= selinux/built-in.o
+obj-$(CONFIG_SECURITY_SMACK)		+= commoncap.o smack/built-in.o
 obj-$(CONFIG_SECURITY_CAPABILITIES)	+= commoncap.o capability.o
 obj-$(CONFIG_SECURITY_ROOTPLUG)		+= commoncap.o root_plug.o

diff -uprN -X linux-2.6.23-base/Documentation/dontdiff linux-2.6.23-base/security/smack/Kconfig linux-2.6.23-smack/security/smack/Kconfig
@@ -0,0 +1,10 @@
+config SECURITY_SMACK
+	bool "Simplified Mandatory Access Control Kernel Support"
+	depends on NETLABEL && SECURITY_NETWORK
+	default n
+	help
+	  This selects the Simplified Mandatory Access Control Kernel.
+	  Smack is useful for sensitivity, integrity, and a variety
+	  of other mandatory security schemes.
+	  If you are unsure how to answer this question, answer N.
+

diff -uprN -X linux-2.6.23-base/Documentation/dontdiff linux-2.6.23-base/security/smack/Makefile linux-2.6.23-smack/security/smack/Makefile
@@ -0,0 +1,7 @@
+#
+# Makefile for the SMACK LSM
+#
+
+obj-$(CONFIG_SECURITY_SMACK) := smack.o
+
+smack-y := smack_lsm.o smack_access.o smackfs.o