3 "Good for you, you've decided to clean the elevator!"
4 - The Elevator, from Dark Star
6 Smack is the Simplified Mandatory Access Control Kernel.
7 Smack is a kernel based implementation of mandatory access
8 control that includes simplicity in its primary design goals.
10 Smack is not the only Mandatory Access Control scheme
11 available for Linux. Those new to Mandatory Access Control
12 are encouraged to compare Smack with the other mechanisms
13 available to determine which is best suited to the problem
16 Smack consists of three major components:
18 - Basic utilities, which are helpful but not required
21 The kernel component of Smack is implemented as a Linux
22 Security Modules (LSM) module. It requires netlabel and
23 works best with file systems that support extended attributes,
24 although xattr support is not strictly required.
25 It is safe to run a Smack kernel under a "vanilla" distribution.
27 Smack kernels use the CIPSO IP option. Some network
28 configurations are intolerant of IP options and can impede
29 access to systems that use them as Smack does.
31 Smack is used in the Tizen operating system. Please
32 go to http://wiki.tizen.org for information about how
33 Smack is used in Tizen.
35 The current git repository for Smack user space is:
37 git://github.com/smack-team/smack.git
39 This should make and install on most modern distributions.
40 There are five commands included in smackutil:
42 chsmack - display or set Smack extended attribute values
43 smackctl - load the Smack access rules
44 smackaccess - report if a process with one label has access
45 to an object with another
47 These two commands are obsolete with the introduction of
48 the smackfs/load2 and smackfs/cipso2 interfaces.
50 smackload - properly formats data for writing to smackfs/load
51 smackcipso - properly formats data for writing to smackfs/cipso
53 In keeping with the intent of Smack, configuration data is
54 minimal and not strictly required. The most important
55 configuration step is mounting the smackfs pseudo filesystem.
56 If smackutil is installed the startup script will take care
57 of this, but it can be manually as well.
59 Add this line to /etc/fstab:
61 smackfs /sys/fs/smackfs smackfs defaults 0 0
63 The /sys/fs/smackfs directory is created by the kernel.
65 Smack uses extended attributes (xattrs) to store labels on filesystem
66 objects. The attributes are stored in the extended attribute security
67 name space. A process must have CAP_MAC_ADMIN to change any of these
70 The extended attributes that Smack uses are:
73 Used to make access control decisions. In almost all cases
74 the label given to a new filesystem object will be the label
75 of the process that created it.
77 The Smack label of a process that execs a program file with
78 this attribute set will run with this attribute's value.
80 Don't allow the file to be mmapped by a process whose Smack
81 label does not allow all of the access permitted to a process
82 with the label contained in this attribute. This is a very
83 specific use case for shared libraries.
85 Can only have the value "TRUE". If this attribute is present
86 on a directory when an object is created in the directory and
87 the Smack rule (more below) that permitted the write access
88 to the directory includes the transmute ("t") mode the object
89 gets the label of the directory instead of the label of the
90 creating process. If the object being created is a directory
91 the SMACK64TRANSMUTE attribute is set as well.
93 This attribute is only available on file descriptors for sockets.
94 Use the Smack label in this attribute for access control
95 decisions on packets being delivered to this socket.
97 This attribute is only available on file descriptors for sockets.
98 Use the Smack label in this attribute for access control
99 decisions on packets coming from this socket.
101 There are multiple ways to set a Smack label on a file:
103 # attr -S -s SMACK64 -V "value" path
104 # chsmack -a value path
106 A process can see the Smack label it is running with by
107 reading /proc/self/attr/current. A process with CAP_MAC_ADMIN
108 can set the process Smack by writing there.
110 Most Smack configuration is accomplished by writing to files
111 in the smackfs filesystem. This pseudo-filesystem is mounted
115 Provided for backward compatibility. The access2 interface
116 is preferred and should be used instead.
117 This interface reports whether a subject with the specified
118 Smack label has a particular access to an object with a
119 specified Smack label. Write a fixed format access rule to
120 this file. The next read will indicate whether the access
121 would be permitted. The text will be either "1" indicating
122 access, or "0" indicating denial.
124 This interface reports whether a subject with the specified
125 Smack label has a particular access to an object with a
126 specified Smack label. Write a long format access rule to
127 this file. The next read will indicate whether the access
128 would be permitted. The text will be either "1" indicating
129 access, or "0" indicating denial.
131 This contains the Smack label applied to unlabeled network
134 This interface allows modification of existing access control rules.
135 The format accepted on write is:
137 where the first string is the subject label, the second the
138 object label, the third the access to allow and the fourth the
139 access to deny. The access strings may contain only the characters
140 "rwxat-". If a rule for a given subject and object exists it will be
141 modified by enabling the permissions in the third string and disabling
142 those in the fourth string. If there is no such rule it will be
143 created using the access specified in the third and the fourth strings.
145 Provided for backward compatibility. The cipso2 interface
146 is preferred and should be used instead.
147 This interface allows a specific CIPSO header to be assigned
148 to a Smack label. The format accepted on write is:
149 "%24s%4d%4d"["%4d"]...
150 The first string is a fixed Smack label. The first number is
151 the level to use. The second number is the number of categories.
152 The following numbers are the categories.
153 "level-3-cats-5-19 3 2 5 19"
155 This interface allows a specific CIPSO header to be assigned
156 to a Smack label. The format accepted on write is:
158 The first string is a long Smack label. The first number is
159 the level to use. The second number is the number of categories.
160 The following numbers are the categories.
161 "level-3-cats-5-19 3 2 5 19"
163 This contains the CIPSO level used for Smack direct label
164 representation in network packets.
166 This contains the CIPSO domain of interpretation used in
169 This interface allows specific IPv6 internet addresses to be
170 treated as single label hosts. Packets are sent to single
171 label hosts only from processes that have Smack write access
172 to the host label. All packets received from single label hosts
173 are given the specified label. The format accepted on write is:
174 "%h:%h:%h:%h:%h:%h:%h:%h label" or
175 "%h:%h:%h:%h:%h:%h:%h:%h/%d label".
176 The "::" address shortcut is not supported.
177 If label is "-DELETE" a matched entry will be deleted.
179 Provided for backward compatibility. The load2 interface
180 is preferred and should be used instead.
181 This interface allows access control rules in addition to
182 the system defined rules to be specified. The format accepted
185 where the first string is the subject label, the second the
186 object label, and the third the requested access. The access
187 string may contain only the characters "rwxat-", and specifies
188 which sort of access is allowed. The "-" is a placeholder for
189 permissions that are not allowed. The string "r-x--" would
190 specify read and execute access. Labels are limited to 23
191 characters in length.
193 This interface allows access control rules in addition to
194 the system defined rules to be specified. The format accepted
197 where the first string is the subject label, the second the
198 object label, and the third the requested access. The access
199 string may contain only the characters "rwxat-", and specifies
200 which sort of access is allowed. The "-" is a placeholder for
201 permissions that are not allowed. The string "r-x--" would
202 specify read and execute access.
204 Provided for backward compatibility. The load-self2 interface
205 is preferred and should be used instead.
206 This interface allows process specific access rules to be
207 defined. These rules are only consulted if access would
208 otherwise be permitted, and are intended to provide additional
209 restrictions on the process. The format is the same as for
212 This interface allows process specific access rules to be
213 defined. These rules are only consulted if access would
214 otherwise be permitted, and are intended to provide additional
215 restrictions on the process. The format is the same as for
218 This contains the Smack logging state.
220 This contains the CIPSO level used for Smack mapped label
221 representation in network packets.
223 This interface allows specific internet addresses to be
224 treated as single label hosts. Packets are sent to single
225 label hosts without CIPSO headers, but only from processes
226 that have Smack write access to the host label. All packets
227 received from single label hosts are given the specified
228 label. The format accepted on write is:
229 "%d.%d.%d.%d label" or "%d.%d.%d.%d/%d label".
230 If the label specified is "-CIPSO" the address is treated
231 as a host that supports CIPSO headers.
233 This contains labels processes must have for CAP_MAC_ADMIN
234 and CAP_MAC_OVERRIDE to be effective. If this file is empty
235 these capabilities are effective at for processes with any
236 label. The values are set by writing the desired labels, separated
237 by spaces, to the file or cleared by writing "-" to the file.
239 This is used to define the current ptrace policy
240 0 - default: this is the policy that relies on Smack access rules.
241 For the PTRACE_READ a subject needs to have a read access on
242 object. For the PTRACE_ATTACH a read-write access is required.
243 1 - exact: this is the policy that limits PTRACE_ATTACH. Attach is
244 only allowed when subject's and object's labels are equal.
245 PTRACE_READ is not affected. Can be overridden with CAP_SYS_PTRACE.
246 2 - draconian: this policy behaves like the 'exact' above with an
247 exception that it can't be overridden with CAP_SYS_PTRACE.
249 Writing a Smack label here sets the access to '-' for all access
250 rules with that subject label.
252 If the kernel is configured with CONFIG_SECURITY_SMACK_BRINGUP
253 a process with CAP_MAC_ADMIN can write a label into this interface.
254 Thereafter, accesses that involve that label will be logged and
255 the access permitted if it wouldn't be otherwise. Note that this
256 is dangerous and can ruin the proper labeling of your system.
257 It should never be used in production.
259 If you are using the smackload utility
260 you can add access rules in /etc/smack/accesses. They take the form:
262 subjectlabel objectlabel access
264 access is a combination of the letters rwxatb which specify the
265 kind of access permitted a subject with subjectlabel on an
266 object with objectlabel. If there is no rule no access is allowed.
268 Look for additional programs on http://schaufler-ca.com
270 From the Smack Whitepaper:
272 The Simplified Mandatory Access Control Kernel
275 casey@schaufler-ca.com
277 Mandatory Access Control
279 Computer systems employ a variety of schemes to constrain how information is
280 shared among the people and services using the machine. Some of these schemes
281 allow the program or user to decide what other programs or users are allowed
282 access to pieces of data. These schemes are called discretionary access
283 control mechanisms because the access control is specified at the discretion
284 of the user. Other schemes do not leave the decision regarding what a user or
285 program can access up to users or programs. These schemes are called mandatory
286 access control mechanisms because you don't have a choice regarding the users
287 or programs that have access to pieces of data.
291 From the middle of the 1980's until the turn of the century Mandatory Access
292 Control (MAC) was very closely associated with the Bell & LaPadula security
293 model, a mathematical description of the United States Department of Defense
294 policy for marking paper documents. MAC in this form enjoyed a following
295 within the Capital Beltway and Scandinavian supercomputer centers but was
296 often sited as failing to address general needs.
298 Domain Type Enforcement
300 Around the turn of the century Domain Type Enforcement (DTE) became popular.
301 This scheme organizes users, programs, and data into domains that are
302 protected from each other. This scheme has been widely deployed as a component
303 of popular Linux distributions. The administrative overhead required to
304 maintain this scheme and the detailed understanding of the whole system
305 necessary to provide a secure domain mapping leads to the scheme being
306 disabled or used in limited ways in the majority of cases.
310 Smack is a Mandatory Access Control mechanism designed to provide useful MAC
311 while avoiding the pitfalls of its predecessors. The limitations of Bell &
312 LaPadula are addressed by providing a scheme whereby access can be controlled
313 according to the requirements of the system and its purpose rather than those
314 imposed by an arcane government policy. The complexity of Domain Type
315 Enforcement and avoided by defining access controls in terms of the access
316 modes already in use.
320 The jargon used to talk about Smack will be familiar to those who have dealt
321 with other MAC systems and shouldn't be too difficult for the uninitiated to
322 pick up. There are four terms that are used in a specific way and that are
323 especially important:
325 Subject: A subject is an active entity on the computer system.
326 On Smack a subject is a task, which is in turn the basic unit
329 Object: An object is a passive entity on the computer system.
330 On Smack files of all types, IPC, and tasks can be objects.
332 Access: Any attempt by a subject to put information into or get
333 information from an object is an access.
335 Label: Data that identifies the Mandatory Access Control
336 characteristics of a subject or an object.
338 These definitions are consistent with the traditional use in the security
339 community. There are also some terms from Linux that are likely to crop up:
341 Capability: A task that possesses a capability has permission to
342 violate an aspect of the system security policy, as identified by
343 the specific capability. A task that possesses one or more
344 capabilities is a privileged task, whereas a task with no
345 capabilities is an unprivileged task.
347 Privilege: A task that is allowed to violate the system security
348 policy is said to have privilege. As of this writing a task can
349 have privilege either by possessing capabilities or by having an
350 effective user of root.
354 Smack is an extension to a Linux system. It enforces additional restrictions
355 on what subjects can access which objects, based on the labels attached to
356 each of the subject and the object.
360 Smack labels are ASCII character strings. They can be up to 255 characters
361 long, but keeping them to twenty-three characters is recommended.
362 Single character labels using special characters, that being anything
363 other than a letter or digit, are reserved for use by the Smack development
364 team. Smack labels are unstructured, case sensitive, and the only operation
365 ever performed on them is comparison for equality. Smack labels cannot
366 contain unprintable characters, the "/" (slash), the "\" (backslash), the "'"
367 (quote) and '"' (double-quote) characters.
368 Smack labels cannot begin with a '-'. This is reserved for special options.
370 There are some predefined labels:
372 _ Pronounced "floor", a single underscore character.
373 ^ Pronounced "hat", a single circumflex character.
374 * Pronounced "star", a single asterisk character.
375 ? Pronounced "huh", a single question mark character.
376 @ Pronounced "web", a single at sign character.
378 Every task on a Smack system is assigned a label. The Smack label
379 of a process will usually be assigned by the system initialization
384 Smack uses the traditional access modes of Linux. These modes are read,
385 execute, write, and occasionally append. There are a few cases where the
386 access mode may not be obvious. These include:
388 Signals: A signal is a write operation from the subject task to
390 Internet Domain IPC: Transmission of a packet is considered a
391 write operation from the source task to the destination task.
393 Smack restricts access based on the label attached to a subject and the label
394 attached to the object it is trying to access. The rules enforced are, in
397 1. Any access requested by a task labeled "*" is denied.
398 2. A read or execute access requested by a task labeled "^"
400 3. A read or execute access requested on an object labeled "_"
402 4. Any access requested on an object labeled "*" is permitted.
403 5. Any access requested by a task on an object with the same
405 6. Any access requested that is explicitly defined in the loaded
406 rule set is permitted.
407 7. Any other access is denied.
411 With the isolation provided by Smack access separation is simple. There are
412 many interesting cases where limited access by subjects to objects with
413 different labels is desired. One example is the familiar spy model of
414 sensitivity, where a scientist working on a highly classified project would be
415 able to read documents of lower classifications and anything she writes will
416 be "born" highly classified. To accommodate such schemes Smack includes a
417 mechanism for specifying rules allowing access between labels.
421 The format of an access rule is:
423 subject-label object-label access
425 Where subject-label is the Smack label of the task, object-label is the Smack
426 label of the thing being accessed, and access is a string specifying the sort
427 of access allowed. The access specification is searched for letters that
428 describe access modes:
430 a: indicates that append access should be granted.
431 r: indicates that read access should be granted.
432 w: indicates that write access should be granted.
433 x: indicates that execute access should be granted.
434 t: indicates that the rule requests transmutation.
435 b: indicates that the rule should be reported for bring-up.
437 Uppercase values for the specification letters are allowed as well.
438 Access mode specifications can be in any order. Examples of acceptable rules
449 Examples of unacceptable rules are:
455 Spaces are not allowed in labels. Since a subject always has access to files
456 with the same label specifying a rule for that case is pointless. Only
457 valid letters (rwxatbRWXATB) and the dash ('-') character are allowed in
458 access specifications. The dash is a placeholder, so "a-r" is the same
459 as "ar". A lone dash is used to specify that no access should be allowed.
461 Applying Access Rules
463 The developers of Linux rarely define new sorts of things, usually importing
464 schemes and concepts from other systems. Most often, the other systems are
465 variants of Unix. Unix has many endearing properties, but consistency of
466 access control models is not one of them. Smack strives to treat accesses as
467 uniformly as is sensible while keeping with the spirit of the underlying
470 File system objects including files, directories, named pipes, symbolic links,
471 and devices require access permissions that closely match those used by mode
472 bit access. To open a file for reading read access is required on the file. To
473 search a directory requires execute access. Creating a file with write access
474 requires both read and write access on the containing directory. Deleting a
475 file requires read and write access to the file and to the containing
476 directory. It is possible that a user may be able to see that a file exists
477 but not any of its attributes by the circumstance of having read access to the
478 containing directory but not to the differently labeled file. This is an
479 artifact of the file name being data in the directory, not a part of the file.
481 If a directory is marked as transmuting (SMACK64TRANSMUTE=TRUE) and the
482 access rule that allows a process to create an object in that directory
483 includes 't' access the label assigned to the new object will be that
484 of the directory, not the creating process. This makes it much easier
485 for two processes with different labels to share data without granting
486 access to all of their files.
488 IPC objects, message queues, semaphore sets, and memory segments exist in flat
489 namespaces and access requests are only required to match the object in
492 Process objects reflect tasks on the system and the Smack label used to access
493 them is the same Smack label that the task would use for its own access
494 attempts. Sending a signal via the kill() system call is a write operation
495 from the signaler to the recipient. Debugging a process requires both reading
496 and writing. Creating a new task is an internal operation that results in two
497 tasks with identical Smack labels and requires no access checks.
499 Sockets are data structures attached to processes and sending a packet from
500 one process to another requires that the sender have write access to the
501 receiver. The receiver is not required to have read access to the sender.
505 The configuration file /etc/smack/accesses contains the rules to be set at
506 system startup. The contents are written to the special file
507 /sys/fs/smackfs/load2. Rules can be added at any time and take effect
508 immediately. For any pair of subject and object labels there can be only
509 one rule, with the most recently specified overriding any earlier
514 The Smack label of a process can be read from /proc/<pid>/attr/current. A
515 process can read its own Smack label from /proc/self/attr/current. A
516 privileged process can change its own Smack label by writing to
517 /proc/self/attr/current but not the label of another process.
521 The Smack label of a filesystem object is stored as an extended attribute
522 named SMACK64 on the file. This attribute is in the security namespace. It can
523 only be changed by a process with privilege.
527 A process with CAP_MAC_OVERRIDE or CAP_MAC_ADMIN is privileged.
528 CAP_MAC_OVERRIDE allows the process access to objects it would
529 be denied otherwise. CAP_MAC_ADMIN allows a process to change
530 Smack data, including rules and attributes.
534 As mentioned before, Smack enforces access control on network protocol
535 transmissions. Every packet sent by a Smack process is tagged with its Smack
536 label. This is done by adding a CIPSO tag to the header of the IP packet. Each
537 packet received is expected to have a CIPSO tag that identifies the label and
538 if it lacks such a tag the network ambient label is assumed. Before the packet
539 is delivered a check is made to determine that a subject with the label on the
540 packet has write access to the receiving process and if that is not the case
541 the packet is dropped.
545 It is normally unnecessary to specify the CIPSO configuration. The default
546 values used by the system handle all internal cases. Smack will compose CIPSO
547 label values to match the Smack labels being used without administrative
548 intervention. Unlabeled packets that come into the system will be given the
551 Smack requires configuration in the case where packets from a system that is
552 not Smack that speaks CIPSO may be encountered. Usually this will be a Trusted
553 Solaris system, but there are other, less widely deployed systems out there.
554 CIPSO provides 3 important values, a Domain Of Interpretation (DOI), a level,
555 and a category set with each packet. The DOI is intended to identify a group
556 of systems that use compatible labeling schemes, and the DOI specified on the
557 Smack system must match that of the remote system or packets will be
558 discarded. The DOI is 3 by default. The value can be read from
559 /sys/fs/smackfs/doi and can be changed by writing to /sys/fs/smackfs/doi.
561 The label and category set are mapped to a Smack label as defined in
564 A Smack/CIPSO mapping has the form:
566 smack level [category [category]*]
568 Smack does not expect the level or category sets to be related in any
569 particular way and does not assume or assign accesses based on them. Some
570 examples of mappings:
577 The ":" and "," characters are permitted in a Smack label but have no special
580 The mapping of Smack labels to CIPSO values is defined by writing to
581 /sys/fs/smackfs/cipso2.
583 In addition to explicit mappings Smack supports direct CIPSO mappings. One
584 CIPSO level is used to indicate that the category set passed in the packet is
585 in fact an encoding of the Smack label. The level used is 250 by default. The
586 value can be read from /sys/fs/smackfs/direct and changed by writing to
587 /sys/fs/smackfs/direct.
591 There are two attributes that are associated with sockets. These attributes
592 can only be set by privileged tasks, but any task can read them for their own
595 SMACK64IPIN: The Smack label of the task object. A privileged
596 program that will enforce policy may set this to the star label.
598 SMACK64IPOUT: The Smack label transmitted with outgoing packets.
599 A privileged program may set this to match the label of another
600 task with which it hopes to communicate.
602 Smack Netlabel Exceptions
604 You will often find that your labeled application has to talk to the outside,
605 unlabeled world. To do this there's a special file /sys/fs/smackfs/netlabel
606 where you can add some exceptions in the form of :
610 It means that your application will have unlabeled access to @IP1 if it has
611 write access on LABEL1, and access to the subnet @IP2/MASK if it has write
614 Entries in the /sys/fs/smackfs/netlabel file are matched by longest mask
615 first, like in classless IPv4 routing.
617 A special label '@' and an option '-CIPSO' can be used there :
618 @ means Internet, any application with any label has access to it
619 -CIPSO means standard CIPSO networking
621 If you don't know what CIPSO is and don't plan to use it, you can just do :
622 echo 127.0.0.1 -CIPSO > /sys/fs/smackfs/netlabel
623 echo 0.0.0.0/0 @ > /sys/fs/smackfs/netlabel
625 If you use CIPSO on your 192.168.0.0/16 local network and need also unlabeled
626 Internet access, you can have :
627 echo 127.0.0.1 -CIPSO > /sys/fs/smackfs/netlabel
628 echo 192.168.0.0/16 -CIPSO > /sys/fs/smackfs/netlabel
629 echo 0.0.0.0/0 @ > /sys/fs/smackfs/netlabel
632 Writing Applications for Smack
634 There are three sorts of applications that will run on a Smack system. How an
635 application interacts with Smack will determine what it will have to do to
636 work properly under Smack.
638 Smack Ignorant Applications
640 By far the majority of applications have no reason whatever to care about the
641 unique properties of Smack. Since invoking a program has no impact on the
642 Smack label associated with the process the only concern likely to arise is
643 whether the process has execute access to the program.
645 Smack Relevant Applications
647 Some programs can be improved by teaching them about Smack, but do not make
648 any security decisions themselves. The utility ls(1) is one example of such a
651 Smack Enforcing Applications
653 These are special programs that not only know about Smack, but participate in
654 the enforcement of system policy. In most cases these are the programs that
655 set up user sessions. There are also network services that provide information
656 to processes running with various labels.
658 File System Interfaces
660 Smack maintains labels on file system objects using extended attributes. The
661 Smack label of a file, directory, or other file system object can be obtained
664 len = getxattr("/", "security.SMACK64", value, sizeof (value));
666 will put the Smack label of the root directory into value. A privileged
667 process can set the Smack label of a file system object with setxattr(2).
669 len = strlen("Rubble");
670 rc = setxattr("/foo", "security.SMACK64", "Rubble", len, 0);
672 will set the Smack label of /foo to "Rubble" if the program has appropriate
677 The socket attributes can be read using fgetxattr(2).
679 A privileged process can set the Smack label of outgoing packets with
682 len = strlen("Rubble");
683 rc = fsetxattr(fd, "security.SMACK64IPOUT", "Rubble", len, 0);
685 will set the Smack label "Rubble" on packets going out from the socket if the
686 program has appropriate privilege.
688 rc = fsetxattr(fd, "security.SMACK64IPIN, "*", strlen("*"), 0);
690 will set the Smack label "*" as the object label against which incoming
691 packets will be checked if the program has appropriate privilege.
695 Smack supports some mount options:
697 smackfsdef=label: specifies the label to give files that lack
698 the Smack label extended attribute.
700 smackfsroot=label: specifies the label to assign the root of the
701 file system if it lacks the Smack extended attribute.
703 smackfshat=label: specifies a label that must have read access to
704 all labels set on the filesystem. Not yet enforced.
706 smackfsfloor=label: specifies a label to which all labels set on the
707 filesystem must have read access. Not yet enforced.
709 These mount options apply to all file system types.
713 If you want Smack auditing of security events, you need to set CONFIG_AUDIT
714 in your kernel configuration.
715 By default, all denied events will be audited. You can change this behavior by
716 writing a single character to the /sys/fs/smackfs/logging file :
718 1 : log denied (default)
720 3 : log denied & accepted
722 Events are logged as 'key=value' pairs, for each event you at least will get
723 the subject, the object, the rights requested, the action, the kernel function
724 that triggered the event, plus other pairs depending on the type of event
729 Bringup mode provides logging features that can make application
730 configuration and system bringup easier. Configure the kernel with
731 CONFIG_SECURITY_SMACK_BRINGUP to enable these features. When bringup
732 mode is enabled accesses that succeed due to rules marked with the "b"
733 access mode will logged. When a new label is introduced for processes
734 rules can be added aggressively, marked with the "b". The logging allows
735 tracking of which rules actual get used for that label.
737 Another feature of bringup mode is the "unconfined" option. Writing
738 a label to /sys/fs/smackfs/unconfined makes subjects with that label
739 able to access any object, and objects with that label accessible to
740 all subjects. Any access that is granted because a label is unconfined
741 is logged. This feature is dangerous, as files and directories may
742 be created in places they couldn't if the policy were being enforced.
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