Based on kernel version 3.12. Page generated on 2013-11-13 22:00 EST.
1 2 3 "Good for you, you've decided to clean the elevator!" 4 - The Elevator, from Dark Star 5 6 Smack is the 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. 9 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 14 at hand. 15 16 Smack consists of three major components: 17 - The kernel 18 - Basic utilities, which are helpful but not required 19 - Configuration data 20 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. 26 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. 30 31 The current git repository for Smack user space is: 32 33 git://github.com/smack-team/smack.git 34 35 This should make and install on most modern distributions. 36 There are three commands included in smackutil: 37 38 smackload - properly formats data for writing to /smack/load 39 smackcipso - properly formats data for writing to /smack/cipso 40 chsmack - display or set Smack extended attribute values 41 42 In keeping with the intent of Smack, configuration data is 43 minimal and not strictly required. The most important 44 configuration step is mounting the smackfs pseudo filesystem. 45 If smackutil is installed the startup script will take care 46 of this, but it can be manually as well. 47 48 Add this line to /etc/fstab: 49 50 smackfs /smack smackfs smackfsdef=* 0 0 51 52 and create the /smack directory for mounting. 53 54 Smack uses extended attributes (xattrs) to store labels on filesystem 55 objects. The attributes are stored in the extended attribute security 56 name space. A process must have CAP_MAC_ADMIN to change any of these 57 attributes. 58 59 The extended attributes that Smack uses are: 60 61 SMACK64 62 Used to make access control decisions. In almost all cases 63 the label given to a new filesystem object will be the label 64 of the process that created it. 65 SMACK64EXEC 66 The Smack label of a process that execs a program file with 67 this attribute set will run with this attribute's value. 68 SMACK64MMAP 69 Don't allow the file to be mmapped by a process whose Smack 70 label does not allow all of the access permitted to a process 71 with the label contained in this attribute. This is a very 72 specific use case for shared libraries. 73 SMACK64TRANSMUTE 74 Can only have the value "TRUE". If this attribute is present 75 on a directory when an object is created in the directory and 76 the Smack rule (more below) that permitted the write access 77 to the directory includes the transmute ("t") mode the object 78 gets the label of the directory instead of the label of the 79 creating process. If the object being created is a directory 80 the SMACK64TRANSMUTE attribute is set as well. 81 SMACK64IPIN 82 This attribute is only available on file descriptors for sockets. 83 Use the Smack label in this attribute for access control 84 decisions on packets being delivered to this socket. 85 SMACK64IPOUT 86 This attribute is only available on file descriptors for sockets. 87 Use the Smack label in this attribute for access control 88 decisions on packets coming from this socket. 89 90 There are multiple ways to set a Smack label on a file: 91 92 # attr -S -s SMACK64 -V "value" path 93 # chsmack -a value path 94 95 A process can see the smack label it is running with by 96 reading /proc/self/attr/current. A process with CAP_MAC_ADMIN 97 can set the process smack by writing there. 98 99 Most Smack configuration is accomplished by writing to files 100 in the smackfs filesystem. This pseudo-filesystem is usually 101 mounted on /smack. 102 103 access 104 This interface reports whether a subject with the specified 105 Smack label has a particular access to an object with a 106 specified Smack label. Write a fixed format access rule to 107 this file. The next read will indicate whether the access 108 would be permitted. The text will be either "1" indicating 109 access, or "0" indicating denial. 110 access2 111 This interface reports whether a subject with the specified 112 Smack label has a particular access to an object with a 113 specified Smack label. Write a long format access rule to 114 this file. The next read will indicate whether the access 115 would be permitted. The text will be either "1" indicating 116 access, or "0" indicating denial. 117 ambient 118 This contains the Smack label applied to unlabeled network 119 packets. 120 change-rule 121 This interface allows modification of existing access control rules. 122 The format accepted on write is: 123 "%s %s %s %s" 124 where the first string is the subject label, the second the 125 object label, the third the access to allow and the fourth the 126 access to deny. The access strings may contain only the characters 127 "rwxat-". If a rule for a given subject and object exists it will be 128 modified by enabling the permissions in the third string and disabling 129 those in the fourth string. If there is no such rule it will be 130 created using the access specified in the third and the fourth strings. 131 cipso 132 This interface allows a specific CIPSO header to be assigned 133 to a Smack label. The format accepted on write is: 134 "%24s%4d%4d"["%4d"]... 135 The first string is a fixed Smack label. The first number is 136 the level to use. The second number is the number of categories. 137 The following numbers are the categories. 138 "level-3-cats-5-19 3 2 5 19" 139 cipso2 140 This interface allows a specific CIPSO header to be assigned 141 to a Smack label. The format accepted on write is: 142 "%s%4d%4d"["%4d"]... 143 The first string is a long Smack label. The first number is 144 the level to use. The second number is the number of categories. 145 The following numbers are the categories. 146 "level-3-cats-5-19 3 2 5 19" 147 direct 148 This contains the CIPSO level used for Smack direct label 149 representation in network packets. 150 doi 151 This contains the CIPSO domain of interpretation used in 152 network packets. 153 load 154 This interface allows access control rules in addition to 155 the system defined rules to be specified. The format accepted 156 on write is: 157 "%24s%24s%5s" 158 where the first string is the subject label, the second the 159 object label, and the third the requested access. The access 160 string may contain only the characters "rwxat-", and specifies 161 which sort of access is allowed. The "-" is a placeholder for 162 permissions that are not allowed. The string "r-x--" would 163 specify read and execute access. Labels are limited to 23 164 characters in length. 165 load2 166 This interface allows access control rules in addition to 167 the system defined rules to be specified. The format accepted 168 on write is: 169 "%s %s %s" 170 where the first string is the subject label, the second the 171 object label, and the third the requested access. The access 172 string may contain only the characters "rwxat-", and specifies 173 which sort of access is allowed. The "-" is a placeholder for 174 permissions that are not allowed. The string "r-x--" would 175 specify read and execute access. 176 load-self 177 This interface allows process specific access rules to be 178 defined. These rules are only consulted if access would 179 otherwise be permitted, and are intended to provide additional 180 restrictions on the process. The format is the same as for 181 the load interface. 182 load-self2 183 This interface allows process specific access rules to be 184 defined. These rules are only consulted if access would 185 otherwise be permitted, and are intended to provide additional 186 restrictions on the process. The format is the same as for 187 the load2 interface. 188 logging 189 This contains the Smack logging state. 190 mapped 191 This contains the CIPSO level used for Smack mapped label 192 representation in network packets. 193 netlabel 194 This interface allows specific internet addresses to be 195 treated as single label hosts. Packets are sent to single 196 label hosts without CIPSO headers, but only from processes 197 that have Smack write access to the host label. All packets 198 received from single label hosts are given the specified 199 label. The format accepted on write is: 200 "%d.%d.%d.%d label" or "%d.%d.%d.%d/%d label". 201 onlycap 202 This contains the label processes must have for CAP_MAC_ADMIN 203 and CAP_MAC_OVERRIDE to be effective. If this file is empty 204 these capabilities are effective at for processes with any 205 label. The value is set by writing the desired label to the 206 file or cleared by writing "-" to the file. 207 revoke-subject 208 Writing a Smack label here sets the access to '-' for all access 209 rules with that subject label. 210 211 You can add access rules in /etc/smack/accesses. They take the form: 212 213 subjectlabel objectlabel access 214 215 access is a combination of the letters rwxa which specify the 216 kind of access permitted a subject with subjectlabel on an 217 object with objectlabel. If there is no rule no access is allowed. 218 219 Look for additional programs on http://schaufler-ca.com 220 221 From the Smack Whitepaper: 222 223 The Simplified Mandatory Access Control Kernel 224 225 Casey Schaufler 226 email@example.com 227 228 Mandatory Access Control 229 230 Computer systems employ a variety of schemes to constrain how information is 231 shared among the people and services using the machine. Some of these schemes 232 allow the program or user to decide what other programs or users are allowed 233 access to pieces of data. These schemes are called discretionary access 234 control mechanisms because the access control is specified at the discretion 235 of the user. Other schemes do not leave the decision regarding what a user or 236 program can access up to users or programs. These schemes are called mandatory 237 access control mechanisms because you don't have a choice regarding the users 238 or programs that have access to pieces of data. 239 240 Bell & LaPadula 241 242 From the middle of the 1980's until the turn of the century Mandatory Access 243 Control (MAC) was very closely associated with the Bell & LaPadula security 244 model, a mathematical description of the United States Department of Defense 245 policy for marking paper documents. MAC in this form enjoyed a following 246 within the Capital Beltway and Scandinavian supercomputer centers but was 247 often sited as failing to address general needs. 248 249 Domain Type Enforcement 250 251 Around the turn of the century Domain Type Enforcement (DTE) became popular. 252 This scheme organizes users, programs, and data into domains that are 253 protected from each other. This scheme has been widely deployed as a component 254 of popular Linux distributions. The administrative overhead required to 255 maintain this scheme and the detailed understanding of the whole system 256 necessary to provide a secure domain mapping leads to the scheme being 257 disabled or used in limited ways in the majority of cases. 258 259 Smack 260 261 Smack is a Mandatory Access Control mechanism designed to provide useful MAC 262 while avoiding the pitfalls of its predecessors. The limitations of Bell & 263 LaPadula are addressed by providing a scheme whereby access can be controlled 264 according to the requirements of the system and its purpose rather than those 265 imposed by an arcane government policy. The complexity of Domain Type 266 Enforcement and avoided by defining access controls in terms of the access 267 modes already in use. 268 269 Smack Terminology 270 271 The jargon used to talk about Smack will be familiar to those who have dealt 272 with other MAC systems and shouldn't be too difficult for the uninitiated to 273 pick up. There are four terms that are used in a specific way and that are 274 especially important: 275 276 Subject: A subject is an active entity on the computer system. 277 On Smack a subject is a task, which is in turn the basic unit 278 of execution. 279 280 Object: An object is a passive entity on the computer system. 281 On Smack files of all types, IPC, and tasks can be objects. 282 283 Access: Any attempt by a subject to put information into or get 284 information from an object is an access. 285 286 Label: Data that identifies the Mandatory Access Control 287 characteristics of a subject or an object. 288 289 These definitions are consistent with the traditional use in the security 290 community. There are also some terms from Linux that are likely to crop up: 291 292 Capability: A task that possesses a capability has permission to 293 violate an aspect of the system security policy, as identified by 294 the specific capability. A task that possesses one or more 295 capabilities is a privileged task, whereas a task with no 296 capabilities is an unprivileged task. 297 298 Privilege: A task that is allowed to violate the system security 299 policy is said to have privilege. As of this writing a task can 300 have privilege either by possessing capabilities or by having an 301 effective user of root. 302 303 Smack Basics 304 305 Smack is an extension to a Linux system. It enforces additional restrictions 306 on what subjects can access which objects, based on the labels attached to 307 each of the subject and the object. 308 309 Labels 310 311 Smack labels are ASCII character strings, one to twenty-three characters in 312 length. Single character labels using special characters, that being anything 313 other than a letter or digit, are reserved for use by the Smack development 314 team. Smack labels are unstructured, case sensitive, and the only operation 315 ever performed on them is comparison for equality. Smack labels cannot 316 contain unprintable characters, the "/" (slash), the "\" (backslash), the "'" 317 (quote) and '"' (double-quote) characters. 318 Smack labels cannot begin with a '-'. This is reserved for special options. 319 320 There are some predefined labels: 321 322 _ Pronounced "floor", a single underscore character. 323 ^ Pronounced "hat", a single circumflex character. 324 * Pronounced "star", a single asterisk character. 325 ? Pronounced "huh", a single question mark character. 326 @ Pronounced "web", a single at sign character. 327 328 Every task on a Smack system is assigned a label. System tasks, such as 329 init(8) and systems daemons, are run with the floor ("_") label. User tasks 330 are assigned labels according to the specification found in the 331 /etc/smack/user configuration file. 332 333 Access Rules 334 335 Smack uses the traditional access modes of Linux. These modes are read, 336 execute, write, and occasionally append. There are a few cases where the 337 access mode may not be obvious. These include: 338 339 Signals: A signal is a write operation from the subject task to 340 the object task. 341 Internet Domain IPC: Transmission of a packet is considered a 342 write operation from the source task to the destination task. 343 344 Smack restricts access based on the label attached to a subject and the label 345 attached to the object it is trying to access. The rules enforced are, in 346 order: 347 348 1. Any access requested by a task labeled "*" is denied. 349 2. A read or execute access requested by a task labeled "^" 350 is permitted. 351 3. A read or execute access requested on an object labeled "_" 352 is permitted. 353 4. Any access requested on an object labeled "*" is permitted. 354 5. Any access requested by a task on an object with the same 355 label is permitted. 356 6. Any access requested that is explicitly defined in the loaded 357 rule set is permitted. 358 7. Any other access is denied. 359 360 Smack Access Rules 361 362 With the isolation provided by Smack access separation is simple. There are 363 many interesting cases where limited access by subjects to objects with 364 different labels is desired. One example is the familiar spy model of 365 sensitivity, where a scientist working on a highly classified project would be 366 able to read documents of lower classifications and anything she writes will 367 be "born" highly classified. To accommodate such schemes Smack includes a 368 mechanism for specifying rules allowing access between labels. 369 370 Access Rule Format 371 372 The format of an access rule is: 373 374 subject-label object-label access 375 376 Where subject-label is the Smack label of the task, object-label is the Smack 377 label of the thing being accessed, and access is a string specifying the sort 378 of access allowed. The access specification is searched for letters that 379 describe access modes: 380 381 a: indicates that append access should be granted. 382 r: indicates that read access should be granted. 383 w: indicates that write access should be granted. 384 x: indicates that execute access should be granted. 385 t: indicates that the rule requests transmutation. 386 387 Uppercase values for the specification letters are allowed as well. 388 Access mode specifications can be in any order. Examples of acceptable rules 389 are: 390 391 TopSecret Secret rx 392 Secret Unclass R 393 Manager Game x 394 User HR w 395 New Old rRrRr 396 Closed Off - 397 398 Examples of unacceptable rules are: 399 400 Top Secret Secret rx 401 Ace Ace r 402 Odd spells waxbeans 403 404 Spaces are not allowed in labels. Since a subject always has access to files 405 with the same label specifying a rule for that case is pointless. Only 406 valid letters (rwxatRWXAT) and the dash ('-') character are allowed in 407 access specifications. The dash is a placeholder, so "a-r" is the same 408 as "ar". A lone dash is used to specify that no access should be allowed. 409 410 Applying Access Rules 411 412 The developers of Linux rarely define new sorts of things, usually importing 413 schemes and concepts from other systems. Most often, the other systems are 414 variants of Unix. Unix has many endearing properties, but consistency of 415 access control models is not one of them. Smack strives to treat accesses as 416 uniformly as is sensible while keeping with the spirit of the underlying 417 mechanism. 418 419 File system objects including files, directories, named pipes, symbolic links, 420 and devices require access permissions that closely match those used by mode 421 bit access. To open a file for reading read access is required on the file. To 422 search a directory requires execute access. Creating a file with write access 423 requires both read and write access on the containing directory. Deleting a 424 file requires read and write access to the file and to the containing 425 directory. It is possible that a user may be able to see that a file exists 426 but not any of its attributes by the circumstance of having read access to the 427 containing directory but not to the differently labeled file. This is an 428 artifact of the file name being data in the directory, not a part of the file. 429 430 If a directory is marked as transmuting (SMACK64TRANSMUTE=TRUE) and the 431 access rule that allows a process to create an object in that directory 432 includes 't' access the label assigned to the new object will be that 433 of the directory, not the creating process. This makes it much easier 434 for two processes with different labels to share data without granting 435 access to all of their files. 436 437 IPC objects, message queues, semaphore sets, and memory segments exist in flat 438 namespaces and access requests are only required to match the object in 439 question. 440 441 Process objects reflect tasks on the system and the Smack label used to access 442 them is the same Smack label that the task would use for its own access 443 attempts. Sending a signal via the kill() system call is a write operation 444 from the signaler to the recipient. Debugging a process requires both reading 445 and writing. Creating a new task is an internal operation that results in two 446 tasks with identical Smack labels and requires no access checks. 447 448 Sockets are data structures attached to processes and sending a packet from 449 one process to another requires that the sender have write access to the 450 receiver. The receiver is not required to have read access to the sender. 451 452 Setting Access Rules 453 454 The configuration file /etc/smack/accesses contains the rules to be set at 455 system startup. The contents are written to the special file /smack/load. 456 Rules can be written to /smack/load at any time and take effect immediately. 457 For any pair of subject and object labels there can be only one rule, with the 458 most recently specified overriding any earlier specification. 459 460 The program smackload is provided to ensure data is formatted 461 properly when written to /smack/load. This program reads lines 462 of the form 463 464 subjectlabel objectlabel mode. 465 466 Task Attribute 467 468 The Smack label of a process can be read from /proc/<pid>/attr/current. A 469 process can read its own Smack label from /proc/self/attr/current. A 470 privileged process can change its own Smack label by writing to 471 /proc/self/attr/current but not the label of another process. 472 473 File Attribute 474 475 The Smack label of a filesystem object is stored as an extended attribute 476 named SMACK64 on the file. This attribute is in the security namespace. It can 477 only be changed by a process with privilege. 478 479 Privilege 480 481 A process with CAP_MAC_OVERRIDE is privileged. 482 483 Smack Networking 484 485 As mentioned before, Smack enforces access control on network protocol 486 transmissions. Every packet sent by a Smack process is tagged with its Smack 487 label. This is done by adding a CIPSO tag to the header of the IP packet. Each 488 packet received is expected to have a CIPSO tag that identifies the label and 489 if it lacks such a tag the network ambient label is assumed. Before the packet 490 is delivered a check is made to determine that a subject with the label on the 491 packet has write access to the receiving process and if that is not the case 492 the packet is dropped. 493 494 CIPSO Configuration 495 496 It is normally unnecessary to specify the CIPSO configuration. The default 497 values used by the system handle all internal cases. Smack will compose CIPSO 498 label values to match the Smack labels being used without administrative 499 intervention. Unlabeled packets that come into the system will be given the 500 ambient label. 501 502 Smack requires configuration in the case where packets from a system that is 503 not smack that speaks CIPSO may be encountered. Usually this will be a Trusted 504 Solaris system, but there are other, less widely deployed systems out there. 505 CIPSO provides 3 important values, a Domain Of Interpretation (DOI), a level, 506 and a category set with each packet. The DOI is intended to identify a group 507 of systems that use compatible labeling schemes, and the DOI specified on the 508 smack system must match that of the remote system or packets will be 509 discarded. The DOI is 3 by default. The value can be read from /smack/doi and 510 can be changed by writing to /smack/doi. 511 512 The label and category set are mapped to a Smack label as defined in 513 /etc/smack/cipso. 514 515 A Smack/CIPSO mapping has the form: 516 517 smack level [category [category]*] 518 519 Smack does not expect the level or category sets to be related in any 520 particular way and does not assume or assign accesses based on them. Some 521 examples of mappings: 522 523 TopSecret 7 524 TS:A,B 7 1 2 525 SecBDE 5 2 4 6 526 RAFTERS 7 12 26 527 528 The ":" and "," characters are permitted in a Smack label but have no special 529 meaning. 530 531 The mapping of Smack labels to CIPSO values is defined by writing to 532 /smack/cipso. Again, the format of data written to this special file 533 is highly restrictive, so the program smackcipso is provided to 534 ensure the writes are done properly. This program takes mappings 535 on the standard input and sends them to /smack/cipso properly. 536 537 In addition to explicit mappings Smack supports direct CIPSO mappings. One 538 CIPSO level is used to indicate that the category set passed in the packet is 539 in fact an encoding of the Smack label. The level used is 250 by default. The 540 value can be read from /smack/direct and changed by writing to /smack/direct. 541 542 Socket Attributes 543 544 There are two attributes that are associated with sockets. These attributes 545 can only be set by privileged tasks, but any task can read them for their own 546 sockets. 547 548 SMACK64IPIN: The Smack label of the task object. A privileged 549 program that will enforce policy may set this to the star label. 550 551 SMACK64IPOUT: The Smack label transmitted with outgoing packets. 552 A privileged program may set this to match the label of another 553 task with which it hopes to communicate. 554 555 Smack Netlabel Exceptions 556 557 You will often find that your labeled application has to talk to the outside, 558 unlabeled world. To do this there's a special file /smack/netlabel where you can 559 add some exceptions in the form of : 560 @IP1 LABEL1 or 561 @IP2/MASK LABEL2 562 563 It means that your application will have unlabeled access to @IP1 if it has 564 write access on LABEL1, and access to the subnet @IP2/MASK if it has write 565 access on LABEL2. 566 567 Entries in the /smack/netlabel file are matched by longest mask first, like in 568 classless IPv4 routing. 569 570 A special label '@' and an option '-CIPSO' can be used there : 571 @ means Internet, any application with any label has access to it 572 -CIPSO means standard CIPSO networking 573 574 If you don't know what CIPSO is and don't plan to use it, you can just do : 575 echo 127.0.0.1 -CIPSO > /smack/netlabel 576 echo 0.0.0.0/0 @ > /smack/netlabel 577 578 If you use CIPSO on your 192.168.0.0/16 local network and need also unlabeled 579 Internet access, you can have : 580 echo 127.0.0.1 -CIPSO > /smack/netlabel 581 echo 192.168.0.0/16 -CIPSO > /smack/netlabel 582 echo 0.0.0.0/0 @ > /smack/netlabel 583 584 585 Writing Applications for Smack 586 587 There are three sorts of applications that will run on a Smack system. How an 588 application interacts with Smack will determine what it will have to do to 589 work properly under Smack. 590 591 Smack Ignorant Applications 592 593 By far the majority of applications have no reason whatever to care about the 594 unique properties of Smack. Since invoking a program has no impact on the 595 Smack label associated with the process the only concern likely to arise is 596 whether the process has execute access to the program. 597 598 Smack Relevant Applications 599 600 Some programs can be improved by teaching them about Smack, but do not make 601 any security decisions themselves. The utility ls(1) is one example of such a 602 program. 603 604 Smack Enforcing Applications 605 606 These are special programs that not only know about Smack, but participate in 607 the enforcement of system policy. In most cases these are the programs that 608 set up user sessions. There are also network services that provide information 609 to processes running with various labels. 610 611 File System Interfaces 612 613 Smack maintains labels on file system objects using extended attributes. The 614 Smack label of a file, directory, or other file system object can be obtained 615 using getxattr(2). 616 617 len = getxattr("/", "security.SMACK64", value, sizeof (value)); 618 619 will put the Smack label of the root directory into value. A privileged 620 process can set the Smack label of a file system object with setxattr(2). 621 622 len = strlen("Rubble"); 623 rc = setxattr("/foo", "security.SMACK64", "Rubble", len, 0); 624 625 will set the Smack label of /foo to "Rubble" if the program has appropriate 626 privilege. 627 628 Socket Interfaces 629 630 The socket attributes can be read using fgetxattr(2). 631 632 A privileged process can set the Smack label of outgoing packets with 633 fsetxattr(2). 634 635 len = strlen("Rubble"); 636 rc = fsetxattr(fd, "security.SMACK64IPOUT", "Rubble", len, 0); 637 638 will set the Smack label "Rubble" on packets going out from the socket if the 639 program has appropriate privilege. 640 641 rc = fsetxattr(fd, "security.SMACK64IPIN, "*", strlen("*"), 0); 642 643 will set the Smack label "*" as the object label against which incoming 644 packets will be checked if the program has appropriate privilege. 645 646 Administration 647 648 Smack supports some mount options: 649 650 smackfsdef=label: specifies the label to give files that lack 651 the Smack label extended attribute. 652 653 smackfsroot=label: specifies the label to assign the root of the 654 file system if it lacks the Smack extended attribute. 655 656 smackfshat=label: specifies a label that must have read access to 657 all labels set on the filesystem. Not yet enforced. 658 659 smackfsfloor=label: specifies a label to which all labels set on the 660 filesystem must have read access. Not yet enforced. 661 662 These mount options apply to all file system types. 663 664 Smack auditing 665 666 If you want Smack auditing of security events, you need to set CONFIG_AUDIT 667 in your kernel configuration. 668 By default, all denied events will be audited. You can change this behavior by 669 writing a single character to the /smack/logging file : 670 0 : no logging 671 1 : log denied (default) 672 2 : log accepted 673 3 : log denied & accepted 674 675 Events are logged as 'key=value' pairs, for each event you at least will get 676 the subject, the object, the rights requested, the action, the kernel function 677 that triggered the event, plus other pairs depending on the type of event 678 audited.