1 2 3 "Good for you, you've decided to clean the elevator!" 4 - The Elevator, from Dark Star 5 6Smack is the Simplified Mandatory Access Control Kernel. 7Smack is a kernel based implementation of mandatory access 8control that includes simplicity in its primary design goals. 9 10Smack is not the only Mandatory Access Control scheme 11available for Linux. Those new to Mandatory Access Control 12are encouraged to compare Smack with the other mechanisms 13available to determine which is best suited to the problem 14at hand. 15 16Smack consists of three major components: 17 - The kernel 18 - Basic utilities, which are helpful but not required 19 - Configuration data 20 21The kernel component of Smack is implemented as a Linux 22Security Modules (LSM) module. It requires netlabel and 23works best with file systems that support extended attributes, 24although xattr support is not strictly required. 25It is safe to run a Smack kernel under a "vanilla" distribution. 26 27Smack kernels use the CIPSO IP option. Some network 28configurations are intolerant of IP options and can impede 29access to systems that use them as Smack does. 30 31The current git repository for Smack user space is: 32 33 git://github.com/smack-team/smack.git 34 35This should make and install on most modern distributions. 36There are three commands included in smackutil: 37 38smackload - properly formats data for writing to /smack/load 39smackcipso - properly formats data for writing to /smack/cipso 40chsmack - display or set Smack extended attribute values 41 42In keeping with the intent of Smack, configuration data is 43minimal and not strictly required. The most important 44configuration step is mounting the smackfs pseudo filesystem. 45If smackutil is installed the startup script will take care 46of this, but it can be manually as well. 47 48Add this line to /etc/fstab: 49 50 smackfs /smack smackfs smackfsdef=* 0 0 51 52and create the /smack directory for mounting. 53 54Smack uses extended attributes (xattrs) to store labels on filesystem 55objects. The attributes are stored in the extended attribute security 56name space. A process must have CAP_MAC_ADMIN to change any of these 57attributes. 58 59The extended attributes that Smack uses are: 60 61SMACK64 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. 65SMACK64EXEC 66 The Smack label of a process that execs a program file with 67 this attribute set will run with this attribute's value. 68SMACK64MMAP 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. 73SMACK64TRANSMUTE 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. 81SMACK64IPIN 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. 85SMACK64IPOUT 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 90There 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 95A process can see the smack label it is running with by 96reading /proc/self/attr/current. A process with CAP_MAC_ADMIN 97can set the process smack by writing there. 98 99Most Smack configuration is accomplished by writing to files 100in the smackfs filesystem. This pseudo-filesystem is usually 101mounted on /smack. 102 103access 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. 110access2 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. 117ambient 118 This contains the Smack label applied to unlabeled network 119 packets. 120change-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. 131cipso 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" 139cipso2 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" 147direct 148 This contains the CIPSO level used for Smack direct label 149 representation in network packets. 150doi 151 This contains the CIPSO domain of interpretation used in 152 network packets. 153load 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. 165load2 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. 176load-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. 182load-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. 188logging 189 This contains the Smack logging state. 190mapped 191 This contains the CIPSO level used for Smack mapped label 192 representation in network packets. 193netlabel 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". 201onlycap 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. 207ptrace 208 This is used to define the current ptrace policy 209 0 - default: this is the policy that relies on smack access rules. 210 For the PTRACE_READ a subject needs to have a read access on 211 object. For the PTRACE_ATTACH a read-write access is required. 212 1 - exact: this is the policy that limits PTRACE_ATTACH. Attach is 213 only allowed when subject's and object's labels are equal. 214 PTRACE_READ is not affected. Can be overriden with CAP_SYS_PTRACE. 215 2 - draconian: this policy behaves like the 'exact' above with an 216 exception that it can't be overriden with CAP_SYS_PTRACE. 217revoke-subject 218 Writing a Smack label here sets the access to '-' for all access 219 rules with that subject label. 220 221You can add access rules in /etc/smack/accesses. They take the form: 222 223 subjectlabel objectlabel access 224 225access is a combination of the letters rwxa which specify the 226kind of access permitted a subject with subjectlabel on an 227object with objectlabel. If there is no rule no access is allowed. 228 229Look for additional programs on http://schaufler-ca.com 230 231From the Smack Whitepaper: 232 233The Simplified Mandatory Access Control Kernel 234 235Casey Schaufler 236casey@schaufler-ca.com 237 238Mandatory Access Control 239 240Computer systems employ a variety of schemes to constrain how information is 241shared among the people and services using the machine. Some of these schemes 242allow the program or user to decide what other programs or users are allowed 243access to pieces of data. These schemes are called discretionary access 244control mechanisms because the access control is specified at the discretion 245of the user. Other schemes do not leave the decision regarding what a user or 246program can access up to users or programs. These schemes are called mandatory 247access control mechanisms because you don't have a choice regarding the users 248or programs that have access to pieces of data. 249 250Bell & LaPadula 251 252From the middle of the 1980's until the turn of the century Mandatory Access 253Control (MAC) was very closely associated with the Bell & LaPadula security 254model, a mathematical description of the United States Department of Defense 255policy for marking paper documents. MAC in this form enjoyed a following 256within the Capital Beltway and Scandinavian supercomputer centers but was 257often sited as failing to address general needs. 258 259Domain Type Enforcement 260 261Around the turn of the century Domain Type Enforcement (DTE) became popular. 262This scheme organizes users, programs, and data into domains that are 263protected from each other. This scheme has been widely deployed as a component 264of popular Linux distributions. The administrative overhead required to 265maintain this scheme and the detailed understanding of the whole system 266necessary to provide a secure domain mapping leads to the scheme being 267disabled or used in limited ways in the majority of cases. 268 269Smack 270 271Smack is a Mandatory Access Control mechanism designed to provide useful MAC 272while avoiding the pitfalls of its predecessors. The limitations of Bell & 273LaPadula are addressed by providing a scheme whereby access can be controlled 274according to the requirements of the system and its purpose rather than those 275imposed by an arcane government policy. The complexity of Domain Type 276Enforcement and avoided by defining access controls in terms of the access 277modes already in use. 278 279Smack Terminology 280 281The jargon used to talk about Smack will be familiar to those who have dealt 282with other MAC systems and shouldn't be too difficult for the uninitiated to 283pick up. There are four terms that are used in a specific way and that are 284especially important: 285 286 Subject: A subject is an active entity on the computer system. 287 On Smack a subject is a task, which is in turn the basic unit 288 of execution. 289 290 Object: An object is a passive entity on the computer system. 291 On Smack files of all types, IPC, and tasks can be objects. 292 293 Access: Any attempt by a subject to put information into or get 294 information from an object is an access. 295 296 Label: Data that identifies the Mandatory Access Control 297 characteristics of a subject or an object. 298 299These definitions are consistent with the traditional use in the security 300community. There are also some terms from Linux that are likely to crop up: 301 302 Capability: A task that possesses a capability has permission to 303 violate an aspect of the system security policy, as identified by 304 the specific capability. A task that possesses one or more 305 capabilities is a privileged task, whereas a task with no 306 capabilities is an unprivileged task. 307 308 Privilege: A task that is allowed to violate the system security 309 policy is said to have privilege. As of this writing a task can 310 have privilege either by possessing capabilities or by having an 311 effective user of root. 312 313Smack Basics 314 315Smack is an extension to a Linux system. It enforces additional restrictions 316on what subjects can access which objects, based on the labels attached to 317each of the subject and the object. 318 319Labels 320 321Smack labels are ASCII character strings, one to twenty-three characters in 322length. Single character labels using special characters, that being anything 323other than a letter or digit, are reserved for use by the Smack development 324team. Smack labels are unstructured, case sensitive, and the only operation 325ever performed on them is comparison for equality. Smack labels cannot 326contain unprintable characters, the "/" (slash), the "\" (backslash), the "'" 327(quote) and '"' (double-quote) characters. 328Smack labels cannot begin with a '-'. This is reserved for special options. 329 330There are some predefined labels: 331 332 _ Pronounced "floor", a single underscore character. 333 ^ Pronounced "hat", a single circumflex character. 334 * Pronounced "star", a single asterisk character. 335 ? Pronounced "huh", a single question mark character. 336 @ Pronounced "web", a single at sign character. 337 338Every task on a Smack system is assigned a label. System tasks, such as 339init(8) and systems daemons, are run with the floor ("_") label. User tasks 340are assigned labels according to the specification found in the 341/etc/smack/user configuration file. 342 343Access Rules 344 345Smack uses the traditional access modes of Linux. These modes are read, 346execute, write, and occasionally append. There are a few cases where the 347access mode may not be obvious. These include: 348 349 Signals: A signal is a write operation from the subject task to 350 the object task. 351 Internet Domain IPC: Transmission of a packet is considered a 352 write operation from the source task to the destination task. 353 354Smack restricts access based on the label attached to a subject and the label 355attached to the object it is trying to access. The rules enforced are, in 356order: 357 358 1. Any access requested by a task labeled "*" is denied. 359 2. A read or execute access requested by a task labeled "^" 360 is permitted. 361 3. A read or execute access requested on an object labeled "_" 362 is permitted. 363 4. Any access requested on an object labeled "*" is permitted. 364 5. Any access requested by a task on an object with the same 365 label is permitted. 366 6. Any access requested that is explicitly defined in the loaded 367 rule set is permitted. 368 7. Any other access is denied. 369 370Smack Access Rules 371 372With the isolation provided by Smack access separation is simple. There are 373many interesting cases where limited access by subjects to objects with 374different labels is desired. One example is the familiar spy model of 375sensitivity, where a scientist working on a highly classified project would be 376able to read documents of lower classifications and anything she writes will 377be "born" highly classified. To accommodate such schemes Smack includes a 378mechanism for specifying rules allowing access between labels. 379 380Access Rule Format 381 382The format of an access rule is: 383 384 subject-label object-label access 385 386Where subject-label is the Smack label of the task, object-label is the Smack 387label of the thing being accessed, and access is a string specifying the sort 388of access allowed. The access specification is searched for letters that 389describe access modes: 390 391 a: indicates that append access should be granted. 392 r: indicates that read access should be granted. 393 w: indicates that write access should be granted. 394 x: indicates that execute access should be granted. 395 t: indicates that the rule requests transmutation. 396 397Uppercase values for the specification letters are allowed as well. 398Access mode specifications can be in any order. Examples of acceptable rules 399are: 400 401 TopSecret Secret rx 402 Secret Unclass R 403 Manager Game x 404 User HR w 405 New Old rRrRr 406 Closed Off - 407 408Examples of unacceptable rules are: 409 410 Top Secret Secret rx 411 Ace Ace r 412 Odd spells waxbeans 413 414Spaces are not allowed in labels. Since a subject always has access to files 415with the same label specifying a rule for that case is pointless. Only 416valid letters (rwxatRWXAT) and the dash ('-') character are allowed in 417access specifications. The dash is a placeholder, so "a-r" is the same 418as "ar". A lone dash is used to specify that no access should be allowed. 419 420Applying Access Rules 421 422The developers of Linux rarely define new sorts of things, usually importing 423schemes and concepts from other systems. Most often, the other systems are 424variants of Unix. Unix has many endearing properties, but consistency of 425access control models is not one of them. Smack strives to treat accesses as 426uniformly as is sensible while keeping with the spirit of the underlying 427mechanism. 428 429File system objects including files, directories, named pipes, symbolic links, 430and devices require access permissions that closely match those used by mode 431bit access. To open a file for reading read access is required on the file. To 432search a directory requires execute access. Creating a file with write access 433requires both read and write access on the containing directory. Deleting a 434file requires read and write access to the file and to the containing 435directory. It is possible that a user may be able to see that a file exists 436but not any of its attributes by the circumstance of having read access to the 437containing directory but not to the differently labeled file. This is an 438artifact of the file name being data in the directory, not a part of the file. 439 440If a directory is marked as transmuting (SMACK64TRANSMUTE=TRUE) and the 441access rule that allows a process to create an object in that directory 442includes 't' access the label assigned to the new object will be that 443of the directory, not the creating process. This makes it much easier 444for two processes with different labels to share data without granting 445access to all of their files. 446 447IPC objects, message queues, semaphore sets, and memory segments exist in flat 448namespaces and access requests are only required to match the object in 449question. 450 451Process objects reflect tasks on the system and the Smack label used to access 452them is the same Smack label that the task would use for its own access 453attempts. Sending a signal via the kill() system call is a write operation 454from the signaler to the recipient. Debugging a process requires both reading 455and writing. Creating a new task is an internal operation that results in two 456tasks with identical Smack labels and requires no access checks. 457 458Sockets are data structures attached to processes and sending a packet from 459one process to another requires that the sender have write access to the 460receiver. The receiver is not required to have read access to the sender. 461 462Setting Access Rules 463 464The configuration file /etc/smack/accesses contains the rules to be set at 465system startup. The contents are written to the special file /smack/load. 466Rules can be written to /smack/load at any time and take effect immediately. 467For any pair of subject and object labels there can be only one rule, with the 468most recently specified overriding any earlier specification. 469 470The program smackload is provided to ensure data is formatted 471properly when written to /smack/load. This program reads lines 472of the form 473 474 subjectlabel objectlabel mode. 475 476Task Attribute 477 478The Smack label of a process can be read from /proc/<pid>/attr/current. A 479process can read its own Smack label from /proc/self/attr/current. A 480privileged process can change its own Smack label by writing to 481/proc/self/attr/current but not the label of another process. 482 483File Attribute 484 485The Smack label of a filesystem object is stored as an extended attribute 486named SMACK64 on the file. This attribute is in the security namespace. It can 487only be changed by a process with privilege. 488 489Privilege 490 491A process with CAP_MAC_OVERRIDE is privileged. 492 493Smack Networking 494 495As mentioned before, Smack enforces access control on network protocol 496transmissions. Every packet sent by a Smack process is tagged with its Smack 497label. This is done by adding a CIPSO tag to the header of the IP packet. Each 498packet received is expected to have a CIPSO tag that identifies the label and 499if it lacks such a tag the network ambient label is assumed. Before the packet 500is delivered a check is made to determine that a subject with the label on the 501packet has write access to the receiving process and if that is not the case 502the packet is dropped. 503 504CIPSO Configuration 505 506It is normally unnecessary to specify the CIPSO configuration. The default 507values used by the system handle all internal cases. Smack will compose CIPSO 508label values to match the Smack labels being used without administrative 509intervention. Unlabeled packets that come into the system will be given the 510ambient label. 511 512Smack requires configuration in the case where packets from a system that is 513not smack that speaks CIPSO may be encountered. Usually this will be a Trusted 514Solaris system, but there are other, less widely deployed systems out there. 515CIPSO provides 3 important values, a Domain Of Interpretation (DOI), a level, 516and a category set with each packet. The DOI is intended to identify a group 517of systems that use compatible labeling schemes, and the DOI specified on the 518smack system must match that of the remote system or packets will be 519discarded. The DOI is 3 by default. The value can be read from /smack/doi and 520can be changed by writing to /smack/doi. 521 522The label and category set are mapped to a Smack label as defined in 523/etc/smack/cipso. 524 525A Smack/CIPSO mapping has the form: 526 527 smack level [category [category]*] 528 529Smack does not expect the level or category sets to be related in any 530particular way and does not assume or assign accesses based on them. Some 531examples of mappings: 532 533 TopSecret 7 534 TS:A,B 7 1 2 535 SecBDE 5 2 4 6 536 RAFTERS 7 12 26 537 538The ":" and "," characters are permitted in a Smack label but have no special 539meaning. 540 541The mapping of Smack labels to CIPSO values is defined by writing to 542/smack/cipso. Again, the format of data written to this special file 543is highly restrictive, so the program smackcipso is provided to 544ensure the writes are done properly. This program takes mappings 545on the standard input and sends them to /smack/cipso properly. 546 547In addition to explicit mappings Smack supports direct CIPSO mappings. One 548CIPSO level is used to indicate that the category set passed in the packet is 549in fact an encoding of the Smack label. The level used is 250 by default. The 550value can be read from /smack/direct and changed by writing to /smack/direct. 551 552Socket Attributes 553 554There are two attributes that are associated with sockets. These attributes 555can only be set by privileged tasks, but any task can read them for their own 556sockets. 557 558 SMACK64IPIN: The Smack label of the task object. A privileged 559 program that will enforce policy may set this to the star label. 560 561 SMACK64IPOUT: The Smack label transmitted with outgoing packets. 562 A privileged program may set this to match the label of another 563 task with which it hopes to communicate. 564 565Smack Netlabel Exceptions 566 567You will often find that your labeled application has to talk to the outside, 568unlabeled world. To do this there's a special file /smack/netlabel where you can 569add some exceptions in the form of : 570@IP1 LABEL1 or 571@IP2/MASK LABEL2 572 573It means that your application will have unlabeled access to @IP1 if it has 574write access on LABEL1, and access to the subnet @IP2/MASK if it has write 575access on LABEL2. 576 577Entries in the /smack/netlabel file are matched by longest mask first, like in 578classless IPv4 routing. 579 580A special label '@' and an option '-CIPSO' can be used there : 581@ means Internet, any application with any label has access to it 582-CIPSO means standard CIPSO networking 583 584If you don't know what CIPSO is and don't plan to use it, you can just do : 585echo 127.0.0.1 -CIPSO > /smack/netlabel 586echo 0.0.0.0/0 @ > /smack/netlabel 587 588If you use CIPSO on your 192.168.0.0/16 local network and need also unlabeled 589Internet access, you can have : 590echo 127.0.0.1 -CIPSO > /smack/netlabel 591echo 192.168.0.0/16 -CIPSO > /smack/netlabel 592echo 0.0.0.0/0 @ > /smack/netlabel 593 594 595Writing Applications for Smack 596 597There are three sorts of applications that will run on a Smack system. How an 598application interacts with Smack will determine what it will have to do to 599work properly under Smack. 600 601Smack Ignorant Applications 602 603By far the majority of applications have no reason whatever to care about the 604unique properties of Smack. Since invoking a program has no impact on the 605Smack label associated with the process the only concern likely to arise is 606whether the process has execute access to the program. 607 608Smack Relevant Applications 609 610Some programs can be improved by teaching them about Smack, but do not make 611any security decisions themselves. The utility ls(1) is one example of such a 612program. 613 614Smack Enforcing Applications 615 616These are special programs that not only know about Smack, but participate in 617the enforcement of system policy. In most cases these are the programs that 618set up user sessions. There are also network services that provide information 619to processes running with various labels. 620 621File System Interfaces 622 623Smack maintains labels on file system objects using extended attributes. The 624Smack label of a file, directory, or other file system object can be obtained 625using getxattr(2). 626 627 len = getxattr("/", "security.SMACK64", value, sizeof (value)); 628 629will put the Smack label of the root directory into value. A privileged 630process can set the Smack label of a file system object with setxattr(2). 631 632 len = strlen("Rubble"); 633 rc = setxattr("/foo", "security.SMACK64", "Rubble", len, 0); 634 635will set the Smack label of /foo to "Rubble" if the program has appropriate 636privilege. 637 638Socket Interfaces 639 640The socket attributes can be read using fgetxattr(2). 641 642A privileged process can set the Smack label of outgoing packets with 643fsetxattr(2). 644 645 len = strlen("Rubble"); 646 rc = fsetxattr(fd, "security.SMACK64IPOUT", "Rubble", len, 0); 647 648will set the Smack label "Rubble" on packets going out from the socket if the 649program has appropriate privilege. 650 651 rc = fsetxattr(fd, "security.SMACK64IPIN, "*", strlen("*"), 0); 652 653will set the Smack label "*" as the object label against which incoming 654packets will be checked if the program has appropriate privilege. 655 656Administration 657 658Smack supports some mount options: 659 660 smackfsdef=label: specifies the label to give files that lack 661 the Smack label extended attribute. 662 663 smackfsroot=label: specifies the label to assign the root of the 664 file system if it lacks the Smack extended attribute. 665 666 smackfshat=label: specifies a label that must have read access to 667 all labels set on the filesystem. Not yet enforced. 668 669 smackfsfloor=label: specifies a label to which all labels set on the 670 filesystem must have read access. Not yet enforced. 671 672These mount options apply to all file system types. 673 674Smack auditing 675 676If you want Smack auditing of security events, you need to set CONFIG_AUDIT 677in your kernel configuration. 678By default, all denied events will be audited. You can change this behavior by 679writing a single character to the /smack/logging file : 6800 : no logging 6811 : log denied (default) 6822 : log accepted 6833 : log denied & accepted 684 685Events are logged as 'key=value' pairs, for each event you at least will get 686the subject, the object, the rights requested, the action, the kernel function 687that triggered the event, plus other pairs depending on the type of event 688audited. 689