Based on kernel version 4.9. Page generated on 2016-12-21 14:37 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 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 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. 34 35 The current git repository for Smack user space is: 36 37 git://github.com/smack-team/smack.git 38 39 This should make and install on most modern distributions. 40 There are five commands included in smackutil: 41 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 46 47 These two commands are obsolete with the introduction of 48 the smackfs/load2 and smackfs/cipso2 interfaces. 49 50 smackload - properly formats data for writing to smackfs/load 51 smackcipso - properly formats data for writing to smackfs/cipso 52 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. 58 59 Add this line to /etc/fstab: 60 61 smackfs /sys/fs/smackfs smackfs defaults 0 0 62 63 The /sys/fs/smackfs directory is created by the kernel. 64 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 68 attributes. 69 70 The extended attributes that Smack uses are: 71 72 SMACK64 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. 76 SMACK64EXEC 77 The Smack label of a process that execs a program file with 78 this attribute set will run with this attribute's value. 79 SMACK64MMAP 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. 84 SMACK64TRANSMUTE 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. 92 SMACK64IPIN 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. 96 SMACK64IPOUT 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. 100 101 There are multiple ways to set a Smack label on a file: 102 103 # attr -S -s SMACK64 -V "value" path 104 # chsmack -a value path 105 106 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. 109 110 Most Smack configuration is accomplished by writing to files 111 in the smackfs filesystem. This pseudo-filesystem is mounted 112 on /sys/fs/smackfs. 113 114 access 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. 123 access2 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. 130 ambient 131 This contains the Smack label applied to unlabeled network 132 packets. 133 change-rule 134 This interface allows modification of existing access control rules. 135 The format accepted on write is: 136 "%s %s %s %s" 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. 144 cipso 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" 154 cipso2 155 This interface allows a specific CIPSO header to be assigned 156 to a Smack label. The format accepted on write is: 157 "%s%4d%4d"["%4d"]... 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" 162 direct 163 This contains the CIPSO level used for Smack direct label 164 representation in network packets. 165 doi 166 This contains the CIPSO domain of interpretation used in 167 network packets. 168 ipv6host 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. 178 load 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 183 on write is: 184 "%24s%24s%5s" 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. 192 load2 193 This interface allows access control rules in addition to 194 the system defined rules to be specified. The format accepted 195 on write is: 196 "%s %s %s" 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. 203 load-self 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 210 the load interface. 211 load-self2 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 216 the load2 interface. 217 logging 218 This contains the Smack logging state. 219 mapped 220 This contains the CIPSO level used for Smack mapped label 221 representation in network packets. 222 netlabel 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. 232 onlycap 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. 238 ptrace 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. 248 revoke-subject 249 Writing a Smack label here sets the access to '-' for all access 250 rules with that subject label. 251 unconfined 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. 258 relabel-self 259 This interface contains a list of labels to which the process can 260 transition to, by writing to /proc/self/attr/current. 261 Normally a process can change its own label to any legal value, but only 262 if it has CAP_MAC_ADMIN. This interface allows a process without 263 CAP_MAC_ADMIN to relabel itself to one of labels from predefined list. 264 A process without CAP_MAC_ADMIN can change its label only once. When it 265 does, this list will be cleared. 266 The values are set by writing the desired labels, separated 267 by spaces, to the file or cleared by writing "-" to the file. 268 269 If you are using the smackload utility 270 you can add access rules in /etc/smack/accesses. They take the form: 271 272 subjectlabel objectlabel access 273 274 access is a combination of the letters rwxatb which specify the 275 kind of access permitted a subject with subjectlabel on an 276 object with objectlabel. If there is no rule no access is allowed. 277 278 Look for additional programs on http://schaufler-ca.com 279 280 From the Smack Whitepaper: 281 282 The Simplified Mandatory Access Control Kernel 283 284 Casey Schaufler 285 email@example.com 286 287 Mandatory Access Control 288 289 Computer systems employ a variety of schemes to constrain how information is 290 shared among the people and services using the machine. Some of these schemes 291 allow the program or user to decide what other programs or users are allowed 292 access to pieces of data. These schemes are called discretionary access 293 control mechanisms because the access control is specified at the discretion 294 of the user. Other schemes do not leave the decision regarding what a user or 295 program can access up to users or programs. These schemes are called mandatory 296 access control mechanisms because you don't have a choice regarding the users 297 or programs that have access to pieces of data. 298 299 Bell & LaPadula 300 301 From the middle of the 1980's until the turn of the century Mandatory Access 302 Control (MAC) was very closely associated with the Bell & LaPadula security 303 model, a mathematical description of the United States Department of Defense 304 policy for marking paper documents. MAC in this form enjoyed a following 305 within the Capital Beltway and Scandinavian supercomputer centers but was 306 often sited as failing to address general needs. 307 308 Domain Type Enforcement 309 310 Around the turn of the century Domain Type Enforcement (DTE) became popular. 311 This scheme organizes users, programs, and data into domains that are 312 protected from each other. This scheme has been widely deployed as a component 313 of popular Linux distributions. The administrative overhead required to 314 maintain this scheme and the detailed understanding of the whole system 315 necessary to provide a secure domain mapping leads to the scheme being 316 disabled or used in limited ways in the majority of cases. 317 318 Smack 319 320 Smack is a Mandatory Access Control mechanism designed to provide useful MAC 321 while avoiding the pitfalls of its predecessors. The limitations of Bell & 322 LaPadula are addressed by providing a scheme whereby access can be controlled 323 according to the requirements of the system and its purpose rather than those 324 imposed by an arcane government policy. The complexity of Domain Type 325 Enforcement and avoided by defining access controls in terms of the access 326 modes already in use. 327 328 Smack Terminology 329 330 The jargon used to talk about Smack will be familiar to those who have dealt 331 with other MAC systems and shouldn't be too difficult for the uninitiated to 332 pick up. There are four terms that are used in a specific way and that are 333 especially important: 334 335 Subject: A subject is an active entity on the computer system. 336 On Smack a subject is a task, which is in turn the basic unit 337 of execution. 338 339 Object: An object is a passive entity on the computer system. 340 On Smack files of all types, IPC, and tasks can be objects. 341 342 Access: Any attempt by a subject to put information into or get 343 information from an object is an access. 344 345 Label: Data that identifies the Mandatory Access Control 346 characteristics of a subject or an object. 347 348 These definitions are consistent with the traditional use in the security 349 community. There are also some terms from Linux that are likely to crop up: 350 351 Capability: A task that possesses a capability has permission to 352 violate an aspect of the system security policy, as identified by 353 the specific capability. A task that possesses one or more 354 capabilities is a privileged task, whereas a task with no 355 capabilities is an unprivileged task. 356 357 Privilege: A task that is allowed to violate the system security 358 policy is said to have privilege. As of this writing a task can 359 have privilege either by possessing capabilities or by having an 360 effective user of root. 361 362 Smack Basics 363 364 Smack is an extension to a Linux system. It enforces additional restrictions 365 on what subjects can access which objects, based on the labels attached to 366 each of the subject and the object. 367 368 Labels 369 370 Smack labels are ASCII character strings. They can be up to 255 characters 371 long, but keeping them to twenty-three characters is recommended. 372 Single character labels using special characters, that being anything 373 other than a letter or digit, are reserved for use by the Smack development 374 team. Smack labels are unstructured, case sensitive, and the only operation 375 ever performed on them is comparison for equality. Smack labels cannot 376 contain unprintable characters, the "/" (slash), the "\" (backslash), the "'" 377 (quote) and '"' (double-quote) characters. 378 Smack labels cannot begin with a '-'. This is reserved for special options. 379 380 There are some predefined labels: 381 382 _ Pronounced "floor", a single underscore character. 383 ^ Pronounced "hat", a single circumflex character. 384 * Pronounced "star", a single asterisk character. 385 ? Pronounced "huh", a single question mark character. 386 @ Pronounced "web", a single at sign character. 387 388 Every task on a Smack system is assigned a label. The Smack label 389 of a process will usually be assigned by the system initialization 390 mechanism. 391 392 Access Rules 393 394 Smack uses the traditional access modes of Linux. These modes are read, 395 execute, write, and occasionally append. There are a few cases where the 396 access mode may not be obvious. These include: 397 398 Signals: A signal is a write operation from the subject task to 399 the object task. 400 Internet Domain IPC: Transmission of a packet is considered a 401 write operation from the source task to the destination task. 402 403 Smack restricts access based on the label attached to a subject and the label 404 attached to the object it is trying to access. The rules enforced are, in 405 order: 406 407 1. Any access requested by a task labeled "*" is denied. 408 2. A read or execute access requested by a task labeled "^" 409 is permitted. 410 3. A read or execute access requested on an object labeled "_" 411 is permitted. 412 4. Any access requested on an object labeled "*" is permitted. 413 5. Any access requested by a task on an object with the same 414 label is permitted. 415 6. Any access requested that is explicitly defined in the loaded 416 rule set is permitted. 417 7. Any other access is denied. 418 419 Smack Access Rules 420 421 With the isolation provided by Smack access separation is simple. There are 422 many interesting cases where limited access by subjects to objects with 423 different labels is desired. One example is the familiar spy model of 424 sensitivity, where a scientist working on a highly classified project would be 425 able to read documents of lower classifications and anything she writes will 426 be "born" highly classified. To accommodate such schemes Smack includes a 427 mechanism for specifying rules allowing access between labels. 428 429 Access Rule Format 430 431 The format of an access rule is: 432 433 subject-label object-label access 434 435 Where subject-label is the Smack label of the task, object-label is the Smack 436 label of the thing being accessed, and access is a string specifying the sort 437 of access allowed. The access specification is searched for letters that 438 describe access modes: 439 440 a: indicates that append access should be granted. 441 r: indicates that read access should be granted. 442 w: indicates that write access should be granted. 443 x: indicates that execute access should be granted. 444 t: indicates that the rule requests transmutation. 445 b: indicates that the rule should be reported for bring-up. 446 447 Uppercase values for the specification letters are allowed as well. 448 Access mode specifications can be in any order. Examples of acceptable rules 449 are: 450 451 TopSecret Secret rx 452 Secret Unclass R 453 Manager Game x 454 User HR w 455 Snap Crackle rwxatb 456 New Old rRrRr 457 Closed Off - 458 459 Examples of unacceptable rules are: 460 461 Top Secret Secret rx 462 Ace Ace r 463 Odd spells waxbeans 464 465 Spaces are not allowed in labels. Since a subject always has access to files 466 with the same label specifying a rule for that case is pointless. Only 467 valid letters (rwxatbRWXATB) and the dash ('-') character are allowed in 468 access specifications. The dash is a placeholder, so "a-r" is the same 469 as "ar". A lone dash is used to specify that no access should be allowed. 470 471 Applying Access Rules 472 473 The developers of Linux rarely define new sorts of things, usually importing 474 schemes and concepts from other systems. Most often, the other systems are 475 variants of Unix. Unix has many endearing properties, but consistency of 476 access control models is not one of them. Smack strives to treat accesses as 477 uniformly as is sensible while keeping with the spirit of the underlying 478 mechanism. 479 480 File system objects including files, directories, named pipes, symbolic links, 481 and devices require access permissions that closely match those used by mode 482 bit access. To open a file for reading read access is required on the file. To 483 search a directory requires execute access. Creating a file with write access 484 requires both read and write access on the containing directory. Deleting a 485 file requires read and write access to the file and to the containing 486 directory. It is possible that a user may be able to see that a file exists 487 but not any of its attributes by the circumstance of having read access to the 488 containing directory but not to the differently labeled file. This is an 489 artifact of the file name being data in the directory, not a part of the file. 490 491 If a directory is marked as transmuting (SMACK64TRANSMUTE=TRUE) and the 492 access rule that allows a process to create an object in that directory 493 includes 't' access the label assigned to the new object will be that 494 of the directory, not the creating process. This makes it much easier 495 for two processes with different labels to share data without granting 496 access to all of their files. 497 498 IPC objects, message queues, semaphore sets, and memory segments exist in flat 499 namespaces and access requests are only required to match the object in 500 question. 501 502 Process objects reflect tasks on the system and the Smack label used to access 503 them is the same Smack label that the task would use for its own access 504 attempts. Sending a signal via the kill() system call is a write operation 505 from the signaler to the recipient. Debugging a process requires both reading 506 and writing. Creating a new task is an internal operation that results in two 507 tasks with identical Smack labels and requires no access checks. 508 509 Sockets are data structures attached to processes and sending a packet from 510 one process to another requires that the sender have write access to the 511 receiver. The receiver is not required to have read access to the sender. 512 513 Setting Access Rules 514 515 The configuration file /etc/smack/accesses contains the rules to be set at 516 system startup. The contents are written to the special file 517 /sys/fs/smackfs/load2. Rules can be added at any time and take effect 518 immediately. For any pair of subject and object labels there can be only 519 one rule, with the most recently specified overriding any earlier 520 specification. 521 522 Task Attribute 523 524 The Smack label of a process can be read from /proc/<pid>/attr/current. A 525 process can read its own Smack label from /proc/self/attr/current. A 526 privileged process can change its own Smack label by writing to 527 /proc/self/attr/current but not the label of another process. 528 529 File Attribute 530 531 The Smack label of a filesystem object is stored as an extended attribute 532 named SMACK64 on the file. This attribute is in the security namespace. It can 533 only be changed by a process with privilege. 534 535 Privilege 536 537 A process with CAP_MAC_OVERRIDE or CAP_MAC_ADMIN is privileged. 538 CAP_MAC_OVERRIDE allows the process access to objects it would 539 be denied otherwise. CAP_MAC_ADMIN allows a process to change 540 Smack data, including rules and attributes. 541 542 Smack Networking 543 544 As mentioned before, Smack enforces access control on network protocol 545 transmissions. Every packet sent by a Smack process is tagged with its Smack 546 label. This is done by adding a CIPSO tag to the header of the IP packet. Each 547 packet received is expected to have a CIPSO tag that identifies the label and 548 if it lacks such a tag the network ambient label is assumed. Before the packet 549 is delivered a check is made to determine that a subject with the label on the 550 packet has write access to the receiving process and if that is not the case 551 the packet is dropped. 552 553 CIPSO Configuration 554 555 It is normally unnecessary to specify the CIPSO configuration. The default 556 values used by the system handle all internal cases. Smack will compose CIPSO 557 label values to match the Smack labels being used without administrative 558 intervention. Unlabeled packets that come into the system will be given the 559 ambient label. 560 561 Smack requires configuration in the case where packets from a system that is 562 not Smack that speaks CIPSO may be encountered. Usually this will be a Trusted 563 Solaris system, but there are other, less widely deployed systems out there. 564 CIPSO provides 3 important values, a Domain Of Interpretation (DOI), a level, 565 and a category set with each packet. The DOI is intended to identify a group 566 of systems that use compatible labeling schemes, and the DOI specified on the 567 Smack system must match that of the remote system or packets will be 568 discarded. The DOI is 3 by default. The value can be read from 569 /sys/fs/smackfs/doi and can be changed by writing to /sys/fs/smackfs/doi. 570 571 The label and category set are mapped to a Smack label as defined in 572 /etc/smack/cipso. 573 574 A Smack/CIPSO mapping has the form: 575 576 smack level [category [category]*] 577 578 Smack does not expect the level or category sets to be related in any 579 particular way and does not assume or assign accesses based on them. Some 580 examples of mappings: 581 582 TopSecret 7 583 TS:A,B 7 1 2 584 SecBDE 5 2 4 6 585 RAFTERS 7 12 26 586 587 The ":" and "," characters are permitted in a Smack label but have no special 588 meaning. 589 590 The mapping of Smack labels to CIPSO values is defined by writing to 591 /sys/fs/smackfs/cipso2. 592 593 In addition to explicit mappings Smack supports direct CIPSO mappings. One 594 CIPSO level is used to indicate that the category set passed in the packet is 595 in fact an encoding of the Smack label. The level used is 250 by default. The 596 value can be read from /sys/fs/smackfs/direct and changed by writing to 597 /sys/fs/smackfs/direct. 598 599 Socket Attributes 600 601 There are two attributes that are associated with sockets. These attributes 602 can only be set by privileged tasks, but any task can read them for their own 603 sockets. 604 605 SMACK64IPIN: The Smack label of the task object. A privileged 606 program that will enforce policy may set this to the star label. 607 608 SMACK64IPOUT: The Smack label transmitted with outgoing packets. 609 A privileged program may set this to match the label of another 610 task with which it hopes to communicate. 611 612 Smack Netlabel Exceptions 613 614 You will often find that your labeled application has to talk to the outside, 615 unlabeled world. To do this there's a special file /sys/fs/smackfs/netlabel 616 where you can add some exceptions in the form of : 617 @IP1 LABEL1 or 618 @IP2/MASK LABEL2 619 620 It means that your application will have unlabeled access to @IP1 if it has 621 write access on LABEL1, and access to the subnet @IP2/MASK if it has write 622 access on LABEL2. 623 624 Entries in the /sys/fs/smackfs/netlabel file are matched by longest mask 625 first, like in classless IPv4 routing. 626 627 A special label '@' and an option '-CIPSO' can be used there : 628 @ means Internet, any application with any label has access to it 629 -CIPSO means standard CIPSO networking 630 631 If you don't know what CIPSO is and don't plan to use it, you can just do : 632 echo 127.0.0.1 -CIPSO > /sys/fs/smackfs/netlabel 633 echo 0.0.0.0/0 @ > /sys/fs/smackfs/netlabel 634 635 If you use CIPSO on your 192.168.0.0/16 local network and need also unlabeled 636 Internet access, you can have : 637 echo 127.0.0.1 -CIPSO > /sys/fs/smackfs/netlabel 638 echo 192.168.0.0/16 -CIPSO > /sys/fs/smackfs/netlabel 639 echo 0.0.0.0/0 @ > /sys/fs/smackfs/netlabel 640 641 642 Writing Applications for Smack 643 644 There are three sorts of applications that will run on a Smack system. How an 645 application interacts with Smack will determine what it will have to do to 646 work properly under Smack. 647 648 Smack Ignorant Applications 649 650 By far the majority of applications have no reason whatever to care about the 651 unique properties of Smack. Since invoking a program has no impact on the 652 Smack label associated with the process the only concern likely to arise is 653 whether the process has execute access to the program. 654 655 Smack Relevant Applications 656 657 Some programs can be improved by teaching them about Smack, but do not make 658 any security decisions themselves. The utility ls(1) is one example of such a 659 program. 660 661 Smack Enforcing Applications 662 663 These are special programs that not only know about Smack, but participate in 664 the enforcement of system policy. In most cases these are the programs that 665 set up user sessions. There are also network services that provide information 666 to processes running with various labels. 667 668 File System Interfaces 669 670 Smack maintains labels on file system objects using extended attributes. The 671 Smack label of a file, directory, or other file system object can be obtained 672 using getxattr(2). 673 674 len = getxattr("/", "security.SMACK64", value, sizeof (value)); 675 676 will put the Smack label of the root directory into value. A privileged 677 process can set the Smack label of a file system object with setxattr(2). 678 679 len = strlen("Rubble"); 680 rc = setxattr("/foo", "security.SMACK64", "Rubble", len, 0); 681 682 will set the Smack label of /foo to "Rubble" if the program has appropriate 683 privilege. 684 685 Socket Interfaces 686 687 The socket attributes can be read using fgetxattr(2). 688 689 A privileged process can set the Smack label of outgoing packets with 690 fsetxattr(2). 691 692 len = strlen("Rubble"); 693 rc = fsetxattr(fd, "security.SMACK64IPOUT", "Rubble", len, 0); 694 695 will set the Smack label "Rubble" on packets going out from the socket if the 696 program has appropriate privilege. 697 698 rc = fsetxattr(fd, "security.SMACK64IPIN, "*", strlen("*"), 0); 699 700 will set the Smack label "*" as the object label against which incoming 701 packets will be checked if the program has appropriate privilege. 702 703 Administration 704 705 Smack supports some mount options: 706 707 smackfsdef=label: specifies the label to give files that lack 708 the Smack label extended attribute. 709 710 smackfsroot=label: specifies the label to assign the root of the 711 file system if it lacks the Smack extended attribute. 712 713 smackfshat=label: specifies a label that must have read access to 714 all labels set on the filesystem. Not yet enforced. 715 716 smackfsfloor=label: specifies a label to which all labels set on the 717 filesystem must have read access. Not yet enforced. 718 719 These mount options apply to all file system types. 720 721 Smack auditing 722 723 If you want Smack auditing of security events, you need to set CONFIG_AUDIT 724 in your kernel configuration. 725 By default, all denied events will be audited. You can change this behavior by 726 writing a single character to the /sys/fs/smackfs/logging file : 727 0 : no logging 728 1 : log denied (default) 729 2 : log accepted 730 3 : log denied & accepted 731 732 Events are logged as 'key=value' pairs, for each event you at least will get 733 the subject, the object, the rights requested, the action, the kernel function 734 that triggered the event, plus other pairs depending on the type of event 735 audited. 736 737 Bringup Mode 738 739 Bringup mode provides logging features that can make application 740 configuration and system bringup easier. Configure the kernel with 741 CONFIG_SECURITY_SMACK_BRINGUP to enable these features. When bringup 742 mode is enabled accesses that succeed due to rules marked with the "b" 743 access mode will logged. When a new label is introduced for processes 744 rules can be added aggressively, marked with the "b". The logging allows 745 tracking of which rules actual get used for that label. 746 747 Another feature of bringup mode is the "unconfined" option. Writing 748 a label to /sys/fs/smackfs/unconfined makes subjects with that label 749 able to access any object, and objects with that label accessible to 750 all subjects. Any access that is granted because a label is unconfined 751 is logged. This feature is dangerous, as files and directories may 752 be created in places they couldn't if the policy were being enforced.