Based on kernel version 4.1. Page generated on 2015-06-28 12:14 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 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 five commands included in smackutil: 37 38 chsmack - display or set Smack extended attribute values 39 smackctl - load the Smack access rules 40 smackaccess - report if a process with one label has access 41 to an object with another 42 43 These two commands are obsolete with the introduction of 44 the smackfs/load2 and smackfs/cipso2 interfaces. 45 46 smackload - properly formats data for writing to smackfs/load 47 smackcipso - properly formats data for writing to smackfs/cipso 48 49 In keeping with the intent of Smack, configuration data is 50 minimal and not strictly required. The most important 51 configuration step is mounting the smackfs pseudo filesystem. 52 If smackutil is installed the startup script will take care 53 of this, but it can be manually as well. 54 55 Add this line to /etc/fstab: 56 57 smackfs /sys/fs/smackfs smackfs defaults 0 0 58 59 The /sys/fs/smackfs directory is created by the kernel. 60 61 Smack uses extended attributes (xattrs) to store labels on filesystem 62 objects. The attributes are stored in the extended attribute security 63 name space. A process must have CAP_MAC_ADMIN to change any of these 64 attributes. 65 66 The extended attributes that Smack uses are: 67 68 SMACK64 69 Used to make access control decisions. In almost all cases 70 the label given to a new filesystem object will be the label 71 of the process that created it. 72 SMACK64EXEC 73 The Smack label of a process that execs a program file with 74 this attribute set will run with this attribute's value. 75 SMACK64MMAP 76 Don't allow the file to be mmapped by a process whose Smack 77 label does not allow all of the access permitted to a process 78 with the label contained in this attribute. This is a very 79 specific use case for shared libraries. 80 SMACK64TRANSMUTE 81 Can only have the value "TRUE". If this attribute is present 82 on a directory when an object is created in the directory and 83 the Smack rule (more below) that permitted the write access 84 to the directory includes the transmute ("t") mode the object 85 gets the label of the directory instead of the label of the 86 creating process. If the object being created is a directory 87 the SMACK64TRANSMUTE attribute is set as well. 88 SMACK64IPIN 89 This attribute is only available on file descriptors for sockets. 90 Use the Smack label in this attribute for access control 91 decisions on packets being delivered to this socket. 92 SMACK64IPOUT 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 coming from this socket. 96 97 There are multiple ways to set a Smack label on a file: 98 99 # attr -S -s SMACK64 -V "value" path 100 # chsmack -a value path 101 102 A process can see the Smack label it is running with by 103 reading /proc/self/attr/current. A process with CAP_MAC_ADMIN 104 can set the process Smack by writing there. 105 106 Most Smack configuration is accomplished by writing to files 107 in the smackfs filesystem. This pseudo-filesystem is mounted 108 on /sys/fs/smackfs. 109 110 access 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 fixed 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 access2 118 This interface reports whether a subject with the specified 119 Smack label has a particular access to an object with a 120 specified Smack label. Write a long format access rule to 121 this file. The next read will indicate whether the access 122 would be permitted. The text will be either "1" indicating 123 access, or "0" indicating denial. 124 ambient 125 This contains the Smack label applied to unlabeled network 126 packets. 127 change-rule 128 This interface allows modification of existing access control rules. 129 The format accepted on write is: 130 "%s %s %s %s" 131 where the first string is the subject label, the second the 132 object label, the third the access to allow and the fourth the 133 access to deny. The access strings may contain only the characters 134 "rwxat-". If a rule for a given subject and object exists it will be 135 modified by enabling the permissions in the third string and disabling 136 those in the fourth string. If there is no such rule it will be 137 created using the access specified in the third and the fourth strings. 138 cipso 139 This interface allows a specific CIPSO header to be assigned 140 to a Smack label. The format accepted on write is: 141 "%24s%4d%4d"["%4d"]... 142 The first string is a fixed Smack label. The first number is 143 the level to use. The second number is the number of categories. 144 The following numbers are the categories. 145 "level-3-cats-5-19 3 2 5 19" 146 cipso2 147 This interface allows a specific CIPSO header to be assigned 148 to a Smack label. The format accepted on write is: 149 "%s%4d%4d"["%4d"]... 150 The first string is a long 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 direct 155 This contains the CIPSO level used for Smack direct label 156 representation in network packets. 157 doi 158 This contains the CIPSO domain of interpretation used in 159 network packets. 160 load 161 This interface allows access control rules in addition to 162 the system defined rules to be specified. The format accepted 163 on write is: 164 "%24s%24s%5s" 165 where the first string is the subject label, the second the 166 object label, and the third the requested access. The access 167 string may contain only the characters "rwxat-", and specifies 168 which sort of access is allowed. The "-" is a placeholder for 169 permissions that are not allowed. The string "r-x--" would 170 specify read and execute access. Labels are limited to 23 171 characters in length. 172 load2 173 This interface allows access control rules in addition to 174 the system defined rules to be specified. The format accepted 175 on write is: 176 "%s %s %s" 177 where the first string is the subject label, the second the 178 object label, and the third the requested access. The access 179 string may contain only the characters "rwxat-", and specifies 180 which sort of access is allowed. The "-" is a placeholder for 181 permissions that are not allowed. The string "r-x--" would 182 specify read and execute access. 183 load-self 184 This interface allows process specific access rules to be 185 defined. These rules are only consulted if access would 186 otherwise be permitted, and are intended to provide additional 187 restrictions on the process. The format is the same as for 188 the load interface. 189 load-self2 190 This interface allows process specific access rules to be 191 defined. These rules are only consulted if access would 192 otherwise be permitted, and are intended to provide additional 193 restrictions on the process. The format is the same as for 194 the load2 interface. 195 logging 196 This contains the Smack logging state. 197 mapped 198 This contains the CIPSO level used for Smack mapped label 199 representation in network packets. 200 netlabel 201 This interface allows specific internet addresses to be 202 treated as single label hosts. Packets are sent to single 203 label hosts without CIPSO headers, but only from processes 204 that have Smack write access to the host label. All packets 205 received from single label hosts are given the specified 206 label. The format accepted on write is: 207 "%d.%d.%d.%d label" or "%d.%d.%d.%d/%d label". 208 onlycap 209 This contains the label processes must have for CAP_MAC_ADMIN 210 and CAP_MAC_OVERRIDE to be effective. If this file is empty 211 these capabilities are effective at for processes with any 212 label. The value is set by writing the desired label to the 213 file or cleared by writing "-" to the file. 214 ptrace 215 This is used to define the current ptrace policy 216 0 - default: this is the policy that relies on Smack access rules. 217 For the PTRACE_READ a subject needs to have a read access on 218 object. For the PTRACE_ATTACH a read-write access is required. 219 1 - exact: this is the policy that limits PTRACE_ATTACH. Attach is 220 only allowed when subject's and object's labels are equal. 221 PTRACE_READ is not affected. Can be overridden with CAP_SYS_PTRACE. 222 2 - draconian: this policy behaves like the 'exact' above with an 223 exception that it can't be overridden with CAP_SYS_PTRACE. 224 revoke-subject 225 Writing a Smack label here sets the access to '-' for all access 226 rules with that subject label. 227 unconfined 228 If the kernel is configured with CONFIG_SECURITY_SMACK_BRINGUP 229 a process with CAP_MAC_ADMIN can write a label into this interface. 230 Thereafter, accesses that involve that label will be logged and 231 the access permitted if it wouldn't be otherwise. Note that this 232 is dangerous and can ruin the proper labeling of your system. 233 It should never be used in production. 234 235 You can add access rules in /etc/smack/accesses. They take the form: 236 237 subjectlabel objectlabel access 238 239 access is a combination of the letters rwxatb which specify the 240 kind of access permitted a subject with subjectlabel on an 241 object with objectlabel. If there is no rule no access is allowed. 242 243 Look for additional programs on http://schaufler-ca.com 244 245 From the Smack Whitepaper: 246 247 The Simplified Mandatory Access Control Kernel 248 249 Casey Schaufler 250 email@example.com 251 252 Mandatory Access Control 253 254 Computer systems employ a variety of schemes to constrain how information is 255 shared among the people and services using the machine. Some of these schemes 256 allow the program or user to decide what other programs or users are allowed 257 access to pieces of data. These schemes are called discretionary access 258 control mechanisms because the access control is specified at the discretion 259 of the user. Other schemes do not leave the decision regarding what a user or 260 program can access up to users or programs. These schemes are called mandatory 261 access control mechanisms because you don't have a choice regarding the users 262 or programs that have access to pieces of data. 263 264 Bell & LaPadula 265 266 From the middle of the 1980's until the turn of the century Mandatory Access 267 Control (MAC) was very closely associated with the Bell & LaPadula security 268 model, a mathematical description of the United States Department of Defense 269 policy for marking paper documents. MAC in this form enjoyed a following 270 within the Capital Beltway and Scandinavian supercomputer centers but was 271 often sited as failing to address general needs. 272 273 Domain Type Enforcement 274 275 Around the turn of the century Domain Type Enforcement (DTE) became popular. 276 This scheme organizes users, programs, and data into domains that are 277 protected from each other. This scheme has been widely deployed as a component 278 of popular Linux distributions. The administrative overhead required to 279 maintain this scheme and the detailed understanding of the whole system 280 necessary to provide a secure domain mapping leads to the scheme being 281 disabled or used in limited ways in the majority of cases. 282 283 Smack 284 285 Smack is a Mandatory Access Control mechanism designed to provide useful MAC 286 while avoiding the pitfalls of its predecessors. The limitations of Bell & 287 LaPadula are addressed by providing a scheme whereby access can be controlled 288 according to the requirements of the system and its purpose rather than those 289 imposed by an arcane government policy. The complexity of Domain Type 290 Enforcement and avoided by defining access controls in terms of the access 291 modes already in use. 292 293 Smack Terminology 294 295 The jargon used to talk about Smack will be familiar to those who have dealt 296 with other MAC systems and shouldn't be too difficult for the uninitiated to 297 pick up. There are four terms that are used in a specific way and that are 298 especially important: 299 300 Subject: A subject is an active entity on the computer system. 301 On Smack a subject is a task, which is in turn the basic unit 302 of execution. 303 304 Object: An object is a passive entity on the computer system. 305 On Smack files of all types, IPC, and tasks can be objects. 306 307 Access: Any attempt by a subject to put information into or get 308 information from an object is an access. 309 310 Label: Data that identifies the Mandatory Access Control 311 characteristics of a subject or an object. 312 313 These definitions are consistent with the traditional use in the security 314 community. There are also some terms from Linux that are likely to crop up: 315 316 Capability: A task that possesses a capability has permission to 317 violate an aspect of the system security policy, as identified by 318 the specific capability. A task that possesses one or more 319 capabilities is a privileged task, whereas a task with no 320 capabilities is an unprivileged task. 321 322 Privilege: A task that is allowed to violate the system security 323 policy is said to have privilege. As of this writing a task can 324 have privilege either by possessing capabilities or by having an 325 effective user of root. 326 327 Smack Basics 328 329 Smack is an extension to a Linux system. It enforces additional restrictions 330 on what subjects can access which objects, based on the labels attached to 331 each of the subject and the object. 332 333 Labels 334 335 Smack labels are ASCII character strings. They can be up to 255 characters 336 long, but keeping them to twenty-three characters is recommended. 337 Single character labels using special characters, that being anything 338 other than a letter or digit, are reserved for use by the Smack development 339 team. Smack labels are unstructured, case sensitive, and the only operation 340 ever performed on them is comparison for equality. Smack labels cannot 341 contain unprintable characters, the "/" (slash), the "\" (backslash), the "'" 342 (quote) and '"' (double-quote) characters. 343 Smack labels cannot begin with a '-'. This is reserved for special options. 344 345 There are some predefined labels: 346 347 _ Pronounced "floor", a single underscore character. 348 ^ Pronounced "hat", a single circumflex character. 349 * Pronounced "star", a single asterisk character. 350 ? Pronounced "huh", a single question mark character. 351 @ Pronounced "web", a single at sign character. 352 353 Every task on a Smack system is assigned a label. The Smack label 354 of a process will usually be assigned by the system initialization 355 mechanism. 356 357 Access Rules 358 359 Smack uses the traditional access modes of Linux. These modes are read, 360 execute, write, and occasionally append. There are a few cases where the 361 access mode may not be obvious. These include: 362 363 Signals: A signal is a write operation from the subject task to 364 the object task. 365 Internet Domain IPC: Transmission of a packet is considered a 366 write operation from the source task to the destination task. 367 368 Smack restricts access based on the label attached to a subject and the label 369 attached to the object it is trying to access. The rules enforced are, in 370 order: 371 372 1. Any access requested by a task labeled "*" is denied. 373 2. A read or execute access requested by a task labeled "^" 374 is permitted. 375 3. A read or execute access requested on an object labeled "_" 376 is permitted. 377 4. Any access requested on an object labeled "*" is permitted. 378 5. Any access requested by a task on an object with the same 379 label is permitted. 380 6. Any access requested that is explicitly defined in the loaded 381 rule set is permitted. 382 7. Any other access is denied. 383 384 Smack Access Rules 385 386 With the isolation provided by Smack access separation is simple. There are 387 many interesting cases where limited access by subjects to objects with 388 different labels is desired. One example is the familiar spy model of 389 sensitivity, where a scientist working on a highly classified project would be 390 able to read documents of lower classifications and anything she writes will 391 be "born" highly classified. To accommodate such schemes Smack includes a 392 mechanism for specifying rules allowing access between labels. 393 394 Access Rule Format 395 396 The format of an access rule is: 397 398 subject-label object-label access 399 400 Where subject-label is the Smack label of the task, object-label is the Smack 401 label of the thing being accessed, and access is a string specifying the sort 402 of access allowed. The access specification is searched for letters that 403 describe access modes: 404 405 a: indicates that append access should be granted. 406 r: indicates that read access should be granted. 407 w: indicates that write access should be granted. 408 x: indicates that execute access should be granted. 409 t: indicates that the rule requests transmutation. 410 b: indicates that the rule should be reported for bring-up. 411 412 Uppercase values for the specification letters are allowed as well. 413 Access mode specifications can be in any order. Examples of acceptable rules 414 are: 415 416 TopSecret Secret rx 417 Secret Unclass R 418 Manager Game x 419 User HR w 420 Snap Crackle rwxatb 421 New Old rRrRr 422 Closed Off - 423 424 Examples of unacceptable rules are: 425 426 Top Secret Secret rx 427 Ace Ace r 428 Odd spells waxbeans 429 430 Spaces are not allowed in labels. Since a subject always has access to files 431 with the same label specifying a rule for that case is pointless. Only 432 valid letters (rwxatbRWXATB) and the dash ('-') character are allowed in 433 access specifications. The dash is a placeholder, so "a-r" is the same 434 as "ar". A lone dash is used to specify that no access should be allowed. 435 436 Applying Access Rules 437 438 The developers of Linux rarely define new sorts of things, usually importing 439 schemes and concepts from other systems. Most often, the other systems are 440 variants of Unix. Unix has many endearing properties, but consistency of 441 access control models is not one of them. Smack strives to treat accesses as 442 uniformly as is sensible while keeping with the spirit of the underlying 443 mechanism. 444 445 File system objects including files, directories, named pipes, symbolic links, 446 and devices require access permissions that closely match those used by mode 447 bit access. To open a file for reading read access is required on the file. To 448 search a directory requires execute access. Creating a file with write access 449 requires both read and write access on the containing directory. Deleting a 450 file requires read and write access to the file and to the containing 451 directory. It is possible that a user may be able to see that a file exists 452 but not any of its attributes by the circumstance of having read access to the 453 containing directory but not to the differently labeled file. This is an 454 artifact of the file name being data in the directory, not a part of the file. 455 456 If a directory is marked as transmuting (SMACK64TRANSMUTE=TRUE) and the 457 access rule that allows a process to create an object in that directory 458 includes 't' access the label assigned to the new object will be that 459 of the directory, not the creating process. This makes it much easier 460 for two processes with different labels to share data without granting 461 access to all of their files. 462 463 IPC objects, message queues, semaphore sets, and memory segments exist in flat 464 namespaces and access requests are only required to match the object in 465 question. 466 467 Process objects reflect tasks on the system and the Smack label used to access 468 them is the same Smack label that the task would use for its own access 469 attempts. Sending a signal via the kill() system call is a write operation 470 from the signaler to the recipient. Debugging a process requires both reading 471 and writing. Creating a new task is an internal operation that results in two 472 tasks with identical Smack labels and requires no access checks. 473 474 Sockets are data structures attached to processes and sending a packet from 475 one process to another requires that the sender have write access to the 476 receiver. The receiver is not required to have read access to the sender. 477 478 Setting Access Rules 479 480 The configuration file /etc/smack/accesses contains the rules to be set at 481 system startup. The contents are written to the special file 482 /sys/fs/smackfs/load2. Rules can be added at any time and take effect 483 immediately. For any pair of subject and object labels there can be only 484 one rule, with the most recently specified overriding any earlier 485 specification. 486 487 Task Attribute 488 489 The Smack label of a process can be read from /proc/<pid>/attr/current. A 490 process can read its own Smack label from /proc/self/attr/current. A 491 privileged process can change its own Smack label by writing to 492 /proc/self/attr/current but not the label of another process. 493 494 File Attribute 495 496 The Smack label of a filesystem object is stored as an extended attribute 497 named SMACK64 on the file. This attribute is in the security namespace. It can 498 only be changed by a process with privilege. 499 500 Privilege 501 502 A process with CAP_MAC_OVERRIDE or CAP_MAC_ADMIN is privileged. 503 CAP_MAC_OVERRIDE allows the process access to objects it would 504 be denied otherwise. CAP_MAC_ADMIN allows a process to change 505 Smack data, including rules and attributes. 506 507 Smack Networking 508 509 As mentioned before, Smack enforces access control on network protocol 510 transmissions. Every packet sent by a Smack process is tagged with its Smack 511 label. This is done by adding a CIPSO tag to the header of the IP packet. Each 512 packet received is expected to have a CIPSO tag that identifies the label and 513 if it lacks such a tag the network ambient label is assumed. Before the packet 514 is delivered a check is made to determine that a subject with the label on the 515 packet has write access to the receiving process and if that is not the case 516 the packet is dropped. 517 518 CIPSO Configuration 519 520 It is normally unnecessary to specify the CIPSO configuration. The default 521 values used by the system handle all internal cases. Smack will compose CIPSO 522 label values to match the Smack labels being used without administrative 523 intervention. Unlabeled packets that come into the system will be given the 524 ambient label. 525 526 Smack requires configuration in the case where packets from a system that is 527 not Smack that speaks CIPSO may be encountered. Usually this will be a Trusted 528 Solaris system, but there are other, less widely deployed systems out there. 529 CIPSO provides 3 important values, a Domain Of Interpretation (DOI), a level, 530 and a category set with each packet. The DOI is intended to identify a group 531 of systems that use compatible labeling schemes, and the DOI specified on the 532 Smack system must match that of the remote system or packets will be 533 discarded. The DOI is 3 by default. The value can be read from 534 /sys/fs/smackfs/doi and can be changed by writing to /sys/fs/smackfs/doi. 535 536 The label and category set are mapped to a Smack label as defined in 537 /etc/smack/cipso. 538 539 A Smack/CIPSO mapping has the form: 540 541 smack level [category [category]*] 542 543 Smack does not expect the level or category sets to be related in any 544 particular way and does not assume or assign accesses based on them. Some 545 examples of mappings: 546 547 TopSecret 7 548 TS:A,B 7 1 2 549 SecBDE 5 2 4 6 550 RAFTERS 7 12 26 551 552 The ":" and "," characters are permitted in a Smack label but have no special 553 meaning. 554 555 The mapping of Smack labels to CIPSO values is defined by writing to 556 /sys/fs/smackfs/cipso2. 557 558 In addition to explicit mappings Smack supports direct CIPSO mappings. One 559 CIPSO level is used to indicate that the category set passed in the packet is 560 in fact an encoding of the Smack label. The level used is 250 by default. The 561 value can be read from /sys/fs/smackfs/direct and changed by writing to 562 /sys/fs/smackfs/direct. 563 564 Socket Attributes 565 566 There are two attributes that are associated with sockets. These attributes 567 can only be set by privileged tasks, but any task can read them for their own 568 sockets. 569 570 SMACK64IPIN: The Smack label of the task object. A privileged 571 program that will enforce policy may set this to the star label. 572 573 SMACK64IPOUT: The Smack label transmitted with outgoing packets. 574 A privileged program may set this to match the label of another 575 task with which it hopes to communicate. 576 577 Smack Netlabel Exceptions 578 579 You will often find that your labeled application has to talk to the outside, 580 unlabeled world. To do this there's a special file /sys/fs/smackfs/netlabel 581 where you can add some exceptions in the form of : 582 @IP1 LABEL1 or 583 @IP2/MASK LABEL2 584 585 It means that your application will have unlabeled access to @IP1 if it has 586 write access on LABEL1, and access to the subnet @IP2/MASK if it has write 587 access on LABEL2. 588 589 Entries in the /sys/fs/smackfs/netlabel file are matched by longest mask 590 first, like in classless IPv4 routing. 591 592 A special label '@' and an option '-CIPSO' can be used there : 593 @ means Internet, any application with any label has access to it 594 -CIPSO means standard CIPSO networking 595 596 If you don't know what CIPSO is and don't plan to use it, you can just do : 597 echo 127.0.0.1 -CIPSO > /sys/fs/smackfs/netlabel 598 echo 0.0.0.0/0 @ > /sys/fs/smackfs/netlabel 599 600 If you use CIPSO on your 192.168.0.0/16 local network and need also unlabeled 601 Internet access, you can have : 602 echo 127.0.0.1 -CIPSO > /sys/fs/smackfs/netlabel 603 echo 192.168.0.0/16 -CIPSO > /sys/fs/smackfs/netlabel 604 echo 0.0.0.0/0 @ > /sys/fs/smackfs/netlabel 605 606 607 Writing Applications for Smack 608 609 There are three sorts of applications that will run on a Smack system. How an 610 application interacts with Smack will determine what it will have to do to 611 work properly under Smack. 612 613 Smack Ignorant Applications 614 615 By far the majority of applications have no reason whatever to care about the 616 unique properties of Smack. Since invoking a program has no impact on the 617 Smack label associated with the process the only concern likely to arise is 618 whether the process has execute access to the program. 619 620 Smack Relevant Applications 621 622 Some programs can be improved by teaching them about Smack, but do not make 623 any security decisions themselves. The utility ls(1) is one example of such a 624 program. 625 626 Smack Enforcing Applications 627 628 These are special programs that not only know about Smack, but participate in 629 the enforcement of system policy. In most cases these are the programs that 630 set up user sessions. There are also network services that provide information 631 to processes running with various labels. 632 633 File System Interfaces 634 635 Smack maintains labels on file system objects using extended attributes. The 636 Smack label of a file, directory, or other file system object can be obtained 637 using getxattr(2). 638 639 len = getxattr("/", "security.SMACK64", value, sizeof (value)); 640 641 will put the Smack label of the root directory into value. A privileged 642 process can set the Smack label of a file system object with setxattr(2). 643 644 len = strlen("Rubble"); 645 rc = setxattr("/foo", "security.SMACK64", "Rubble", len, 0); 646 647 will set the Smack label of /foo to "Rubble" if the program has appropriate 648 privilege. 649 650 Socket Interfaces 651 652 The socket attributes can be read using fgetxattr(2). 653 654 A privileged process can set the Smack label of outgoing packets with 655 fsetxattr(2). 656 657 len = strlen("Rubble"); 658 rc = fsetxattr(fd, "security.SMACK64IPOUT", "Rubble", len, 0); 659 660 will set the Smack label "Rubble" on packets going out from the socket if the 661 program has appropriate privilege. 662 663 rc = fsetxattr(fd, "security.SMACK64IPIN, "*", strlen("*"), 0); 664 665 will set the Smack label "*" as the object label against which incoming 666 packets will be checked if the program has appropriate privilege. 667 668 Administration 669 670 Smack supports some mount options: 671 672 smackfsdef=label: specifies the label to give files that lack 673 the Smack label extended attribute. 674 675 smackfsroot=label: specifies the label to assign the root of the 676 file system if it lacks the Smack extended attribute. 677 678 smackfshat=label: specifies a label that must have read access to 679 all labels set on the filesystem. Not yet enforced. 680 681 smackfsfloor=label: specifies a label to which all labels set on the 682 filesystem must have read access. Not yet enforced. 683 684 These mount options apply to all file system types. 685 686 Smack auditing 687 688 If you want Smack auditing of security events, you need to set CONFIG_AUDIT 689 in your kernel configuration. 690 By default, all denied events will be audited. You can change this behavior by 691 writing a single character to the /sys/fs/smackfs/logging file : 692 0 : no logging 693 1 : log denied (default) 694 2 : log accepted 695 3 : log denied & accepted 696 697 Events are logged as 'key=value' pairs, for each event you at least will get 698 the subject, the object, the rights requested, the action, the kernel function 699 that triggered the event, plus other pairs depending on the type of event 700 audited. 701 702 Bringup Mode 703 704 Bringup mode provides logging features that can make application 705 configuration and system bringup easier. Configure the kernel with 706 CONFIG_SECURITY_SMACK_BRINGUP to enable these features. When bringup 707 mode is enabled accesses that succeed due to rules marked with the "b" 708 access mode will logged. When a new label is introduced for processes 709 rules can be added aggressively, marked with the "b". The logging allows 710 tracking of which rules actual get used for that label. 711 712 Another feature of bringup mode is the "unconfined" option. Writing 713 a label to /sys/fs/smackfs/unconfined makes subjects with that label 714 able to access any object, and objects with that label accessible to 715 all subjects. Any access that is granted because a label is unconfined 716 is logged. This feature is dangerous, as files and directories may 717 be created in places they couldn't if the policy were being enforced.