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Headers	show Return-Path: <selinux-owner@kernel.org> From: Richard Haines <richard_c_haines@btinternet.com> To: paul@paul-moore.com, selinux@vger.kernel.org Cc: Richard Haines <richard_c_haines@btinternet.com> Subject: [PATCH] mls_mcs.md: Convert section to markdown Date: Fri, 20 Nov 2020 11:38:07 +0000 Message-Id: <20201120113807.11605-1-richard_c_haines@btinternet.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	mls_mcs.md: Convert section to markdown \| expand mls_mcs.md: Convert section to markdown

diff --git a/src/mls_mcs.md b/src/mls_mcs.md index 4b4c15c..0c25108 100644 --- a/src/mls_mcs.md +++ b/src/mls_mcs.md @@ -1,5 +1,13 @@ # Multi-Level and Multi-Category Security +- [MLS or MCS Policy](#mls-or-mcs-policy) +- [Security Levels](#security-levels) + - [MLS / MCS Range Format](#mls-mcs-range-format) + - [Translating Levels](#translating-levels) + - [Managing Security Levels via Dominance Rules](#managing-security-levels-via-dominance-rules) +- [MLS Labeled Network and Database Support](#mls-labeled-network-and-database-support) +- [Common Criteria Certification](#common-criteria-certification) + As stated in the [**Mandatory Access Control (MAC)**](mac.md#mandatory-access-control) section as well as supporting Type Enforcement (TE), SELinux also supports @@ -32,89 +40,104 @@ except that the statement is called *mlsconstrain*. However, as always life is not so simple as: -1. Processes and objects can be given a range that represents the low - and high security levels. -2. The security level can be more complex, in that it is a hierarchical - sensitivity and zero or more non-hierarchical categories. -3. Allowing a process access to an object is managed by 'dominance' - rules applied to the security levels. -4. Trusted processes can be given privileges that will allow them to - bypass the BLP rules and basically do anything (that the security - policy allowed of course). -5. Some objects do not support separate read / write functions as they - need to read / respond in cases such as networks. +1. Processes and objects can be given a range that represents the low + and high security levels. +2. The security level can be more complex, in that it is a hierarchical + sensitivity and zero or more non-hierarchical categories. +3. Allowing a process access to an object is managed by 'dominance' + rules applied to the security levels. +4. Trusted processes can be given privileges that will allow them to + bypass the BLP rules and basically do anything (that the security + policy allowed of course). +5. Some objects do not support separate read / write functions as they + need to read / respond in cases such as networks. The sections that follow discuss the format of a security level and range, and how these are managed by the constraints mechanism within SELinux using dominance rules. +## MLS or MCS Policy + +SELinux only knows of MLS, i.e. it has a MLS engine in the security +server[^fn_mls_1] and a MLS portion of the policy configuration that drives +that engine. The MLS engine has been leveraged by two different types of +policy: + +- The MLS configuration modeled after Bell-LaPadula. +- The MCS configuration that allows a process or object to be labeled with + categories. This has proved useful as a transparent isolation mechanism + for sandbox, container, and virtualization runtimes (see the + [**Virtual Machine Support**](vm_support.md#selinux-virtual-machine-support) + section). + +As a security level is a combination of a hierarchical sensitivity and a +non-hierarchical (potentially empty) category set, MCS doesn't employ +sensitivities since there is no hierarchical relationship to be enforced. +Note however, that the SELinux kernel policy language defines *sensitivity* +as a single value such as *s0*, *s1* etc.. Therefore the BLP defined +sensitivity is formed in an SELinux MLS policy by a combination of the +following (excluding the category statements): + +``` +sensitivity s0; +sensitivity s1; +dominance { s0 s1 } # s1 dominates s0 +``` + +While an MCS policy does not use the BLP sensitivity definition, an SELinux +policy still requires the following entries (basically defining a single level): + +``` +sensitivity s0; +dominance { s0 } +``` + +The number of sensitivities, number of categories, and the set of MLS +constraints used to determine whether a permission is allowed are entirely up +to the policy author. See the +[**The Reference Policy**](reference_policy.md#the-reference-policy) section +for its configuration parameters. + ## Security Levels -**Table 1: Level, Label, Category or Compartment** shows the components that -make up a security level and how two security levels form a range for the -fourth and optional *\[:range\]* of the -[**Security Context**](security_context.md#security-context) -within an MLS / MCS environment. - -The table also adds terminology in general use as other terms can be -used that have the same meanings. - -<table> -<tbody> -<tr> -<td><center>Security Level (or Level)</center> -<center>Consisting of a sensitivity and zero or more category entries:</center></td> -<td colspan="2"; rowspan="2";><center>Note that SELinux uses <code>level</code>, <code>sensitivity</code> and <code>category</code> in the language statements (see the <a href="mls_statements.md#mls-statements"> MLS Language Statements</a> section), however when discussing these the following terms can also be used: labels, classifications, and compartments.</center></td> -</tr> -<tr> -<td><center><code>sensitivity [: category, ... ]</code> also known as: -Sensitivity Label -Consisting of a classification and compartment.</center></td> -</tr> -<tr> -<td colspan="3"><center><-------------- Range --------------></center></td> -</tr> -<tr> -<td><center>Low</center></td> -<td rowspan="6"><center>-</center></td> -<td><center>High</center></td> -</tr> -<tr> -<td><center><code>sensitivity [: category, ... ]</code></center></td> -<td><center><code>sensitivity [: category, ... ]</code></center></td> -</tr> -<tr> -<td><center>For a process or subject this is the current level or sensitivity</center></td> -<td><center>For a process or subject this is the Clearance</center></td> -</tr> -<tr> -<td><center>For an object this is the current level or sensitivity</center></td> -<td><center>For an object this is the maximum range</center></td> -</tr> -<tr> -<td><center>SystemLow</center></td> - -<td><center>SystemHigh</center></td> -</tr> -<tr> -<td><center>This is the lowest level or classification for the system (for SELinux this is generally 's0', note that there are no categories).</center></td> - -<td><center>This is the highest level or classification for the system (for SELinux this is generally 's15:c0,c255', although note that they will be the highest set by the policy).</center></td> -</tr> -</tbody> -</table> - -**Table 1: Level, Label, Category or Compartment** - *this table shows the meanings depending on the context -being discussed.* +The optional MLS policy extension adds an additional security context +component that consists of the following highlighted entries: + +*user:role:type* ***:sensitivity[:category,...] - sensitivity[:category,...]*** + +Note that: + +- Security Levels on objects are called Classifications. +- Security Levels on subjects are called Clearances. + +The list below describes the components that make up a security level and how +two security levels form a range for an MLS +[**Security Context**](security_context.md#security-context): + +- **Low** + - *sensitivity[:category, ... ]* + - For a process or subject this is the current level or sensitivity. + For an object this is the current level or sensitivity. +- **SystemLow** + - This is the lowest level or classification for the system (for SELinux this + is generally *s0*, note that there are no categories). +- **High** + - *sensitivity[:category, ... ]* + - For a process or subject this is the Clearance. For an object this is + the maximum range. +- **SystemHigh** + - This is the highest level or classification for the system (for an MLS + Reference Policy the default is *s15:c0,c255*, although this is a + configurable build option). The format used in the policy language statements is fully described in the [MLS Statements](mls_statements.md#mls-statements) section, however a brief overview follows. -#### MLS / MCS Range Format +### MLS / MCS Range Format -The following components (shown in bold) are used to define the MLS / -MCS security levels within the security context: +The components are used to define the MLS security levels and MCS categories +within the security context are: ``` user:role:type:sensitivity[:category,...] - sensitivity [:category,...] @@ -125,26 +148,57 @@ user:role:type:sensitivity[:category,...] - sensitivity [:category,...] **Where:** -<table> -<tbody> -<tr> -<td>sensitivity</td> -<td>Sensitivity levels are hierarchical with (traditionally) <code>s0</code> being the lowest. These values are defined using the sensitivity statement. To define their hierarchy, the dominance statement is used. -For MLS systems the highest sensitivity is the last one defined in the dominance statement (low to high). Traditionally the maximum for MLS systems is <code>s15</code> (although the maximum value for the Reference Policy is a build time option). -For MCS systems there is only one sensitivity defined, and that is <code>s0</code>.</td> -</tr> -<tr> -<td>category</td> -<td>Categories are optional (i.e. there can be zero or more categories) and they form unordered and unrelated lists of 'compartments'. These values are defined using the <code>category</code> statement, where for example <code>c0.c3</code> represents a <code>range (c0 c1 c3)</code> and <code>c0, c3, c7</code> represent an unordered list. Traditionally the values are between <code>c0</code> and <code>c255</code> (although the maximum value for the Reference Policy is a build time option).</td> -</tr> -<tr> -<td>level</td> -<td>The level is a combination of the <code>sensitivity</code> and <code>category</code> values that form the actual security level. These values are defined using the <code>level</code> statement.</td> -</tr> -</tbody> -</table> - -#### Translating Levels +*sensitivity* + +- Sensitivity levels are hierarchical with (traditionally) *s0* being the + lowest. These values are defined using the *sensitivity* statement. + To define their hierarchy, the *dominance* statement is used. +- For MLS systems the highest sensitivity is the last one defined in the + *dominance* statement (low to high). Traditionally the maximum for MLS systems + is *s15* (although the maximum value for the *Reference Policy* is a build + time option). +- For MCS systems there is only one *sensitivity* statement defined, and that + is *s0*. + +*category* + +- Categories are optional (i.e. there can be zero or more categories) and they + form unordered and unrelated lists of 'compartments'. These values are + defined using the *category* statement, where for example *c0.c3* + represents the range that consists of *c0 c1 c2 c3* and *c0, c3, c7* that + represents an unordered list. Traditionally the values are between*c0* and + *c255* (although the maximum value for the Reference Policy is a build time + option). + +*level* + +- The level is a combination of the *sensitivity* and *category* values that + form the actual security level. These values are defined using the *level* + statement. + +Example policy entries: + +``` +# MLS Policy statements: +sensitivity s0; +sensitivity s1; +dominance { s0 s1 } +category c0; +category c1; +level s0:c0.c1; +level s1:c0.c1; +``` + +``` +# MCS Policy statements: +sensitivity s0; +dominance { s0 } +category c0; +category c1; +level s0:c0.c1; +``` + +### Translating Levels When writing policy for MLS / MCS security level components it is usual to use an abbreviated form such as *s0*, *s1* etc. to represent @@ -165,26 +219,30 @@ As stated earlier, allowing a process access to an object is managed by [***dominance***](mls_statements.md#dominance) rules applied to the security levels. These rules are as follows: -**Security Level 1 dominates Security Level 2** - If the sensitivity of -Security Level 1 is equal to or higher than the sensitivity of Security -Level 2 and the categories of Security Level 1 are the same or a -superset of the categories of Security Level 2. +**Security Level 1 dominates Security Level 2** + + - If the sensitivity of *Security Level 1* is equal to or higher than the + sensitivity of *Security Level 2* and the categories of *Security Level 1* + are the same or a superset of the categories of *Security Level 2*. + +**Security Level 1 is dominated by Security Level 2** -**Security Level 1 is dominated by Security Level 2** - If the -sensitivity of Security Level 1 is equal to or lower than the -sensitivity of Security Level 2 and the categories of Security Level 1 -are a subset of the categories of Security Level 2. + - If the sensitivity of *Security Level 1* is equal to or lower than the + sensitivity of *Security Level 2* and the categories of *Security Level 1* + are a subset of the categories of *Security Level 2*. -**Security Level 1 equals Security Level 2** - If the sensitivity of -Security Level 1 is equal to Security Level 2 and the categories of -Security Level 1 and Security Level 2 are the same set (sometimes -expressed as: both Security Levels dominate each other). +**Security Level 1 equals Security Level 2** -**Security Level 1 is incomparable to Security Level 2** - If the -categories of Security Level 1 and Security Level 2 cannot be compared -(i.e. neither Security Level dominates the other). + - If the sensitivity of *Security Level 1* is equal to *Security Level 2* + and the categories of *Security Level 1* and *Security Level 2* are the + same set (sometimes expressed as: both Security Levels dominate each other). -To illustrate the usage of these rules, **Table 2: MLS Security Levels** lists +**Security Level 1 is incomparable to Security Level 2** + + - If the categories of *Security Level 1* and *Security Level 2* cannot be + compared (i.e. neither Security Level dominates the other). + +To illustrate the usage of these rules, **Table 1: MLS Security Levels** lists the security level attributes in a table to show example files (or documents) that have been allocated labels such as *s3:c0*. The process that accesses these files (e.g. an editor) is running with a range of @@ -199,112 +257,48 @@ and within the dominance rules, the process will be constrained by using the *mlsconstrain* statement as illustrated in **Figure 9: *mlsconstrain* Statements controlling Read Down & Write Up**. -<table> -<tbody> -<tr> -<td></td> -<td><center>Category -></center></td> -<td>c0</td> -<td>c1</td> -<td>c2</td> -<td>c3</td> -<td>c4</td> -<td>c5</td> -<td>c6</td> -<td>c7</td> -</tr> -<tr> -<td>s3</td> -<td>Secret</td> -<td>s3:c0</td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;">s3:c5</td> -<td>s3:c6</td> -<td></td> -</tr> -<tr> -<td>s2</td> -<td>Confidential</td> -<td></td> -<td style="background-color:#D3D3D3;">s2:c1</td> -<td style="background-color:#D3D3D3;">s2:c2</td> -<td style="background-color:#D3D3D3;">s2:c3</td> -<td style="background-color:#D3D3D3;">s2:c4</td> -<td style="background-color:#D3D3D3;"></td> -<td></td> -<td>s2:c7</td> -</tr> -<tr> -<td>s1</td> -<td>Restricted</td> -<td>s1:c0</td> -<td style="background-color:#D3D3D3;">s1:c1</td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td></td> -<td>s1:c7</td> -</tr> -<tr> -<td>s0</td> -<td>Unclassified</td> -<td>s0:c0</td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;">s0:c3</td> -<td style="background-color:#D3D3D3;"></td> -<td style="background-color:#D3D3D3;"></td> -<td></td> -<td>s0:c7</td> -</tr> -<tr> -<td><center>^ Sensitivity</center> -</td> -<td><center>^ Security Level -(sensitivity:category) aka: classification</center> -</td> -<td colspan="8"><center>^-------- File Labels --------^</center> -<center>A process running with a range of <code>s0 - s3:c1.c5</code> has access to the files within the grey boxed area.</center></td> -</tr> -</tbody> -</table> - -**Table 2: MLS Security Levels** - *Showing the scope of a process running -at a security range of *s0 - s3:c1.c5*.* +| Security Level | Sensitivity | | | | | | | | | +| :------------- | :------------: | :---: | :-------: | :-------: | :-------: | :-------: | :-------: | :---: | :-: | +| |**Category -\>**| *c0* | *c1* | *c2* | *c3* | *c4* | *c5* | *c6* |*c7* | +|**Secret** |*s3* |*s3:c0*| | | | |***s3:c5***|*s3:c6*| | +|**Confidential**|*s2* | |***s2:c1***|***s2:c2***|***s2:c3***|***s2:c4***| | |s2:c7| +|**Restricted** |*s1* |*s1:c0*|***s1:c1***| | | | | |s1:c7| +|**Unclassified**|*s0* |*s0:c0*| | |***s0:c3***| | | |s0:c7| + +**Table 1: MLS Security Levels** - *Showing that a process running at +s0 - s3:c1.c5 has access to the highlighted **sensitivity:category** files*. ![](./images/9-mls-constrain.png) -**Figure 9: Showing the mlsconstrain Statements controlling Read Down & Write Up** - *This ties in with* **Table 2: MLS Security Levels** *that shows a process running with a security range of s0 - s3:c1.c5.* +**Figure 9: Showing mlsconstrain Statements controlling Read Down & Write Up** - +*This ties in with* **Table 1: MLS Security Levels** *that shows a process +running with a security range of s0 - s3:c1.c5.* Using **Figure 9: *mlsconstrain* Statements controlling Read Down & Write Up**: -1. To allow write-up, the source level (l1) must be **dominated by** - the target level (l2): -- Source level = s0:c3 or s1:c1 -- Target level = s2:c1.c4 +- To allow write-up, the source level (*l1*) must be **dominated by** + the target level (*l2*): + - Source level = *s0:c3* or *s1:c1* + - Target level = *s2:c1.c4* As can be seen, either of the source levels are **dominated by** the target level. -2. To allow read-down, the source level (l1) must **dominate** the - target level (l2): -- Source level = s2:c1.c4 -- Target level = s0:c3 +- To allow read-down, the source level (*l1*) must **dominate** the + target level (*l2*): + - Source level = *s2:c1.c4* + - Target level = *s0:c3* As can be seen, the source level does **dominate** the target level. However in the real world the SELinux MLS Reference Policy does not allow the write-up unless the process has a special privilege (by having the domain type added to an attribute), although it does allow the -read-down. The default is to use l1 eq l2 (i.e. the levels are equal). +read-down. The default is to use *l1 eq l2* (i.e. the levels are equal). The reference policy MLS source file (policy/mls) shows these *mlsconstrain* statements. -### MLS Labeled Network and Database Support +## MLS Labeled Network and Database Support Networking for MLS is supported via the NetLabel CIPSO (commercial IP security option) and CALIPSO (Common Architecture Label @@ -316,7 +310,7 @@ PostgreSQL supports labeling for MLS database services as discussed in the [**SE-PostgreSQL Support**](postgresql.md#postgresql-selinux-support) section. -### Common Criteria Certification +## Common Criteria Certification While the [*Common Criteria*](http://www.commoncriteriaportal.org/) certification process is beyond the scope of this Notebook, it is worth @@ -329,22 +323,25 @@ certificate should be obtained. The Red Hat evaluation process cover the: -- Labeled Security Protection Profile - ([*LSPP*](http://www.commoncriteriaportal.org/files/ppfiles/lspp.pdf) - ) - This describes how systems that implement security labels (i.e. - MLS) should function. -- Controlled Access Protection Profile - ([*CAPP*](http://www.commoncriteriaportal.org/files/ppfiles/capp.pdf)) - - This describes how systems that implement DAC should function. +- Labeled Security Protection Profile + ([*LSPP*](http://www.commoncriteriaportal.org/files/ppfiles/lspp.pdf)) - + This describes how systems that implement security labels (i.e. MLS) should + function. +- Controlled Access Protection Profile + ([*CAPP*](http://www.commoncriteriaportal.org/files/ppfiles/capp.pdf)) - + This describes how systems that implement DAC should function. An interesting point: -- Both Red Hat Linux 5.1 and Microsoft Server 2003 (with XP) have both - been certified to EAL4+ , however while the evaluation levels may be - the same the Protection Profiles that they were evaluated under - were: Microsoft CAPP only, Red Hat CAPP and LSPP. Therefore always - look at the protection profiles as they define what was actually - evaluated. +- Both Red Hat Linux 5.1 and Microsoft Server 2003 (with XP) have both + been certified to EAL4+ , however while the evaluation levels may be + the same the Protection Profiles that they were evaluated under + were: Microsoft CAPP only, Red Hat CAPP and LSPP. Therefore always + look at the protection profiles as they define what was actually + evaluated. + +[^fn_mls_1]: See [**Figure 2: High Level SELinux Architecture**](core_components.md#core-selinux-components) +in the 'Core SELinux Components' section.

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