From 8125e96bd5858b37651fe559a7251ac5de76fa11 Mon Sep 17 00:00:00 2001 From: Marc Lepage <67919234+mlepage-google@users.noreply.github.com> Date: Fri, 4 Mar 2022 19:18:30 -0500 Subject: [PATCH] Add access control guide (#15873) * Add access control guide Basic documentation for access control. * Update access-control-guide.md Fixing spelling errors Co-authored-by: Justin Wood --- docs/guides/access-control-guide.md | 571 ++++++++++++++++++++++++++++ 1 file changed, 571 insertions(+) create mode 100644 docs/guides/access-control-guide.md diff --git a/docs/guides/access-control-guide.md b/docs/guides/access-control-guide.md new file mode 100644 index 00000000000000..8d81b32298acc7 --- /dev/null +++ b/docs/guides/access-control-guide.md @@ -0,0 +1,571 @@ +# Access Control Guide + +All Interaction Model operations (read attribute, write attribute, invoke +command, read event) are governed by access control, and will be denied (status +0x7E Access Denied) if sufficient privilege for the operation is not obtained. + +## Overview + +The initial `Administer` privilege is obtained by the commissioner implicitly +over the PASE commissioning channel. This implicit `Administer` privilege is +used to invoke commands on the server node during commissioning. + +As part of commissioning, the commissioner invokes the `AddNOC` command, +providing a `CaseAdminNode` argument. As well as commissioning the server node +onto the fabric, that command automatically installs an ACL on the server node +for `Administer` privilege using the provided `CaseAdminNode` argument as CASE +subject. The subject may be a single node, or multiple nodes (by providing a +CAT). These nodes become fabric administrators on that server node. + +During and after commissioning, administrators manage ACLs for the fabric on the +server node by reading and writing the fabric-scoped `ACL` attribute of the +Access Control Cluster, which is always present on endpoint 0 on the server +node. It is these ACLs that govern which Interaction Model operations are +allowed or denied on that server node, for subjects on the fabric, via CASE and +group messaging. + +## ACLs + +ACLs are fabric-scoped data structures with the following fields: + +- Privilege +- AuthMode +- Subjects +- Targets + +### Privilege + +Privileges are: + +- View +- Operate +- Manage +- Administer + +An additional `ProxyView` privilege is not yet supported in the Matter SDK. + +By default, the `View` privilege is required to read attributes or events, and +the `Operate` privilege is required to write attributes or invoke commands. + +However, clusters may require stricter privileges for certain operations on +certain endpoints. For example, the Access Control Cluster requires the +`Administer` privilege for all its operations. + +If applicable, the ACL grants the privilege, and all less strict privileges +subsumed by it. Therefore an ACL for `Manage` privilege will work for operations +which require `Operate` or `View` privilege (but not `Administer` privilege). + +### AuthMode + +Authentication modes are: + +- CASE +- Group + +The ACL applies only to subjects using that authentication mode. + +### Subjects + +Subjects is a list containing zero, one, or more subject identifiers, which are: + +- Node ID for CASE auth mode +- Group ID for Group auth mode + +A CASE subject may be a CAT, which has its own tag and version mechanism. + +The ACL applies only to the listed subjects; if no subjects are listed, the ACL +applies to any subjects using the authentication mode. + +### Targets + +Targets is a list containing zero, one, or more structured entries with fields: + +- Cluster +- Endpoint +- DeviceType + +All fields are nullable, but at least one must be present, and the endpoint and +device type fields are mutually exclusive (only one of those two may be +present). + +If cluster is present, the ACL is targeted to just that cluster. + +If endpoint is present, the ACL is targeted to just that endpoint. + +If device type is present, the ACL is targeted to just endpoints which contain +that device type (as reported by the Descriptor Cluster). + +Specifying device type in targets is not yet supported in the Matter SDK. + +The ACL applies only to the listed targets; if no targets are listed, the ACL +applies to any targets on the server node. + +## Limitations and Restrictions + +The Matter Specification states that a Matter implementation must support at +least: + +- 3 ACLs per fabric +- 4 subjects per ACL +- 3 targets per ACL + +There is no guarantee that an implementation supports any more than those +minimums. + +In the Matter SDK, using the example access control implementation, these values +can be configured globally in `CHIPConfig.h` or per-app in +`CHIPProjectAppConfig.h` by setting: + +- CHIP_CONFIG_EXAMPLE_ACCESS_CONTROL_MAX_ENTRIES_PER_FABRIC +- CHIP_CONFIG_EXAMPLE_ACCESS_CONTROL_MAX_SUBJECTS_PER_ENTRY +- CHIP_CONFIG_EXAMPLE_ACCESS_CONTROL_MAX_TARGETS_PER_ENTRY + +## Case Studies + +### Single Administrator + +A single controller commissions a server node, providing its own CASE node ID +for the automatically installed ACL: + +- Privilege: `Administer` +- AuthMode: `CASE` +- Subjects: `112233` +- Targets: (all) + +The controller will be able to perform all Interaction Model operations on the +server node, since it is the administrator. + +### Multiple Administrators + +The commissioner provides a CAT for the automatically installed ACL: + +- Privilege: `Administer` +- AuthMode: `CASE` +- Subjects: `0xFFFFFFFD00010001` +- Targets: (all) + +All controllers which have the CAT as part of their CASE credentials will be +administrators for the server node. + +### Client Controllers + +The commissioner installs an ACL for non-administrative controllers: + +- Privilege: `View` +- AuthMode: `CASE` +- Subjects: `4444`, `5555`, `6666` +- Targets: (all) + +The non-administrative controllers are granted `View` privilege for the entire +server node. This doesn't mean they can view the entire server node, as some +clusters may require stricter privileges for reading attributes or events. + +### Group Messaging + +The commissioner installs an ACL for group messaging: + +- Privilege: `Operate` +- AuthMode: `Group` +- Subjects: `123`, `456` +- Targets: `{cluster:onoff}`, `{endpoint:1}`, + `{cluster:levelcontrol,endpoint:2}` + +Members of groups 123 and 456 are granted `Operate` privilege for the on/off +cluster on any endpoint, any cluster on endpoint 1, and the level control +cluster on endpoint 2. + +## Managing ACLs Using Chip-Tool + +### Usage + +#### Entire List + +The Access Control Cluster's `ACL` attribute is a list. + +Currently, list operations for single entries (append, update, delete) are not +yet supported in the Matter SDK, so the entire list must be written to the +attribute to change any ACL. + +The write operation may employ multiple messages, making it unreliable. In any +case, ACLs are updated as they are processed, and take effect immediately. + +The implication of this is that the administrator must ensure the first ACL in +the list it is writing to the `ACL` attribute is one granting itself +`Administer` privilege. Otherwise, the administrator may lose its administrative +access during the write operation. + +#### Null Fields + +The tool requires all fields to be provided, even if null. + +Incorrect: `{"cluster": 6}` + +Correct: `{"cluster": 6, "endpoint": null, "deviceType": null}` + +#### Fabric Index + +The `ACL` attribute is fabric-scoped, so each ACL has a fabric index. + +The tool requires this field to be provided, but ignores it when performing the +actual write. + +When reading ACLs, the proper fabric index is shown. + +#### Enums Identifiers + +The tool requires numerical values for enums and identifiers. + +The privileges are: + +- View: 1 +- Operate: 3 +- Manage: 4 +- Administer: 5 + +The authentication modes are: + +- CASE: 2 +- Group: 3 + +Some typical clusters: + +- On/Off: 6 +- Level Control: 8 +- Descriptor: 29 +- Binding: 30 +- Access Control: 31 +- Basic: 40 + +### Examples + +#### Automatically Installed ACL + +After commissioning with chip-tool, assuming `CaseAdminNode` is 112233, the +automatically installed ACL is: + +``` +out/debug/standalone/chip-tool accesscontrol read acl 1 0 +``` + +``` +Endpoint: 0 Cluster: 0x0000_001F Attribute 0x0000_0000 DataVersion: 2578401031 + ACL: 1 entries + [1]: { + FabricIndex: 1 + Privilege: 5 + AuthMode: 2 + Subjects: 1 entries + [1]: 112233 + Targets: null + } +``` + +#### Installing a CASE ACL + +``` +out/debug/standalone/chip-tool accesscontrol write acl '[{"fabricIndex": 0, "privilege": 5, "authMode": 2, "subjects": [112233], "targets": null}, {"fabricIndex": 0, "privilege": 1, "authMode": 2, "subjects": [4444, 5555, 6666], "targets": null}]' 1 0 +``` + +``` +Endpoint: 0 Cluster: 0x0000_001F Attribute 0x0000_0000 DataVersion: 2578401034 + ACL: 2 entries + [1]: { + FabricIndex: 1 + Privilege: 5 + AuthMode: 2 + Subjects: 1 entries + [1]: 112233 + Targets: null + } + [2]: { + FabricIndex: 1 + Privilege: 1 + AuthMode: 2 + Subjects: 3 entries + [1]: 4444 + [2]: 5555 + [3]: 6666 + Targets: null + } +``` + +#### Installing a Group ACL + +``` +out/debug/standalone/chip-tool accesscontrol write acl '[{"fabricIndex": 0, "privilege": 5, "authMode": 2, "subjects": [112233], "targets": null}, {"fabricIndex": 0, "privilege": 1, "authMode": 2, "subjects": [4444, 5555, 6666], "targets": null}, {"fabricIndex": 0, "privilege": 3, "authMode": 3, "subjects": [123, 456], "targets": [{"cluster": 6, "endpoint": null, "deviceType": null}, {"cluster": null, "endpoint": 1, "deviceType": null}, {"cluster": 8, "endpoint": 2, "deviceType": null}]}]' 1 0 +``` + +``` +Endpoint: 0 Cluster: 0x0000_001F Attribute 0x0000_0000DataVersion: 2578401041 + ACL: 3 entries + [1]: { + FabricIndex: 1 + Privilege: 5 + AuthMode: 2 + Subjects: 1 entries + [1]: 112233 + Targets: null + } + [2]: { + FabricIndex: 1 + Privilege: 1 + AuthMode: 2 + Subjects: 3 entries + [1]: 4444 + [2]: 5555 + [3]: 6666 + Targets: null + } + [3]: { + FabricIndex: 1 + Privilege: 3 + AuthMode: 3 + Subjects: 2 entries + [1]: 123 + [2]: 456 + Targets: 3 entries + [1]: { + Cluster: 6 + Endpoint: null + DeviceType: null + } + [2]: { + Cluster: null + Endpoint: 1 + DeviceType: null + } + [3]: { + Cluster: 8 + Endpoint: 2 + DeviceType: null + } + } +``` + +## Managing ACLs Using Chip-Repl + +### Usage + +#### Entire List + +See the important notes in the chip-tool section, as they also apply to +chip-repl. + +### Null Fields + +Null fields may be omitted. + +OK: `Target(cluster=6, endpoint=Null, deviceType=Null)` + +Also OK: `Target(cluster=6)` + +The above assumes Target and Null are defined at global scope, which is not +normally the case. + +#### Fabric Index + +The `ACL` attribute is fabric-scoped, so each ACL has a fabric index. + +The REPL ignores it when performing the actual write. Because null fields can be +omitted, simply do not provide it when writing ACLs. + +When reading ACLs, the proper fabric index is shown. + +#### Enums and Identifiers + +The REPL accepts numerical values for enums and identifiers, but it also accepts +strongly typed values: + +The privileges are: + +- Clusters.AccessControl.Enums.Privilege.kView +- Clusters.AccessControl.Enums.Privilege.kOperate +- Clusters.AccessControl.Enums.Privilege.kManage +- Clusters.AccessControl.Enums.Privilege.kAdminister + +The authentication modes are: + +- Clusters.AccessControl.Enums.AuthMode.kCASE +- Clusters.AccessControl.Enums.AuthMode.kGroup + +Some typical clusters: + +- Clusters.OnOff.id +- Clusters.LevelControl.id +- Clusters.Descriptor.id +- Clusters.Binding.id +- Clusters.AccessControl.id +- Clusters.Basic.id + +### Examples + +#### Automatically Installed ACL + +After commissioning with chip-repl, assuming `CaseAdminNode` is 1, the +automatically installed ACL is: + +``` +await devCtrl.ReadAttribute(1, [ (0, Clusters.AccessControl.Attributes.Acl ) ] ) +``` + +``` +{ +│ 0: { +│ │ : { +│ │ │ : 556798280, +│ │ │ : [ +│ │ │ │ AccessControlEntry( +│ │ │ │ │ fabricIndex=1, +│ │ │ │ │ privilege=, +│ │ │ │ │ authMode=, +│ │ │ │ │ subjects=[ +│ │ │ │ │ │ 1 +│ │ │ │ │ ], +│ │ │ │ │ targets=Null +│ │ │ │ ) +│ │ │ ] +│ │ } +│ } +} +``` + +#### Installing a CASE ACL + +``` +await devCtrl.WriteAttribute(1, [ (0, Clusters.AccessControl.Attributes.Acl( [ + Clusters.AccessControl.Structs.AccessControlEntry( + privilege = Clusters.AccessControl.Enums.Privilege.kAdminister, + authMode = Clusters.AccessControl.Enums.AuthMode.kCase, + subjects = [ 1 ] + ), + Clusters.AccessControl.Structs.AccessControlEntry( + privilege = Clusters.AccessControl.Enums.Privilege.kView, + authMode = Clusters.AccessControl.Enums.AuthMode.kCase, + subjects = [ 4444, 5555, 6666 ], + ), +] ) ) ] ) +``` + +``` +{ +│ 0: { +│ │ : { +│ │ │ : 556798289, +│ │ │ : [ +│ │ │ │ AccessControlEntry( +│ │ │ │ │ fabricIndex=1, +│ │ │ │ │ privilege=, +│ │ │ │ │ authMode=, +│ │ │ │ │ subjects=[ +│ │ │ │ │ │ 1 +│ │ │ │ │ ], +│ │ │ │ │ targets=Null +│ │ │ │ ), +│ │ │ │ AccessControlEntry( +│ │ │ │ │ fabricIndex=1, +│ │ │ │ │ privilege=, +│ │ │ │ │ authMode=, +│ │ │ │ │ subjects=[ +│ │ │ │ │ │ 4444, +│ │ │ │ │ │ 5555, +│ │ │ │ │ │ 6666 +│ │ │ │ │ ], +│ │ │ │ │ targets=Null +│ │ │ │ ) +│ │ │ ] +│ │ } +│ } +} +``` + +#### Installing a Group ACL + +``` +await devCtrl.WriteAttribute(1, [ (0, Clusters.AccessControl.Attributes.Acl( [ + Clusters.AccessControl.Structs.AccessControlEntry( + privilege = Clusters.AccessControl.Enums.Privilege.kAdminister, + authMode = Clusters.AccessControl.Enums.AuthMode.kCase, + subjects = [ 1 ] + ), + Clusters.AccessControl.Structs.AccessControlEntry( + privilege = Clusters.AccessControl.Enums.Privilege.kView, + authMode = Clusters.AccessControl.Enums.AuthMode.kCase, + subjects = [ 4444, 5555, 6666 ], + ), + Clusters.AccessControl.Structs.AccessControlEntry( + privilege = Clusters.AccessControl.Enums.Privilege.kOperate, + authMode = Clusters.AccessControl.Enums.AuthMode.kGroup, + subjects = [ 123, 456 ], + targets = [ + Clusters.AccessControl.Structs.Target( + cluster = Clusters.OnOff.id, + ), + Clusters.AccessControl.Structs.Target( + endpoint = 1, + ), + Clusters.AccessControl.Structs.Target( + cluster = Clusters.LevelControl.id, + endpoint = 2, + ), + ] + ), +] ) ) ] ) +``` + +``` +{ +│ 0: { +│ │ : { +│ │ │ : 556798301, +│ │ │ : [ +│ │ │ │ AccessControlEntry( +│ │ │ │ │ fabricIndex=1, +│ │ │ │ │ privilege=, +│ │ │ │ │ authMode=, +│ │ │ │ │ subjects=[ +│ │ │ │ │ │ 1 +│ │ │ │ │ ], +│ │ │ │ │ targets=Null +│ │ │ │ ), +│ │ │ │ AccessControlEntry( +│ │ │ │ │ fabricIndex=1, +│ │ │ │ │ privilege=, +│ │ │ │ │ authMode=, +│ │ │ │ │ subjects=[ +│ │ │ │ │ │ 4444, +│ │ │ │ │ │ 5555, +│ │ │ │ │ │ 6666 +│ │ │ │ │ ], +│ │ │ │ │ targets=Null +│ │ │ │ ), +│ │ │ │ AccessControlEntry( +│ │ │ │ │ fabricIndex=1, +│ │ │ │ │ privilege=, +│ │ │ │ │ authMode=, +│ │ │ │ │ subjects=[ +│ │ │ │ │ │ 123, +│ │ │ │ │ │ 456 +│ │ │ │ │ ], +│ │ │ │ │ targets=[ +│ │ │ │ │ │ Target( +│ │ │ │ │ │ │ cluster=6, +│ │ │ │ │ │ │ endpoint=Null, +│ │ │ │ │ │ │ deviceType=Null +│ │ │ │ │ │ ), +│ │ │ │ │ │ Target( +│ │ │ │ │ │ │ cluster=Null, +│ │ │ │ │ │ │ endpoint=1, +│ │ │ │ │ │ │ deviceType=Null +│ │ │ │ │ │ ), +│ │ │ │ │ │ Target( +│ │ │ │ │ │ │ cluster=8, +│ │ │ │ │ │ │ endpoint=2, +│ │ │ │ │ │ │ deviceType=Null +│ │ │ │ │ │ ) +│ │ │ │ │ ] +│ │ │ │ ) +│ │ │ ] +│ │ } +│ } +} +```