Documentation ¶
Overview ¶
Package access defines types and interfaces for dynamic access control. Examples: "allow app to read this photo", "prevent user from modifying this file".
Target Developers ¶
Developers creating functionality to share data or services between multiple users/devices/apps.
Overview ¶
Vanadium objects provide GetPermissions and SetPermissions methods. An AccessList contains the set of blessings that grant principals access to the object. All methods on objects can have "tags" on them and the AccessList used for the method is selected based on that tag (from a Permissions).
An object can have multiple names, so GetPermissions and SetPermissions can be invoked on any of these names, but the object itself has a single AccessList.
SetPermissions completely replaces the Permissions. To perform an atomic read-modify-write of the AccessList, use the version parameter.
Conventions ¶
Service implementors should follow the conventions below to be consistent with other parts of Vanadium and with each other.
All methods that create an object (e.g. Put, Mount, Link) should take an optional AccessList parameter. If the AccessList is not specified, the new object, O, copies its AccessList from the parent. Subsequent changes to the parent AccessList are not automatically propagated to O. Instead, a client library must make recursive AccessList changes.
Resolve access is required on all components of a name, except the last one, in order to access the object referenced by that name. For example, for principal P to access the name "a/b/c", P must have resolve access to "a" and "a/b".
The Resolve tag means that a principal can traverse that component of the name to access the child. It does not give the principal permission to list the children via Glob or a similar method. For example, a server might have an object named "home" with a child for each user of the system. If these users were allowed to list the contents of "home", they could discover the other users of the system. That could be a privacy violation. Without Resolve, every user of the system would need read access to "home" to access "home/<user>". If the user called Glob("home/*"), it would then be up to the server to filter out the names that the user could not access. That could be a very expensive operation if there were a lot of children of "home". Resolve protects these servers against potential denial of service attacks on these large, shared directories.
Blessings allow for sweeping access changes. In particular, a blessing is useful for controlling access to objects that are always accessed together. For example, a document may have embedded images and comments, each with a unique name. When accessing a document, the server would generate a blessing that the client would use to fetch the images and comments; the images and comments would have this blessed identity in their AccessLists. Changes to the document's AccessLists are therefore "propagated" to the images and comments.
In the future, we may add some sort of "groups" mechanism to provide an alternative way to express access control policies.
Some services will want a concept of implicit access control. They are free to implement this as appropriate for their service. However, GetPermissions should respond with the correct Permissions. For example, a corporate file server would allow all employees to create their own directory and have full control within that directory. Employees should not be allowed to modify other employee directories. In other words, within the directory "home", employee E should be allowed to modify only "home/E". The file server doesn't know the list of all employees a priori, so it uses an implementation-specific rule to map employee identities to their home directory.
Examples
client := access.ObjectClient(name) for { perms, version, err := client.GetPermissions() if err != nil { return err } perms[newTag] = AccessList{In: []security.BlessingPattern{newPattern}} // Use the same version with the modified perms to ensure that no other // client has modified the perms since GetPermissions returned. if err := client.SetPermissions(perms, version); err != nil { if verror.ErrorID(err) == verror.ErrBadVersion.Id { // Another client replaced the Permissions after our GetPermissions // returned. Try again. continue } return err } }
Index ¶
- Constants
- Variables
- func IsUnenforceablePatterns(err error) []security.BlessingPattern
- func NewAccessTagCaveat(tags ...Tag) (security.Caveat, error)
- func NewErrAccessListMatch(ctx *context.T, validBlessings []string, ...) error
- func NewErrAccessTagCaveatValidation(ctx *context.T, methodTags []string, caveatTags []Tag) error
- func NewErrInvalidOpenAccessList(ctx *context.T) error
- func NewErrNoPermissions(ctx *context.T, validBlessings []string, ...) error
- func NewErrTooBig(ctx *context.T) error
- func NewErrUnenforceablePatterns(ctx *context.T, rejectedPatterns []security.BlessingPattern) error
- func PermissionsAuthorizer(perms Permissions, tagType *vdl.Type) (security.Authorizer, error)
- func PermissionsAuthorizerFromFile(filename string, tagType *vdl.Type) (security.Authorizer, error)
- func TagStrings(tags ...Tag) []string
- func TypicalTagType() *vdl.Type
- func TypicalTagTypePermissionsAuthorizer(perms Permissions) security.Authorizer
- func WritePermissions(w io.Writer, m Permissions) error
- type AccessList
- func (acl AccessList) Authorize(ctx *context.T, call security.Call) error
- func (acl AccessList) Enforceable(ctx *context.T, p security.Principal) error
- func (acl AccessList) Includes(blessings ...string) bool
- func (x AccessList) VDLIsZero() bool
- func (x *AccessList) VDLRead(dec vdl.Decoder) error
- func (x AccessList) VDLWrite(enc vdl.Encoder) error
- type Permissions
- func (m Permissions) Add(pattern security.BlessingPattern, tags ...string) Permissions
- func (m Permissions) Blacklist(blessing string, tags ...string) Permissions
- func (m Permissions) Clear(blessingOrPattern string, tags ...string) Permissions
- func (m Permissions) Copy() Permissions
- func (m Permissions) Normalize() Permissions
- func (x Permissions) VDLIsZero() bool
- func (x *Permissions) VDLRead(dec vdl.Decoder) error
- func (x Permissions) VDLWrite(enc vdl.Encoder) error
- type Tag
Constants ¶
const Admin = Tag("Admin") // Operations that require privileged access for object administration.
const Debug = Tag("Debug") // Operations that return debugging information (e.g., logs, statistics etc.) about the object.
const Read = Tag("Read") // Operations that do not mutate the state of the object.
const Resolve = Tag("Resolve") // Operations involving namespace navigation.
const Write = Tag("Write") // Operations that mutate the state of the object.
Variables ¶
var ( // The AccessList is too big. Use groups to represent large sets of principals. ErrTooBig = verror.Register("v.io/v23/security/access.TooBig", verror.NoRetry, "{1:}{2:} AccessList is too big") ErrNoPermissions = verror.Register("v.io/v23/security/access.NoPermissions", verror.NoRetry, "{1:}{2:} {3} does not have {5} access (rejected blessings: {4})") ErrAccessListMatch = verror.Register("v.io/v23/security/access.AccessListMatch", verror.NoRetry, "{1:}{2:} {3} does not match the access list (rejected blessings: {4})") ErrUnenforceablePatterns = verror.Register("v.io/v23/security/access.UnenforceablePatterns", verror.NoRetry, "{1:}{2:} AccessList contains the following invalid or unrecognized patterns in the In list: {3}") ErrInvalidOpenAccessList = verror.Register("v.io/v23/security/access.InvalidOpenAccessList", verror.NoRetry, "{1:}{2:} AccessList with the pattern ... in its In list must have no other patterns in the In or NotIn lists") ErrAccessTagCaveatValidation = verror.Register("v.io/v23/security/access.AccessTagCaveatValidation", verror.NoRetry, "{1:}{2:} access tags on method ({3}) do not include any of the ones in the caveat ({4}), or the method is using a different tag type") )
var AccessTagCaveat = security.CaveatDescriptor{ Id: uniqueid.Id{ 239, 205, 227, 117, 20, 22, 199, 59, 24, 156, 232, 156, 204, 147, 128, 0, }, ParamType: __VDLType_list_7, }
AccessTagCaveat represents a caveat that validates iff the method being invoked has at least one of the tags listed in the caveat.
Functions ¶
func IsUnenforceablePatterns ¶
func IsUnenforceablePatterns(err error) []security.BlessingPattern
UnenforceablePatterns checks if the error has the identifier ErrUnenforceablePatterns.ID, and if so returns the set of unenforceable patterns encapsulated in it. It returns nil otherwise.
func NewAccessTagCaveat ¶
NewAccessTagCaveat returns a Caveat that will validate iff the intersection of the tags on the method being invoked and those in 'tags' is non-empty.
func NewErrAccessListMatch ¶
func NewErrAccessListMatch(ctx *context.T, validBlessings []string, rejectedBlessings []security.RejectedBlessing) error
NewErrAccessListMatch returns an error with the ErrAccessListMatch ID.
func NewErrAccessTagCaveatValidation ¶
NewErrAccessTagCaveatValidation returns an error with the ErrAccessTagCaveatValidation ID.
func NewErrInvalidOpenAccessList ¶
NewErrInvalidOpenAccessList returns an error with the ErrInvalidOpenAccessList ID.
func NewErrNoPermissions ¶
func NewErrNoPermissions(ctx *context.T, validBlessings []string, rejectedBlessings []security.RejectedBlessing, tag string) error
NewErrNoPermissions returns an error with the ErrNoPermissions ID.
func NewErrTooBig ¶
NewErrTooBig returns an error with the ErrTooBig ID.
func NewErrUnenforceablePatterns ¶
func NewErrUnenforceablePatterns(ctx *context.T, rejectedPatterns []security.BlessingPattern) error
NewErrUnenforceablePatterns returns an error with the ErrUnenforceablePatterns ID.
func PermissionsAuthorizer ¶
func PermissionsAuthorizer(perms Permissions, tagType *vdl.Type) (security.Authorizer, error)
PermissionsAuthorizer implements an authorization policy where access is granted if the remote end presents blessings included in the Access Control Lists (AccessLists) associated with the set of relevant tags.
The set of relevant tags is the subset of tags associated with the method (security.Call.MethodTags) that have the same type as tagType. Currently, tagType.Kind must be reflect.String, i.e., only tags that are named string types are supported.
PermissionsAuthorizer expects exactly one tag of tagType to be associated with the method. If there are multiple, it fails authorization and returns an error. However, if multiple tags become a common occurrence, then this behavior may change.
If the Permissions provided is nil, then a nil authorizer is returned.
Sample usage:
(1) Attach tags to methods in the VDL (eg. myservice.vdl)
package myservice type MyTag string const ( ReadAccess = MyTag("R") WriteAccess = MyTag("W") ) type MyService interface { Get() ([]string, error) {ReadAccess} GetIndex(int) (string, error) {ReadAccess} Set([]string) error {WriteAccess} SetIndex(int, string) error {WriteAccess} }
(2) Configure the rpc.Dispatcher to use the PermissionsAuthorizer
import ( "reflect" "v.io/v23/rpc" "v.io/v23/security" "v.io/v23/security/access" ) type dispatcher struct{} func (d dispatcher) Lookup(suffix, method) (rpc.Invoker, security.Authorizer, error) { perms := access.Permissions{ "R": access.AccessList{In: []security.BlessingPattern{"alice:friends", "alice:family"} }, "W": access.AccessList{In: []security.BlessingPattern{"alice:family", "alice:colleagues" } }, } typ := reflect.TypeOf(ReadAccess) // equivalently, reflect.TypeOf(WriteAccess) return newInvoker(), access.PermissionsAuthorizer(perms, typ), nil }
With the above dispatcher, the server will grant access to a peer with the blessing "alice:friend:bob" access only to the "Get" and "GetIndex" methods. A peer presenting the blessing "alice:colleague:carol" will get access only to the "Set" and "SetIndex" methods. A peer presenting "alice:family:mom" will get access to all methods.
func PermissionsAuthorizerFromFile ¶
PermissionsAuthorizerFromFile applies the same authorization policy as PermissionsAuthorizer, with the Permissions to be used sourced from a file named filename.
Changes to the file are monitored and affect subsequent calls to Authorize. Currently, this is achieved by re-reading the file on every call to Authorize. TODO(ashankar,ataly): Use inotify or a similar mechanism to watch for changes.
func TagStrings ¶
TagStrings converts access.Tag values into []string for use with methods on access.Permissions.
func TypicalTagType ¶
TypicalTagType returns the type of the predefined tags in this access package.
Typical use of this is to setup an Authorizer that uses these predefined tags:
authorizer, err := PermissionsAuthorizerFromFile(name, TypicalTagType())
For the common case of setting up an Authorizer for a Permissions object with these predefined tags, a convenience function is provided:
authorizer := TypicalTagTypePermissionsAuthorizer(myperms)
func TypicalTagTypePermissionsAuthorizer ¶
func TypicalTagTypePermissionsAuthorizer(perms Permissions) security.Authorizer
TypicalTagTypePermissionsAuthorizer is like PermissionsAuthorizer, but assumes TypicalTagType and thus avoids returning an error.
func WritePermissions ¶
func WritePermissions(w io.Writer, m Permissions) error
WritePermissions writes the JSON-encoded representation of a Permissions to w.
Types ¶
type AccessList ¶
type AccessList struct { // In denotes the set of blessings (represented as BlessingPatterns) that // should be granted access, unless blacklisted by an entry in NotIn. // // For example: // In: {"alice:family"} // grants access to a principal that presents at least one of // "alice:family", "alice:family:friend", "alice:family:friend:spouse" etc. // as a blessing. In []security.BlessingPattern // NotIn denotes the set of blessings (and their delegates) that // have been explicitly blacklisted from the In set. // // For example: // In: {"alice:friend"}, NotIn: {"alice:friend:bob"} // grants access to principals that present "alice:friend", // "alice:friend:carol" etc. but NOT to a principal that presents // "alice:friend:bob" or "alice:friend:bob:spouse" etc. NotIn []string }
AccessList represents a set of blessings that should be granted access.
See also: https://vanadium.github.io/glossary.html#access-list
func (AccessList) Authorize ¶
Authorize implements security.Authorizer where the request is authorized only if the remote blessings are included in the AccessList.
func (AccessList) Enforceable ¶
Enforceable checks if the AccessList is enforceable by the provided principal.
It returns nil if all blessing patterns in the 'In' list are valid and matched by a blessing name that is recognized by one of the provided principal's roots.
An error with identifier ErrOpenAccessList.ID is returned if the 'In' list contains the pattern "..." along with other patterns in the 'In' or 'NotIn' lists. Otherwise an error with identifier ErrUnenforceablePatterns.ID is returned.
func (AccessList) Includes ¶
func (acl AccessList) Includes(blessings ...string) bool
Includes returns true iff the AccessList grants access to a principal that presents blessings (i.e., if at least one of the blessings matches the AccessList).
func (AccessList) VDLIsZero ¶
func (x AccessList) VDLIsZero() bool
type Permissions ¶
type Permissions map[string]AccessList
Permissions maps string tags to access lists specifying the blessings required to invoke methods with that tag.
These tags are meant to add a layer of interposition between the set of users (blessings, specifically) and the set of methods, much like "Roles" do in Role Based Access Control. (http://en.wikipedia.org/wiki/Role-based_access_control)
func ReadPermissions ¶
func ReadPermissions(r io.Reader) (m Permissions, err error)
ReadPermissions reads the JSON-encoded representation of a Permissions from r.
func (Permissions) Add ¶
func (m Permissions) Add(pattern security.BlessingPattern, tags ...string) Permissions
Add updates m to so that blessings matching pattern will be included in the access lists for the provided tags (by adding to the "In" lists). It returns m.
func (Permissions) Blacklist ¶
func (m Permissions) Blacklist(blessing string, tags ...string) Permissions
Blacklist updates m so that the provided blessing will be excluded from the access lists for the provided tags (by adding to the "NotIn" lists). It returns m.
func (Permissions) Clear ¶
func (m Permissions) Clear(blessingOrPattern string, tags ...string) Permissions
Clear removes all references to blessingOrPattern from all the provided tags in the AccessList, or all tags if len(tags) = 0. It returns m.
func (Permissions) Copy ¶
func (m Permissions) Copy() Permissions
Copy returns a new Permissions that is a copy of m.
func (Permissions) Normalize ¶
func (m Permissions) Normalize() Permissions
Normalize re-organizes 'm' so that two equivalent Permissions are comparable via reflection. It returns 'm'.
func (Permissions) VDLIsZero ¶
func (x Permissions) VDLIsZero() bool
type Tag ¶
type Tag string
Tag is used to associate methods with an AccessList in a Permissions.
While services can define their own tag type and values, many services should be able to use the type and values defined in this package.
func AllTypicalTags ¶
func AllTypicalTags() []Tag
AllTypicalTags returns all access.Tag values defined in this package.