v.io: v.io/v23/security/access Index | Files | Directories

package access

import "v.io/v23/security/access"

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.


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.


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.


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 errors.Is(err, verror.ErrBadVersion) {
      // Another client replaced the Permissions after our GetPermissions
      // returned. Try again.
    return err



Package Files

access.vdl.go acl.go authorizer.go caveat.go tags.go


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.


var (
    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, "" /* 134 byte string literal not displayed */)
    ErrMultipleTags              = verror.Register("v.io/v23/security/access.MultipleTags", verror.NoRetry, "{1:}{2:} authorizer on {3}.{4} cannot handle multiple tags of type {5}; this is likely unintentional")
    ErrNoTags                    = verror.Register("v.io/v23/security/access.NoTags", verror.NoRetry, "{1:}{2:} authorizer on {3}.{4} has no tags of type {5}; this is likely unintentional")
var AccessTagCaveat = security.CaveatDescriptor{
    Id: uniqueid.Id{
    ParamType: vdl.TypeOf((*[]Tag)(nil)),

AccessTagCaveat represents a caveat that validates iff the method being invoked has at least one of the tags listed in the caveat.

func AuthorizerFromSpec Uses

func AuthorizerFromSpec(ps PermissionsSpec, name string, tagType *vdl.Type) (security.Authorizer, error)

AuthorizerFromSpec creates an authorizer as specified by the supplied specification. If no permissions are specified then the default, (ie. nil) Authorizer is returned.

func IsUnenforceablePatterns Uses

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 Uses

func NewAccessTagCaveat(tags ...Tag) (security.Caveat, error)

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 Uses

func NewErrAccessListMatch(ctx *context.T, validBlessings []string, rejectedBlessings []security.RejectedBlessing) error

NewErrAccessListMatch returns an error with the ErrAccessListMatch ID.

func NewErrAccessTagCaveatValidation Uses

func NewErrAccessTagCaveatValidation(ctx *context.T, methodTags []string, caveatTags []Tag) error

NewErrAccessTagCaveatValidation returns an error with the ErrAccessTagCaveatValidation ID.

func NewErrInvalidOpenAccessList Uses

func NewErrInvalidOpenAccessList(ctx *context.T) error

NewErrInvalidOpenAccessList returns an error with the ErrInvalidOpenAccessList ID.

func NewErrMultipleTags Uses

func NewErrMultipleTags(ctx *context.T, suffix string, method string, tag string) error

NewErrMultipleTags returns an error with the ErrMultipleTags ID.

func NewErrNoPermissions Uses

func NewErrNoPermissions(ctx *context.T, validBlessings []string, rejectedBlessings []security.RejectedBlessing, tag string) error

NewErrNoPermissions returns an error with the ErrNoPermissions ID.

func NewErrNoTags Uses

func NewErrNoTags(ctx *context.T, suffix string, method string, tag string) error

NewErrNoTags returns an error with the ErrNoTags ID.

func NewErrTooBig Uses

func NewErrTooBig(ctx *context.T) error

NewErrTooBig returns an error with the ErrTooBig ID.

func NewErrUnenforceablePatterns Uses

func NewErrUnenforceablePatterns(ctx *context.T, rejectedPatterns []security.BlessingPattern) error

NewErrUnenforceablePatterns returns an error with the ErrUnenforceablePatterns ID.

func PermissionsAuthorizer Uses

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 (


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 Uses

func PermissionsAuthorizerFromFile(filename string, tagType *vdl.Type) (security.Authorizer, error)

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 Uses

func TagStrings(tags ...Tag) []string

TagStrings converts access.Tag values into []string for use with methods on access.Permissions.

func TypicalTagType Uses

func TypicalTagType() *vdl.Type

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 Uses

func TypicalTagTypePermissionsAuthorizer(perms Permissions) security.Authorizer

TypicalTagTypePermissionsAuthorizer is like PermissionsAuthorizer, but assumes TypicalTagType and thus avoids returning an error.

func WritePermissions Uses

func WritePermissions(w io.Writer, m Permissions) error

WritePermissions writes the JSON-encoded representation of a Permissions to w.

type AccessList Uses

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 Uses

func (acl AccessList) Authorize(ctx *context.T, call security.Call) error

Authorize implements security.Authorizer where the request is authorized only if the remote blessings are included in the AccessList.

func (AccessList) Enforceable Uses

func (acl AccessList) Enforceable(ctx *context.T, p security.Principal) error

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 Uses

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 Uses

func (x AccessList) VDLIsZero() bool

func (*AccessList) VDLRead Uses

func (x *AccessList) VDLRead(dec vdl.Decoder) error

func (AccessList) VDLReflect Uses

func (AccessList) VDLReflect(struct {
    Name string `vdl:"v.io/v23/security/access.AccessList"`

func (AccessList) VDLWrite Uses

func (x AccessList) VDLWrite(enc vdl.Encoder) error

type Permissions Uses

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 Uses

func ReadPermissions(r io.Reader) (m Permissions, err error)

ReadPermissions reads the JSON-encoded representation of a Permissions from r.

func (Permissions) Add Uses

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 Uses

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 Uses

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 Uses

func (m Permissions) Copy() Permissions

Copy returns a new Permissions that is a copy of m.

func (Permissions) Normalize Uses

func (m Permissions) Normalize() Permissions

Normalize re-organizes 'm' so that two equivalent Permissions are comparable via reflection. It returns 'm'.

func (Permissions) VDLIsZero Uses

func (x Permissions) VDLIsZero() bool

func (*Permissions) VDLRead Uses

func (x *Permissions) VDLRead(dec vdl.Decoder) error

func (Permissions) VDLReflect Uses

func (Permissions) VDLReflect(struct {
    Name string `vdl:"v.io/v23/security/access.Permissions"`

func (Permissions) VDLWrite Uses

func (x Permissions) VDLWrite(enc vdl.Encoder) error

type PermissionsSpec Uses

type PermissionsSpec struct {
    // ExplicitlySpecified is true if any part of the specification was obtained
    // from an explicitly specified command line flag.
    ExplicitlySpecified bool
    // Files represents a set of named files that contain permissions.
    // The name 'runtime' is reserved for use by the runtime.
    Files map[string]string
    // Literal represents a literal, ie. json, permissions specification.
    Literal string

PermissionsSpec represents a specification for permissions derived from command line flags or some other means.

func (*PermissionsSpec) Copy Uses

func (ps *PermissionsSpec) Copy() PermissionsSpec

Copy returns a copy of the PermissionSpec.

type Tag Uses

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 Uses

func AllTypicalTags() []Tag

AllTypicalTags returns all access.Tag values defined in this package.

func (Tag) VDLIsZero Uses

func (x Tag) VDLIsZero() bool

func (*Tag) VDLRead Uses

func (x *Tag) VDLRead(dec vdl.Decoder) error

func (Tag) VDLReflect Uses

func (Tag) VDLReflect(struct {
    Name string `vdl:"v.io/v23/security/access.Tag"`

func (Tag) VDLWrite Uses

func (x Tag) VDLWrite(enc vdl.Encoder) error


internalPackage internal provides a VDL specification for a service used in the unittest of the access package.

Package access imports 14 packages (graph) and is imported by 132 packages. Updated 2020-09-27. Refresh now. Tools for package owners.