Access Control Lists (ACLs)¶
Normally to create, read and modify containers and objects, you must have the appropriate roles on the project associated with the account, i.e., you must be the owner of the account. However, an owner can grant access to other users by using an Access Control List (ACL).
There are two types of ACLs:
Container ACLs. These are specified on a container and apply to that container only and the objects in the container.
Account ACLs. These are specified at the account level and apply to all containers and objects in the account.
Container ACLs¶
Container ACLs are stored in the X-Container-Write
and X-Container-Read
metadata. The scope of the ACL is limited to the container where the
metadata is set and the objects in the container. In addition:
X-Container-Write
grants the ability to perform PUT, POST and DELETE operations on objects within a container. It does not grant the ability to perform POST or DELETE operations on the container itself. Some ACL elements also grant the ability to perform HEAD or GET operations on the container.X-Container-Read
grants the ability to perform GET and HEAD operations on objects within a container. Some of the ACL elements also grant the ability to perform HEAD or GET operations on the container itself. However, a container ACL does not allow access to privileged metadata (such asX-Container-Sync-Key
).
Container ACLs use the “V1” ACL syntax which is a comma separated string of elements as shown in the following example:
.r:*,.rlistings,7ec59e87c6584c348b563254aae4c221:*
Spaces may occur between elements as shown in the following example:
.r : *, .rlistings, 7ec59e87c6584c348b563254aae4c221:*
However, these spaces are removed from the value stored in the
X-Container-Write
and X-Container-Read
metadata. In addition,
the .r:
string can be written as .referrer:
, but is stored as .r:
.
While all auth systems use the same syntax, the meaning of some elements is different because of the different concepts used by different auth systems as explained in the following sections:
Common ACL Elements¶
The following table describes elements of an ACL that are
supported by both Keystone auth and TempAuth. These elements
should only be used with X-Container-Read
(with the exception
of .rlistings
, an error will occur if used with
X-Container-Write
):
Element |
Description |
---|---|
|
Any user has access to objects. No token is required in the request. |
|
The referrer is granted access to objects. The
referrer is identified by the |
|
This syntax (with “-” prepended to the
referrer) is supported. However, it does not
deny access if another element (e.g., |
|
Any user can perform a HEAD or GET operation
on the container provided the user also has
read access on objects (e.g., also has |
Keystone Auth ACL Elements¶
The following table describes elements of an ACL that are supported only by Keystone auth. Keystone auth also supports the elements described in Common ACL Elements.
A token must be included in the request for any of these ACL elements to take effect.
Element |
Description |
---|---|
|
The specified user, provided a token
scoped to the project is included
in the request, is granted access.
Access to the container is also granted
when used in |
|
Any user with a role in the specified Keystone
project has access. A token scoped to the
project must be included in the request.
Access to the container is also granted
when used in |
|
The specified user has access. A token
for the user (scoped to any
project) must be included in the request.
Access to the container is also granted
when used in |
|
Any user has access.
Access to the container is also granted
when used in |
|
A user with the specified role name on the
project within which the container is stored is
granted access. A user token scoped to the
project must be included in the request. Access
to the container is also granted when used in
|
Note
Keystone project (tenant) or user names (i.e.,
<project-name>:<user-name
) must no longer be
used because with the introduction
of domains in Keystone, names are not globally unique. You should
use user and project ids instead.
For backwards compatibility, ACLs using names will be granted by
keystoneauth when it can be established that
the grantee project, the grantee user and the project being
accessed are either not yet in a domain (e.g. the X-Auth-Token
has
been obtained via the Keystone V2 API) or are all in the default domain
to which legacy accounts would have been migrated.
TempAuth ACL Elements¶
The following table describes elements of an ACL that are supported only by TempAuth. TempAuth auth also supports the elements described in Common ACL Elements.
Element |
Description |
---|---|
|
The named user is granted access. The wildcard (“*”) character is not supported. A token from the user must be included in the request. |
Container ACL Examples¶
Container ACLs may be set by including X-Container-Write
and/or
X-Container-Read
headers with a PUT or a POST request to the container URL.
The following examples use the swift
command line client which support
these headers being set via its --write-acl
and --read-acl
options.
Example: Public Container¶
The following allows anybody to list objects in the www
container and
download objects. The users do not need to include a token in
their request. This ACL is commonly referred to as making the
container “public”. It is useful when used with StaticWeb:
swift post www --read-acl ".r:*,.rlistings"
Example: Sharing a Container with Project Members¶
The following allows any member of the 77b8f82565f14814bece56e50c4c240f
project to upload and download objects or to list the contents
of the www
container. A token scoped to the 77b8f82565f14814bece56e50c4c240f
project must be included in the request:
swift post www --read-acl "77b8f82565f14814bece56e50c4c240f:*" \
--write-acl "77b8f82565f14814bece56e50c4c240f:*"
Example: Sharing a Container with Users having a specified Role¶
The following allows any user that has been assigned the
my_read_access_role
on the project within which the www
container is
stored to download objects or to list the contents of the www
container. A
user token scoped to the project must be included in the download or list
request:
swift post www --read-acl "my_read_access_role"
Example: Allowing a Referrer Domain to Download Objects¶
The following allows any request from
the example.com
domain to access an object in the container:
swift post www --read-acl ".r:.example.com"
However, the request from the user must contain the appropriate Referer header as shown in this example request:
curl -i $publicURL/www/document --head -H "Referer: http://www.example.com/index.html"
Note
The Referer header is included in requests by many browsers. However, since it is easy to create a request with any desired value in the Referer header, the referrer ACL has very weak security.
Example: Sharing a Container with Another User¶
Sharing a Container with another user requires the knowledge of few parameters regarding the users.
The sharing user must know:
the
OpenStack user id
of the other user
The sharing user must communicate to the other user:
the name of the shared container
the
OS_STORAGE_URL
Usually the OS_STORAGE_URL
is not exposed directly to the user
because the swift client
by default automatically construct the
OS_STORAGE_URL
based on the User credential.
We assume that in the current directory there are the two client
environment script for the two users sharing.openrc
and
other.openrc
.
The sharing.openrc
should be similar to the following:
export OS_USERNAME=sharing
# WARNING: Save the password in clear text only for testing purposes
export OS_PASSWORD=password
export OS_TENANT_NAME=projectName
export OS_AUTH_URL=https://identityHost:portNumber/v2.0
# The following lines can be omitted
export OS_TENANT_ID=tenantIDString
export OS_REGION_NAME=regionName
export OS_CACERT=/path/to/cacertFile
The other.openrc
should be similar to the following:
export OS_USERNAME=other
# WARNING: Save the password in clear text only for testing purposes
export OS_PASSWORD=otherPassword
export OS_TENANT_NAME=otherProjectName
export OS_AUTH_URL=https://identityHost:portNumber/v2.0
# The following lines can be omitted
export OS_TENANT_ID=tenantIDString
export OS_REGION_NAME=regionName
export OS_CACERT=/path/to/cacertFile
For more information see using the OpenStack RC file
First we figure out the other user id:
. other.openrc
OUID="$(openstack user show --format json "${OS_USERNAME}" | jq -r .id)"
or alternatively:
. other.openrc
OUID="$(openstack token issue -f json | jq -r .user_id)"
Then we figure out the storage url of the sharing user:
sharing.openrc
SURL="$(swift auth | awk -F = '/OS_STORAGE_URL/ {print $2}')"
Running as the sharing user create a shared container named shared
in read-only mode with the other user using the proper acl:
sharing.openrc
swift post --read-acl "*:${OUID}" shared
Running as the sharing user create and upload a test file:
touch void
swift upload shared void
Running as the other user list the files in the shared
container:
other.openrc
swift --os-storage-url="${SURL}" list shared
Running as the other user download the shared
container in the
/tmp
directory:
cd /tmp
swift --os-storage-url="${SURL}" download shared
Account ACLs¶
Note
Account ACLs are not currently supported by Keystone auth
The X-Account-Access-Control
header is used to specify
account-level ACLs in a format specific to the auth system.
These headers are visible and settable only by account owners (those for whom
swift_owner
is true).
Behavior of account ACLs is auth-system-dependent. In the case of TempAuth,
if an authenticated user has membership in a group which is listed in the
ACL, then the user is allowed the access level of that ACL.
Account ACLs use the “V2” ACL syntax, which is a JSON dictionary with keys
named “admin”, “read-write”, and “read-only”. (Note the case sensitivity.)
An example value for the X-Account-Access-Control
header looks like this,
where a
, b
and c
are user names:
{"admin":["a","b"],"read-only":["c"]}
Keys may be absent (as shown in above example).
The recommended way to generate ACL strings is as follows:
from swift.common.middleware.acl import format_acl
acl_data = { 'admin': ['alice'], 'read-write': ['bob', 'carol'] }
acl_string = format_acl(version=2, acl_dict=acl_data)
Using the format_acl()
method will ensure
that JSON is encoded as ASCII (using e.g. ‘u1234’ for Unicode). While
it’s permissible to manually send curl
commands containing
X-Account-Access-Control
headers, you should exercise caution when
doing so, due to the potential for human error.
Within the JSON dictionary stored in X-Account-Access-Control
, the keys
have the following meanings:
Access Level |
Description |
---|---|
read-only |
These identities can read everything (except privileged headers) in the account. Specifically, a user with read-only account access can get a list of containers in the account, list the contents of any container, retrieve any object, and see the (non-privileged) headers of the account, any container, or any object. |
read-write |
These identities can read or write (or create) any container. A user with read-write account access can create new containers, set any unprivileged container headers, overwrite objects, delete containers, etc. A read-write user can NOT set account headers (or perform any PUT/POST/DELETE requests on the account). |
admin |
These identities have “swift_owner” privileges. A user with admin account access can do anything the account owner can, including setting account headers and any privileged headers – and thus granting read-only, read-write, or admin access to other users. |
For more details, see swift.common.middleware.tempauth
. For details
on the ACL format, see swift.common.middleware.acl
.