Bucket Policy¶

Bucket policies provide centralized, access control to buckets and objects based on a variety of conditions, including OBS operations, requesters, resources, and aspects of the request (e.g., IP address). The permissions attached to a bucket apply to all of the objects in that bucket.

Individuals as well as companies can use bucket policies. When companies register with OBS they create an account. Thereafter, the company becomes synonymous with the account. Accounts are financially responsible for the resources they (and their employees) create. Accounts have the power to grant bucket policy permissions and assign employees permissions based on a variety of conditions. For example, an account could create a policy that gives a user write access:

To a particular bucket

From an account's corporate network

From an account's custom application

Unlike access control lists (ACL), which can add (grant) permissions only on individual objects, policies can either add or deny permissions across all (or a subset) of objects within a bucket. With one request an account can set the permissions of any number of objects in a bucket. An account can use wildcards (similar to regular expression operators) on Amazon resource names (ARNs) and other values, so that an account can control access to groups of objects.

A bucket owner can perform the PUT Bucket policy operation to set a bucket access policy. However, a new policy will overwrite the existing one. A bucket owner can also perform the Get Bucket policy or DELETE Bucket policy operation to obtain or delete a bucket policy. After a policy is set for a bucket, all subsequent access to the bucket is controlled by the policy. Requests for accessing the bucket are accepted or denied according to the policy.

In the following example bucket policy, accounts 783fc6652cf246c096ea836694f71855 (Domain ID) and 219d520ceac84c5a98b237431a2cf4c2 (Domain ID) are granted the GetObject permission for all objects in mybucket.

{
   "Version":"2008-10-17",
   "Id":"aaaa-bbbb-cccc-dddd",
   "Statement" : [
      {
       "Effect":"Allow",
       "Sid":"1",
       "Principal" : {
         "AWS":["arn:aws:iam::783fc6652cf246c096ea836694f71855:root","arn:aws:iam::219d520ceac84c5a98b237431a2cf4c2:root"]
       },
       "Action":["s3:GetObject"],
       "Resource":"arn:aws:s3:::mybucket/*"
      }
   ]
 }

Policy Format¶

A policy is described in the JSON format, as shown in the following syntax:

{
 "Version" : "version",
 "Id" : "id",
 "Statement" : [statement]
 }

The Id and Version parameters are optional.

**Table 1** Policy¶
Element	Description	Required
Id	Indicates the ID of a policy. The value is a string that describes the policy.	No
Version	Possible values are 2008-10-17.	No

A policy can contain multiple statements and each statement contains the following elements:

**Table 2** statement elements¶
Element	Description	Required
Sid	Indicates the ID of a statement. The value is a string that describes the statement.	No
Principal	Indicates the grantee of a statement. The value can be a wildcard character (``) that indicates all users. When the grantee is a domain, Principal* is in the AWS:domainid, AWS:arn:aws:iam::domainid:root, or CanonicalUser: format. When the grantee is a user, Principal is in the AWS:arn:aws:iam::domainid:user/userId or AWS:arn:aws:iam::domainid:user/userName format. A statement grantee can specify whether the statement grantors are agency users or federated users. For agency users, the principal format is AWS:arn:aws:iam::domainid:agency/agencyName. For federated users, the principal format is Federated:arn:aws:iam::domainid:identity-provider/providername or Federated:arn:aws:iam::domainid:group/groupname.	No, Choose either Principal or NotPrincipal
NotPrincipal	Specifies an exception to a list of principals in the statement. You can deny access to all principals except the one named in the NotPrincipal element. The value of this element is similar to that of Principal.	No, Choose either Principal or NotPrincipal
Action	Specifies operations that a grantee can perform. The value is a case-insensitive string consisting of a set of operations supported by OBS. The value can be a wildcard character (``) that indicates all operations. Example: "Action":["s3:List", "s3:Get*"]	No, Choose either Action or NotAction
NotAction	Specifies an exception to a list of actions in the statement. All actions are performed except the one specified in NotAction. The value of this element is similar to Action.	No, Choose either Action or NotAction
Effect	Indicates whether permission in a statement is allowed or denied. The value is Allow or Deny.	Yes
Resource	Specifies resources that the statement covers. A resource is defined in the Amazon Resource Name (ARN) format. You can use a wildcard character (`*`) to represent all resources.	No, Choose either Resource or NotResource
NotResource	Specifies an exception to a list of resources in the statement. A policy is not applied to resources specified in NotResource. The value of this parameter is similar to that of Resource.	No, Choose either Resource or NotResource
Condition	Indicates the conditions for a statement to take effect.	No

Note

A statement contains either:

Action or NotAction
Resource or NotResource
Principal or NotPrincipal

In OBS, Action can be the following operations on buckets:

s3:DeleteBucket
s3:ListBucket
s3:ListBucketVersions
s3:ListBucketMultipartUploads
s3:GetBucketAcl
s3:PutBucketAcl
s3:GetBucketCORS
s3:PutBucketCORS
s3:GetBucketVersioning
s3:PutBucketVersioning
s3:GetBucketLocation
s3:GetBucketLogging
s3:PutBucketLogging
s3:GetBucketWebsite
s3:PutBucketWebsite
s3:DeleteBucketWebsite
s3:GetLifecycleConfiguration
s3:PutLifecycleConfiguration
s3:GetBucketNotification
s3:PutBucketNotification
s3:PutBucketPolicy
s3:GetBucketPolicy
s3:DeleteBucketPolicy
s3:PutBucketQuota
s3:GetBucketQuota
s3:PutBucketStoragePolicy
s3:GetBucketStoragePolicy
s3:GetBucketStorage
s3:PutBucketTagging
s3:GetBucketTagging
s3:PutBucketObjectLockConfiguration
s3:GetBucketObjectLockConfiguration

In OBS, Action can be the following operations on objects:

s3:GetObject (applies to GET Object and HEAD Object)
s3:GetObjectVersion
s3:PutObject (applies to PUT Object, POST Object, Initiate Multipart Upload, Upload Part, and Complete Multipart Upload)
s3:GetObjectAcl
s3:GetObjectVersionAcl
s3:PutObjectAcl
s3:PutObjectVersionAcl
s3:DeleteObject
s3:DeleteObjectVersion
s3:ListMultipartUploadParts
s3:AbortMultipartUpload
s3:RestoreObject
s3:PutObjectRetention

OBS supports S3 resources in the ARN format:

arn:aws:s3:::bucketname (operations on buckets)
arn:aws:s3:::bucketname/path/objectname (operations on objects)

The following policy grants all permissions (including bucket and object operations) for bucket examplebucket to 71f3901173514e6988115ea2c26d1999 (user ID) in b4bf1b36d9ca43d984fbcb9491b6fce9 (domain ID).

{
    "Statement":[
    {
      "Sid":"test",
      "Effect":"Allow",
      "Principal": {"AWS": ["arn:aws:iam::b4bf1b36d9ca43d984fbcb9491b6fce9:user/71f3901173514e6988115ea2c26d1999"]},
      "Action":["s3:*"],
      "Resource":[
        "arn:aws:s3:::examplebucket/*",
        "arn:aws:s3:::examplebucket"
      ]
    }
  ]
}

{
    "Statement":[
    {
      "Sid":"test",
      "Effect":"Allow",
      "Principal": {"AWS": ["arn:aws:iam::b4bf1b36d9ca43d984fbcb9491b6fce9:user/user1"]},
      "Action":["s3:*"],
      "Resource":[
        "arn:aws:s3:::examplebucket/*",
        "arn:aws:s3:::examplebucket"
      ]
    }
  ]
}

Note

If you do not specify a path when uploading an object, omit /path in the ARN.

Table 3 lists the general types of Condition that you can specify.

**Table 3** Condition¶
Type	Element	Description
String	StringEquals	Strict matching Short version: streq
	StringNotEquals	Strict negated matching Short version: strneq
	StringEqualsIgnoreCase	Strict matching, ignoring case Short version: streqi
	StringNotEqualsIgnoreCase	Strict negated matching, ignoring case Short version: strneqi
	StringLike	Loose case-insensitive matching. The values can include a multi-character match wildcard (`*`) or a single-character match wildcard (?) anywhere in the string. Short version: strl
	StringNotLike	Negated loose case-insensitive matching. The values can include a multi-character match wildcard (`*`) or a single-character match wildcard (?) anywhere in the string. Short version: strnl
Numeric	NumericEquals	Strict matching Short version: numeq
	NumericNotEquals	Strict negated matching Short version: numneq
	NumericLessThan	"Less than" matching Short version: numlt
	NumericLessThanEquals	"Less than or equals" matching Short version: numlteq
	NumericGreaterThan	"Greater than" matching Short version: numgt
	NumericGreaterThanEquals	"Greater than or equals" matching Short version: numgteq
Date	DateEquals	Strict matching Short version: dateeq
	DateNotEquals	Strict negated matching Short version: dateneq
	DateLessThan	A point in time at which a key stops taking effect Short version: datelt
	DateLessThanEquals	A point in time at which a key stops taking effect Short version: datelteq
	DateGreaterThan	A point in time at which a key starts to take effect Short version: dategt
	DateGreaterThanEquals	A point in time at which a key starts to take effect Short version: dategteq
Boolean	Bool	Strict Boolean matching
IP address	IpAddress	Approved based on the IP address or range
	NotIpAddress	Denial based on the IP address or range

Note

Elements in Condition are case-sensitive. Date conditions must be in the ISO 8601 format. For details, see http://www.w3.org/TR/NOTE-datetime.

A Condition block (element) can contain multiple key value pairs. The following example Condition block specifies requests initiated between 2009-04-16T12:00:00Z and 2009-04-16T15:00:00Z from IP addresses on network segment 192.168.176.0/24 or 192.168.143.0/24:

"Condition" : {
    "DateGreaterThan": {
        "aws:CurrentTime" : "2009-04-16T12:00:00Z"
    },
    "DateLessThan": {
        "aws:CurrentTime" : "2009-04-16T15:00:00Z"
    },
    "IpAddress": {
        "aws:SourceIp" : ["192.168.176.0/24", "192.168.143.0/24"]
    }
 }

A Condition block can contain two types of keys:

General keys that have nothing to do with Action.
S3 service-specific keys associated with Action.

Table 4 lists the general keys.

**Table 4** Common Condition Key¶
Condition Key	Condition Type
aws:CurrentTime	Date
aws:EpochTime	Numeric
aws:SecureTransport	Boolean
aws:SourceIp	IP address
aws:UserAgent	String
aws:Referer	String

Table 5 lists the OBS service-specific keys.

**Table 5** OBS Action Condition Key¶
Action	Key	Description
s3:CreateBucket	s3:x-amz-acl	x-amz-acl can contain the canned ACL. Valid values: private\| public-read\| public-read-write\|authenticated-read\|bucket-owner-read\|bucket-owner-full-control\|log-delivery-write
	s3:x-amz-grant-permission	Not supported
	s3:LocationConstraint	Not supported
s3:ListBucket	s3:prefix	String
	s3:delimiter	String
	s3:max-keys	Numeric
s3:ListBucketVersions	s3:prefix	String
	s3:delimiter	String
	s3:max-keys	Numeric
s3:PutBucketAcl	s3:x-amz-acl	x-amz-acl can contain the canned ACL. Valid values: private\| public-read\| public-read-write\|authenticated-read\|bucket-owner-read\|bucket-owner-full-control\|log-delivery-write
	s3:x-amz-grant-permission	Not supported
s3:PutObject	s3:x-amz-acl	x-amz-acl can contain the canned ACL. Valid values: private\| public-read\| public-read-write\|authenticated-read\|bucket-owner-read\|bucket-owner-full-control\|log-delivery-write
	s3:x-amz-copy-source	String Example format: /bucketname/keyname
	s3:x-amz-metadata-di rective	Valid values: COPY\| REPLACE
	s3:x-amz-grant-permission	Not supported
	s3:x-amz-storage-class	Not supported
s3:PutObjectAcl	s3:x-amz-acl	x-amz-acl can contain the canned ACL. Valid values: private\| public-read\| public-read-write\|authenticated-read\|bucket-owner-read\|bucket-owner-full-control\|log-delivery-write
	s3:x-amz-grant-permission	Not supported
s3:GetObjectVersion	s3:VersionId	String
s3:GetObjectVersionAcl	s3:VersionId	String
s3:PutObjectVersionAcl	s3:VersionId	String
	s3:x-amz-acl	x-amz-acl can contain the canned ACL. Valid values: private\| public-read\| public-read-write\|authenticated-read\|bucket-owner-read\|bucket-owner-full-control\|log-delivery-write
	s3:x-amz-grant-permission	Not supported
s3:DeleteObjectVersion	s3:VersionId	String
s3:* (Actions or any of the S3 Actions)	s3:signatureversion	Not supported
	s3:authType	Not supported
	s3:signatureAge	Not supported
	s3:x-amz-content-sha256	Not supported

Policy Permission Judgment Logic¶

A policy results in a default deny if conditions in any statement of the policy are not met. If all conditions in statements are met, the policy results in either an allow or an explicit deny. If a bucket policy contains multiple statements, the policy determines which statement prevails according to the following rules:

If conditions in any statement of a policy are not met, the policy results in a default deny.
An explicit deny overrides allows.
An allow overrides default denies.
Statements can be in any order in a policy.

**Table 6** Statement results¶
Name	Description
explicit deny	A statement defines effect="deny". All requests for resources to which the statement applies are denied. No permission is returned.
allow	A statement defines effect="allow". All requests for resources to which the statement applies are allowed.
default deny	Conditions defined in a statement are not met. Requests are denied.

URL Validation Settings¶

OBS is charged based on the services that you use. To prevent user data from being stolen, OBS supports URL validation based on HTTP headers. OBS also supports both whitelist and blacklist settings.

Whitelist settings

Users can set a whitelist to allow requests from the websites added in the whitelist and deny requests from any other website.

For the requests that are initialized from browsers' address boxes, that is, those HTTP requests with a blank referer, users can add the ${null} field to "aws:Referer" of Condition to specify whether to allow the requests with a blank referer.

Set a whitelist based on the following policy setting:

"Statement": [
    {"Sid": "1",
     "Effect": "Allow",
     "Principal": {"CanonicalUser":["*"]},
     "Action": "s3:*",
     "Resource":["arn:aws:s3:::bucket/*"],
    },
    {"Sid": "2",
     "Effect": "Deny",
     "Principal":{"CanonicalUser":["*"]},
     "Action": ["s3:*"],
     "Resource": ["arn:aws:s3:::bucket/*"],
     "Condition":{
         "StringNotEquals":{
              "aws:Referer": ["www.example01.com","${null}"]
             }
         }
     }
]

If you set a whitelist in this way, you can perform operations on resources in buckets only when the value of the referer parameter is www.example01.com or is blank.

Blacklist settings

You can refer to the following policy settings to set a blacklist for access.

"Statement": [
    {"Sid":"1",
     "Effect":"Deny",
     "Principal":{"CanonicalUser":["*"]},
     "Action":["s3: *"],
     "Resource":["arn:aws:s3:::bucket/*"],
     "Condition":{
         "StringEquals":{
             "aws:Referer":["www.example01.com", "www.example02.com"]
             }
         }
     }
 ]

If you set a blacklist in this way, you cannot perform operations on resources in buckets when the value of the referer parameter is www.example01.com or www.example02.com.

last updated: 2024-11-14 08:51 UTC - commit: c2bf2e27e452e727da999792ea626796d0094467