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minio/bucket-policy-parser.go

330 lines
10 KiB

/*
* Minio Cloud Storage, (C) 2015, 2016 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// This file implements AWS Access Policy Language parser in
// accordance with http://docs.aws.amazon.com/AmazonS3/latest/dev/access-policy-language-overview.html
package main
import (
"encoding/json"
"errors"
"fmt"
"path"
"sort"
"strings"
)
const (
// AWSResourcePrefix - bucket policy resource prefix.
AWSResourcePrefix = "arn:aws:s3:::"
)
// supportedActionMap - lists all the actions supported by minio.
var supportedActionMap = map[string]struct{}{
"*": {},
"s3:*": {},
"s3:GetObject": {},
"s3:ListBucket": {},
"s3:PutObject": {},
"s3:GetBucketLocation": {},
"s3:DeleteObject": {},
"s3:AbortMultipartUpload": {},
"s3:ListBucketMultipartUploads": {},
"s3:ListMultipartUploadParts": {},
}
// supported Conditions type.
var supportedConditionsType = map[string]struct{}{
"StringEquals": {},
"StringNotEquals": {},
}
// Validate s3:prefix, s3:max-keys are present if not
// supported keys for the conditions.
var supportedConditionsKey = map[string]struct{}{
"s3:prefix": {},
"s3:max-keys": {},
}
// User - canonical users list.
type policyUser struct {
AWS []string
}
// Statement - minio policy statement
type policyStatement struct {
Sid string
Effect string
Principal policyUser `json:"Principal"`
Actions []string `json:"Action"`
Resources []string `json:"Resource"`
Conditions map[string]map[string]string `json:"Condition"`
}
// BucketPolicy - minio policy collection
type BucketPolicy struct {
Version string // date in 0000-00-00 format
Statements []policyStatement `json:"Statement"`
}
// supportedEffectMap - supported effects.
var supportedEffectMap = map[string]struct{}{
"Allow": {},
"Deny": {},
}
// isValidActions - are actions valid.
func isValidActions(actions []string) (err error) {
// Statement actions cannot be empty.
if len(actions) == 0 {
err = errors.New("Action list cannot be empty.")
return err
}
for _, action := range actions {
if _, ok := supportedActionMap[action]; !ok {
err = errors.New("Unsupported action found: ‘" + action + "’, please validate your policy document.")
return err
}
}
return nil
}
// isValidEffect - is effect valid.
func isValidEffect(effect string) error {
// Statement effect cannot be empty.
if len(effect) == 0 {
err := errors.New("Policy effect cannot be empty.")
return err
}
_, ok := supportedEffectMap[effect]
if !ok {
err := errors.New("Unsupported Effect found: ‘" + effect + "’, please validate your policy document.")
return err
}
return nil
}
// isValidResources - are valid resources.
func isValidResources(resources []string) (err error) {
// Statement resources cannot be empty.
if len(resources) == 0 {
err = errors.New("Resource list cannot be empty.")
return err
}
for _, resource := range resources {
if !strings.HasPrefix(resource, AWSResourcePrefix) {
err = errors.New("Unsupported resource style found: ‘" + resource + "’, please validate your policy document.")
return err
}
resourceSuffix := strings.SplitAfter(resource, AWSResourcePrefix)[1]
if len(resourceSuffix) == 0 || strings.HasPrefix(resourceSuffix, "/") {
err = errors.New("Invalid resource style found: ‘" + resource + "’, please validate your policy document.")
return err
}
}
return nil
}
// isValidPrincipals - are valid principals.
func isValidPrincipals(principals []string) (err error) {
// Statement principal should have a value.
if len(principals) == 0 {
err = errors.New("Principal cannot be empty.")
return err
}
for _, principal := range principals {
// Minio does not support or implement IAM, "*" is the only valid value.
// Amazon s3 doc on principals: http://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements.html#Principal
if principal != "*" {
err = fmt.Errorf("Unsupported principal style found: ‘%s’, please validate your policy document.", principal)
return err
}
}
return nil
}
// isValidConditions - are valid conditions.
func isValidConditions(conditions map[string]map[string]string) (err error) {
// Returns true if string 'a' is found in the list.
findString := func(a string, list []string) bool {
for _, b := range list {
if b == a {
return true
}
}
return false
}
conditionKeyVal := make(map[string][]string)
// Verify conditions should be valid.
// Validate if stringEquals, stringNotEquals are present
// if not throw an error.
for conditionType := range conditions {
_, validType := supportedConditionsType[conditionType]
if !validType {
err = fmt.Errorf("Unsupported condition type '%s', please validate your policy document.", conditionType)
return err
}
for key := range conditions[conditionType] {
_, validKey := supportedConditionsKey[key]
if !validKey {
err = fmt.Errorf("Unsupported condition key '%s', please validate your policy document.", conditionType)
return err
}
conditionArray, ok := conditionKeyVal[key]
if ok && findString(conditions[conditionType][key], conditionArray) {
err = fmt.Errorf("Ambigious condition values for key '%s', please validate your policy document.", key)
return err
}
conditionKeyVal[key] = append(conditionKeyVal[key], conditions[conditionType][key])
}
}
return nil
}
// List of actions for which prefixes are not allowed.
var invalidPrefixActions = map[string]struct{}{
"s3:GetBucketLocation": {},
"s3:ListBucket": {},
"s3:ListBucketMultipartUploads": {},
// Add actions which do not honor prefixes.
}
// resourcePrefix - provides the prefix removing any wildcards.
func resourcePrefix(resource string) string {
if strings.HasSuffix(resource, "*") {
resource = strings.TrimSuffix(resource, "*")
}
return path.Clean(resource)
}
// checkBucketPolicyResources validates Resources in unmarshalled bucket policy structure.
// First valation of Resources done for given set of Actions.
// Later its validated for recursive Resources.
func checkBucketPolicyResources(bucket string, bucketPolicy BucketPolicy) APIErrorCode {
// Validate statements for special actions and collect resources
// for others to validate nesting.
var resourceMap = make(map[string]struct{})
for _, statement := range bucketPolicy.Statements {
for _, action := range statement.Actions {
for _, resource := range statement.Resources {
resourcePrefix := strings.SplitAfter(resource, AWSResourcePrefix)[1]
if _, ok := invalidPrefixActions[action]; ok {
// Resource prefix is not equal to bucket for
// prefix invalid actions, reject them.
if resourcePrefix != bucket {
return ErrMalformedPolicy
}
} else {
// For all other actions validate if resourcePrefix begins
// with bucket name, if not reject them.
if strings.Split(resourcePrefix, "/")[0] != bucket {
return ErrMalformedPolicy
}
// All valid resources collect them separately to verify nesting.
resourceMap[resourcePrefix] = struct{}{}
}
}
}
}
var resources []string
for resource := range resourceMap {
resources = append(resources, resourcePrefix(resource))
}
// Sort strings as shorter first.
sort.Strings(resources)
for len(resources) > 1 {
var resource string
resource, resources = resources[0], resources[1:]
// Loop through all resources, if one of them matches with
// previous shorter one, it means we have detected
// nesting. Reject such rules.
for _, otherResource := range resources {
// Common prefix reject such rules.
if strings.HasPrefix(otherResource, resource) {
return ErrPolicyNesting
}
}
}
// No errors found.
return ErrNone
}
// parseBucketPolicy - parses and validates if bucket policy is of
// proper JSON and follows allowed restrictions with policy standards.
func parseBucketPolicy(bucketPolicyBuf []byte) (policy BucketPolicy, err error) {
if err = json.Unmarshal(bucketPolicyBuf, &policy); err != nil {
return BucketPolicy{}, err
}
// Policy version cannot be empty.
if len(policy.Version) == 0 {
err = errors.New("Policy version cannot be empty.")
return BucketPolicy{}, err
}
// Policy statements cannot be empty.
if len(policy.Statements) == 0 {
err = errors.New("Policy statement cannot be empty.")
return BucketPolicy{}, err
}
// Loop through all policy statements and validate entries.
for _, statement := range policy.Statements {
// Statement effect should be valid.
if err := isValidEffect(statement.Effect); err != nil {
return BucketPolicy{}, err
}
// Statement principal should be supported format.
if err := isValidPrincipals(statement.Principal.AWS); err != nil {
return BucketPolicy{}, err
}
// Statement actions should be valid.
if err := isValidActions(statement.Actions); err != nil {
return BucketPolicy{}, err
}
// Statement resources should be valid.
if err := isValidResources(statement.Resources); err != nil {
return BucketPolicy{}, err
}
// Statement conditions should be valid.
if err := isValidConditions(statement.Conditions); err != nil {
return BucketPolicy{}, err
}
}
// Separate deny and allow statements, so that we can apply deny
// statements in the beginning followed by Allow statements.
var denyStatements []policyStatement
var allowStatements []policyStatement
for _, statement := range policy.Statements {
if statement.Effect == "Deny" {
denyStatements = append(denyStatements, statement)
continue
}
// else if statement.Effect == "Allow"
allowStatements = append(allowStatements, statement)
}
// Deny statements are enforced first once matched.
policy.Statements = append(denyStatements, allowStatements...)
// Return successfully parsed policy structure.
return policy, nil
}