/*
* Minio Cloud Storage, (C) 2015, 2016, 2017 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.
*/
package cmd
import (
"encoding/json"
"errors"
"fmt"
"net/http"
"reflect"
"strconv"
"strings"
"time"
)
// startWithConds - map which indicates if a given condition supports starts-with policy operator
var startsWithConds = map[string]bool{
"$acl": true,
"$bucket": false,
"$cache-control": true,
"$content-type": true,
"$content-disposition": true,
"$content-encoding": true,
"$expires": true,
"$key": true,
"$success_action_redirect": true,
"$redirect": true,
"$success_action_status": false,
"$x-amz-algorithm": false,
"$x-amz-credential": false,
"$x-amz-date": false,
}
// Add policy conditionals.
const (
policyCondEqual = "eq"
policyCondStartsWith = "starts-with"
policyCondContentLength = "content-length-range"
)
// toString - Safely convert interface to string without causing panic.
func toString(val interface{}) string {
switch v := val.(type) {
case string:
return v
}
return ""
}
// toLowerString - safely convert interface to lower string
func toLowerString(val interface{}) string {
return strings.ToLower(toString(val))
}
// toInteger _ Safely convert interface to integer without causing panic.
func toInteger(val interface{}) (int64, error) {
switch v := val.(type) {
case float64:
return int64(v), nil
case int64:
return v, nil
case int:
return int64(v), nil
case string:
i, err := strconv.Atoi(v)
return int64(i), err
}
return 0, errors.New("Invalid number format")
}
// isString - Safely check if val is of type string without causing panic.
func isString(val interface{}) bool {
switch val.(type) {
case string:
return true
}
return false
}
// ContentLengthRange - policy content-length-range field.
type contentLengthRange struct {
Min int64
Max int64
Valid bool // If content-length-range was part of policy
}
// PostPolicyForm provides strict static type conversion and validation for Amazon S3's POST policy JSON string.
type PostPolicyForm struct {
Expiration time.Time // Expiration date and time of the POST policy.
Conditions struct { // Conditional policy structure.
Policies map[string]struct {
Operator string
Value string
}
ContentLengthRange contentLengthRange
}
}
// parsePostPolicyForm - Parse JSON policy string into typed POostPolicyForm structure.
func parsePostPolicyForm(policy string) (PostPolicyForm, error) {
// Convert po into interfaces and
// perform strict type conversion using reflection.
var rawPolicy struct {
Expiration string `json:"expiration"`
Conditions []interface{} `json:"conditions"`
}
err := json.Unmarshal([]byte(policy), &rawPolicy)
if err != nil {
return PostPolicyForm{}, err
}
parsedPolicy := PostPolicyForm{}
// Parse expiry time.
parsedPolicy.Expiration, err = time.Parse(time.RFC3339Nano, rawPolicy.Expiration)
if err != nil {
return PostPolicyForm{}, err
}
parsedPolicy.Conditions.Policies = make(map[string]struct {
Operator string
Value string
})
// Parse conditions.
for _, val := range rawPolicy.Conditions {
switch condt := val.(type) {
case map[string]interface{}: // Handle key:value map types.
for k, v := range condt {
if !isString(v) { // Pre-check value type.
// All values must be of type string.
return parsedPolicy, fmt.Errorf("Unknown type %s of conditional field value %s found in POST policy form", reflect.TypeOf(condt).String(), condt)
}
// {"acl": "public-read" } is an alternate way to indicate - [ "eq", "$acl", "public-read" ]
// In this case we will just collapse this into "eq" for all use cases.
parsedPolicy.Conditions.Policies["$"+strings.ToLower(k)] = struct {
Operator string
Value string
}{
Operator: policyCondEqual,
Value: toString(v),
}
}
case []interface{}: // Handle array types.
if len(condt) != 3 { // Return error if we have insufficient elements.
return parsedPolicy, fmt.Errorf("Malformed conditional fields %s of type %s found in POST policy form", condt, reflect.TypeOf(condt).String())
}
switch toLowerString(condt[0]) {
case policyCondEqual, policyCondStartsWith:
for _, v := range condt { // Pre-check all values for type.
if !isString(v) {
// All values must be of type string.
return parsedPolicy, fmt.Errorf("Unknown type %s of conditional field value %s found in POST policy form", reflect.TypeOf(condt).String(), condt)
}
}
operator, matchType, value := toLowerString(condt[0]), toLowerString(condt[1]), toString(condt[2])
parsedPolicy.Conditions.Policies[matchType] = struct {
Operator string
Value string
}{
Operator: operator,
Value: value,
}
case policyCondContentLength:
min, err := toInteger(condt[1])
if err != nil {
return parsedPolicy, err
}
max, err := toInteger(condt[2])
if err != nil {
return parsedPolicy, err
}
parsedPolicy.Conditions.ContentLengthRange = contentLengthRange{
Min: min,
Max: max,
Valid: true,
}
default:
// Condition should be valid.
return parsedPolicy, fmt.Errorf("Unknown type %s of conditional field value %s found in POST policy form",
reflect.TypeOf(condt).String(), condt)
}
default:
return parsedPolicy, fmt.Errorf("Unknown field %s of type %s found in POST policy form",
condt, reflect.TypeOf(condt).String())
}
}
return parsedPolicy, nil
}
// checkPolicyCond returns a boolean to indicate if a condition is satisified according
// to the passed operator
func checkPolicyCond(op string, input1, input2 string) bool {
switch op {
case policyCondEqual:
return input1 == input2
case policyCondStartsWith:
return strings.HasPrefix(input1, input2)
}
return false
}
// checkPostPolicy - apply policy conditions and validate input values.
// (http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-HTTPPOSTConstructPolicy.html)
func checkPostPolicy(formValues http.Header, postPolicyForm PostPolicyForm) APIErrorCode {
// Check if policy document expiry date is still not reached
if !postPolicyForm.Expiration.After(UTCNow()) {
return ErrPolicyAlreadyExpired
}
// Flag to indicate if all policies conditions are satisfied
condPassed := true
// Iterate over policy conditions and check them against received form fields
for cond, v := range postPolicyForm.Conditions.Policies {
// Form fields names are in canonical format, convert conditions names
// to canonical for simplification purpose, so `$key` will become `Key`
formCanonicalName := http.CanonicalHeaderKey(strings.TrimPrefix(cond, "$"))
// Operator for the current policy condition
op := v.Operator
// If the current policy condition is known
if startsWithSupported, condFound := startsWithConds[cond]; condFound {
// Check if the current condition supports starts-with operator
if op == policyCondStartsWith && !startsWithSupported {
return ErrAccessDenied
}
// Check if current policy condition is satisfied
condPassed = checkPolicyCond(op, formValues.Get(formCanonicalName), v.Value)
} else {
// This covers all conditions X-Amz-Meta-* and X-Amz-*
if strings.HasPrefix(cond, "$x-amz-meta-") || strings.HasPrefix(cond, "$x-amz-") {
// Check if policy condition is satisfied
condPassed = checkPolicyCond(op, formValues.Get(formCanonicalName), v.Value)
}
}
// Check if current policy condition is satisfied, quit immediately otherwise
if !condPassed {
return ErrAccessDenied
}
}
return ErrNone
}