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Add option 'elide_list_responses' to audit backends (#18128) 

This PR relates to a feature request logged through HashiCorp commercial
support.

Vault lacks pagination in its APIs. As a result, certain list operations
can return **very** large responses.  The user's chosen audit sinks may
experience difficulty consuming audit records that swell to tens of
megabytes of JSON.

In our case, one of the systems consuming audit log data could not cope,
and failed.

The responses of list operations are typically not very interesting, as
they are mostly lists of keys, or, even when they include a "key_info"
field, are not returning confidential information. They become even less
interesting once HMAC-ed by the audit system.

Some example Vault "list" operations that are prone to becoming very
large in an active Vault installation are:

    auth/token/accessors/
    identity/entity/id/
    identity/entity-alias/id/
    pki/certs/

In response, I've coded a new option that can be applied to audit
backends, `elide_list_responses`. When enabled, response data is elided
from audit logs, only when the operation type is "list".

For added safety, the elision only applies to the "keys" and "key_info"
fields within the response data - these are conventionally the only
fields present in a list response - see logical.ListResponse, and
logical.ListResponseWithInfo. However, other fields are technically
possible if a plugin author writes unusual code, and these will be
preserved in the audit log even with this option enabled.

The elision replaces the values of the "keys" and "key_info" fields with
an integer count of the number of entries. This allows even the elided
audit logs to still be useful for answering questions like "Was any data
returned?" or "How many records were listed?".
This commit is contained in:
Max Bowsher 2023-01-11 21:15:52 +00:00 committed by GitHub
parent 5f5cad736a
commit d1f2b101b5
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
13 changed files with 362 additions and 71 deletions
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46
audit/format.go
View File

@ -192,7 +192,24 @@ func (f *AuditFormatter) FormatResponse(ctx context.Context, w io.Writer, config
connState = in.Request.Connection.ConnState
}
if !config.Raw {
elideListResponseData := config.ElideListResponses && req.Operation == logical.ListOperation
var respData map[string]interface{}
if config.Raw {
// In the non-raw case, elision of list response data occurs inside HashResponse, to avoid redundant deep
// copies and hashing of data only to elide it later. In the raw case, we need to do it here.
if elideListResponseData && resp.Data != nil {
// Copy the data map before making changes, but we only need to go one level deep in this case
respData = make(map[string]interface{}, len(resp.Data))
for k, v := range resp.Data {
respData[k] = v
}
doElideListResponseData(respData)
} else {
respData = resp.Data
}
} else {
auth, err = HashAuth(salt, auth, config.HMACAccessor)
if err != nil {
return err
@ -203,10 +220,12 @@ func (f *AuditFormatter) FormatResponse(ctx context.Context, w io.Writer, config
return err
}
resp, err = HashResponse(salt, resp, config.HMACAccessor, in.NonHMACRespDataKeys)
resp, err = HashResponse(salt, resp, config.HMACAccessor, in.NonHMACRespDataKeys, elideListResponseData)
if err != nil {
return err
}
respData = resp.Data
}
var errString string
@ -315,7 +334,7 @@ func (f *AuditFormatter) FormatResponse(ctx context.Context, w io.Writer, config
MountAccessor: req.MountAccessor,
Auth: respAuth,
Secret: respSecret,
Data: resp.Data,
Data: respData,
Warnings: resp.Warnings,
Redirect: resp.Redirect,
WrapInfo: respWrapInfo,
@ -495,7 +514,7 @@ func parseVaultTokenFromJWT(token string) *string {
return &claims.ID
}
// Create a formatter not backed by a persistent salt.
// NewTemporaryFormatter creates a formatter not backed by a persistent salt
func NewTemporaryFormatter(format, prefix string) *AuditFormatter {
temporarySalt := func(ctx context.Context) (*salt.Salt, error) {
return salt.NewNonpersistentSalt(), nil
@ -516,3 +535,22 @@ func NewTemporaryFormatter(format, prefix string) *AuditFormatter {
}
return ret
}
// doElideListResponseData performs the actual elision of list operation response data, once surrounding code has
// determined it should apply to a particular request. The data map that is passed in must be a copy that is safe to
// modify in place, but need not be a full recursive deep copy, as only top-level keys are changed.
//
// See the documentation of the controlling option in FormatterConfig for more information on the purpose.
func doElideListResponseData(data map[string]interface{}) {
for k, v := range data {
if k == "keys" {
if vSlice, ok := v.([]string); ok {
data[k] = len(vSlice)
}
} else if k == "key_info" {
if vMap, ok := v.(map[string]interface{}); ok {
data[k] = len(vMap)
}
}
}
}

179
audit/format_test.go
View File

@ -3,45 +3,74 @@ package audit
import (
"context"
"io"
"io/ioutil"
"testing"
"github.com/hashicorp/vault/helper/namespace"
"github.com/hashicorp/vault/sdk/helper/salt"
"github.com/hashicorp/vault/sdk/logical"
"github.com/mitchellh/copystructure"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
)
type noopFormatWriter struct {
salt *salt.Salt
SaltFunc func() (*salt.Salt, error)
type testingFormatWriter struct {
salt *salt.Salt
lastRequest *AuditRequestEntry
lastResponse *AuditResponseEntry
}
func (n *noopFormatWriter) WriteRequest(_ io.Writer, _ *AuditRequestEntry) error {
func (fw *testingFormatWriter) WriteRequest(_ io.Writer, entry *AuditRequestEntry) error {
fw.lastRequest = entry
return nil
}
func (n *noopFormatWriter) WriteResponse(_ io.Writer, _ *AuditResponseEntry) error {
func (fw *testingFormatWriter) WriteResponse(_ io.Writer, entry *AuditResponseEntry) error {
fw.lastResponse = entry
return nil
}
func (n *noopFormatWriter) Salt(ctx context.Context) (*salt.Salt, error) {
if n.salt != nil {
return n.salt, nil
func (fw *testingFormatWriter) Salt(ctx context.Context) (*salt.Salt, error) {
if fw.salt != nil {
return fw.salt, nil
}
var err error
n.salt, err = salt.NewSalt(ctx, nil, nil)
fw.salt, err = salt.NewSalt(ctx, nil, nil)
if err != nil {
return nil, err
}
return n.salt, nil
return fw.salt, nil
}
// hashExpectedValueForComparison replicates enough of the audit HMAC process on a piece of expected data in a test,
// so that we can use assert.Equal to compare the expected and output values.
func (fw *testingFormatWriter) hashExpectedValueForComparison(input map[string]interface{}) map[string]interface{} {
// Copy input before modifying, since we may re-use the same data in another test
copied, err := copystructure.Copy(input)
if err != nil {
panic(err)
}
copiedAsMap := copied.(map[string]interface{})
salter, err := fw.Salt(context.Background())
if err != nil {
panic(err)
}
err = hashMap(salter.GetIdentifiedHMAC, copiedAsMap, nil)
if err != nil {
panic(err)
}
return copiedAsMap
}
func TestFormatRequestErrors(t *testing.T) {
config := FormatterConfig{}
formatter := AuditFormatter{
AuditFormatWriter: &noopFormatWriter{},
AuditFormatWriter: &testingFormatWriter{},
}
if err := formatter.FormatRequest(context.Background(), ioutil.Discard, config, &logical.LogInput{}); err == nil {
if err := formatter.FormatRequest(context.Background(), io.Discard, config, &logical.LogInput{}); err == nil {
t.Fatal("expected error due to nil request")
}
@ -56,10 +85,10 @@ func TestFormatRequestErrors(t *testing.T) {
func TestFormatResponseErrors(t *testing.T) {
config := FormatterConfig{}
formatter := AuditFormatter{
AuditFormatWriter: &noopFormatWriter{},
AuditFormatWriter: &testingFormatWriter{},
}
if err := formatter.FormatResponse(context.Background(), ioutil.Discard, config, &logical.LogInput{}); err == nil {
if err := formatter.FormatResponse(context.Background(), io.Discard, config, &logical.LogInput{}); err == nil {
t.Fatal("expected error due to nil request")
}
@ -70,3 +99,123 @@ func TestFormatResponseErrors(t *testing.T) {
t.Fatal("expected error due to nil writer")
}
}
func TestElideListResponses(t *testing.T) {
tfw := testingFormatWriter{}
formatter := AuditFormatter{&tfw}
ctx := namespace.RootContext(context.Background())
type test struct {
name string
inputData map[string]interface{}
expectedData map[string]interface{}
}
tests := []test{
{
"nil data",
nil,
nil,
},
{
"Normal list (keys only)",
map[string]interface{}{
"keys": []string{"foo", "bar", "baz"},
},
map[string]interface{}{
"keys": 3,
},
},
{
"Enhanced list (has key_info)",
map[string]interface{}{
"keys": []string{"foo", "bar", "baz", "quux"},
"key_info": map[string]interface{}{
"foo": "alpha",
"bar": "beta",
"baz": "gamma",
"quux": "delta",
},
},
map[string]interface{}{
"keys": 4,
"key_info": 4,
},
},
{
"Unconventional other values in a list response are not touched",
map[string]interface{}{
"keys": []string{"foo", "bar"},
"something_else": "baz",
},
map[string]interface{}{
"keys": 2,
"something_else": "baz",
},
},
{
"Conventional values in a list response are not elided if their data types are unconventional",
map[string]interface{}{
"keys": map[string]interface{}{
"You wouldn't expect keys to be a map": nil,
},
"key_info": []string{
"You wouldn't expect key_info to be a slice",
},
},
map[string]interface{}{
"keys": map[string]interface{}{
"You wouldn't expect keys to be a map": nil,
},
"key_info": []string{
"You wouldn't expect key_info to be a slice",
},
},
},
}
oneInterestingTestCase := tests[2]
formatResponse := func(
t *testing.T,
config FormatterConfig,
operation logical.Operation,
inputData map[string]interface{},
) {
err := formatter.FormatResponse(ctx, io.Discard, config, &logical.LogInput{
Request: &logical.Request{Operation: operation},
Response: &logical.Response{Data: inputData},
})
require.Nil(t, err)
}
t.Run("Default case", func(t *testing.T) {
config := FormatterConfig{ElideListResponses: true}
for _, tc := range tests {
t.Run(tc.name, func(t *testing.T) {
formatResponse(t, config, logical.ListOperation, tc.inputData)
assert.Equal(t, tfw.hashExpectedValueForComparison(tc.expectedData), tfw.lastResponse.Response.Data)
})
}
})
t.Run("When Operation is not list, eliding does not happen", func(t *testing.T) {
config := FormatterConfig{ElideListResponses: true}
tc := oneInterestingTestCase
formatResponse(t, config, logical.ReadOperation, tc.inputData)
assert.Equal(t, tfw.hashExpectedValueForComparison(tc.inputData), tfw.lastResponse.Response.Data)
})
t.Run("When ElideListResponses is false, eliding does not happen", func(t *testing.T) {
config := FormatterConfig{ElideListResponses: false}
tc := oneInterestingTestCase
formatResponse(t, config, logical.ListOperation, tc.inputData)
assert.Equal(t, tfw.hashExpectedValueForComparison(tc.inputData), tfw.lastResponse.Response.Data)
})
t.Run("When Raw is true, eliding still happens", func(t *testing.T) {
config := FormatterConfig{ElideListResponses: true, Raw: true}
tc := oneInterestingTestCase
formatResponse(t, config, logical.ListOperation, tc.inputData)
assert.Equal(t, tc.expectedData, tfw.lastResponse.Response.Data)
})
}

24
audit/formatter.go
View File

@ -7,7 +7,7 @@ import (
"github.com/hashicorp/vault/sdk/logical"
)
// Formatter is an interface that is responsible for formating a
// Formatter is an interface that is responsible for formatting a
// request/response into some format. Formatters write their output
// to an io.Writer.
//
@ -21,6 +21,28 @@ type FormatterConfig struct {
Raw bool
HMACAccessor bool
// Vault lacks pagination in its APIs. As a result, certain list operations can return **very** large responses.
// The user's chosen audit sinks may experience difficulty consuming audit records that swell to tens of megabytes
// of JSON. The responses of list operations are typically not very interesting, as they are mostly lists of keys,
// or, even when they include a "key_info" field, are not returning confidential information. They become even less
// interesting once HMAC-ed by the audit system.
//
// Some example Vault "list" operations that are prone to becoming very large in an active Vault installation are:
// auth/token/accessors/
// identity/entity/id/
// identity/entity-alias/id/
// pki/certs/
//
// This option exists to provide such users with the option to have response data elided from audit logs, only when
// the operation type is "list". For added safety, the elision only applies to the "keys" and "key_info" fields
// within the response data - these are conventionally the only fields present in a list response - see
// logical.ListResponse, and logical.ListResponseWithInfo. However, other fields are technically possible if a
// plugin author writes unusual code, and these will be preserved in the audit log even with this option enabled.
// The elision replaces the values of the "keys" and "key_info" fields with an integer count of the number of
// entries. This allows even the elided audit logs to still be useful for answering questions like
// "Was any data returned?" or "How many records were listed?".
ElideListResponses bool
// This should only ever be used in a testing context
OmitTime bool
}

16
audit/hashstructure.go
View File

@ -98,7 +98,13 @@ func hashMap(fn func(string) string, data map[string]interface{}, nonHMACDataKey
}
// HashResponse returns a hashed copy of the logical.Request input.
func HashResponse(salter *salt.Salt, in *logical.Response, HMACAccessor bool, nonHMACDataKeys []string) (*logical.Response, error) {
func HashResponse(
salter *salt.Salt,
in *logical.Response,
HMACAccessor bool,
nonHMACDataKeys []string,
elideListResponseData bool,
) (*logical.Response, error) {
if in == nil {
return nil, nil
}
@ -129,12 +135,20 @@ func HashResponse(salter *salt.Salt, in *logical.Response, HMACAccessor bool, no
mapCopy[logical.HTTPRawBody] = string(b)
}
// Processing list response data elision takes place at this point in the code for performance reasons:
// - take advantage of the deep copy of resp.Data that was going to be done anyway for hashing
// - but elide data before potentially spending time hashing it
if elideListResponseData {
doElideListResponseData(mapCopy)
}
err = hashMap(fn, mapCopy, nonHMACDataKeys)
if err != nil {
return nil, err
}
resp.Data = mapCopy
}
if resp.WrapInfo != nil {
var err error
resp.WrapInfo, err = HashWrapInfo(salter, resp.WrapInfo, HMACAccessor)

2
audit/hashstructure_test.go
View File

@ -293,7 +293,7 @@ func TestHashResponse(t *testing.T) {
}
for _, tc := range cases {
input := fmt.Sprintf("%#v", tc.Input)
out, err := HashResponse(localSalt, tc.Input, tc.HMACAccessor, tc.NonHMACDataKeys)
out, err := HashResponse(localSalt, tc.Input, tc.HMACAccessor, tc.NonHMACDataKeys, false)
if err != nil {
t.Fatalf("err: %s\n\n%s", err, input)
}

14
builtin/audit/file/backend.go
View File

@ -71,6 +71,15 @@ func Factory(ctx context.Context, conf *audit.BackendConfig) (audit.Backend, err
logRaw = b
}
elideListResponses := false
if elideListResponsesRaw, ok := conf.Config["elide_list_responses"]; ok {
value, err := strconv.ParseBool(elideListResponsesRaw)
if err != nil {
return nil, err
}
elideListResponses = value
}
// Check if mode is provided
mode := os.FileMode(0o600)
if modeRaw, ok := conf.Config["mode"]; ok {
@ -102,8 +111,9 @@ func Factory(ctx context.Context, conf *audit.BackendConfig) (audit.Backend, err
saltView: conf.SaltView,
salt: new(atomic.Value),
formatConfig: audit.FormatterConfig{
Raw: logRaw,
HMACAccessor: hmacAccessor,
Raw: logRaw,
HMACAccessor: hmacAccessor,
ElideListResponses: elideListResponses,
},
}

16
builtin/audit/socket/backend.go
View File

@ -9,7 +9,7 @@ import (
"sync"
"time"
multierror "github.com/hashicorp/go-multierror"
"github.com/hashicorp/go-multierror"
"github.com/hashicorp/go-secure-stdlib/parseutil"
"github.com/hashicorp/vault/audit"
"github.com/hashicorp/vault/sdk/helper/salt"
@ -73,12 +73,22 @@ func Factory(ctx context.Context, conf *audit.BackendConfig) (audit.Backend, err
logRaw = b
}
elideListResponses := false
if elideListResponsesRaw, ok := conf.Config["elide_list_responses"]; ok {
value, err := strconv.ParseBool(elideListResponsesRaw)
if err != nil {
return nil, err
}
elideListResponses = value
}
b := &Backend{
saltConfig: conf.SaltConfig,
saltView: conf.SaltView,
formatConfig: audit.FormatterConfig{
Raw: logRaw,
HMACAccessor: hmacAccessor,
Raw: logRaw,
HMACAccessor: hmacAccessor,
ElideListResponses: elideListResponses,
},
writeDuration: writeDuration,

14
builtin/audit/syslog/backend.go
View File

@ -63,6 +63,15 @@ func Factory(ctx context.Context, conf *audit.BackendConfig) (audit.Backend, err
logRaw = b
}
elideListResponses := false
if elideListResponsesRaw, ok := conf.Config["elide_list_responses"]; ok {
value, err := strconv.ParseBool(elideListResponsesRaw)
if err != nil {
return nil, err
}
elideListResponses = value
}
// Get the logger
logger, err := gsyslog.NewLogger(gsyslog.LOG_INFO, facility, tag)
if err != nil {
@ -74,8 +83,9 @@ func Factory(ctx context.Context, conf *audit.BackendConfig) (audit.Backend, err
saltConfig: conf.SaltConfig,
saltView: conf.SaltView,
formatConfig: audit.FormatterConfig{
Raw: logRaw,
HMACAccessor: hmacAccessor,
Raw: logRaw,
HMACAccessor: hmacAccessor,
ElideListResponses: elideListResponses,
},
}

3
changelog/18128.txt Normal file
View File

@ -0,0 +1,3 @@
```release-note:improvement
audit: Add `elide_list_responses` option, providing a countermeasure for a common source of oversized audit log entries
```

15
website/content/docs/audit/file.mdx
View File

@ -41,9 +41,10 @@ $ vault audit enable file file_path=stdout
Note the difference between `audit enable` command options and the `file` backend
configuration options. Use `vault audit enable -help` to see the command options.
Following are the configuration options available for the backend.
## Configuration
The `file` audit device supports the common configuration options documented on
the [main Audit Devices page](/docs/audit#common-configuration-options), and
these device-specific options:
- `file_path` `(string: <required>)` - The path to where the audit log will be
written. If a file already exists at the given path, the audit backend will
@ -53,21 +54,11 @@ Following are the configuration options available for the backend.
- `discard` writes output (useful in testing scenarios)
- `log_raw` `(bool: false)` - If enabled, logs the security sensitive
information without hashing, in the raw format.
- `hmac_accessor` `(bool: true)` - If enabled, enables the hashing of token
accessor.
- `mode` `(string: "0600")` - A string containing an octal number representing
the bit pattern for the file mode, similar to `chmod`. Set to `"0000"` to
prevent Vault from modifying the file mode.
- `format` `(string: "json")` - Allows selecting the output format. Valid values
are `"json"` and `"jsonx"`, which formats the normal log entries as XML.
- `prefix` `(string: "")` - A customizable string prefix to write before the
actual log line.
## Log File Rotation

66
website/content/docs/audit/index.mdx
View File

@ -105,3 +105,69 @@ Refer to [Blocked Audit Devices](https://learn.hashicorp.com/tutorials/vault/blo
Audit devices also have a full HTTP API. Please see the [Audit device API
docs](/api-docs/system/audit) for more details.
## Common configuration options
- `elide_list_responses` `(bool: false)` - See [Eliding list response
bodies](docs/audit#eliding-list-response-bodies) below.
- `format` `(string: "json")` - Allows selecting the output format. Valid values
are `"json"` and `"jsonx"`, which formats the normal log entries as XML.
- `hmac_accessor` `(bool: true)` - If enabled, enables the hashing of token
accessor.
- `log_raw` `(bool: false)` - If enabled, logs the security sensitive
information without hashing, in the raw format.
- `prefix` `(string: "")` - A customizable string prefix to write before the
actual log line.
## Eliding list response bodies
Some Vault responses can be very large. Primarily, this affects list operations -
as Vault lacks pagination in its APIs, listing a very large collection can result
in a response that is tens of megabytes long. Some audit backends are unable to
process individual audit records of larger sizes.
The contents of the response for a list operation is often not very interesting;
most contain only a "keys" field, containing a list of IDs. Select API endpoints
additionally return a "key_info" field, a map from ID to some additional
information about the list entry - `identity/entity/id/` is an example of this.
Even in this case, the response to a list operation is usually less-confidential
or public information, for which having the full response in the audit logs is of
lesser importance.
The `elide_list_responses` audit option provides the flexibility to not write the
full list response data from the audit log, to mitigate the creation of very long
individual audit records.
When enabled, it affects only audit records of `type=response` and
`request.operation=list`. The values of `response.data.keys` and
`response.data.key_info` will be replaced with a simple integer, recording how
many entries were contained in the list (`keys`) or map (`key_info`) - therefore
even with this feature enabled, it is still possible to see how many items were
returned by a list operation.
This extra processing only affects the response data fields `keys` and `key_info`,
and only when they have the expected data types - in the event a list response
contains data outside of the usual conventions that apply to Vault list responses,
it will be left as is by this feature.
Here is an example of an audit record that has been processed by this feature
(formatted with extra whitespace, and with fields not relevant to the example
omitted):
```json
{
"type": "response",
"request": {
"operation": "list"
},
"response": {
"data": {
"key_info": 4,
"keys": 4
}
}
}
```

19
website/content/docs/audit/socket.mdx
View File

@ -28,6 +28,10 @@ $ vault audit enable socket address=127.0.0.1:9090 socket_type=tcp
## Configuration
The `socket` audit device supports the common configuration options documented on
the [main Audit Devices page](/docs/audit#common-configuration-options), and
these device-specific options:
- `address` `(string: "")` - The socket server address to use. Example
`127.0.0.1:9090` or `/tmp/audit.sock`.
@ -35,18 +39,3 @@ $ vault audit enable socket address=127.0.0.1:9090 socket_type=tcp
with <a href="https://golang.org/pkg/net/#Dial">net.Dial</a> is acceptable. It's
important to note if TCP is used and the destination socket becomes unavailable
Vault may become unresponsive per [Blocked Audit Devices](docs/audit/#blocked-audit-devices).
- `log_raw` `(bool: false)` - If enabled, logs the security sensitive
information without hashing, in the raw format.
- `hmac_accessor` `(bool: true)` - If enabled, enables the hashing of token
accessor.
- `mode` `(string: "0600")` - A string containing an octal number representing
the bit pattern for the file mode, similar to `chmod`.
- `format` `(string: "json")` - Allows selecting the output format. Valid values
are `"json"` and `"jsonx"`, which formats the normal log entries as XML.
- `prefix` `(string: "")` - A customizable string prefix to write before the
actual log line.

19
website/content/docs/audit/syslog.mdx
View File

@ -36,21 +36,10 @@ $ vault audit enable syslog tag="vault" facility="AUTH"
## Configuration
The `syslog` audit device supports the common configuration options documented on
the [main Audit Devices page](/docs/audit#common-configuration-options), and
these device-specific options:
- `facility` `(string: "AUTH")` - The syslog facility to use.
- `tag` `(string: "vault")` - The syslog tag to use.
- `log_raw` `(bool: false)` - If enabled, logs the security sensitive
information without hashing, in the raw format.
- `hmac_accessor` `(bool: true)` - If enabled, enables the hashing of token
accessor.
- `mode` `(string: "0600")` - A string containing an octal number representing
the bit pattern for the file mode, similar to `chmod`.
- `format` `(string: "json")` - Allows selecting the output format. Valid values
are `"json"` and `"jsonx"`, which formats the normal log entries as XML.
- `prefix` `(string: "")` - A customizable string prefix to write before the
actual log line.