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fix(pass): copy bytes in PassValue.Unmarshal to survive backend zeroing #536

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Merged
Benehiko merged 1 commit into from
May 28, 2026
+42 −2
Merged

fix(pass): copy bytes in PassValue.Unmarshal to survive backend zeroing #536

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4 changes: 3 additions & 1 deletion plugins/pass/store/store.go
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,9 @@ func (m *PassValue) Marshal() ([]byte, error) {
}

func (m *PassValue) Unmarshal(data []byte) error {
m.value = data
// Copy: store backends zero the source buffer after Unmarshal returns
// (see store/keychain and store/posixage), so we must not alias it.
m.value = append([]byte(nil), data...)
return nil
}

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36 changes: 36 additions & 0 deletions plugins/pass/store/store_test.go
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@@ -0,0 +1,36 @@
// Copyright 2025-2026 Docker, 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 store

import (
"testing"

"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
)

// TestPassValueUnmarshalCopies guards the contract that store backends zero
// the source buffer after Unmarshal returns. PassValue must own its bytes.
func TestPassValueUnmarshalCopies(t *testing.T) {
src := []byte("hunter2")
pv := &PassValue{}
require.NoError(t, pv.Unmarshal(src))

clear(src)

out, err := pv.Marshal()
require.NoError(t, err)
assert.Equal(t, []byte("hunter2"), out)
}
4 changes: 3 additions & 1 deletion store/store.go
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,9 @@ var (
type Secret interface {
// Marshal the secret into a slice of bytes
Marshal() ([]byte, error)
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@docker-agent docker-agent Bot May 28, 2026

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[HIGH] Incomplete interface contract: Marshal() return value is also zeroed by backends

All four store backends call defer clear(data) on the slice returned by Marshal():

// keychain_darwin.go:183, keychain_linux.go:322, keychain_windows.go:63, posixage/store.go:351
data, err := secret.Marshal()
defer clear(data)  // ← zeroes m.value in PassValue via the alias

Since PassValue.Marshal() returns m.value directly (return m.value, nil) without copying, every Save()/Upsert() call silently zeroes the PassValue's internal state. Any subsequent Marshal() call on the same instance returns all-zero bytes.

The new comment added in this PR documents that Unmarshal implementations must copy retained bytes, but misses the symmetric contract for Marshal: backends zero the returned buffer, so Marshal() must return a fresh copy (or the contract must state that Marshal() output will be zeroed and callers must not reuse the instance).

Suggested fixes:

Option A — Copy in PassValue.Marshal():

func (m *PassValue) Marshal() ([]byte, error) {
    return append([]byte(nil), m.value...), nil
}

Option B — Document the contract on the Marshal interface comment (alongside the Unmarshal note already added):

// Marshal the secret into a slice of bytes.
// Callers (store backends) may zero the returned buffer after use;
// implementations that need to retain state must not return an alias.
Marshal() ([]byte, error)

// Unmarshal the secret from a slice of bytes into its structured format
// Unmarshal the secret from a slice of bytes into its structured format.
// Implementations must copy any bytes they retain: store backends zero
// the source buffer after Unmarshal returns to avoid leaking plaintext.
Unmarshal(data []byte) error
// Metadata returns a key-value pair of non-sensitive data about the secret
Metadata() map[string]string
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