metadata: reorganize and add consistency checks

This commit adds in IsValid() checks for the metadata structures that
let us enforce stronger invariants than those imposed by the protobuf
package. The main uses of this will be to check that metadata is valid
before writing it to the filesystem, and to check that the filesystem
contains valid metadata before returning it to the user. These functions
also will log the exact reason if the validity checks fail.

To have these checks in the metadata package, all of the various
constants have been moved to a single metadata/constants.go file. The
uses of these constants were changed accordingly.

Finally, this commit standardizes our use of errors so that they always
begin with an appropriate prefix.

Change-Id: I99008e2ee803ebe5f6236eb8d83fc83efcd22718

1 files changed, 197 insertions, 0 deletions

diff --git a/metadata/checks.go b/metadata/checks.go
new file mode 100644
index 0000000..5d0ce59
--- /dev/null
+++ b/metadata/checks.go
@@ -0,0 +1,197 @@
+/*
+ * checks.go - Some sanity check methods for our metadata structures
+ *
+ * Copyright 2017 Google Inc.
+ * Author: Joe Richey (joerichey@google.com)
+ *
+ * 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 metadata
+
+import (
+	"log"
+
+	"github.com/golang/protobuf/proto"
+
+	"fscrypt/util"
+)
+
+// Metadata is the interface to all of the protobuf structures that can be
+// checked with the IsValid method.
+type Metadata interface {
+	IsValid() bool
+	proto.Message
+}
+
+// checkValidLength returns true if expected == actual, otherwise it logs an
+// InvalidLengthError.
+func checkValidLength(name string, expected int, actual int) bool {
+	if expected != actual {
+		log.Print(util.InvalidLengthError(name, expected, actual))
+		return false
+	}
+	return true
+}
+
+// IsValid ensures the mode has a name and isn't empty.
+func (m EncryptionOptions_Mode) IsValid() bool {
+	if m.String() == "" {
+		log.Print("Encryption mode cannot be the empty string")
+		return false
+	}
+	if m == EncryptionOptions_default {
+		log.Print("Encryption mode must be set to a non-default value")
+		return false
+	}
+	return true
+}
+
+// IsValid ensures the source has a name and isn't empty.
+func (s SourceType) IsValid() bool {
+	if s.String() == "" {
+		log.Print("SourceType cannot be the empty string")
+		return false
+	}
+	if s == SourceType_default {
+		log.Print("SourceType must be set to a non-default value")
+		return false
+	}
+	return true
+}
+
+// IsValid ensures the hash costs will be accepted by Argon2.
+func (h *HashingCosts) IsValid() bool {
+	if h == nil {
+		log.Print("HashingCosts not initialized")
+		return false
+	}
+	if h.Time == 0 {
+		log.Print("Hashing time cost not initialized")
+		return false
+	}
+	if h.Parallelism == 0 {
+		log.Print("Hashing parallelism cost not initialized")
+		return false
+	}
+	minMemory := 8 * h.Parallelism
+	if h.Memory < minMemory {
+		log.Printf("Hashing memory cost must be at least %d", minMemory)
+		return false
+	}
+	return true
+}
+
+// IsValid ensures our buffers are the correct length (or just exist).
+func (w *WrappedKeyData) IsValid() bool {
+	if w == nil {
+		log.Print("WrappedKeyData not initialized")
+		return false
+	}
+	if len(w.EncryptedKey) == 0 {
+		log.Print("EncryptedKey not initialized")
+		return false
+	}
+	return checkValidLength("IV", IVLen, len(w.IV)) &&
+		checkValidLength("HMAC", HMACLen, len(w.Hmac))
+}
+
+// IsValid ensures our ProtectorData has the correct fields for its source.
+func (p *ProtectorData) IsValid() bool {
+	if p == nil {
+		log.Print("ProtectorData not initialized")
+		return false
+	}
+
+	// Source specific checks
+	switch p.Source {
+	case SourceType_pam_passphrase:
+		if p.Uid < 0 {
+			log.Print("The UID should never be negative")
+			return false
+		}
+		fallthrough
+	case SourceType_custom_passphrase:
+		if !p.Costs.IsValid() || !checkValidLength("Salt", SaltLen, len(p.Salt)) {
+			return false
+		}
+	}
+
+	// Generic checks
+	return p.Source.IsValid() &&
+		p.WrappedKey.IsValid() &&
+		checkValidLength("EncryptedKey", InternalKeyLen, len(p.WrappedKey.EncryptedKey)) &&
+		checkValidLength("ProtectorDescriptor", DescriptorLen, len(p.ProtectorDescriptor))
+
+}
+
+// IsValid ensures each of the options is valid.
+func (e *EncryptionOptions) IsValid() bool {
+	if e == nil {
+		log.Print("EncryptionOptions not initialized")
+		return false
+	}
+	if _, ok := util.Index(e.Padding, paddingArray); !ok {
+		log.Printf("Padding of %d is invalid", e.Padding)
+		return false
+	}
+
+	return e.Contents.IsValid() && e.Filenames.IsValid()
+}
+
+// IsValid ensures the fields are valid and have the correct lengths.
+func (w *WrappedPolicyKey) IsValid() bool {
+	if w == nil {
+		log.Print("WrappedPolicyKey not initialized")
+		return false
+	}
+	return w.WrappedKey.IsValid() &&
+		checkValidLength("EncryptedKey", PolicyKeyLen, len(w.WrappedKey.EncryptedKey)) &&
+		checkValidLength("ProtectorDescriptor", DescriptorLen, len(w.ProtectorDescriptor))
+}
+
+// IsValid ensures the fields and each wrapped key are valid.
+func (p *PolicyData) IsValid() bool {
+	if p == nil {
+		log.Print("PolicyData not initialized")
+		return false
+	}
+	// Check each wrapped key
+	for _, w := range p.WrappedPolicyKeys {
+		if !w.IsValid() {
+			return false
+		}
+	}
+	return p.Options.IsValid() &&
+		checkValidLength("KeyDescriptor", DescriptorLen, len(p.KeyDescriptor))
+}
+
+// IsValid ensures the Config has all the necessary info for its Source.
+func (c *Config) IsValid() bool {
+	// General checks
+	if c == nil {
+		log.Print("Config not initialized")
+		return false
+	}
+	if !c.Source.IsValid() || !c.Options.IsValid() {
+		return false
+	}
+
+	// Source specific checks
+	switch c.Source {
+	case SourceType_pam_passphrase, SourceType_custom_passphrase:
+		return c.HashCosts.IsValid()
+	default:
+		return true
+	}
+}