1 files changed, 211 insertions, 0 deletions
diff --git a/keyring/fs_keyring.go b/keyring/fs_keyring.go
new file mode 100644
index 0000000..bed23af
--- /dev/null
+++ b/keyring/fs_keyring.go
@@ -0,0 +1,211 @@
+/*
+ * fs_keyring.go - Add/remove encryption policy keys to/from filesystem
+ *
+ * Copyright 2019 Google LLC
+ * Author: Eric Biggers (ebiggers@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 keyring
+
+/*
+#include <string.h>
+*/
+import "C"
+
+import (
+	"encoding/hex"
+	"log"
+	"os"
+	"os/user"
+	"sync"
+	"unsafe"
+
+	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
+
+	"github.com/google/fscrypt/crypto"
+	"github.com/google/fscrypt/filesystem"
+)
+
+var (
+	fsKeyringSupported      bool
+	fsKeyringSupportedKnown bool
+	fsKeyringSupportedLock  sync.Mutex
+)
+
+func checkForFsKeyringSupport(mount *filesystem.Mount) bool {
+	dir, err := os.Open(mount.Path)
+	if err != nil {
+		log.Printf("Unexpected error opening %q. Assuming filesystem keyring is unsupported.",
+			mount.Path)
+		return false
+	}
+	defer dir.Close()
+
+	// FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY
+	// if the ioctl isn't supported.  Otherwise it should fail with EFAULT.
+	//
+	// Note that there's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY
+	// support separately, since it's guaranteed to be available if
+	// FS_IOC_ADD_ENCRYPTION_KEY is.  There's also no need to check for
+	// support on every filesystem separately, since either the kernel
+	// supports the ioctls on all fscrypt-capable filesystems or it doesn't.
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL, dir.Fd(), unix.FS_IOC_ADD_ENCRYPTION_KEY, 0)
+	if errno == unix.ENOTTY {
+		log.Printf("Kernel doesn't support filesystem keyring. Falling back to user keyring.")
+		return false
+	}
+	if errno == unix.EFAULT {
+		log.Printf("Detected support for filesystem keyring")
+	} else {
+		// EFAULT is expected, but as long as we didn't get ENOTTY the
+		// ioctl should be available.
+		log.Printf("Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY(%q, NULL): %v", mount.Path, errno)
+	}
+	return true
+}
+
+// isFsKeyringSupported returns true if the kernel supports the ioctls to
+// add/remove fscrypt keys directly to/from the filesystem.  For support to be
+// detected, the given Mount must be for a filesystem that supports fscrypt.
+func isFsKeyringSupported(mount *filesystem.Mount) bool {
+	fsKeyringSupportedLock.Lock()
+	defer fsKeyringSupportedLock.Unlock()
+	if !fsKeyringSupportedKnown {
+		fsKeyringSupported = checkForFsKeyringSupport(mount)
+		fsKeyringSupportedKnown = true
+	}
+	return fsKeyringSupported
+}
+
+// buildKeySpecifier converts the key descriptor string to an FscryptKeySpecifier.
+func buildKeySpecifier(spec *unix.FscryptKeySpecifier, descriptor string) error {
+	descriptorBytes, err := hex.DecodeString(descriptor)
+	if err != nil {
+		return errors.Errorf("key descriptor %q is invalid", descriptor)
+	}
+	switch len(descriptorBytes) {
+	case unix.FSCRYPT_KEY_DESCRIPTOR_SIZE:
+		spec.Type = unix.FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR
+	default:
+		return errors.Errorf("key descriptor %q has unknown length", descriptor)
+	}
+	copy(spec.U[:], descriptorBytes)
+	return nil
+}
+
+// fsAddEncryptionKey adds the specified encryption key to the specified filesystem.
+func fsAddEncryptionKey(key *crypto.Key, descriptor string,
+	mount *filesystem.Mount, user *user.User) error {
+
+	dir, err := os.Open(mount.Path)
+	if err != nil {
+		return err
+	}
+	defer dir.Close()
+
+	argKey, err := crypto.NewBlankKey(int(unsafe.Sizeof(unix.FscryptAddKeyArg{})) + key.Len())
+	if err != nil {
+		return err
+	}
+	defer argKey.Wipe()
+	arg := (*unix.FscryptAddKeyArg)(argKey.UnsafePtr())
+
+	if err = buildKeySpecifier(&arg.Key_spec, descriptor); err != nil {
+		return err
+	}
+
+	raw := unsafe.Pointer(uintptr(argKey.UnsafePtr()) + unsafe.Sizeof(*arg))
+	arg.Raw_size = uint32(key.Len())
+	C.memcpy(raw, key.UnsafePtr(), C.size_t(key.Len()))
+
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL, dir.Fd(),
+		unix.FS_IOC_ADD_ENCRYPTION_KEY, uintptr(argKey.UnsafePtr()))
+	log.Printf("FS_IOC_ADD_ENCRYPTION_KEY(%q, %s, <raw>) = %v", mount.Path, descriptor, errno)
+	if errno != 0 {
+		return errors.Wrap(ErrKeyAdd, errno.Error())
+	}
+	return nil
+}
+
+// fsRemoveEncryptionKey removes the specified encryption key from the specified
+// filesystem.
+func fsRemoveEncryptionKey(descriptor string, mount *filesystem.Mount,
+	user *user.User) error {
+
+	dir, err := os.Open(mount.Path)
+	if err != nil {
+		return err
+	}
+	defer dir.Close()
+
+	var arg unix.FscryptRemoveKeyArg
+	if err = buildKeySpecifier(&arg.Key_spec, descriptor); err != nil {
+		return err
+	}
+
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL, dir.Fd(),
+		unix.FS_IOC_REMOVE_ENCRYPTION_KEY, uintptr(unsafe.Pointer(&arg)))
+	log.Printf("FS_IOC_REMOVE_ENCRYPTION_KEY(%q, %s) = %v, removal_status_flags=0x%x",
+		mount.Path, descriptor, errno, arg.Removal_status_flags)
+	switch errno {
+	case 0:
+		if arg.Removal_status_flags&unix.FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY != 0 {
+			return ErrKeyFilesOpen
+		}
+		return nil
+	case unix.ENOKEY:
+		return ErrKeyNotPresent
+	default:
+		return errors.Wrap(ErrKeyRemove, errno.Error())
+	}
+}
+
+// fsGetEncryptionKeyStatus gets the status of the specified encryption key on
+// the specified filesystem.
+func fsGetEncryptionKeyStatus(descriptor string, mount *filesystem.Mount,
+	user *user.User) (KeyStatus, error) {
+
+	dir, err := os.Open(mount.Path)
+	if err != nil {
+		return KeyStatusUnknown, err
+	}
+	defer dir.Close()
+
+	var arg unix.FscryptGetKeyStatusArg
+	err = buildKeySpecifier(&arg.Key_spec, descriptor)
+	if err != nil {
+		return KeyStatusUnknown, err
+	}
+
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL, dir.Fd(),
+		unix.FS_IOC_GET_ENCRYPTION_KEY_STATUS, uintptr(unsafe.Pointer(&arg)))
+	log.Printf("FS_IOC_GET_ENCRYPTION_KEY_STATUS(%q, %s) = %v, status=%d, status_flags=0x%x",
+		mount.Path, descriptor, errno, arg.Status, arg.Status_flags)
+	if errno != 0 {
+		return KeyStatusUnknown, errors.Wrap(ErrKeySearch, errno.Error())
+	}
+	switch arg.Status {
+	case unix.FSCRYPT_KEY_STATUS_ABSENT:
+		return KeyAbsent, nil
+	case unix.FSCRYPT_KEY_STATUS_PRESENT:
+		return KeyPresent, nil
+	case unix.FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED:
+		return KeyAbsentButFilesBusy, nil
+	default:
+		return KeyStatusUnknown,
+			errors.Wrapf(ErrKeySearch, "unknown key status (%d)", arg.Status)
+	}
+}