libfscrypt/fscrypt.cpp - platform/system/extras - Git at Google

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * 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.
  */

 #include "fscrypt/fscrypt.h"

 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/unique_fd.h>
 #include <asm/ioctl.h>
 #include <cutils/properties.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/fs.h>
 #include <logwrap/logwrap.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <utils/misc.h>

 #include <array>

 // TODO: switch to <linux/fscrypt.h> once it's in Bionic
 #ifndef FSCRYPT_POLICY_V1

 // Careful: due to an API quirk this is actually 0, not 1.  We use 1 everywhere
 // else, so make sure to only use this constant in the ioctl itself.
 #define FSCRYPT_POLICY_V1 0
 #define FSCRYPT_KEY_DESCRIPTOR_SIZE 8
 struct fscrypt_policy_v1 {
     __u8 version;
     __u8 contents_encryption_mode;
     __u8 filenames_encryption_mode;
     __u8 flags;
     __u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
 };

 #define FSCRYPT_POLICY_V2 2
 #define FSCRYPT_KEY_IDENTIFIER_SIZE 16
 struct fscrypt_policy_v2 {
     __u8 version;
     __u8 contents_encryption_mode;
     __u8 filenames_encryption_mode;
     __u8 flags;
     __u8 __reserved[4];
     __u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
 };

 #endif /* FSCRYPT_POLICY_V1 */

 /* modes not supported by upstream kernel, so not in <linux/fs.h> */
 #define FS_ENCRYPTION_MODE_AES_256_HEH      126
 #define FS_ENCRYPTION_MODE_PRIVATE          127

 #define HEX_LOOKUP "0123456789abcdef"

 #define MAX_KEY_REF_SIZE_HEX (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)

 bool fscrypt_is_native() {
     char value[PROPERTY_VALUE_MAX];
     property_get("ro.crypto.type", value, "none");
     return !strcmp(value, "file");
 }

 static void log_ls(const char* dirname) {
     std::array<const char*, 3> argv = {"ls", "-laZ", dirname};
     int status = 0;
     auto res =
         logwrap_fork_execvp(argv.size(), argv.data(), &status, false, LOG_ALOG, false, nullptr);
     if (res != 0) {
         PLOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2] << "failed";
         return;
     }
     if (!WIFEXITED(status)) {
         LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
                    << " did not exit normally, status: " << status;
         return;
     }
     if (WEXITSTATUS(status) != 0) {
         LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
                    << " returned failure: " << WEXITSTATUS(status);
         return;
     }
 }

 static void keyrefstring(const char* key_raw_ref, size_t key_raw_ref_length, char* hex) {
     size_t j = 0;
     for (size_t i = 0; i < key_raw_ref_length; i++) {
         hex[j++] = HEX_LOOKUP[(key_raw_ref[i] & 0xF0) >> 4];
         hex[j++] = HEX_LOOKUP[key_raw_ref[i] & 0x0F];
     }
     hex[j] = '\0';
 }

 static uint8_t fscrypt_get_policy_flags(int filenames_encryption_mode, int policy_version) {
     uint8_t flags = 0;

     // In the original setting of v1 policies and AES-256-CTS we used 4-byte
     // padding of filenames, so we have to retain that for compatibility.
     //
     // For everything else, use 16-byte padding.  This is more secure (it helps
     // hide the length of filenames), and it makes the inputs evenly divisible
     // into cipher blocks which is more efficient for encryption and decryption.
     if (policy_version == 1 && filenames_encryption_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
         flags |= FS_POLICY_FLAGS_PAD_4;
     } else {
         flags |= FS_POLICY_FLAGS_PAD_16;
     }

     // Use DIRECT_KEY for Adiantum, since it's much more efficient but just as
     // secure since Android doesn't reuse the same master key for multiple
     // encryption modes.
     if (filenames_encryption_mode == FS_ENCRYPTION_MODE_ADIANTUM) {
         flags |= FS_POLICY_FLAG_DIRECT_KEY;
     }

     return flags;
 }

 static bool fscrypt_is_encrypted(int fd) {
     fscrypt_policy_v1 policy;

     // success => encrypted with v1 policy
     // EINVAL => encrypted with v2 policy
     // ENODATA => not encrypted
     return ioctl(fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) == 0 || errno == EINVAL;
 }

 int fscrypt_policy_ensure(const char* directory, const char* key_raw_ref, size_t key_raw_ref_length,
                           const char* contents_encryption_mode,
                           const char* filenames_encryption_mode, int policy_version) {
     int contents_mode = 0;
     int filenames_mode = 0;

     if (!strcmp(contents_encryption_mode, "software") ||
         !strcmp(contents_encryption_mode, "aes-256-xts")) {
         contents_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
     } else if (!strcmp(contents_encryption_mode, "adiantum")) {
         contents_mode = FS_ENCRYPTION_MODE_ADIANTUM;
     } else if (!strcmp(contents_encryption_mode, "ice")) {
         contents_mode = FS_ENCRYPTION_MODE_PRIVATE;
     } else {
         LOG(ERROR) << "Invalid file contents encryption mode: "
                    << contents_encryption_mode;
         return -1;
     }

     if (!strcmp(filenames_encryption_mode, "aes-256-cts")) {
         filenames_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
     } else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
         filenames_mode = FS_ENCRYPTION_MODE_AES_256_HEH;
     } else if (!strcmp(filenames_encryption_mode, "adiantum")) {
         filenames_mode = FS_ENCRYPTION_MODE_ADIANTUM;
     } else {
         LOG(ERROR) << "Invalid file names encryption mode: "
                    << filenames_encryption_mode;
         return -1;
     }

     union {
         fscrypt_policy_v1 v1;
         fscrypt_policy_v2 v2;
     } policy;
     memset(&policy, 0, sizeof(policy));

     switch (policy_version) {
         case 1:
             if (key_raw_ref_length != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
                 LOG(ERROR) << "Invalid key ref length for v1 policy: " << key_raw_ref_length;
                 return -1;
             }
             // Careful: FSCRYPT_POLICY_V1 is actually 0 in the API, so make sure
             // to use it here instead of a literal 1.
             policy.v1.version = FSCRYPT_POLICY_V1;
             policy.v1.contents_encryption_mode = contents_mode;
             policy.v1.filenames_encryption_mode = filenames_mode;
             policy.v1.flags = fscrypt_get_policy_flags(filenames_mode, policy_version);
             memcpy(policy.v1.master_key_descriptor, key_raw_ref, FSCRYPT_KEY_DESCRIPTOR_SIZE);
             break;
         case 2:
             if (key_raw_ref_length != FSCRYPT_KEY_IDENTIFIER_SIZE) {
                 LOG(ERROR) << "Invalid key ref length for v2 policy: " << key_raw_ref_length;
                 return -1;
             }
             policy.v2.version = FSCRYPT_POLICY_V2;
             policy.v2.contents_encryption_mode = contents_mode;
             policy.v2.filenames_encryption_mode = filenames_mode;
             policy.v2.flags = fscrypt_get_policy_flags(filenames_mode, policy_version);
             memcpy(policy.v2.master_key_identifier, key_raw_ref, FSCRYPT_KEY_IDENTIFIER_SIZE);
             break;
         default:
             LOG(ERROR) << "Invalid encryption policy version: " << policy_version;
             return -1;
     }

     char ref[MAX_KEY_REF_SIZE_HEX];
     keyrefstring(key_raw_ref, key_raw_ref_length, ref);

     android::base::unique_fd fd(open(directory, O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC));
     if (fd == -1) {
         PLOG(ERROR) << "Failed to open directory " << directory;
         return -1;
     }

     bool already_encrypted = fscrypt_is_encrypted(fd);

     // FS_IOC_SET_ENCRYPTION_POLICY will set the policy if the directory is
     // unencrypted; otherwise it will verify that the existing policy matches.
     // Setting the policy will fail if the directory is already nonempty.
     if (ioctl(fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) != 0) {
         std::string reason;
         switch (errno) {
             case EEXIST:
                 reason = "The directory already has a different encryption policy.";
                 break;
             default:
                 reason = strerror(errno);
                 break;
         }
         LOG(ERROR) << "Failed to set encryption policy of " << directory << " to " << ref
                    << " modes " << contents_mode << "/" << filenames_mode << ": " << reason;
         if (errno == ENOTEMPTY) {
             log_ls(directory);
         }
         return -1;
     }

     if (already_encrypted) {
         LOG(INFO) << "Verified that " << directory << " has the encryption policy " << ref
                   << " modes " << contents_mode << "/" << filenames_mode;
     } else {
         LOG(INFO) << "Encryption policy of " << directory << " set to " << ref << " modes "
                   << contents_mode << "/" << filenames_mode;
     }
     return 0;
 }
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* 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.
	*/

	#include "fscrypt/fscrypt.h"

	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/unique_fd.h>
	#include <asm/ioctl.h>
	#include <cutils/properties.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <linux/fs.h>
	#include <logwrap/logwrap.h>
	#include <string.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <unistd.h>
	#include <utils/misc.h>

	#include <array>

	// TODO: switch to <linux/fscrypt.h> once it's in Bionic
	#ifndef FSCRYPT_POLICY_V1

	// Careful: due to an API quirk this is actually 0, not 1. We use 1 everywhere
	// else, so make sure to only use this constant in the ioctl itself.
	#define FSCRYPT_POLICY_V1 0
	#define FSCRYPT_KEY_DESCRIPTOR_SIZE 8
	struct fscrypt_policy_v1 {
	__u8 version;
	__u8 contents_encryption_mode;
	__u8 filenames_encryption_mode;
	__u8 flags;
	__u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
	};

	#define FSCRYPT_POLICY_V2 2
	#define FSCRYPT_KEY_IDENTIFIER_SIZE 16
	struct fscrypt_policy_v2 {
	__u8 version;
	__u8 contents_encryption_mode;
	__u8 filenames_encryption_mode;
	__u8 flags;
	__u8 __reserved[4];
	__u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
	};

	#endif /* FSCRYPT_POLICY_V1 */

	/* modes not supported by upstream kernel, so not in <linux/fs.h> */
	#define FS_ENCRYPTION_MODE_AES_256_HEH 126
	#define FS_ENCRYPTION_MODE_PRIVATE 127

	#define HEX_LOOKUP "0123456789abcdef"

	#define MAX_KEY_REF_SIZE_HEX (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)

	bool fscrypt_is_native() {
	char value[PROPERTY_VALUE_MAX];
	property_get("ro.crypto.type", value, "none");
	return !strcmp(value, "file");
	}

	static void log_ls(const char* dirname) {
	std::array<const char*, 3> argv = {"ls", "-laZ", dirname};
	int status = 0;
	auto res =
	logwrap_fork_execvp(argv.size(), argv.data(), &status, false, LOG_ALOG, false, nullptr);
	if (res != 0) {
	PLOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2] << "failed";
	return;
	}
	if (!WIFEXITED(status)) {
	LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
	<< " did not exit normally, status: " << status;
	return;
	}
	if (WEXITSTATUS(status) != 0) {
	LOG(ERROR) << argv[0] << " " << argv[1] << " " << argv[2]
	<< " returned failure: " << WEXITSTATUS(status);
	return;
	}
	}

	static void keyrefstring(const char* key_raw_ref, size_t key_raw_ref_length, char* hex) {
	size_t j = 0;
	for (size_t i = 0; i < key_raw_ref_length; i++) {
	hex[j++] = HEX_LOOKUP[(key_raw_ref[i] & 0xF0) >> 4];
	hex[j++] = HEX_LOOKUP[key_raw_ref[i] & 0x0F];
	}
	hex[j] = '\0';
	}

	static uint8_t fscrypt_get_policy_flags(int filenames_encryption_mode, int policy_version) {
	uint8_t flags = 0;

	// In the original setting of v1 policies and AES-256-CTS we used 4-byte
	// padding of filenames, so we have to retain that for compatibility.
	//
	// For everything else, use 16-byte padding. This is more secure (it helps
	// hide the length of filenames), and it makes the inputs evenly divisible
	// into cipher blocks which is more efficient for encryption and decryption.
	if (policy_version == 1 && filenames_encryption_mode == FS_ENCRYPTION_MODE_AES_256_CTS) {
	flags \|= FS_POLICY_FLAGS_PAD_4;
	} else {
	flags \|= FS_POLICY_FLAGS_PAD_16;
	}

	// Use DIRECT_KEY for Adiantum, since it's much more efficient but just as
	// secure since Android doesn't reuse the same master key for multiple
	// encryption modes.
	if (filenames_encryption_mode == FS_ENCRYPTION_MODE_ADIANTUM) {
	flags \|= FS_POLICY_FLAG_DIRECT_KEY;
	}

	return flags;
	}

	static bool fscrypt_is_encrypted(int fd) {
	fscrypt_policy_v1 policy;

	// success => encrypted with v1 policy
	// EINVAL => encrypted with v2 policy
	// ENODATA => not encrypted
	return ioctl(fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) == 0 \|\| errno == EINVAL;
	}

	int fscrypt_policy_ensure(const char* directory, const char* key_raw_ref, size_t key_raw_ref_length,
	const char* contents_encryption_mode,
	const char* filenames_encryption_mode, int policy_version) {
	int contents_mode = 0;
	int filenames_mode = 0;

	if (!strcmp(contents_encryption_mode, "software") \|\|
	!strcmp(contents_encryption_mode, "aes-256-xts")) {
	contents_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
	} else if (!strcmp(contents_encryption_mode, "adiantum")) {
	contents_mode = FS_ENCRYPTION_MODE_ADIANTUM;
	} else if (!strcmp(contents_encryption_mode, "ice")) {
	contents_mode = FS_ENCRYPTION_MODE_PRIVATE;
	} else {
	LOG(ERROR) << "Invalid file contents encryption mode: "
	<< contents_encryption_mode;
	return -1;
	}

	if (!strcmp(filenames_encryption_mode, "aes-256-cts")) {
	filenames_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
	} else if (!strcmp(filenames_encryption_mode, "aes-256-heh")) {
	filenames_mode = FS_ENCRYPTION_MODE_AES_256_HEH;
	} else if (!strcmp(filenames_encryption_mode, "adiantum")) {
	filenames_mode = FS_ENCRYPTION_MODE_ADIANTUM;
	} else {
	LOG(ERROR) << "Invalid file names encryption mode: "
	<< filenames_encryption_mode;
	return -1;
	}

	union {
	fscrypt_policy_v1 v1;
	fscrypt_policy_v2 v2;
	} policy;
	memset(&policy, 0, sizeof(policy));

	switch (policy_version) {
	case 1:
	if (key_raw_ref_length != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
	LOG(ERROR) << "Invalid key ref length for v1 policy: " << key_raw_ref_length;
	return -1;
	}
	// Careful: FSCRYPT_POLICY_V1 is actually 0 in the API, so make sure
	// to use it here instead of a literal 1.
	policy.v1.version = FSCRYPT_POLICY_V1;
	policy.v1.contents_encryption_mode = contents_mode;
	policy.v1.filenames_encryption_mode = filenames_mode;
	policy.v1.flags = fscrypt_get_policy_flags(filenames_mode, policy_version);
	memcpy(policy.v1.master_key_descriptor, key_raw_ref, FSCRYPT_KEY_DESCRIPTOR_SIZE);
	break;
	case 2:
	if (key_raw_ref_length != FSCRYPT_KEY_IDENTIFIER_SIZE) {
	LOG(ERROR) << "Invalid key ref length for v2 policy: " << key_raw_ref_length;
	return -1;
	}
	policy.v2.version = FSCRYPT_POLICY_V2;
	policy.v2.contents_encryption_mode = contents_mode;
	policy.v2.filenames_encryption_mode = filenames_mode;
	policy.v2.flags = fscrypt_get_policy_flags(filenames_mode, policy_version);
	memcpy(policy.v2.master_key_identifier, key_raw_ref, FSCRYPT_KEY_IDENTIFIER_SIZE);
	break;
	default:
	LOG(ERROR) << "Invalid encryption policy version: " << policy_version;
	return -1;
	}

	char ref[MAX_KEY_REF_SIZE_HEX];
	keyrefstring(key_raw_ref, key_raw_ref_length, ref);

	android::base::unique_fd fd(open(directory, O_DIRECTORY \| O_NOFOLLOW \| O_CLOEXEC));
	if (fd == -1) {
	PLOG(ERROR) << "Failed to open directory " << directory;
	return -1;
	}

	bool already_encrypted = fscrypt_is_encrypted(fd);

	// FS_IOC_SET_ENCRYPTION_POLICY will set the policy if the directory is
	// unencrypted; otherwise it will verify that the existing policy matches.
	// Setting the policy will fail if the directory is already nonempty.
	if (ioctl(fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) != 0) {
	std::string reason;
	switch (errno) {
	case EEXIST:
	reason = "The directory already has a different encryption policy.";
	break;
	default:
	reason = strerror(errno);
	break;
	}
	LOG(ERROR) << "Failed to set encryption policy of " << directory << " to " << ref
	<< " modes " << contents_mode << "/" << filenames_mode << ": " << reason;
	if (errno == ENOTEMPTY) {
	log_ls(directory);
	}
	return -1;
	}

	if (already_encrypted) {
	LOG(INFO) << "Verified that " << directory << " has the encryption policy " << ref
	<< " modes " << contents_mode << "/" << filenames_mode;
	} else {
	LOG(INFO) << "Encryption policy of " << directory << " set to " << ref << " modes "
	<< contents_mode << "/" << filenames_mode;
	}
	return 0;
	}