3e9c996ab0
aosp/1184798 has updated the kernel headers to 5.4, so we no longer need the file fscrypt_uapi.h. In KeyUtil.cpp we also now don't need <linux/fs.h>, but rather just the more specific <linux/fscrypt.h>. Test: build Bug: None Change-Id: I56d17826eb7c3b95c74ce0435a4feae7f3cc325e
370 lines
14 KiB
C++
370 lines
14 KiB
C++
/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "KeyUtil.h"
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#include <iomanip>
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#include <sstream>
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#include <string>
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#include <fcntl.h>
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#include <linux/fscrypt.h>
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#include <openssl/sha.h>
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#include <sys/ioctl.h>
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#include <android-base/file.h>
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#include <android-base/logging.h>
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#include <keyutils.h>
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#include "KeyStorage.h"
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#include "Utils.h"
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namespace android {
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namespace vold {
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constexpr int FS_AES_256_XTS_KEY_SIZE = 64;
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bool randomKey(KeyBuffer* key) {
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*key = KeyBuffer(FS_AES_256_XTS_KEY_SIZE);
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if (ReadRandomBytes(key->size(), key->data()) != 0) {
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// TODO status_t plays badly with PLOG, fix it.
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LOG(ERROR) << "Random read failed";
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return false;
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}
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return true;
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}
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// Return true if the kernel supports the ioctls to add/remove fscrypt keys
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// directly to/from the filesystem.
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bool isFsKeyringSupported(void) {
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static bool initialized = false;
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static bool supported;
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if (!initialized) {
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android::base::unique_fd fd(open("/data", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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// FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY
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// if the ioctl isn't supported. Otherwise it will fail with another
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// error code such as EFAULT.
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errno = 0;
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(void)ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, NULL);
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if (errno == ENOTTY) {
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LOG(INFO) << "Kernel doesn't support FS_IOC_ADD_ENCRYPTION_KEY. Falling back to "
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"session keyring";
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supported = false;
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} else {
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if (errno != EFAULT) {
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PLOG(WARNING) << "Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY";
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}
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LOG(DEBUG) << "Detected support for FS_IOC_ADD_ENCRYPTION_KEY";
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supported = true;
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}
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// There's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY, since it's
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// guaranteed to be available if FS_IOC_ADD_ENCRYPTION_KEY is. There's
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// also no need to check for support on external volumes separately from
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// /data, since either the kernel supports the ioctls on all
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// fscrypt-capable filesystems or it doesn't.
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initialized = true;
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}
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return supported;
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}
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// Get raw keyref - used to make keyname and to pass to ioctl
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static std::string generateKeyRef(const uint8_t* key, int length) {
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SHA512_CTX c;
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SHA512_Init(&c);
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SHA512_Update(&c, key, length);
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unsigned char key_ref1[SHA512_DIGEST_LENGTH];
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SHA512_Final(key_ref1, &c);
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SHA512_Init(&c);
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SHA512_Update(&c, key_ref1, SHA512_DIGEST_LENGTH);
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unsigned char key_ref2[SHA512_DIGEST_LENGTH];
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SHA512_Final(key_ref2, &c);
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static_assert(FS_KEY_DESCRIPTOR_SIZE <= SHA512_DIGEST_LENGTH, "Hash too short for descriptor");
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return std::string((char*)key_ref2, FS_KEY_DESCRIPTOR_SIZE);
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}
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static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
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if (key.size() != FS_AES_256_XTS_KEY_SIZE) {
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LOG(ERROR) << "Wrong size key " << key.size();
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return false;
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}
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static_assert(FS_AES_256_XTS_KEY_SIZE <= sizeof(fs_key->raw), "Key too long!");
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fs_key->mode = FS_ENCRYPTION_MODE_AES_256_XTS;
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fs_key->size = key.size();
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memset(fs_key->raw, 0, sizeof(fs_key->raw));
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memcpy(fs_key->raw, key.data(), key.size());
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return true;
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}
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static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};
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static std::string keyrefstring(const std::string& raw_ref) {
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std::ostringstream o;
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for (unsigned char i : raw_ref) {
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o << std::hex << std::setw(2) << std::setfill('0') << (int)i;
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}
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return o.str();
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}
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static std::string buildLegacyKeyName(const std::string& prefix, const std::string& raw_ref) {
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return prefix + ":" + keyrefstring(raw_ref);
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}
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// Get the ID of the keyring we store all fscrypt keys in when the kernel is too
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// old to support FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.
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static bool fscryptKeyring(key_serial_t* device_keyring) {
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*device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "fscrypt", 0);
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if (*device_keyring == -1) {
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PLOG(ERROR) << "Unable to find device keyring";
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return false;
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}
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return true;
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}
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// Add an encryption key to the legacy global session keyring.
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static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
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// Place fscrypt_key into automatically zeroing buffer.
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KeyBuffer fsKeyBuffer(sizeof(fscrypt_key));
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fscrypt_key& fs_key = *reinterpret_cast<fscrypt_key*>(fsKeyBuffer.data());
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if (!fillKey(key, &fs_key)) return false;
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key_serial_t device_keyring;
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if (!fscryptKeyring(&device_keyring)) return false;
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for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
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auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
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key_serial_t key_id =
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add_key("logon", ref.c_str(), (void*)&fs_key, sizeof(fs_key), device_keyring);
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if (key_id == -1) {
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PLOG(ERROR) << "Failed to insert key into keyring " << device_keyring;
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return false;
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}
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LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
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<< " in process " << getpid();
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}
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return true;
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}
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// Build a struct fscrypt_key_specifier for use in the key management ioctls.
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static bool buildKeySpecifier(fscrypt_key_specifier* spec, const std::string& raw_ref,
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int policy_version) {
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switch (policy_version) {
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case 1:
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if (raw_ref.size() != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
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LOG(ERROR) << "Invalid key specifier size for v1 encryption policy: "
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<< raw_ref.size();
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return false;
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}
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spec->type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
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memcpy(spec->u.descriptor, raw_ref.c_str(), FSCRYPT_KEY_DESCRIPTOR_SIZE);
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return true;
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case 2:
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if (raw_ref.size() != FSCRYPT_KEY_IDENTIFIER_SIZE) {
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LOG(ERROR) << "Invalid key specifier size for v2 encryption policy: "
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<< raw_ref.size();
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return false;
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}
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spec->type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
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memcpy(spec->u.identifier, raw_ref.c_str(), FSCRYPT_KEY_IDENTIFIER_SIZE);
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return true;
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default:
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LOG(ERROR) << "Invalid encryption policy version: " << policy_version;
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return false;
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}
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}
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// Install a file-based encryption key to the kernel, for use by encrypted files
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// on the specified filesystem using the specified encryption policy version.
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//
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// For v1 policies, we use FS_IOC_ADD_ENCRYPTION_KEY if the kernel supports it.
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// Otherwise we add the key to the legacy global session keyring.
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//
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// For v2 policies, we always use FS_IOC_ADD_ENCRYPTION_KEY; it's the only way
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// the kernel supports.
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//
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// Returns %true on success, %false on failure. On success also sets *raw_ref
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// to the raw key reference for use in the encryption policy.
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bool installKey(const KeyBuffer& key, const std::string& mountpoint, int policy_version,
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std::string* raw_ref) {
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// Put the fscrypt_add_key_arg in an automatically-zeroing buffer, since we
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// have to copy the raw key into it.
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KeyBuffer arg_buf(sizeof(struct fscrypt_add_key_arg) + key.size(), 0);
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struct fscrypt_add_key_arg* arg = (struct fscrypt_add_key_arg*)arg_buf.data();
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// Initialize the "key specifier", which is like a name for the key.
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switch (policy_version) {
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case 1:
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// A key for a v1 policy is specified by an arbitrary 8-byte
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// "descriptor", which must be provided by userspace. We use the
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// first 8 bytes from the double SHA-512 of the key itself.
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*raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size());
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if (!isFsKeyringSupported()) {
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return installKeyLegacy(key, *raw_ref);
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}
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if (!buildKeySpecifier(&arg->key_spec, *raw_ref, policy_version)) {
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return false;
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}
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break;
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case 2:
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// A key for a v2 policy is specified by an 16-byte "identifier",
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// which is a cryptographic hash of the key itself which the kernel
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// computes and returns. Any user-provided value is ignored; we
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// just need to set the specifier type to indicate that we're adding
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// this type of key.
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arg->key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
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break;
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default:
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LOG(ERROR) << "Invalid encryption policy version: " << policy_version;
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return false;
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}
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// Provide the raw key.
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arg->raw_size = key.size();
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memcpy(arg->raw, key.data(), key.size());
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android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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if (fd == -1) {
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PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
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return false;
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}
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if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
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PLOG(ERROR) << "Failed to install fscrypt key to " << mountpoint;
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return false;
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}
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if (arg->key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
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// Retrieve the key identifier that the kernel computed.
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*raw_ref = std::string((char*)arg->key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
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}
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LOG(DEBUG) << "Installed fscrypt key with ref " << keyrefstring(*raw_ref) << " to "
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<< mountpoint;
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return true;
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}
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// Remove an encryption key from the legacy global session keyring.
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static bool evictKeyLegacy(const std::string& raw_ref) {
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key_serial_t device_keyring;
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if (!fscryptKeyring(&device_keyring)) return false;
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bool success = true;
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for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
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auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
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auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);
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// Unlink the key from the keyring. Prefer unlinking to revoking or
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// invalidating, since unlinking is actually no less secure currently, and
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// it avoids bugs in certain kernel versions where the keyring key is
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// referenced from places it shouldn't be.
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if (keyctl_unlink(key_serial, device_keyring) != 0) {
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PLOG(ERROR) << "Failed to unlink key with serial " << key_serial << " ref " << ref;
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success = false;
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} else {
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LOG(DEBUG) << "Unlinked key with serial " << key_serial << " ref " << ref;
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}
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}
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return success;
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}
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// Evict a file-based encryption key from the kernel.
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//
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// We use FS_IOC_REMOVE_ENCRYPTION_KEY if the kernel supports it. Otherwise we
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// remove the key from the legacy global session keyring.
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//
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// In the latter case, the caller is responsible for dropping caches.
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bool evictKey(const std::string& mountpoint, const std::string& raw_ref, int policy_version) {
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if (policy_version == 1 && !isFsKeyringSupported()) {
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return evictKeyLegacy(raw_ref);
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}
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android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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if (fd == -1) {
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PLOG(ERROR) << "Failed to open " << mountpoint << " to evict key";
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return false;
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}
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struct fscrypt_remove_key_arg arg;
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memset(&arg, 0, sizeof(arg));
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if (!buildKeySpecifier(&arg.key_spec, raw_ref, policy_version)) {
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return false;
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}
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std::string ref = keyrefstring(raw_ref);
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if (ioctl(fd, FS_IOC_REMOVE_ENCRYPTION_KEY, &arg) != 0) {
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PLOG(ERROR) << "Failed to evict fscrypt key with ref " << ref << " from " << mountpoint;
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return false;
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}
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LOG(DEBUG) << "Evicted fscrypt key with ref " << ref << " from " << mountpoint;
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if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS) {
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// Should never happen because keys are only added/removed as root.
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LOG(ERROR) << "Unexpected case: key with ref " << ref << " is still added by other users!";
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} else if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY) {
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LOG(ERROR) << "Files still open after removing key with ref " << ref
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<< ". These files were not locked!";
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}
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return true;
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}
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bool retrieveAndInstallKey(bool create_if_absent, const KeyAuthentication& key_authentication,
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const std::string& key_path, const std::string& tmp_path,
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const std::string& volume_uuid, int policy_version,
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std::string* key_ref) {
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KeyBuffer key;
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if (pathExists(key_path)) {
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LOG(DEBUG) << "Key exists, using: " << key_path;
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if (!retrieveKey(key_path, key_authentication, &key)) return false;
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} else {
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if (!create_if_absent) {
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LOG(ERROR) << "No key found in " << key_path;
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return false;
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}
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LOG(INFO) << "Creating new key in " << key_path;
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if (!randomKey(&key)) return false;
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if (!storeKeyAtomically(key_path, tmp_path, key_authentication, key)) return false;
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}
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if (!installKey(key, BuildDataPath(volume_uuid), policy_version, key_ref)) {
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LOG(ERROR) << "Failed to install key in " << key_path;
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return false;
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}
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return true;
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}
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bool retrieveKey(bool create_if_absent, const std::string& key_path, const std::string& tmp_path,
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KeyBuffer* key, bool keepOld) {
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if (pathExists(key_path)) {
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LOG(DEBUG) << "Key exists, using: " << key_path;
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if (!retrieveKey(key_path, kEmptyAuthentication, key, keepOld)) return false;
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} else {
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if (!create_if_absent) {
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LOG(ERROR) << "No key found in " << key_path;
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return false;
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}
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LOG(INFO) << "Creating new key in " << key_path;
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if (!randomKey(key)) return false;
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if (!storeKeyAtomically(key_path, tmp_path, kEmptyAuthentication, *key)) return false;
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}
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return true;
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}
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} // namespace vold
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} // namespace android
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