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vold: use new ioctls to add/remove fscrypt keys when supported

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am: f3dc4203dd

Change-Id: I31edb0db46b471233e716b5d277460bb99693d78
This commit is contained in:
Eric Biggers 2019-10-07 12:27:11 -07:00 committed by android-build-merger
commit 12a9212ac1
4 changed files with 221 additions and 31 deletions
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44
FsCrypt.cpp
View file

@ -199,13 +199,23 @@ static bool read_and_fixate_user_ce_key(userid_t user_id,
return false;
}
// Install a key for use by encrypted files on the /data filesystem.
static bool install_data_key(const KeyBuffer& key, std::string* raw_ref) {
return android::vold::installKey(key, DATA_MNT_POINT, raw_ref);
}
// Evict a key for use by encrypted files on the /data filesystem.
static bool evict_data_key(const std::string& raw_ref) {
return android::vold::evictKey(DATA_MNT_POINT, raw_ref);
}
static bool read_and_install_user_ce_key(userid_t user_id,
const android::vold::KeyAuthentication& auth) {
if (s_ce_key_raw_refs.count(user_id) != 0) return true;
KeyBuffer ce_key;
if (!read_and_fixate_user_ce_key(user_id, auth, &ce_key)) return false;
std::string ce_raw_ref;
if (!android::vold::installKey(ce_key, &ce_raw_ref)) return false;
if (!install_data_key(ce_key, &ce_raw_ref)) return false;
s_ce_keys[user_id] = std::move(ce_key);
s_ce_key_raw_refs[user_id] = ce_raw_ref;
LOG(DEBUG) << "Installed ce key for user " << user_id;
@ -255,10 +265,10 @@ static bool create_and_install_user_keys(userid_t user_id, bool create_ephemeral
return false;
}
std::string de_raw_ref;
if (!android::vold::installKey(de_key, &de_raw_ref)) return false;
if (!install_data_key(de_key, &de_raw_ref)) return false;
s_de_key_raw_refs[user_id] = de_raw_ref;
std::string ce_raw_ref;
if (!android::vold::installKey(ce_key, &ce_raw_ref)) return false;
if (!install_data_key(ce_key, &ce_raw_ref)) return false;
s_ce_keys[user_id] = ce_key;
s_ce_key_raw_refs[user_id] = ce_raw_ref;
LOG(DEBUG) << "Created keys for user " << user_id;
@ -325,7 +335,7 @@ static bool load_all_de_keys() {
KeyBuffer key;
if (!android::vold::retrieveKey(key_path, kEmptyAuthentication, &key)) return false;
std::string raw_ref;
if (!android::vold::installKey(key, &raw_ref)) return false;
if (!install_data_key(key, &raw_ref)) return false;
s_de_key_raw_refs[user_id] = raw_ref;
LOG(DEBUG) << "Installed de key for user " << user_id;
}
@ -345,7 +355,7 @@ bool fscrypt_initialize_systemwide_keys() {
PolicyKeyRef device_ref;
if (!android::vold::retrieveAndInstallKey(true, kEmptyAuthentication, device_key_path,
device_key_temp, &device_ref.key_raw_ref))
device_key_temp, "", &device_ref.key_raw_ref))
return false;
get_data_file_encryption_modes(&device_ref);
@ -360,7 +370,7 @@ bool fscrypt_initialize_systemwide_keys() {
KeyBuffer per_boot_key;
if (!android::vold::randomKey(&per_boot_key)) return false;
std::string per_boot_raw_ref;
if (!android::vold::installKey(per_boot_key, &per_boot_raw_ref)) return false;
if (!install_data_key(per_boot_key, &per_boot_raw_ref)) return false;
std::string per_boot_ref_filename = std::string("/data") + fscrypt_key_per_boot_ref;
if (!android::vold::writeStringToFile(per_boot_raw_ref, per_boot_ref_filename)) return false;
LOG(INFO) << "Wrote per boot key reference to:" << per_boot_ref_filename;
@ -419,15 +429,20 @@ bool fscrypt_vold_create_user_key(userid_t user_id, int serial, bool ephemeral)
}
// "Lock" all encrypted directories whose key has been removed. This is needed
// because merely removing the keyring key doesn't affect inodes in the kernel's
// inode cache whose per-file key was already set up. So to remove the per-file
// keys and make the files "appear encrypted", these inodes must be evicted.
// in the case where the keys are being put in the session keyring (rather in
// the newer filesystem-level keyrings), because removing a key from the session
// keyring doesn't affect inodes in the kernel's inode cache whose per-file key
// was already set up. So to remove the per-file keys and make the files
// "appear encrypted", these inodes must be evicted.
//
// To do this, sync() to clean all dirty inodes, then drop all reclaimable slab
// objects systemwide. This is overkill, but it's the best available method
// currently. Don't use drop_caches mode "3" because that also evicts pagecache
// for in-use files; all files relevant here are already closed and sync'ed.
static void drop_caches() {
static void drop_caches_if_needed() {
if (android::vold::isFsKeyringSupported()) {
return;
}
sync();
if (!writeStringToFile("2", "/proc/sys/vm/drop_caches")) {
PLOG(ERROR) << "Failed to drop caches during key eviction";
@ -440,8 +455,8 @@ static bool evict_ce_key(userid_t user_id) {
std::string raw_ref;
// If we haven't loaded the CE key, no need to evict it.
if (lookup_key_ref(s_ce_key_raw_refs, user_id, &raw_ref)) {
success &= android::vold::evictKey(raw_ref);
drop_caches();
success &= evict_data_key(raw_ref);
drop_caches_if_needed();
}
s_ce_key_raw_refs.erase(user_id);
return success;
@ -455,8 +470,7 @@ bool fscrypt_destroy_user_key(userid_t user_id) {
bool success = true;
std::string raw_ref;
success &= evict_ce_key(user_id);
success &=
lookup_key_ref(s_de_key_raw_refs, user_id, &raw_ref) && android::vold::evictKey(raw_ref);
success &= lookup_key_ref(s_de_key_raw_refs, user_id, &raw_ref) && evict_data_key(raw_ref);
s_de_key_raw_refs.erase(user_id);
auto it = s_ephemeral_users.find(user_id);
if (it != s_ephemeral_users.end()) {
@ -546,7 +560,7 @@ static bool read_or_create_volkey(const std::string& misc_path, const std::strin
return false;
}
android::vold::KeyAuthentication auth("", secdiscardable_hash);
if (!android::vold::retrieveAndInstallKey(true, auth, key_path, key_path + "_tmp",
if (!android::vold::retrieveAndInstallKey(true, auth, key_path, key_path + "_tmp", volume_uuid,
&key_ref->key_raw_ref))
return false;
key_ref->contents_mode =

151
KeyUtil.cpp
View file

@ -16,12 +16,14 @@
#include "KeyUtil.h"
#include <linux/fs.h>
#include <iomanip>
#include <sstream>
#include <string>
#include <fcntl.h>
#include <linux/fs.h>
#include <openssl/sha.h>
#include <sys/ioctl.h>
#include <android-base/file.h>
#include <android-base/logging.h>
@ -29,6 +31,7 @@
#include "KeyStorage.h"
#include "Utils.h"
#include "fscrypt_uapi.h"
namespace android {
namespace vold {
@ -45,6 +48,42 @@ bool randomKey(KeyBuffer* key) {
return true;
}
// Return true if the kernel supports the ioctls to add/remove fscrypt keys
// directly to/from the filesystem.
bool isFsKeyringSupported(void) {
static bool initialized = false;
static bool supported;
if (!initialized) {
android::base::unique_fd fd(open("/data", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
// FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY
// if the ioctl isn't supported. Otherwise it will fail with another
// error code such as EFAULT.
errno = 0;
(void)ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, NULL);
if (errno == ENOTTY) {
LOG(INFO) << "Kernel doesn't support FS_IOC_ADD_ENCRYPTION_KEY. Falling back to "
"session keyring";
supported = false;
} else {
if (errno != EFAULT) {
PLOG(WARNING) << "Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY";
}
LOG(DEBUG) << "Detected support for FS_IOC_ADD_ENCRYPTION_KEY";
supported = true;
}
// There's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY, since it's
// guaranteed to be available if FS_IOC_ADD_ENCRYPTION_KEY is. There's
// also no need to check for support on external volumes separately from
// /data, since either the kernel supports the ioctls on all
// fscrypt-capable filesystems or it doesn't.
initialized = true;
}
return supported;
}
// Get raw keyref - used to make keyname and to pass to ioctl
static std::string generateKeyRef(const uint8_t* key, int length) {
SHA512_CTX c;
@ -78,16 +117,20 @@ static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};
static std::string keyname(const std::string& prefix, const std::string& raw_ref) {
static std::string keyrefstring(const std::string& raw_ref) {
std::ostringstream o;
o << prefix << ":";
for (unsigned char i : raw_ref) {
o << std::hex << std::setw(2) << std::setfill('0') << (int)i;
}
return o.str();
}
// Get the keyring we store all keys in
static std::string buildLegacyKeyName(const std::string& prefix, const std::string& raw_ref) {
return prefix + ":" + keyrefstring(raw_ref);
}
// Get the ID of the keyring we store all fscrypt keys in when the kernel is too
// old to support FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.
static bool fscryptKeyring(key_serial_t* device_keyring) {
*device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "fscrypt", 0);
if (*device_keyring == -1) {
@ -97,19 +140,17 @@ static bool fscryptKeyring(key_serial_t* device_keyring) {
return true;
}
// Install password into global keyring
// Return raw key reference for use in policy
bool installKey(const KeyBuffer& key, std::string* raw_ref) {
// Add an encryption key to the legacy global session keyring.
static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
// Place fscrypt_key into automatically zeroing buffer.
KeyBuffer fsKeyBuffer(sizeof(fscrypt_key));
fscrypt_key& fs_key = *reinterpret_cast<fscrypt_key*>(fsKeyBuffer.data());
if (!fillKey(key, &fs_key)) return false;
*raw_ref = generateKeyRef(fs_key.raw, fs_key.size);
key_serial_t device_keyring;
if (!fscryptKeyring(&device_keyring)) return false;
for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
auto ref = keyname(*name_prefix, *raw_ref);
auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
key_serial_t key_id =
add_key("logon", ref.c_str(), (void*)&fs_key, sizeof(fs_key), device_keyring);
if (key_id == -1) {
@ -122,12 +163,55 @@ bool installKey(const KeyBuffer& key, std::string* raw_ref) {
return true;
}
bool evictKey(const std::string& raw_ref) {
// Install a file-based encryption key to the kernel, for use by encrypted files
// on the specified filesystem.
//
// We use FS_IOC_ADD_ENCRYPTION_KEY if the kernel supports it. Otherwise we add
// the key to the legacy global session keyring.
//
// Returns %true on success, %false on failure. On success also sets *raw_ref
// to the raw key reference for use in the encryption policy.
bool installKey(const KeyBuffer& key, const std::string& mountpoint, std::string* raw_ref) {
*raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size());
if (!isFsKeyringSupported()) {
return installKeyLegacy(key, *raw_ref);
}
// Put the fscrypt_add_key_arg in an automatically-zeroing buffer, since we
// have to copy the raw key into it.
KeyBuffer arg_buf(sizeof(struct fscrypt_add_key_arg) + key.size(), 0);
struct fscrypt_add_key_arg* arg = (struct fscrypt_add_key_arg*)arg_buf.data();
arg->key_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
memcpy(arg->key_spec.u.descriptor, raw_ref.c_str(), FSCRYPT_KEY_DESCRIPTOR_SIZE);
arg->raw_size = key.size();
memcpy(arg->raw, key.data(), key.size());
android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
if (fd == -1) {
PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
return false;
}
if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
PLOG(ERROR) << "Failed to install fscrypt key with ref " << keyrefstring(*raw_ref) << " to "
<< mountpoint;
return false;
}
LOG(DEBUG) << "Installed fscrypt key with ref " << keyrefstring(*raw_ref) << " to "
<< mountpoint;
return true;
}
// Remove an encryption key from the legacy global session keyring.
static bool evictKeyLegacy(const std::string& raw_ref) {
key_serial_t device_keyring;
if (!fscryptKeyring(&device_keyring)) return false;
bool success = true;
for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
auto ref = keyname(*name_prefix, raw_ref);
auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);
// Unlink the key from the keyring. Prefer unlinking to revoking or
@ -144,9 +228,50 @@ bool evictKey(const std::string& raw_ref) {
return success;
}
// Evict a file-based encryption key from the kernel.
//
// We use FS_IOC_REMOVE_ENCRYPTION_KEY if the kernel supports it. Otherwise we
// remove the key from the legacy global session keyring.
//
// In the latter case, the caller is responsible for dropping caches.
bool evictKey(const std::string& mountpoint, const std::string& raw_ref) {
if (!isFsKeyringSupported()) {
return evictKeyLegacy(raw_ref);
}
android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
if (fd == -1) {
PLOG(ERROR) << "Failed to open " << mountpoint << " to evict key";
return false;
}
struct fscrypt_remove_key_arg arg;
memset(&arg, 0, sizeof(arg));
arg.key_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
memcpy(arg.key_spec.u.descriptor, raw_ref.c_str(), FSCRYPT_KEY_DESCRIPTOR_SIZE);
std::string ref = keyrefstring(raw_ref);
if (ioctl(fd, FS_IOC_REMOVE_ENCRYPTION_KEY, &arg) != 0) {
PLOG(ERROR) << "Failed to evict fscrypt key with ref " << ref << " from " << mountpoint;
return false;
}
LOG(DEBUG) << "Evicted fscrypt key with ref " << ref << " from " << mountpoint;
if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS) {
// Should never happen because keys are only added/removed as root.
LOG(ERROR) << "Unexpected case: key with ref " << ref << " is still added by other users!";
} else if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY) {
LOG(ERROR) << "Files still open after removing key with ref " << ref
<< ". These files were not locked!";
}
return true;
}
bool retrieveAndInstallKey(bool create_if_absent, const KeyAuthentication& key_authentication,
const std::string& key_path, const std::string& tmp_path,
std::string* key_ref) {
const std::string& volume_uuid, std::string* key_ref) {
KeyBuffer key;
if (pathExists(key_path)) {
LOG(DEBUG) << "Key exists, using: " << key_path;
@ -161,7 +286,7 @@ bool retrieveAndInstallKey(bool create_if_absent, const KeyAuthentication& key_a
if (!storeKeyAtomically(key_path, tmp_path, key_authentication, key)) return false;
}
if (!installKey(key, key_ref)) {
if (!installKey(key, BuildDataPath(volume_uuid), key_ref)) {
LOG(ERROR) << "Failed to install key in " << key_path;
return false;
}

9
KeyUtil.h
View file

@ -27,11 +27,14 @@ namespace android {
namespace vold {
bool randomKey(KeyBuffer* key);
bool installKey(const KeyBuffer& key, std::string* raw_ref);
bool evictKey(const std::string& raw_ref);
bool isFsKeyringSupported(void);
bool installKey(const KeyBuffer& key, const std::string& mountpoint, std::string* raw_ref);
bool evictKey(const std::string& mountpoint, const std::string& raw_ref);
bool retrieveAndInstallKey(bool create_if_absent, const KeyAuthentication& key_authentication,
const std::string& key_path, const std::string& tmp_path,
std::string* key_ref);
const std::string& volume_uuid, std::string* key_ref);
bool retrieveKey(bool create_if_absent, const std::string& key_path, const std::string& tmp_path,
KeyBuffer* key, bool keepOld = true);

48
fscrypt_uapi.h Normal file
View file

@ -0,0 +1,48 @@
#ifndef _UAPI_LINUX_FSCRYPT_H
#define _UAPI_LINUX_FSCRYPT_H
// Definitions for FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY
// TODO: switch to <linux/fscrypt.h> once it's in Bionic
#ifndef FS_IOC_ADD_ENCRYPTION_KEY
#include <linux/types.h>
#define FSCRYPT_KEY_DESCRIPTOR_SIZE 8
#define FSCRYPT_KEY_IDENTIFIER_SIZE 16
#define FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR 1
#define FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER 2
struct fscrypt_key_specifier {
__u32 type;
__u32 __reserved;
union {
__u8 __reserved[32];
__u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
__u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
} u;
};
struct fscrypt_add_key_arg {
struct fscrypt_key_specifier key_spec;
__u32 raw_size;
__u32 __reserved[9];
__u8 raw[];
};
struct fscrypt_remove_key_arg {
struct fscrypt_key_specifier key_spec;
#define FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY 0x00000001
#define FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS 0x00000002
__u32 removal_status_flags;
__u32 __reserved[5];
};
#define FS_IOC_ADD_ENCRYPTION_KEY _IOWR('f', 23, struct fscrypt_add_key_arg)
#define FS_IOC_REMOVE_ENCRYPTION_KEY _IOWR('f', 24, struct fscrypt_remove_key_arg)
#endif /* FS_IOC_ADD_ENCRYPTION_KEY */
#endif /* _UAPI_LINUX_FSCRYPT_H */