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Systemd/src/home/homework-fscrypt.c

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/* SPDX-License-Identifier: LGPL-2.1+ */
#include <linux/fs.h>
#include <openssl/evp.h>
#include <openssl/sha.h>
#include <sys/ioctl.h>
#include <sys/xattr.h>
#include "errno-util.h"
#include "fd-util.h"
#include "hexdecoct.h"
#include "homework-fscrypt.h"
#include "homework-quota.h"
#include "memory-util.h"
#include "missing_keyctl.h"
#include "missing_syscall.h"
#include "mkdir.h"
#include "nulstr-util.h"
#include "openssl-util.h"
#include "parse-util.h"
#include "process-util.h"
#include "random-util.h"
#include "rm-rf.h"
#include "stdio-util.h"
#include "strv.h"
#include "tmpfile-util.h"
#include "user-util.h"
#include "xattr-util.h"
static int fscrypt_upload_volume_key(
const uint8_t key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
const void *volume_key,
size_t volume_key_size,
key_serial_t where) {
_cleanup_free_ char *hex = NULL;
const char *description;
struct fscrypt_key key;
key_serial_t serial;
assert(key_descriptor);
assert(volume_key);
assert(volume_key_size > 0);
if (volume_key_size > sizeof(key.raw))
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Volume key too long.");
hex = hexmem(key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
if (!hex)
return log_oom();
description = strjoina("fscrypt:", hex);
key = (struct fscrypt_key) {
.size = volume_key_size,
};
memcpy(key.raw, volume_key, volume_key_size);
/* Upload to the kernel */
serial = add_key("logon", description, &key, sizeof(key), where);
explicit_bzero_safe(&key, sizeof(key));
if (serial < 0)
return log_error_errno(errno, "Failed to install master key in keyring: %m");
log_info("Uploaded encryption key to kernel.");
return 0;
}
static void calculate_key_descriptor(
const void *key,
size_t key_size,
uint8_t ret_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE]) {
uint8_t hashed[512 / 8] = {}, hashed2[512 / 8] = {};
/* Derive the key descriptor from the volume key via double SHA512, in order to be compatible with e4crypt */
assert_se(SHA512(key, key_size, hashed) == hashed);
assert_se(SHA512(hashed, sizeof(hashed), hashed2) == hashed2);
assert_cc(sizeof(hashed2) >= FS_KEY_DESCRIPTOR_SIZE);
memcpy(ret_key_descriptor, hashed2, FS_KEY_DESCRIPTOR_SIZE);
}
static int fscrypt_slot_try_one(
const char *password,
const void *salt, size_t salt_size,
const void *encrypted, size_t encrypted_size,
const uint8_t match_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
void **ret_decrypted, size_t *ret_decrypted_size) {
_cleanup_(EVP_CIPHER_CTX_freep) EVP_CIPHER_CTX *context = NULL;
_cleanup_(erase_and_freep) void *decrypted = NULL;
uint8_t key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
int decrypted_size_out1, decrypted_size_out2;
uint8_t derived[512 / 8] = {};
size_t decrypted_size;
const EVP_CIPHER *cc;
int r;
assert(password);
assert(salt);
assert(salt_size > 0);
assert(encrypted);
assert(encrypted_size > 0);
assert(match_key_descriptor);
/* Our construction is like this:
*
* 1. In each key slot we store a salt value plus the encrypted volume key
*
* 2. Unlocking is via calculating PBKDF2-HMAC-SHA512 of the supplied password (in combination with
* the salt), then using the first 256 bit of the hash as key for decrypting the encrypted
* volume key in AES256 counter mode.
*
* 3. Writing a password is similar: calculate PBKDF2-HMAC-SHA512 of the supplied password (in
* combination with the salt), then encrypt the volume key in AES256 counter mode with the
* resulting hash.
*/
if (PKCS5_PBKDF2_HMAC(
password, strlen(password),
salt, salt_size,
0xFFFF, EVP_sha512(),
sizeof(derived), derived) != 1) {
r = log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "PBKDF2 failed");
goto finish;
}
context = EVP_CIPHER_CTX_new();
if (!context) {
r = log_oom();
goto finish;
}
/* We use AES256 in counter mode */
assert_se(cc = EVP_aes_256_ctr());
/* We only use the first half of the derived key */
assert(sizeof(derived) >= (size_t) EVP_CIPHER_key_length(cc));
if (EVP_DecryptInit_ex(context, cc, NULL, derived, NULL) != 1) {
r = log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to initialize decryption context.");
goto finish;
}
/* Flush out the derived key now, we don't need it anymore */
explicit_bzero_safe(derived, sizeof(derived));
decrypted_size = encrypted_size + EVP_CIPHER_key_length(cc) * 2;
decrypted = malloc(decrypted_size);
if (!decrypted)
return log_oom();
if (EVP_DecryptUpdate(context, (uint8_t*) decrypted, &decrypted_size_out1, encrypted, encrypted_size) != 1)
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to decrypt volume key.");
assert((size_t) decrypted_size_out1 <= decrypted_size);
if (EVP_DecryptFinal_ex(context, (uint8_t*) decrypted_size + decrypted_size_out1, &decrypted_size_out2) != 1)
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to finish decryption of volume key.");
assert((size_t) decrypted_size_out1 + (size_t) decrypted_size_out2 < decrypted_size);
decrypted_size = (size_t) decrypted_size_out1 + (size_t) decrypted_size_out2;
calculate_key_descriptor(decrypted, decrypted_size, key_descriptor);
if (memcmp(key_descriptor, match_key_descriptor, FS_KEY_DESCRIPTOR_SIZE) != 0)
return -ENOANO; /* don't log here */
r = fscrypt_upload_volume_key(key_descriptor, decrypted, decrypted_size, KEY_SPEC_THREAD_KEYRING);
if (r < 0)
return r;
if (ret_decrypted)
*ret_decrypted = TAKE_PTR(decrypted);
if (ret_decrypted_size)
*ret_decrypted_size = decrypted_size;
return 0;
finish:
explicit_bzero_safe(derived, sizeof(derived));
return r;
}
static int fscrypt_slot_try_many(
char **passwords,
const void *salt, size_t salt_size,
const void *encrypted, size_t encrypted_size,
const uint8_t match_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
void **ret_decrypted, size_t *ret_decrypted_size) {
char **i;
int r;
STRV_FOREACH(i, passwords) {
r = fscrypt_slot_try_one(*i, salt, salt_size, encrypted, encrypted_size, match_key_descriptor, ret_decrypted, ret_decrypted_size);
if (r != -ENOANO)
return r;
}
return -ENOANO;
}
static int fscrypt_setup(
char **pkcs11_decrypted_passwords,
char **password,
HomeSetup *setup,
void **ret_volume_key,
size_t *ret_volume_key_size) {
_cleanup_free_ char *xattr_buf = NULL;
const char *xa;
int r;
assert(setup);
assert(setup->root_fd >= 0);
r = flistxattr_malloc(setup->root_fd, &xattr_buf);
if (r < 0)
return log_error_errno(errno, "Failed to retrieve xattr list: %m");
NULSTR_FOREACH(xa, xattr_buf) {
_cleanup_free_ void *salt = NULL, *encrypted = NULL;
_cleanup_free_ char *value = NULL;
size_t salt_size, encrypted_size;
const char *nr, *e;
int n;
/* Check if this xattr has the format 'trusted.fscrypt_slot<nr>' where '<nr>' is a 32bit unsigned integer */
nr = startswith(xa, "trusted.fscrypt_slot");
if (!nr)
continue;
if (safe_atou32(nr, NULL) < 0)
continue;
n = fgetxattr_malloc(setup->root_fd, xa, &value);
if (n == -ENODATA) /* deleted by now? */
continue;
if (n < 0)
return log_error_errno(n, "Failed to read %s xattr: %m", xa);
e = memchr(value, ':', n);
if (!e)
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "xattr %s lacks ':' separator: %m", xa);
r = unbase64mem(value, e - value, &salt, &salt_size);
if (r < 0)
return log_error_errno(r, "Failed to decode salt of %s: %m", xa);
r = unbase64mem(e+1, n - (e - value) - 1, &encrypted, &encrypted_size);
if (r < 0)
return log_error_errno(r, "Failed to decode encrypted key of %s: %m", xa);
r = fscrypt_slot_try_many(
pkcs11_decrypted_passwords,
salt, salt_size,
encrypted, encrypted_size,
setup->fscrypt_key_descriptor,
ret_volume_key, ret_volume_key_size);
if (r == -ENOANO)
r = fscrypt_slot_try_many(
password,
salt, salt_size,
encrypted, encrypted_size,
setup->fscrypt_key_descriptor,
ret_volume_key, ret_volume_key_size);
if (r < 0) {
if (r != -ENOANO)
return r;
} else
return 0;
}
return log_error_errno(SYNTHETIC_ERRNO(ENOKEY), "Failed to set up home directory with provided passwords.");
}
int home_prepare_fscrypt(
UserRecord *h,
bool already_activated,
char ***pkcs11_decrypted_passwords,
HomeSetup *setup) {
_cleanup_(erase_and_freep) void *volume_key = NULL;
struct fscrypt_policy policy = {};
size_t volume_key_size = 0;
const char *ip;
int r;
assert(h);
assert(setup);
assert(user_record_storage(h) == USER_FSCRYPT);
assert_se(ip = user_record_image_path(h));
setup->root_fd = open(ip, O_RDONLY|O_CLOEXEC|O_DIRECTORY);
if (setup->root_fd < 0)
return log_error_errno(errno, "Failed to open home directory: %m");
if (ioctl(setup->root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
if (errno == ENODATA)
return log_error_errno(errno, "Home directory %s is not encrypted.", ip);
if (ERRNO_IS_NOT_SUPPORTED(errno)) {
log_error_errno(errno, "File system does not support fscrypt: %m");
return -ENOLINK; /* make recognizable */
}
return log_error_errno(errno, "Failed to acquire encryption policy of %s: %m", ip);
}
memcpy(setup->fscrypt_key_descriptor, policy.master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
r = fscrypt_setup(
pkcs11_decrypted_passwords ? *pkcs11_decrypted_passwords : NULL,
h->password,
setup,
&volume_key,
&volume_key_size);
if (r < 0)
return r;
/* Also install the access key in the user's own keyring */
if (uid_is_valid(h->uid)) {
r = safe_fork("(sd-addkey)", FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_DEATHSIG|FORK_LOG|FORK_WAIT, NULL);
if (r < 0)
return log_error_errno(r, "Failed install encryption key in user's keyring: %m");
if (r == 0) {
gid_t gid;
/* Child */
gid = user_record_gid(h);
if (setresgid(gid, gid, gid) < 0) {
log_error_errno(errno, "Failed to change GID to " GID_FMT ": %m", gid);
_exit(EXIT_FAILURE);
}
if (setgroups(0, NULL) < 0) {
log_error_errno(errno, "Failed to reset auxiliary groups list: %m");
_exit(EXIT_FAILURE);
}
if (setresuid(h->uid, h->uid, h->uid) < 0) {
log_error_errno(errno, "Failed to change UID to " UID_FMT ": %m", h->uid);
_exit(EXIT_FAILURE);
}
r = fscrypt_upload_volume_key(
setup->fscrypt_key_descriptor,
volume_key,
volume_key_size,
KEY_SPEC_USER_KEYRING);
if (r < 0)
_exit(EXIT_FAILURE);
_exit(EXIT_SUCCESS);
}
}
return 0;
}
static int fscrypt_slot_set(
int root_fd,
const void *volume_key,
size_t volume_key_size,
const char *password,
uint32_t nr) {
_cleanup_free_ char *salt_base64 = NULL, *encrypted_base64 = NULL, *joined = NULL;
char label[STRLEN("trusted.fscrypt_slot") + DECIMAL_STR_MAX(nr) + 1];
_cleanup_(EVP_CIPHER_CTX_freep) EVP_CIPHER_CTX *context = NULL;
int r, encrypted_size_out1, encrypted_size_out2;
uint8_t salt[64], derived[512 / 8] = {};
_cleanup_free_ void *encrypted = NULL;
const EVP_CIPHER *cc;
size_t encrypted_size;
r = genuine_random_bytes(salt, sizeof(salt), RANDOM_BLOCK);
if (r < 0)
return log_error_errno(r, "Failed to generate salt: %m");
if (PKCS5_PBKDF2_HMAC(
password, strlen(password),
salt, sizeof(salt),
0xFFFF, EVP_sha512(),
sizeof(derived), derived) != 1) {
r = log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "PBKDF2 failed");
goto finish;
}
context = EVP_CIPHER_CTX_new();
if (!context) {
r = log_oom();
goto finish;
}
/* We use AES256 in counter mode */
cc = EVP_aes_256_ctr();
/* We only use the first half of the derived key */
assert(sizeof(derived) >= (size_t) EVP_CIPHER_key_length(cc));
if (EVP_EncryptInit_ex(context, cc, NULL, derived, NULL) != 1) {
r = log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to initialize encryption context.");
goto finish;
}
/* Flush out the derived key now, we don't need it anymore */
explicit_bzero_safe(derived, sizeof(derived));
encrypted_size = volume_key_size + EVP_CIPHER_key_length(cc) * 2;
encrypted = malloc(encrypted_size);
if (!encrypted)
return log_oom();
if (EVP_EncryptUpdate(context, (uint8_t*) encrypted, &encrypted_size_out1, volume_key, volume_key_size) != 1)
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to encrypt volume key.");
assert((size_t) encrypted_size_out1 <= encrypted_size);
if (EVP_EncryptFinal_ex(context, (uint8_t*) encrypted_size + encrypted_size_out1, &encrypted_size_out2) != 1)
return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to finish encryption of volume key.");
assert((size_t) encrypted_size_out1 + (size_t) encrypted_size_out2 < encrypted_size);
encrypted_size = (size_t) encrypted_size_out1 + (size_t) encrypted_size_out2;
r = base64mem(salt, sizeof(salt), &salt_base64);
if (r < 0)
return log_oom();
r = base64mem(encrypted, encrypted_size, &encrypted_base64);
if (r < 0)
return log_oom();
joined = strjoin(salt_base64, ":", encrypted_base64);
if (!joined)
return log_oom();
xsprintf(label, "trusted.fscrypt_slot%" PRIu32, nr);
if (fsetxattr(root_fd, label, joined, strlen(joined), 0) < 0)
return log_error_errno(errno, "Failed to write xattr %s: %m", label);
log_info("Written key slot %s.", label);
return 0;
finish:
explicit_bzero_safe(derived, sizeof(derived));
return r;
}
int home_create_fscrypt(
UserRecord *h,
char **effective_passwords,
UserRecord **ret_home) {
_cleanup_(rm_rf_physical_and_freep) char *temporary = NULL;
_cleanup_(user_record_unrefp) UserRecord *new_home = NULL;
_cleanup_(erase_and_freep) void *volume_key = NULL;
struct fscrypt_policy policy = {};
size_t volume_key_size = 512 / 8;
_cleanup_close_ int root_fd = -1;
_cleanup_free_ char *d = NULL;
uint32_t nr = 0;
const char *ip;
char **i;
int r;
assert(h);
assert(user_record_storage(h) == USER_FSCRYPT);
assert(ret_home);
assert_se(ip = user_record_image_path(h));
r = tempfn_random(ip, "homework", &d);
if (r < 0)
return log_error_errno(r, "Failed to allocate temporary directory: %m");
(void) mkdir_parents(d, 0755);
if (mkdir(d, 0700) < 0)
return log_error_errno(errno, "Failed to create temporary home directory %s: %m", d);
temporary = TAKE_PTR(d); /* Needs to be destroyed now */
root_fd = open(temporary, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW);
if (root_fd < 0)
return log_error_errno(errno, "Failed to open temporary home directory: %m");
if (ioctl(root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
if (ERRNO_IS_NOT_SUPPORTED(errno)) {
log_error_errno(errno, "File system does not support fscrypt: %m");
return -ENOLINK; /* make recognizable */
}
if (errno != ENODATA)
return log_error_errno(errno, "Failed to get fscrypt policy of directory: %m");
} else
return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Parent of %s already encrypted, refusing.", d);
volume_key = malloc(volume_key_size);
if (!volume_key)
return log_oom();
r = genuine_random_bytes(volume_key, volume_key_size, RANDOM_BLOCK);
if (r < 0)
return log_error_errno(r, "Failed to acquire volume key: %m");
log_info("Generated volume key of size %zu.", volume_key_size);
policy = (struct fscrypt_policy) {
.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS,
.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS,
.flags = FS_POLICY_FLAGS_PAD_32,
};
calculate_key_descriptor(volume_key, volume_key_size, policy.master_key_descriptor);
r = fscrypt_upload_volume_key(policy.master_key_descriptor, volume_key, volume_key_size, KEY_SPEC_THREAD_KEYRING);
if (r < 0)
return r;
log_info("Uploaded volume key to kernel.");
if (ioctl(root_fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) < 0)
return log_error_errno(errno, "Failed to set fscrypt policy on directory: %m");
log_info("Encryption policy set.");
STRV_FOREACH(i, effective_passwords) {
r = fscrypt_slot_set(root_fd, volume_key, volume_key_size, *i, nr);
if (r < 0)
return r;
nr++;
}
(void) home_update_quota_classic(h, temporary);
r = home_populate(h, root_fd);
if (r < 0)
return r;
r = home_sync_and_statfs(root_fd, NULL);
if (r < 0)
return r;
r = user_record_clone(h, USER_RECORD_LOAD_MASK_SECRET, &new_home);
if (r < 0)
return log_error_errno(r, "Failed to clone record: %m");
r = user_record_add_binding(
new_home,
USER_FSCRYPT,
ip,
SD_ID128_NULL,
SD_ID128_NULL,
SD_ID128_NULL,
NULL,
NULL,
UINT64_MAX,
NULL,
NULL,
h->uid,
(gid_t) h->uid);
if (r < 0)
return log_error_errno(r, "Failed to add binding to record: %m");
if (rename(temporary, ip) < 0)
return log_error_errno(errno, "Failed to rename %s to %s: %m", temporary, ip);
temporary = mfree(temporary);
log_info("Everything completed.");
*ret_home = TAKE_PTR(new_home);
return 0;
}
int home_passwd_fscrypt(
UserRecord *h,
HomeSetup *setup,
char **pkcs11_decrypted_passwords, /* the passwords acquired via PKCS#11 security tokens */
char **effective_passwords /* new passwords */) {
_cleanup_(erase_and_freep) void *volume_key = NULL;
_cleanup_free_ char *xattr_buf = NULL;
size_t volume_key_size = 0;
uint32_t slot = 0;
const char *xa;
char **p;
int r;
assert(h);
assert(user_record_storage(h) == USER_FSCRYPT);
assert(setup);
r = fscrypt_setup(
pkcs11_decrypted_passwords,
h->password,
setup,
&volume_key,
&volume_key_size);
if (r < 0)
return r;
STRV_FOREACH(p, effective_passwords) {
r = fscrypt_slot_set(setup->root_fd, volume_key, volume_key_size, *p, slot);
if (r < 0)
return r;
slot++;
}
r = flistxattr_malloc(setup->root_fd, &xattr_buf);
if (r < 0)
return log_error_errno(errno, "Failed to retrieve xattr list: %m");
NULSTR_FOREACH(xa, xattr_buf) {
const char *nr;
uint32_t z;
/* Check if this xattr has the format 'trusted.fscrypt_slot<nr>' where '<nr>' is a 32bit unsigned integer */
nr = startswith(xa, "trusted.fscrypt_slot");
if (!nr)
continue;
if (safe_atou32(nr, &z) < 0)
continue;
if (z < slot)
continue;
if (fremovexattr(setup->root_fd, xa) < 0)
if (errno != ENODATA)
log_warning_errno(errno, "Failed to remove xattr %s: %m", xa);
}
return 0;
}
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