/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #include #include #include "errno-util.h" #include "fd-util.h" #include "hexdecoct.h" #include "homework-fscrypt.h" #include "homework-mount.h" #include "homework-quota.h" #include "memory-util.h" #include "missing_keyctl.h" #include "missing_syscall.h" #include "mkdir.h" #include "mount-util.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) { 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( const PasswordCache *cache, 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; char **list; int n; /* Check if this xattr has the format 'trusted.fscrypt_slot' where '' 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 = -ENOANO; FOREACH_POINTER(list, cache->pkcs11_passwords, cache->fido2_passwords, password) { r = fscrypt_slot_try_many( list, salt, salt_size, encrypted, encrypted_size, setup->fscrypt_key_descriptor, ret_volume_key, ret_volume_key_size); if (r != -ENOANO) break; } 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_setup_fscrypt( UserRecord *h, HomeSetup *setup, const PasswordCache *cache) { _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(user_record_storage(h) == USER_FSCRYPT); assert(setup); assert(setup->root_fd < 0); 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( cache, 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|FORK_REOPEN_LOG, 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); } } /* We'll bind mount the image directory to a new mount point where we'll start adjusting it. Only * once that's complete we'll move the thing to its final place eventually. */ r = home_unshare_and_mkdir(); if (r < 0) return r; r = mount_follow_verbose(LOG_ERR, ip, HOME_RUNTIME_WORK_DIR, NULL, MS_BIND, NULL); if (r < 0) return r; setup->undo_mount = true; /* Turn off any form of propagation for this */ r = mount_nofollow_verbose(LOG_ERR, NULL, HOME_RUNTIME_WORK_DIR, NULL, MS_PRIVATE, NULL); if (r < 0) return r; /* Adjust MS_SUID and similar flags */ r = mount_nofollow_verbose(LOG_ERR, NULL, HOME_RUNTIME_WORK_DIR, NULL, MS_BIND|MS_REMOUNT|user_record_mount_flags(h), NULL); if (r < 0) return r; safe_close(setup->root_fd); setup->root_fd = open(HOME_RUNTIME_WORK_DIR, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW); if (setup->root_fd < 0) return log_error_errno(errno, "Failed to open home directory: %m"); 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, HomeSetup *setup, 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; _cleanup_close_ int mount_fd = -1; struct fscrypt_policy policy = {}; size_t volume_key_size = 512 / 8; _cleanup_free_ char *d = NULL; uint32_t nr = 0; const char *ip; int r; assert(h); assert(user_record_storage(h) == USER_FSCRYPT); assert(setup); 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 */ r = home_unshare_and_mkdir(); if (r < 0) return r; setup->root_fd = open(temporary, O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOFOLLOW); if (setup->root_fd < 0) return log_error_errno(errno, "Failed to open temporary home directory: %m"); if (ioctl(setup->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(setup->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(setup->root_fd, volume_key, volume_key_size, *i, nr); if (r < 0) return r; nr++; } (void) home_update_quota_classic(h, temporary); r = home_shift_uid(setup->root_fd, HOME_RUNTIME_WORK_DIR, h->uid, h->uid, &mount_fd); if (r > 0) setup->undo_mount = true; /* If uidmaps worked we have a mount to undo again */ if (mount_fd >= 0) { /* If we have established a new mount, then we can use that as new root fd to our home directory. */ safe_close(setup->root_fd); setup->root_fd = fd_reopen(mount_fd, O_RDONLY|O_CLOEXEC|O_DIRECTORY); if (setup->root_fd < 0) return log_error_errno(setup->root_fd, "Unable to convert mount fd into proper directory fd: %m"); mount_fd = safe_close(mount_fd); } r = home_populate(h, setup->root_fd); if (r < 0) return r; r = home_sync_and_statfs(setup->root_fd, NULL); if (r < 0) return r; r = user_record_clone(h, USER_RECORD_LOAD_MASK_SECRET|USER_RECORD_PERMISSIVE, &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"); setup->root_fd = safe_close(setup->root_fd); r = home_setup_undo_mount(setup, LOG_ERR); if (r < 0) return r; 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, const PasswordCache *cache, /* the passwords acquired via PKCS#11/FIDO2 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; int r; assert(h); assert(user_record_storage(h) == USER_FSCRYPT); assert(setup); r = fscrypt_setup( cache, 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' where '' 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; }