[thirdparty/systemd.git] / src / home / homework-fscrypt.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#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(
                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<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 = -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,
                const PasswordCache *cache,
                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(
                        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);
                }
        }

        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;
        struct fscrypt_policy policy = {};
        size_t volume_key_size = 512 / 8;
        _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(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 */

        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_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");

        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;
        char **p;
        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<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;
}
Commit	Line	Data
db9ecf05	1	/* SPDX-License-Identifier: LGPL-2.1-or-later */
70a5db58 LP	2
	3	#include <linux/fs.h>
	4	#include <openssl/evp.h>
	5	#include <openssl/sha.h>
	6	#include <sys/ioctl.h>
	7	#include <sys/xattr.h>
	8
	9	#include "errno-util.h"
	10	#include "fd-util.h"
	11	#include "hexdecoct.h"
	12	#include "homework-fscrypt.h"
	13	#include "homework-quota.h"
	14	#include "memory-util.h"
	15	#include "missing_keyctl.h"
	16	#include "missing_syscall.h"
	17	#include "mkdir.h"
	18	#include "nulstr-util.h"
	19	#include "openssl-util.h"
	20	#include "parse-util.h"
	21	#include "process-util.h"
	22	#include "random-util.h"
	23	#include "rm-rf.h"
	24	#include "stdio-util.h"
	25	#include "strv.h"
	26	#include "tmpfile-util.h"
	27	#include "user-util.h"
	28	#include "xattr-util.h"
	29
	30	static int fscrypt_upload_volume_key(
	31	const uint8_t key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
	32	const void *volume_key,
	33	size_t volume_key_size,
	34	key_serial_t where) {
	35
	36	_cleanup_free_ char *hex = NULL;
	37	const char *description;
	38	struct fscrypt_key key;
	39	key_serial_t serial;
	40
	41	assert(key_descriptor);
	42	assert(volume_key);
	43	assert(volume_key_size > 0);
	44
	45	if (volume_key_size > sizeof(key.raw))
	46	return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Volume key too long.");
	47
	48	hex = hexmem(key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
	49	if (!hex)
	50	return log_oom();
	51
	52	description = strjoina("fscrypt:", hex);
	53
	54	key = (struct fscrypt_key) {
	55	.size = volume_key_size,
	56	};
	57	memcpy(key.raw, volume_key, volume_key_size);
	58
	59	/* Upload to the kernel */
	60	serial = add_key("logon", description, &key, sizeof(key), where);
	61	explicit_bzero_safe(&key, sizeof(key));
	62
	63	if (serial < 0)
	64	return log_error_errno(errno, "Failed to install master key in keyring: %m");
	65
66	log_info("Uploaded encryption key to kernel.");
67
68	return 0;
69	}
70
71	static void calculate_key_descriptor(
72	const void *key,
73	size_t key_size,
74	uint8_t ret_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE]) {
75
76	uint8_t hashed[512 / 8] = {}, hashed2[512 / 8] = {};
77
78	/* Derive the key descriptor from the volume key via double SHA512, in order to be compatible with e4crypt */
79
80	assert_se(SHA512(key, key_size, hashed) == hashed);
81	assert_se(SHA512(hashed, sizeof(hashed), hashed2) == hashed2);
82
83	assert_cc(sizeof(hashed2) >= FS_KEY_DESCRIPTOR_SIZE);
84
85	memcpy(ret_key_descriptor, hashed2, FS_KEY_DESCRIPTOR_SIZE);
86	}
87
88	static int fscrypt_slot_try_one(
89	const char *password,
90	const void *salt, size_t salt_size,
91	const void *encrypted, size_t encrypted_size,
92	const uint8_t match_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
93	void *ret_decrypted, size_t ret_decrypted_size) {
94
95
96	_cleanup_(EVP_CIPHER_CTX_freep) EVP_CIPHER_CTX *context = NULL;
97	_cleanup_(erase_and_freep) void *decrypted = NULL;
98	uint8_t key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
99	int decrypted_size_out1, decrypted_size_out2;
100	uint8_t derived[512 / 8] = {};
101	size_t decrypted_size;
102	const EVP_CIPHER *cc;
103	int r;
104
105	assert(password);
106	assert(salt);
107	assert(salt_size > 0);
108	assert(encrypted);
109	assert(encrypted_size > 0);
110	assert(match_key_descriptor);
111
112	/* Our construction is like this:
113	*
114	* 1. In each key slot we store a salt value plus the encrypted volume key
115	*
116	* 2. Unlocking is via calculating PBKDF2-HMAC-SHA512 of the supplied password (in combination with
117	* the salt), then using the first 256 bit of the hash as key for decrypting the encrypted
118	* volume key in AES256 counter mode.
119	*
120	* 3. Writing a password is similar: calculate PBKDF2-HMAC-SHA512 of the supplied password (in
121	* combination with the salt), then encrypt the volume key in AES256 counter mode with the
122	* resulting hash.
123	*/
124
125	if (PKCS5_PBKDF2_HMAC(
126	password, strlen(password),
127	salt, salt_size,
128	0xFFFF, EVP_sha512(),
129	sizeof(derived), derived) != 1) {
130	r = log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "PBKDF2 failed");
131	goto finish;
132	}
133
134	context = EVP_CIPHER_CTX_new();
135	if (!context) {
136	r = log_oom();
137	goto finish;
138	}
139
140	/* We use AES256 in counter mode */
141	assert_se(cc = EVP_aes_256_ctr());
142
143	/* We only use the first half of the derived key */
144	assert(sizeof(derived) >= (size_t) EVP_CIPHER_key_length(cc));
145
146	if (EVP_DecryptInit_ex(context, cc, NULL, derived, NULL) != 1) {
147	r = log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to initialize decryption context.");
148	goto finish;
149	}
150
151	/* Flush out the derived key now, we don't need it anymore */
152	explicit_bzero_safe(derived, sizeof(derived));
153
154	decrypted_size = encrypted_size + EVP_CIPHER_key_length(cc) * 2;
155	decrypted = malloc(decrypted_size);
156	if (!decrypted)
157	return log_oom();
158
159	if (EVP_DecryptUpdate(context, (uint8_t*) decrypted, &decrypted_size_out1, encrypted, encrypted_size) != 1)
160	return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to decrypt volume key.");
161
162	assert((size_t) decrypted_size_out1 <= decrypted_size);
163
164	if (EVP_DecryptFinal_ex(context, (uint8_t*) decrypted_size + decrypted_size_out1, &decrypted_size_out2) != 1)
165	return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to finish decryption of volume key.");
166
167	assert((size_t) decrypted_size_out1 + (size_t) decrypted_size_out2 < decrypted_size);
168	decrypted_size = (size_t) decrypted_size_out1 + (size_t) decrypted_size_out2;
169
170	calculate_key_descriptor(decrypted, decrypted_size, key_descriptor);
171
172	if (memcmp(key_descriptor, match_key_descriptor, FS_KEY_DESCRIPTOR_SIZE) != 0)
173	return -ENOANO; /* don't log here */
174
175	r = fscrypt_upload_volume_key(key_descriptor, decrypted, decrypted_size, KEY_SPEC_THREAD_KEYRING);
176	if (r < 0)
177	return r;
178
179	if (ret_decrypted)
180	*ret_decrypted = TAKE_PTR(decrypted);
181	if (ret_decrypted_size)
182	*ret_decrypted_size = decrypted_size;
183
184	return 0;
185
186	finish:
187	explicit_bzero_safe(derived, sizeof(derived));
188	return r;
189	}
190
191	static int fscrypt_slot_try_many(
192	char **passwords,
193	const void *salt, size_t salt_size,
194	const void *encrypted, size_t encrypted_size,
195	const uint8_t match_key_descriptor[static FS_KEY_DESCRIPTOR_SIZE],
196	void *ret_decrypted, size_t ret_decrypted_size) {
197
198	char **i;
199	int r;
200
201	STRV_FOREACH(i, passwords) {
202	r = fscrypt_slot_try_one(*i, salt, salt_size, encrypted, encrypted_size, match_key_descriptor, ret_decrypted, ret_decrypted_size);
203	if (r != -ENOANO)
204	return r;
205	}
206
207	return -ENOANO;
208	}
209
210	static int fscrypt_setup(
7b78db28	211	const PasswordCache *cache,
70a5db58 LP	212	char **password,
	213	HomeSetup *setup,
	214	void **ret_volume_key,
	215	size_t *ret_volume_key_size) {
	216
	217	_cleanup_free_ char *xattr_buf = NULL;
	218	const char *xa;
	219	int r;
	220
	221	assert(setup);
	222	assert(setup->root_fd >= 0);
	223
	224	r = flistxattr_malloc(setup->root_fd, &xattr_buf);
	225	if (r < 0)
	226	return log_error_errno(errno, "Failed to retrieve xattr list: %m");
	227
	228	NULSTR_FOREACH(xa, xattr_buf) {
	229	_cleanup_free_ void salt = NULL, encrypted = NULL;
	230	_cleanup_free_ char *value = NULL;
	231	size_t salt_size, encrypted_size;
	232	const char nr, e;
7b78db28	233	char **list;
70a5db58 LP	234	int n;
	235
	236	/* Check if this xattr has the format 'trusted.fscrypt_slot<nr>' where '<nr>' is a 32bit unsigned integer */
	237	nr = startswith(xa, "trusted.fscrypt_slot");
	238	if (!nr)
	239	continue;
	240	if (safe_atou32(nr, NULL) < 0)
	241	continue;
	242
	243	n = fgetxattr_malloc(setup->root_fd, xa, &value);
	244	if (n == -ENODATA) /* deleted by now? */
	245	continue;
	246	if (n < 0)
	247	return log_error_errno(n, "Failed to read %s xattr: %m", xa);
	248
	249	e = memchr(value, ':', n);
	250	if (!e)
	251	return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "xattr %s lacks ':' separator: %m", xa);
	252
	253	r = unbase64mem(value, e - value, &salt, &salt_size);
	254	if (r < 0)
	255	return log_error_errno(r, "Failed to decode salt of %s: %m", xa);
	256	r = unbase64mem(e+1, n - (e - value) - 1, &encrypted, &encrypted_size);
	257	if (r < 0)
	258	return log_error_errno(r, "Failed to decode encrypted key of %s: %m", xa);
	259
7b78db28 LP	260	r = -ENOANO;
7b78db28 LP	261	FOREACH_POINTER(list, cache->pkcs11_passwords, cache->fido2_passwords, password) {
70a5db58	262	r = fscrypt_slot_try_many(
7b78db28	263	list,
70a5db58 LP	264	salt, salt_size,
	265	encrypted, encrypted_size,
	266	setup->fscrypt_key_descriptor,
	267	ret_volume_key, ret_volume_key_size);
7b78db28 LP	268	if (r != -ENOANO)
	269	break;
	270	}
70a5db58 LP	271	if (r < 0) {
	272	if (r != -ENOANO)
	273	return r;
	274	} else
	275	return 0;
	276	}
	277
	278	return log_error_errno(SYNTHETIC_ERRNO(ENOKEY), "Failed to set up home directory with provided passwords.");
	279	}
	280
aa0a6214	281	int home_setup_fscrypt(
70a5db58	282	UserRecord *h,
37a1bf7f	283	const PasswordCache *cache,
70a5db58 LP	284	HomeSetup *setup) {
	285
	286	_cleanup_(erase_and_freep) void *volume_key = NULL;
	287	struct fscrypt_policy policy = {};
	288	size_t volume_key_size = 0;
	289	const char *ip;
	290	int r;
	291
	292	assert(h);
	293	assert(setup);
	294	assert(user_record_storage(h) == USER_FSCRYPT);
	295
	296	assert_se(ip = user_record_image_path(h));
	297
	298	setup->root_fd = open(ip, O_RDONLY\|O_CLOEXEC\|O_DIRECTORY);
	299	if (setup->root_fd < 0)
	300	return log_error_errno(errno, "Failed to open home directory: %m");
	301
	302	if (ioctl(setup->root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
	303	if (errno == ENODATA)
	304	return log_error_errno(errno, "Home directory %s is not encrypted.", ip);
	305	if (ERRNO_IS_NOT_SUPPORTED(errno)) {
	306	log_error_errno(errno, "File system does not support fscrypt: %m");
	307	return -ENOLINK; /* make recognizable */
	308	}
	309	return log_error_errno(errno, "Failed to acquire encryption policy of %s: %m", ip);
	310	}
	311
	312	memcpy(setup->fscrypt_key_descriptor, policy.master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE);
	313
	314	r = fscrypt_setup(
7b78db28	315	cache,
70a5db58 LP	316	h->password,
	317	setup,
	318	&volume_key,
	319	&volume_key_size);
	320	if (r < 0)
	321	return r;
	322
	323	/* Also install the access key in the user's own keyring */
	324
	325	if (uid_is_valid(h->uid)) {
7e0ed2e9 SB	326	r = safe_fork("(sd-addkey)",
	327	FORK_RESET_SIGNALS\|FORK_CLOSE_ALL_FDS\|FORK_DEATHSIG\|FORK_LOG\|FORK_WAIT\|FORK_REOPEN_LOG,
	328	NULL);
70a5db58 LP	329	if (r < 0)
	330	return log_error_errno(r, "Failed install encryption key in user's keyring: %m");
	331	if (r == 0) {
	332	gid_t gid;
	333
	334	/* Child */
	335
	336	gid = user_record_gid(h);
	337	if (setresgid(gid, gid, gid) < 0) {
	338	log_error_errno(errno, "Failed to change GID to " GID_FMT ": %m", gid);
	339	_exit(EXIT_FAILURE);
	340	}
	341
	342	if (setgroups(0, NULL) < 0) {
	343	log_error_errno(errno, "Failed to reset auxiliary groups list: %m");
	344	_exit(EXIT_FAILURE);
	345	}
	346
	347	if (setresuid(h->uid, h->uid, h->uid) < 0) {
	348	log_error_errno(errno, "Failed to change UID to " UID_FMT ": %m", h->uid);
	349	_exit(EXIT_FAILURE);
	350	}
	351
	352	r = fscrypt_upload_volume_key(
	353	setup->fscrypt_key_descriptor,
	354	volume_key,
	355	volume_key_size,
	356	KEY_SPEC_USER_KEYRING);
	357	if (r < 0)
	358	_exit(EXIT_FAILURE);
	359
	360	_exit(EXIT_SUCCESS);
	361	}
	362	}
	363
	364	return 0;
	365	}
	366
	367	static int fscrypt_slot_set(
	368	int root_fd,
	369	const void *volume_key,
	370	size_t volume_key_size,
	371	const char *password,
	372	uint32_t nr) {
	373
	374	_cleanup_free_ char salt_base64 = NULL, encrypted_base64 = NULL, *joined = NULL;
	375	char label[STRLEN("trusted.fscrypt_slot") + DECIMAL_STR_MAX(nr) + 1];
	376	_cleanup_(EVP_CIPHER_CTX_freep) EVP_CIPHER_CTX *context = NULL;
	377	int r, encrypted_size_out1, encrypted_size_out2;
	378	uint8_t salt[64], derived[512 / 8] = {};
	379	_cleanup_free_ void *encrypted = NULL;
	380	const EVP_CIPHER *cc;
	381	size_t encrypted_size;
	382
	383	r = genuine_random_bytes(salt, sizeof(salt), RANDOM_BLOCK);
	384	if (r < 0)
	385	return log_error_errno(r, "Failed to generate salt: %m");
	386
	387	if (PKCS5_PBKDF2_HMAC(
	388	password, strlen(password),
	389	salt, sizeof(salt),
	390	0xFFFF, EVP_sha512(),
	391	sizeof(derived), derived) != 1) {
	392	r = log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "PBKDF2 failed");
393	goto finish;
394	}
395
396	context = EVP_CIPHER_CTX_new();
397	if (!context) {
398	r = log_oom();
399	goto finish;
400	}
401
402	/* We use AES256 in counter mode */
403	cc = EVP_aes_256_ctr();
404
405	/* We only use the first half of the derived key */
406	assert(sizeof(derived) >= (size_t) EVP_CIPHER_key_length(cc));
407
408	if (EVP_EncryptInit_ex(context, cc, NULL, derived, NULL) != 1) {
409	r = log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to initialize encryption context.");
410	goto finish;
411	}
412
413	/* Flush out the derived key now, we don't need it anymore */
414	explicit_bzero_safe(derived, sizeof(derived));
415
416	encrypted_size = volume_key_size + EVP_CIPHER_key_length(cc) * 2;
417	encrypted = malloc(encrypted_size);
418	if (!encrypted)
419	return log_oom();
420
421	if (EVP_EncryptUpdate(context, (uint8_t*) encrypted, &encrypted_size_out1, volume_key, volume_key_size) != 1)
422	return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to encrypt volume key.");
423
424	assert((size_t) encrypted_size_out1 <= encrypted_size);
425
426	if (EVP_EncryptFinal_ex(context, (uint8_t*) encrypted_size + encrypted_size_out1, &encrypted_size_out2) != 1)
427	return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to finish encryption of volume key.");
428
429	assert((size_t) encrypted_size_out1 + (size_t) encrypted_size_out2 < encrypted_size);
430	encrypted_size = (size_t) encrypted_size_out1 + (size_t) encrypted_size_out2;
431
432	r = base64mem(salt, sizeof(salt), &salt_base64);
433	if (r < 0)
434	return log_oom();
435
436	r = base64mem(encrypted, encrypted_size, &encrypted_base64);
437	if (r < 0)
438	return log_oom();
439
440	joined = strjoin(salt_base64, ":", encrypted_base64);
441	if (!joined)
442	return log_oom();
443
444	xsprintf(label, "trusted.fscrypt_slot%" PRIu32, nr);
445	if (fsetxattr(root_fd, label, joined, strlen(joined), 0) < 0)
446	return log_error_errno(errno, "Failed to write xattr %s: %m", label);
447
448	log_info("Written key slot %s.", label);
449
450	return 0;
451
452	finish:
453	explicit_bzero_safe(derived, sizeof(derived));
454	return r;
455	}
456
457	int home_create_fscrypt(
458	UserRecord *h,
655807f5	459	HomeSetup *setup,
70a5db58 LP	460	char **effective_passwords,
	461	UserRecord **ret_home) {
	462
	463	_cleanup_(rm_rf_physical_and_freep) char *temporary = NULL;
	464	_cleanup_(user_record_unrefp) UserRecord *new_home = NULL;
	465	_cleanup_(erase_and_freep) void *volume_key = NULL;
	466	struct fscrypt_policy policy = {};
	467	size_t volume_key_size = 512 / 8;
70a5db58 LP	468	_cleanup_free_ char *d = NULL;
	469	uint32_t nr = 0;
	470	const char *ip;
	471	char **i;
	472	int r;
	473
	474	assert(h);
	475	assert(user_record_storage(h) == USER_FSCRYPT);
655807f5	476	assert(setup);
70a5db58 LP	477	assert(ret_home);
	478
	479	assert_se(ip = user_record_image_path(h));
	480
	481	r = tempfn_random(ip, "homework", &d);
	482	if (r < 0)
	483	return log_error_errno(r, "Failed to allocate temporary directory: %m");
	484
	485	(void) mkdir_parents(d, 0755);
	486
	487	if (mkdir(d, 0700) < 0)
	488	return log_error_errno(errno, "Failed to create temporary home directory %s: %m", d);
	489
	490	temporary = TAKE_PTR(d); /* Needs to be destroyed now */
	491
655807f5 LP	492	setup->root_fd = open(temporary, O_RDONLY\|O_CLOEXEC\|O_DIRECTORY\|O_NOFOLLOW);
655807f5 LP	493	if (setup->root_fd < 0)
70a5db58 LP	494	return log_error_errno(errno, "Failed to open temporary home directory: %m");
70a5db58 LP	495
655807f5	496	if (ioctl(setup->root_fd, FS_IOC_GET_ENCRYPTION_POLICY, &policy) < 0) {
70a5db58 LP	497	if (ERRNO_IS_NOT_SUPPORTED(errno)) {
	498	log_error_errno(errno, "File system does not support fscrypt: %m");
	499	return -ENOLINK; /* make recognizable */
	500	}
	501	if (errno != ENODATA)
	502	return log_error_errno(errno, "Failed to get fscrypt policy of directory: %m");
	503	} else
	504	return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Parent of %s already encrypted, refusing.", d);
	505
	506	volume_key = malloc(volume_key_size);
	507	if (!volume_key)
	508	return log_oom();
	509
	510	r = genuine_random_bytes(volume_key, volume_key_size, RANDOM_BLOCK);
	511	if (r < 0)
	512	return log_error_errno(r, "Failed to acquire volume key: %m");
	513
	514	log_info("Generated volume key of size %zu.", volume_key_size);
	515
	516	policy = (struct fscrypt_policy) {
	517	.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS,
	518	.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS,
	519	.flags = FS_POLICY_FLAGS_PAD_32,
	520	};
	521
	522	calculate_key_descriptor(volume_key, volume_key_size, policy.master_key_descriptor);
	523
	524	r = fscrypt_upload_volume_key(policy.master_key_descriptor, volume_key, volume_key_size, KEY_SPEC_THREAD_KEYRING);
	525	if (r < 0)
	526	return r;
	527
	528	log_info("Uploaded volume key to kernel.");
	529
655807f5	530	if (ioctl(setup->root_fd, FS_IOC_SET_ENCRYPTION_POLICY, &policy) < 0)
70a5db58 LP	531	return log_error_errno(errno, "Failed to set fscrypt policy on directory: %m");
	532
	533	log_info("Encryption policy set.");
	534
	535	STRV_FOREACH(i, effective_passwords) {
655807f5	536	r = fscrypt_slot_set(setup->root_fd, volume_key, volume_key_size, *i, nr);
70a5db58 LP	537	if (r < 0)
	538	return r;
	539
	540	nr++;
	541	}
	542
	543	(void) home_update_quota_classic(h, temporary);
	544
655807f5	545	r = home_populate(h, setup->root_fd);
70a5db58 LP	546	if (r < 0)
	547	return r;
	548
655807f5	549	r = home_sync_and_statfs(setup->root_fd, NULL);
70a5db58 LP	550	if (r < 0)
	551	return r;
	552
bfc0cc1a	553	r = user_record_clone(h, USER_RECORD_LOAD_MASK_SECRET\|USER_RECORD_PERMISSIVE, &new_home);
70a5db58 LP	554	if (r < 0)
	555	return log_error_errno(r, "Failed to clone record: %m");
	556
	557	r = user_record_add_binding(
	558	new_home,
	559	USER_FSCRYPT,
	560	ip,
	561	SD_ID128_NULL,
	562	SD_ID128_NULL,
	563	SD_ID128_NULL,
	564	NULL,
	565	NULL,
	566	UINT64_MAX,
	567	NULL,
	568	NULL,
	569	h->uid,
	570	(gid_t) h->uid);
	571	if (r < 0)
	572	return log_error_errno(r, "Failed to add binding to record: %m");
	573
	574	if (rename(temporary, ip) < 0)
	575	return log_error_errno(errno, "Failed to rename %s to %s: %m", temporary, ip);
	576
	577	temporary = mfree(temporary);
	578
	579	log_info("Everything completed.");
	580
	581	*ret_home = TAKE_PTR(new_home);
	582	return 0;
	583	}
	584
	585	int home_passwd_fscrypt(
	586	UserRecord *h,
	587	HomeSetup *setup,
37a1bf7f	588	const PasswordCache cache, / the passwords acquired via PKCS#11/FIDO2 security tokens */
70a5db58 LP	589	char *effective_passwords / new passwords */) {
	590
	591	_cleanup_(erase_and_freep) void *volume_key = NULL;
	592	_cleanup_free_ char *xattr_buf = NULL;
	593	size_t volume_key_size = 0;
	594	uint32_t slot = 0;
	595	const char *xa;
	596	char **p;
	597	int r;
	598
	599	assert(h);
	600	assert(user_record_storage(h) == USER_FSCRYPT);
	601	assert(setup);
	602
	603	r = fscrypt_setup(
7b78db28	604	cache,
70a5db58 LP	605	h->password,
	606	setup,
	607	&volume_key,
	608	&volume_key_size);
	609	if (r < 0)
	610	return r;
	611
	612	STRV_FOREACH(p, effective_passwords) {
	613	r = fscrypt_slot_set(setup->root_fd, volume_key, volume_key_size, *p, slot);
	614	if (r < 0)
	615	return r;
	616
	617	slot++;
	618	}
	619
	620	r = flistxattr_malloc(setup->root_fd, &xattr_buf);
	621	if (r < 0)
	622	return log_error_errno(errno, "Failed to retrieve xattr list: %m");
	623
	624	NULSTR_FOREACH(xa, xattr_buf) {
	625	const char *nr;
	626	uint32_t z;
	627
	628	/* Check if this xattr has the format 'trusted.fscrypt_slot<nr>' where '<nr>' is a 32bit unsigned integer */
	629	nr = startswith(xa, "trusted.fscrypt_slot");
	630	if (!nr)
	631	continue;
	632	if (safe_atou32(nr, &z) < 0)
	633	continue;
	634
	635	if (z < slot)
	636	continue;
	637
	638	if (fremovexattr(setup->root_fd, xa) < 0)
	639
	640	if (errno != ENODATA)
	641	log_warning_errno(errno, "Failed to remove xattr %s: %m", xa);
	642	}
	643
	644	return 0;
	645	}