cryptenroll: support for enrolling FIDO2 tokens in manual mode
systemd-cryptsetup supports a FIDO2 mode with manual parameters, where the user provides all the information necessary for recreating the secret, such as: credential ID, relaying party ID and the salt. This feature works great for implementing 2FA schemes, where the salt file is for example a secret unsealed from the TPM or some other source. While the unlocking part is quite straightforward to set up, enrolling such a keyslot - not so easy. There is no clearly documented way on how to set this up and online resources are scarce on this topic too. By implementing a straightforward way to enroll such a keyslot directly from systemd-cryptenroll we streamline the enrollment process and reduce chances for user error when doing such things manually.
This commit is contained in:
Kamil Szczęk
committed by
Lennart Poettering
Lennart Poettering
parent
ac6eb58f09
commit
e262205eb7
@@ -5,8 +5,10 @@
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#include "ask-password-api.h"
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#include "cryptsetup-fido2.h"
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#include "env-util.h"
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#include "fido2-util.h"
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#include "fileio.h"
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#include "hexdecoct.h"
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#include "iovec-util.h"
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#include "libfido2-util.h"
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#include "parse-util.h"
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#include "random-util.h"
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@@ -33,10 +35,9 @@ int acquire_fido2_key(
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_cleanup_(erase_and_freep) char *envpw = NULL;
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_cleanup_strv_free_erase_ char **pins = NULL;
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_cleanup_free_ void *loaded_salt = NULL;
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_cleanup_(iovec_done_erase) struct iovec loaded_salt = {};
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bool device_exists = false;
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const char *salt;
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size_t salt_size;
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struct iovec salt;
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int r;
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if ((required & (FIDO2ENROLL_PIN | FIDO2ENROLL_UP | FIDO2ENROLL_UV)) && FLAGS_SET(askpw_flags, ASK_PASSWORD_HEADLESS))
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@@ -48,23 +49,17 @@ int acquire_fido2_key(
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assert(cid);
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assert(key_file || key_data);
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if (key_data) {
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salt = key_data;
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salt_size = key_data_size;
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} else {
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_cleanup_free_ char *bindname = NULL;
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if (key_data)
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salt = IOVEC_MAKE(key_data, key_data_size);
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else {
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if (key_file_size > 0)
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log_debug("Ignoring 'keyfile-size=' option for a FIDO2 salt file.");
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/* If we read the salt via AF_UNIX, make this client recognizable */
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if (asprintf(&bindname, "@%" PRIx64"/cryptsetup-fido2/%s", random_u64(), volume_name) < 0)
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return log_oom();
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r = read_full_file_full(
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AT_FDCWD, key_file,
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key_file_offset == 0 ? UINT64_MAX : key_file_offset,
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key_file_size == 0 ? SIZE_MAX : key_file_size,
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READ_FULL_FILE_CONNECT_SOCKET,
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bindname,
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(char**) &loaded_salt, &salt_size);
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r = fido2_read_salt_file(
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key_file, key_file_offset,
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/* client= */ "cryptsetup",
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/* node= */ volume_name,
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&loaded_salt);
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if (r < 0)
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return r;
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@@ -102,7 +97,7 @@ int acquire_fido2_key(
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r = fido2_use_hmac_hash(
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device,
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rp_id ?: "io.systemd.cryptsetup",
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salt, salt_size,
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salt.iov_base, salt.iov_len,
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cid, cid_size,
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pins,
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required,
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@@ -0,0 +1,44 @@
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include "fido2-util.h"
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#include "fileio.h"
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#include "libfido2-util.h"
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#include "random-util.h"
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int fido2_generate_salt(struct iovec *ret_salt) {
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_cleanup_(iovec_done) struct iovec salt = {};
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int r;
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r = crypto_random_bytes_allocate_iovec(FIDO2_SALT_SIZE, &salt);
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if (r < 0)
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return log_error_errno(r, "Failed to generate FIDO2 salt: %m");
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*ret_salt = TAKE_STRUCT(salt);
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return 0;
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}
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int fido2_read_salt_file(const char *filename, uint64_t offset, const char *client, const char *node, struct iovec *ret_salt) {
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_cleanup_(iovec_done_erase) struct iovec salt = {};
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_cleanup_free_ char *bind_name = NULL;
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int r;
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/* If we read the salt via AF_UNIX, make the client recognizable */
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if (asprintf(&bind_name, "@%" PRIx64"/%s-fido2-salt/%s", random_u64(), client, node) < 0)
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return log_oom();
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r = read_full_file_full(
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AT_FDCWD, filename,
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offset == 0 ? UINT64_MAX : offset,
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/* size= */ FIDO2_SALT_SIZE,
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READ_FULL_FILE_SECURE|READ_FULL_FILE_WARN_WORLD_READABLE|
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READ_FULL_FILE_CONNECT_SOCKET|READ_FULL_FILE_FAIL_WHEN_LARGER,
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bind_name, (char**) &salt.iov_base, &salt.iov_len);
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if (r == -E2BIG || (r >= 0 && salt.iov_len != FIDO2_SALT_SIZE))
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return log_error_errno(r < 0 ? r : SYNTHETIC_ERRNO(EINVAL),
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"FIDO2 salt file must contain exactly %u bytes.", FIDO2_SALT_SIZE);
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if (r < 0)
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return log_error_errno(r, "Reading FIDO2 salt file '%s' failed: %m", filename);
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*ret_salt = TAKE_STRUCT(salt);
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return 0;
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}
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@@ -0,0 +1,9 @@
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#pragma once
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#include <stdint.h>
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#include "iovec-util.h"
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int fido2_generate_salt(struct iovec *ret_salt);
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int fido2_read_salt_file(const char *filename, uint64_t offset, const char *client, const char *node, struct iovec *ret_salt);
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@@ -10,7 +10,6 @@
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#include "glyph-util.h"
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#include "log.h"
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#include "memory-util.h"
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#include "random-util.h"
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#include "strv.h"
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#include "unistd.h"
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@@ -683,8 +682,6 @@ finish:
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return r;
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}
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#define FIDO2_SALT_SIZE 32
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int fido2_generate_hmac_hash(
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const char *device,
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const char *rp_id,
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@@ -697,13 +694,13 @@ int fido2_generate_hmac_hash(
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const char *askpw_credential,
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Fido2EnrollFlags lock_with,
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int cred_alg,
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const struct iovec *salt,
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void **ret_cid, size_t *ret_cid_size,
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void **ret_salt, size_t *ret_salt_size,
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void **ret_secret, size_t *ret_secret_size,
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char **ret_usedpin,
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Fido2EnrollFlags *ret_locked_with) {
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_cleanup_(erase_and_freep) void *salt = NULL, *secret_copy = NULL;
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_cleanup_(erase_and_freep) void *secret_copy = NULL;
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_cleanup_(fido_assert_free_wrapper) fido_assert_t *a = NULL;
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_cleanup_(fido_cred_free_wrapper) fido_cred_t *c = NULL;
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_cleanup_(fido_dev_free_wrapper) fido_dev_t *d = NULL;
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@@ -717,12 +714,10 @@ int fido2_generate_hmac_hash(
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assert(device);
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assert(ret_cid);
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assert(ret_cid_size);
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assert(ret_salt);
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assert(ret_salt_size);
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assert(ret_secret);
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assert(ret_secret_size);
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/* Construction is like this: we generate a salt of 32 bytes. We then ask the FIDO2 device to
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/* Construction is like this: we read or generate a salt of 32 bytes. We then ask the FIDO2 device to
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* HMAC-SHA256 it for us with its internal key. The result is the key used by LUKS and account
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* authentication. LUKS and UNIX password auth all do their own salting before hashing, so that FIDO2
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* device never sees the volume key.
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@@ -731,25 +726,18 @@ int fido2_generate_hmac_hash(
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*
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* with: S → LUKS/account authentication key (never stored)
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* I → internal key on FIDO2 device (stored in the FIDO2 device)
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* D → salt we generate here (stored in the privileged part of the JSON record)
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* D → salt (stored in the privileged part of the JSON record or read from a file/socket)
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*
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*/
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assert(device);
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assert((lock_with & ~(FIDO2ENROLL_PIN|FIDO2ENROLL_UP|FIDO2ENROLL_UV)) == 0);
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assert(iovec_is_set(salt));
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r = dlopen_libfido2();
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if (r < 0)
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return log_error_errno(r, "FIDO2 token support is not installed.");
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salt = malloc(FIDO2_SALT_SIZE);
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if (!salt)
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return log_oom();
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r = crypto_random_bytes(salt, FIDO2_SALT_SIZE);
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if (r < 0)
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return log_error_errno(r, "Failed to generate salt: %m");
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d = sym_fido_dev_new();
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if (!d)
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return log_oom();
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@@ -935,7 +923,7 @@ int fido2_generate_hmac_hash(
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return log_error_errno(SYNTHETIC_ERRNO(EIO),
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"Failed to enable HMAC-SECRET extension on FIDO2 assertion: %s", sym_fido_strerr(r));
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r = sym_fido_assert_set_hmac_salt(a, salt, FIDO2_SALT_SIZE);
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r = sym_fido_assert_set_hmac_salt(a, salt->iov_base, salt->iov_len);
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if (r != FIDO_OK)
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return log_error_errno(SYNTHETIC_ERRNO(EIO),
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"Failed to set salt on FIDO2 assertion: %s", sym_fido_strerr(r));
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@@ -1072,8 +1060,6 @@ int fido2_generate_hmac_hash(
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*ret_cid = TAKE_PTR(cid_copy);
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*ret_cid_size = cid_size;
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*ret_salt = TAKE_PTR(salt);
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*ret_salt_size = FIDO2_SALT_SIZE;
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*ret_secret = TAKE_PTR(secret_copy);
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*ret_secret_size = secret_size;
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@@ -1,8 +1,11 @@
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#pragma once
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#include "iovec-util.h"
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#include "macro.h"
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#define FIDO2_SALT_SIZE 32U
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typedef enum Fido2EnrollFlags {
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FIDO2ENROLL_PIN = 1 << 0,
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FIDO2ENROLL_UP = 1 << 1, /* User presence (ie: touching token) */
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@@ -116,8 +119,8 @@ int fido2_generate_hmac_hash(
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const char *askpw_credential,
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Fido2EnrollFlags lock_with,
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int cred_alg,
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const struct iovec *salt,
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void **ret_cid, size_t *ret_cid_size,
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void **ret_salt, size_t *ret_salt_size,
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void **ret_secret, size_t *ret_secret_size,
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char **ret_usedpin,
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Fido2EnrollFlags *ret_locked_with);
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@@ -69,6 +69,7 @@ shared_sources = files(
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'exit-status.c',
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'extension-util.c',
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'fdset.c',
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'fido2-util.c',
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'fileio-label.c',
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'find-esp.c',
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'firewall-util-nft.c',
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