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Prevent attackers from spoofing the tpmKey portion of the AuthSession by adding a trusted key to the LUKS header metadata. Also, use a persistent object rather than a transient object. This provides the following benifits: 1. No way to MITM the tpmKey portion of the session, see [1] for details. 2. Strengthens the encrypted sessions, note that the bindKey could be dropped now. 3. Speed, once it's created we just use it. 4. Owner Auth is needed to call create primary, so using the SRK creates a scratch space for normal users. This is a "first to set" model, in where the first person to set the key in the LUKS header wins. Thus, setup should be done in a known good state. If an SRK, which is a primary key at a special persistent address, is found, it will use whatever is there. If not, it creates an SRK. The SRK follows the convetions used through the tpm2-software organization code on GitHub [2], however, a split has occured between Windows and Linux with respect to SRK templates. The Linux SRK is generated with the unique field size set to 0, in Windows, it properly sets the size to key size in bytes and the unique data to all 0's of that size. Note the proper templates for SRKs is covered in spec [3]. However, the most important thing, is that both SRKs are passwordless, and thus they should be interchangable. If Windows is the first to make the SRK, systemd will gladly accept it and vice-versa. 1. Without the bindKey being utilized, an attacker was able to intercept this and fake a key, thus being able to decrypt and encrypt traffic as needed. Introduction of the bindKey strengthened this, but allows for the attacker to brute force AES128CFB using pin guesses. Introduction of the salt increases the difficulty of this attack as well as DA attacks on the TPM objects itself. 2. https://github.com/tpm2-software 3. https://trustedcomputinggroup.org/wp-content/uploads/TCG-TPM-v2.0-Provisioning-Guidance-Published-v1r1.pdf Fixes: #20668 Fixes: #22637 Signed-off-by: William Roberts <william.c.roberts@intel.com>
293 lines
11 KiB
C
293 lines
11 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include "alloc-util.h"
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#include "ask-password-api.h"
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#include "cryptsetup-tpm2.h"
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#include "env-util.h"
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#include "fileio.h"
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#include "hexdecoct.h"
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#include "json.h"
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#include "parse-util.h"
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#include "random-util.h"
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#include "sha256.h"
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#include "tpm2-util.h"
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static int get_pin(usec_t until, AskPasswordFlags ask_password_flags, bool headless, char **ret_pin_str) {
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_cleanup_free_ char *pin_str = NULL;
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_cleanup_strv_free_erase_ char **pin = NULL;
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int r;
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assert(ret_pin_str);
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r = getenv_steal_erase("PIN", &pin_str);
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if (r < 0)
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return log_error_errno(r, "Failed to acquire PIN from environment: %m");
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if (!r) {
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if (headless)
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return log_error_errno(
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SYNTHETIC_ERRNO(ENOPKG),
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"PIN querying disabled via 'headless' option. "
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"Use the '$PIN' environment variable.");
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pin = strv_free_erase(pin);
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r = ask_password_auto(
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"Please enter TPM2 PIN:",
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"drive-harddisk",
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NULL,
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"tpm2-pin",
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"cryptsetup.tpm2-pin",
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until,
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ask_password_flags,
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&pin);
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if (r < 0)
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return log_error_errno(r, "Failed to ask for user pin: %m");
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assert(strv_length(pin) == 1);
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pin_str = strdup(pin[0]);
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if (!pin_str)
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return log_oom();
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}
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*ret_pin_str = TAKE_PTR(pin_str);
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return r;
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}
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int acquire_tpm2_key(
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const char *volume_name,
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const char *device,
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uint32_t hash_pcr_mask,
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uint16_t pcr_bank,
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const void *pubkey,
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size_t pubkey_size,
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uint32_t pubkey_pcr_mask,
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const char *signature_path,
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uint16_t primary_alg,
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const char *key_file,
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size_t key_file_size,
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uint64_t key_file_offset,
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const void *key_data,
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size_t key_data_size,
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const void *policy_hash,
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size_t policy_hash_size,
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const void *salt,
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size_t salt_size,
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const void *srk_buf,
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size_t srk_buf_size,
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TPM2Flags flags,
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usec_t until,
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bool headless,
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AskPasswordFlags ask_password_flags,
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void **ret_decrypted_key,
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size_t *ret_decrypted_key_size) {
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_cleanup_(json_variant_unrefp) JsonVariant *signature_json = NULL;
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_cleanup_free_ void *loaded_blob = NULL;
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_cleanup_free_ char *auto_device = NULL;
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size_t blob_size;
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const void *blob;
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int r;
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assert(salt || salt_size == 0);
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if (!device) {
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r = tpm2_find_device_auto(LOG_DEBUG, &auto_device);
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if (r == -ENODEV)
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return -EAGAIN; /* Tell the caller to wait for a TPM2 device to show up */
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if (r < 0)
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return r;
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device = auto_device;
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}
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if (key_data) {
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blob = key_data;
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blob_size = key_data_size;
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} else {
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_cleanup_free_ char *bindname = NULL;
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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-tpm2/%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_blob, &blob_size);
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if (r < 0)
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return r;
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blob = loaded_blob;
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}
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if (pubkey_pcr_mask != 0) {
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r = tpm2_load_pcr_signature(signature_path, &signature_json);
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if (r < 0)
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return r;
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}
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if (!(flags & TPM2_FLAGS_USE_PIN))
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return tpm2_unseal(
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device,
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hash_pcr_mask,
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pcr_bank,
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pubkey, pubkey_size,
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pubkey_pcr_mask,
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signature_json,
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/* pin= */ NULL,
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primary_alg,
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blob,
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blob_size,
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policy_hash,
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policy_hash_size,
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srk_buf,
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srk_buf_size,
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ret_decrypted_key,
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ret_decrypted_key_size);
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for (int i = 5;; i--) {
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_cleanup_(erase_and_freep) char *pin_str = NULL, *b64_salted_pin = NULL;
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if (i <= 0)
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return -EACCES;
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r = get_pin(until, ask_password_flags, headless, &pin_str);
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if (r < 0)
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return r;
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if (salt_size > 0) {
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uint8_t salted_pin[SHA256_DIGEST_SIZE] = {};
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CLEANUP_ERASE(salted_pin);
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r = tpm2_util_pbkdf2_hmac_sha256(pin_str, strlen(pin_str), salt, salt_size, salted_pin);
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if (r < 0)
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return log_error_errno(r, "Failed to perform PBKDF2: %m");
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r = base64mem(salted_pin, sizeof(salted_pin), &b64_salted_pin);
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if (r < 0)
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return log_error_errno(r, "Failed to base64 encode salted pin: %m");
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} else
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/* no salting needed, backwards compat with non-salted pins */
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b64_salted_pin = TAKE_PTR(pin_str);
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r = tpm2_unseal(device,
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hash_pcr_mask,
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pcr_bank,
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pubkey, pubkey_size,
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pubkey_pcr_mask,
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signature_json,
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b64_salted_pin,
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primary_alg,
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blob,
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blob_size,
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policy_hash,
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policy_hash_size,
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srk_buf,
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srk_buf_size,
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ret_decrypted_key,
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ret_decrypted_key_size);
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/* We get this error in case there is an authentication policy mismatch. This should
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* not happen, but this avoids confusing behavior, just in case. */
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if (IN_SET(r, -EPERM, -ENOLCK))
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return r;
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if (r < 0)
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continue;
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return r;
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}
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}
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int find_tpm2_auto_data(
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struct crypt_device *cd,
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uint32_t search_pcr_mask,
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int start_token,
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uint32_t *ret_hash_pcr_mask,
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uint16_t *ret_pcr_bank,
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void **ret_pubkey,
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size_t *ret_pubkey_size,
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uint32_t *ret_pubkey_pcr_mask,
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uint16_t *ret_primary_alg,
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void **ret_blob,
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size_t *ret_blob_size,
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void **ret_policy_hash,
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size_t *ret_policy_hash_size,
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void **ret_salt,
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size_t *ret_salt_size,
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void **ret_srk_buf,
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size_t *ret_srk_buf_size,
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TPM2Flags *ret_flags,
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int *ret_keyslot,
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int *ret_token) {
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int r, token;
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assert(cd);
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for (token = start_token; token < sym_crypt_token_max(CRYPT_LUKS2); token++) {
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_cleanup_free_ void *blob = NULL, *policy_hash = NULL, *pubkey = NULL, *salt = NULL, *srk_buf = NULL;
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_cleanup_(json_variant_unrefp) JsonVariant *v = NULL;
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size_t blob_size, policy_hash_size, pubkey_size, salt_size = 0, srk_buf_size = 0;
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uint32_t hash_pcr_mask, pubkey_pcr_mask;
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uint16_t pcr_bank, primary_alg;
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TPM2Flags flags;
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int keyslot;
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r = cryptsetup_get_token_as_json(cd, token, "systemd-tpm2", &v);
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if (IN_SET(r, -ENOENT, -EINVAL, -EMEDIUMTYPE))
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continue;
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if (r < 0)
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return log_error_errno(r, "Failed to read JSON token data off disk: %m");
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r = tpm2_parse_luks2_json(
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v,
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&keyslot,
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&hash_pcr_mask,
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&pcr_bank,
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&pubkey, &pubkey_size,
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&pubkey_pcr_mask,
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&primary_alg,
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&blob, &blob_size,
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&policy_hash, &policy_hash_size,
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&salt, &salt_size,
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&srk_buf, &srk_buf_size,
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&flags);
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if (r == -EUCLEAN) /* Gracefully handle issues in JSON fields not owned by us */
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continue;
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if (r < 0)
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return log_error_errno(r, "Failed to parse TPM2 JSON data: %m");
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if (search_pcr_mask == UINT32_MAX ||
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search_pcr_mask == hash_pcr_mask) {
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if (start_token <= 0)
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log_info("Automatically discovered security TPM2 token unlocks volume.");
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*ret_hash_pcr_mask = hash_pcr_mask;
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*ret_pcr_bank = pcr_bank;
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*ret_pubkey = TAKE_PTR(pubkey);
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*ret_pubkey_size = pubkey_size;
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*ret_pubkey_pcr_mask = pubkey_pcr_mask;
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*ret_primary_alg = primary_alg;
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*ret_blob = TAKE_PTR(blob);
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*ret_blob_size = blob_size;
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*ret_policy_hash = TAKE_PTR(policy_hash);
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*ret_policy_hash_size = policy_hash_size;
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*ret_salt = TAKE_PTR(salt);
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*ret_salt_size = salt_size;
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*ret_keyslot = keyslot;
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*ret_token = token;
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*ret_srk_buf = TAKE_PTR(srk_buf);
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*ret_srk_buf_size = srk_buf_size;
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*ret_flags = flags;
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return 0;
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}
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/* PCR mask doesn't match what is configured, ignore this entry, let's see next */
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}
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return log_error_errno(SYNTHETIC_ERRNO(ENXIO), "No valid TPM2 token data found.");
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}
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