home: add helper to process/normalize modhex64 recovery keys

src/home/meson.build

@@ -7,6 +7,7 @@ systemd_homework_sources = files('''
         homework-cifs.h
         homework-directory.c
         homework-directory.h
+        homework-fido2.h
         homework-fscrypt.c
         homework-fscrypt.h
         homework-luks.c
@@ -14,11 +15,12 @@ systemd_homework_sources = files('''
         homework-mount.c
         homework-mount.h
         homework-pkcs11.h
-        homework-fido2.h
         homework-quota.c
         homework-quota.h
         homework.c
         homework.h
+        modhex.c
+        modhex.h
         user-record-util.c
         user-record-util.h
 '''.split())
@@ -50,6 +52,8 @@ systemd_homed_sources = files('''
         homed-varlink.c
         homed-varlink.h
         homed.c
+        modhex.c
+        modhex.h
         user-record-pwquality.c
         user-record-pwquality.h
         user-record-sign.c
@@ -74,6 +78,8 @@ homectl_sources = files('''
         homectl-pkcs11.c
         homectl-pkcs11.h
         homectl.c
+        modhex.c
+        modhex.h
         user-record-pwquality.c
         user-record-pwquality.h
         user-record-util.c
@@ -84,6 +90,8 @@ pam_systemd_home_sym = 'src/home/pam_systemd_home.sym'
 pam_systemd_home_c = files('''
         home-util.c
         home-util.h
+        modhex.c
+        modhex.h
         pam_systemd_home.c
         user-record-util.c
         user-record-util.h
@@ -100,3 +108,11 @@ if conf.get('ENABLE_HOMED') == 1
         install_data('homed.conf',
                      install_dir : pkgsysconfdir)
 endif
+
+tests += [
+        [['src/home/test-modhex.c',
+          'src/home/modhex.c',
+          'src/home/modhex.h'],
+         [],
+         []],
+]

src/home/modhex.c

@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+
+#include "modhex.h"
+#include "macro.h"
+#include "memory-util.h"
+
+const char modhex_alphabet[16] = {
+        'c', 'b', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'n', 'r', 't', 'u', 'v'
+};
+
+int decode_modhex_char(char x) {
+
+        for (size_t i = 0; i < ELEMENTSOF(modhex_alphabet); i++)
+                /* Check both upper and lowercase */
+                if (modhex_alphabet[i] == x || (modhex_alphabet[i] - 32) == x)
+                        return i;
+
+        return -EINVAL;
+}
+
+int normalize_recovery_key(const char *password, char **ret) {
+        _cleanup_(erase_and_freep) char *mangled = NULL;
+        size_t l;
+
+        assert(password);
+        assert(ret);
+
+        l = strlen(password);
+        if (!IN_SET(l,
+                    MODHEX_RAW_LENGTH*2,          /* syntax without dashes */
+                    MODHEX_FORMATTED_LENGTH-1))   /* syntax with dashes */
+                return -EINVAL;
+
+        mangled = new(char, MODHEX_FORMATTED_LENGTH);
+        if (!mangled)
+                return -ENOMEM;
+
+        for (size_t i = 0, j = 0; i < MODHEX_RAW_LENGTH; i++) {
+                size_t k;
+                int a, b;
+
+                if (l == MODHEX_RAW_LENGTH*2)
+                        /* Syntax without dashes */
+                        k = i * 2;
+                else {
+                        /* Syntax with dashes */
+                        assert(l == MODHEX_FORMATTED_LENGTH-1);
+                        k = i * 2 + i / 4;
+
+                        if (i > 0 && i % 4 == 0 && password[k-1] != '-')
+                                return -EINVAL;
+                }
+
+                a = decode_modhex_char(password[k]);
+                if (a < 0)
+                        return -EINVAL;
+                b = decode_modhex_char(password[k+1]);
+                if (b < 0)
+                        return -EINVAL;
+
+                mangled[j++] = modhex_alphabet[a];
+                mangled[j++] = modhex_alphabet[b];
+
+                if (i % 4 == 3)
+                        mangled[j++] = '-';
+        }
+
+        mangled[MODHEX_FORMATTED_LENGTH-1] = 0;
+
+        *ret = TAKE_PTR(mangled);
+        return 0;
+}

src/home/modhex.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+/* 256 bit keys = 32 bytes */
+#define MODHEX_RAW_LENGTH 32
+
+/* Formatted as sequences of 64 modhex characters, with dashes inserted after multiples of 8 chars (incl. trailing NUL) */
+#define MODHEX_FORMATTED_LENGTH (MODHEX_RAW_LENGTH*2/8*9)
+
+extern const char modhex_alphabet[16];
+
+int decode_modhex_char(char x);
+
+int normalize_recovery_key(const char *password, char **ret);

src/home/test-modhex.c

@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include "modhex.h"
+#include "alloc-util.h"
+#include "string-util.h"
+
+static void test_normalize_recovery_key(const char *t, const char *expected) {
+        _cleanup_free_ char *z = NULL;
+        int r;
+
+        assert(t);
+
+        r = normalize_recovery_key(t, &z);
+        assert_se(expected ?
+                  (r >= 0 && streq(z, expected)) :
+                  (r == -EINVAL && z == NULL));
+}
+
+int main(int argc, char *arv[]) {
+
+        test_normalize_recovery_key("iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj",
+                                    "iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj");
+
+        test_normalize_recovery_key("iefgcelhbiduvkjvcjvuncnkvlfchdidjhtuhhdeurkllkegilkjgbrthjkbgktj",
+                                    "iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj");
+
+        test_normalize_recovery_key("IEFGCELH-BIDUVKJV-CJVUNCNK-VLFCHDID-JHTUHHDE-URKLLKEG-ILKJGBRT-HJKBGKTJ",
+                                    "iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj");
+
+        test_normalize_recovery_key("IEFGCELHBIDUVKJVCJVUNCNKVLFCHDIDJHTUHHDEURKLLKEGILKJGBRTHJKBGKTJ",
+                                    "iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj");
+
+        test_normalize_recovery_key("Iefgcelh-Biduvkjv-Cjvuncnk-Vlfchdid-Jhtuhhde-Urkllkeg-Ilkjgbrt-Hjkbgktj",
+                                    "iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj");
+
+        test_normalize_recovery_key("Iefgcelhbiduvkjvcjvuncnkvlfchdidjhtuhhdeurkllkegilkjgbrthjkbgktj",
+                                    "iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj");
+
+        test_normalize_recovery_key("iefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgkt", NULL);
+        test_normalize_recovery_key("iefgcelhbiduvkjvcjvuncnkvlfchdidjhtuhhdeurkllkegilkjgbrthjkbgkt", NULL);
+        test_normalize_recovery_key("IEFGCELHBIDUVKJVCJVUNCNKVLFCHDIDJHTUHHDEURKLLKEGILKJGBRTHJKBGKT", NULL);
+
+        test_normalize_recovery_key("xefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj", NULL);
+        test_normalize_recovery_key("Xefgcelh-biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj", NULL);
+        test_normalize_recovery_key("iefgcelh+biduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj", NULL);
+        test_normalize_recovery_key("iefgcelhebiduvkjv-cjvuncnk-vlfchdid-jhtuhhde-urkllkeg-ilkjgbrt-hjkbgktj", NULL);
+
+        test_normalize_recovery_key("", NULL);
+
+        return 0;
+}

src/home/user-record-util.c

@@ -4,6 +4,8 @@
 #include "home-util.h"
 #include "id128-util.h"
 #include "libcrypt-util.h"
+#include "memory-util.h"
+#include "modhex.h"
 #include "mountpoint-util.h"
 #include "path-util.h"
 #include "stat-util.h"
@@ -571,6 +573,48 @@ int user_record_test_secret(UserRecord *h, UserRecord *secret) {
         return -ENOKEY;
 }
 
+int user_record_test_recovery_key(UserRecord *h, UserRecord *secret) {
+        char **i;
+        int r;
+
+        assert(h);
+
+        /* Checks whether any of the specified passwords matches any of the hashed recovery keys of the entry */
+
+        if (h->n_recovery_key == 0)
+                return -ENXIO;
+
+        STRV_FOREACH(i, secret->password) {
+                for (size_t j = 0; j < h->n_recovery_key; j++) {
+                        _cleanup_(erase_and_freep) char *mangled = NULL;
+                        const char *p;
+
+                        if (streq(h->recovery_key[j].type, "modhex64")) {
+                                /* If this key is for a modhex64 recovery key, then try to normalize the
+                                 * passphrase to make things more robust: that way the password becomes case
+                                 * insensitive and the dashes become optional. */
+
+                                r = normalize_recovery_key(*i, &mangled);
+                                if (r == -EINVAL) /* Not a valid modhex64 passphrase, don't bother */
+                                        continue;
+                                if (r < 0)
+                                        return r;
+
+                                p = mangled;
+                        } else
+                                p = *i; /* Unknown recovery key types process as is */
+
+                        r = test_password_one(h->recovery_key[j].hashed_password, p);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                return 0;
+                }
+        }
+
+        return -ENOKEY;
+}
+
 int user_record_set_disk_size(UserRecord *h, uint64_t disk_size) {
         _cleanup_(json_variant_unrefp) JsonVariant *new_per_machine = NULL, *midv = NULL, *midav = NULL, *ne = NULL;
         _cleanup_free_ JsonVariant **array = NULL;

src/home/user-record-util.h

@@ -41,6 +41,7 @@ int user_record_test_image_path(UserRecord *h);
 int user_record_test_image_path_and_warn(UserRecord *h);
 
 int user_record_test_secret(UserRecord *h, UserRecord *secret);
+int user_record_test_recovery_key(UserRecord *h, UserRecord *secret);
 
 int user_record_update_last_changed(UserRecord *h, bool with_password);
 int user_record_set_disk_size(UserRecord *h, uint64_t disk_size);