From: Bryan Jacobs <b@q3q.us>
Date: Tue, 16 Apr 2024 03:12:22 +0000 (+1000)
Subject: cryptenroll: Use CTAP2.1 credProtect extension
X-Git-Tag: v256-rc1~167
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=12cf745cceb3dfec858bab6152636e42f1c23bb9;p=thirdparty%2Fsystemd.git

cryptenroll: Use CTAP2.1 credProtect extension

When enrolling a new FIDO2 token with a client PIN, this tells the authenticator to require the PIN on all uses.

It also collects a PIN before attempting to create a credential.

Works around #31443 in most (not all) scenarios.
---

diff --git a/src/shared/libfido2-util.c b/src/shared/libfido2-util.c
index 15b7e42c848..1cc81a6c610 100644
--- a/src/shared/libfido2-util.c
+++ b/src/shared/libfido2-util.c
@@ -40,6 +40,7 @@ DLSYM_FUNCTION(fido_cred_id_ptr);
 DLSYM_FUNCTION(fido_cred_new);
 DLSYM_FUNCTION(fido_cred_set_clientdata_hash);
 DLSYM_FUNCTION(fido_cred_set_extensions);
+DLSYM_FUNCTION(fido_cred_set_prot);
 DLSYM_FUNCTION(fido_cred_set_rk);
 DLSYM_FUNCTION(fido_cred_set_rp);
 DLSYM_FUNCTION(fido_cred_set_type);
@@ -97,6 +98,7 @@ int dlopen_libfido2(void) {
                         DLSYM_ARG(fido_cred_new),
                         DLSYM_ARG(fido_cred_set_clientdata_hash),
                         DLSYM_ARG(fido_cred_set_extensions),
+                        DLSYM_ARG(fido_cred_set_prot),
                         DLSYM_ARG(fido_cred_set_rk),
                         DLSYM_ARG(fido_cred_set_rp),
                         DLSYM_ARG(fido_cred_set_type),
@@ -776,10 +778,21 @@ int fido2_generate_hmac_hash(
         if (!c)
                 return log_oom();
 
-        r = sym_fido_cred_set_extensions(c, FIDO_EXT_HMAC_SECRET);
+        int extensions = FIDO_EXT_HMAC_SECRET;
+        if (FLAGS_SET(lock_with, FIDO2ENROLL_PIN) || FLAGS_SET(lock_with, FIDO2ENROLL_UV)) {
+                /* Attempt to use the "cred protect" extension, requiring user verification (UV) for this
+                 * credential. If the authenticator doesn't support the extension, it will be ignored. */
+                extensions |= FIDO_EXT_CRED_PROTECT;
+
+                r = sym_fido_cred_set_prot(c, FIDO_CRED_PROT_UV_REQUIRED);
+                if (r != FIDO_OK)
+                        log_warning("Failed to set protection level on FIDO2 credential, ignoring: %s", sym_fido_strerr(r));
+        }
+
+        r = sym_fido_cred_set_extensions(c, extensions);
         if (r != FIDO_OK)
                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
-                                       "Failed to enable HMAC-SECRET extension on FIDO2 credential: %s", sym_fido_strerr(r));
+                                       "Failed to enable extensions on FIDO2 credential: %s", sym_fido_strerr(r));
 
         r = sym_fido_cred_set_rp(c, rp_id, rp_name);
         if (r != FIDO_OK)
@@ -830,7 +843,17 @@ int fido2_generate_hmac_hash(
                            emoji_enabled() ? special_glyph(SPECIAL_GLYPH_TOUCH) : "",
                            emoji_enabled() ? " " : "");
 
-        r = sym_fido_dev_make_cred(d, c, NULL);
+        /* If we are using the user PIN, then we must pass that PIN to the get_assertion call below, or
+         * the authenticator will use the non-user-verification HMAC secret (which differs from the one when
+         * the PIN is passed).
+         *
+         * Rather than potentially trying and failing to create the credential, just collect the PIN first
+         * and then pass it to both the make_credential and the get_assertion operations. */
+        if (FLAGS_SET(lock_with, FIDO2ENROLL_PIN))
+                r = FIDO_ERR_PIN_REQUIRED;
+        else
+                r = sym_fido_dev_make_cred(d, c, NULL);
+
         if (r == FIDO_ERR_PIN_REQUIRED) {
 
                 if (!has_client_pin)
diff --git a/src/shared/libfido2-util.h b/src/shared/libfido2-util.h
index 198408fdaf3..5e40b2aafc4 100644
--- a/src/shared/libfido2-util.h
+++ b/src/shared/libfido2-util.h
@@ -43,6 +43,7 @@ DLSYM_PROTOTYPE(fido_cred_id_ptr);
 DLSYM_PROTOTYPE(fido_cred_new);
 DLSYM_PROTOTYPE(fido_cred_set_clientdata_hash);
 DLSYM_PROTOTYPE(fido_cred_set_extensions);
+DLSYM_PROTOTYPE(fido_cred_set_prot);
 DLSYM_PROTOTYPE(fido_cred_set_rk);
 DLSYM_PROTOTYPE(fido_cred_set_rp);
 DLSYM_PROTOTYPE(fido_cred_set_type);