asn/settings: document X509_VERIFY_ONLY/X509_TINY options and fail-closed on critical stripped extensions under TINY

Author: aidangarske

wolfcrypt/src/asn.c

@@ -156,6 +156,12 @@ ASN Options:
  * WOLFSSL_ALLOW_CRIT_AKID:  Allow critical Auth Key Identifier
  * WOLFSSL_ALLOW_CRIT_SKID:  Allow critical Subject Key Identifier
  * WC_ASN_UNKNOWN_EXT_CB:    Callback for unknown extensions
+ * WOLFSSL_X509_VERIFY_ONLY: Verify-only profile. Drops cert/key generation and
+    forces WOLFSSL_NO_PEM unless a gen add-back (WOLFSSL_X509_CERT_GEN /
+    WOLFSSL_X509_KEY_GEN) or WOLFSSL_X509_PEM is set.
+ * WOLFSSL_X509_TINY:        Minimal-extension profile. Compiles out optional
+    X.509 extension decoders behind per-feature WOLFSSL_X509_TINY_<F> add-back
+    macros. Requires WOLFSSL_ASN_TEMPLATE (enforced with #error).
  *
  * ASN.1 Parsing:
  * WOLFSSL_ASN_ALL:          Enable all ASN.1 features
@@ -21354,7 +21360,9 @@ WOLFSSL_TEST_VIS int DecodeExtensionType(const byte* input, word32 length,
         default:
             if (isUnknownExt != NULL)
                 *isUnknownExt = 1;
-        #ifndef WOLFSSL_NO_ASN_STRICT
+        /* TINY reaches default: for stripped extensions too, so reject a
+         * critical one even under NO_ASN_STRICT to stay fail-closed. */
+        #if !defined(WOLFSSL_NO_ASN_STRICT) || defined(WOLFSSL_X509_TINY)
             /* While it is a failure to not support critical extensions,
              * still parse the certificate ignoring the unsupported
              * extension to allow caller to accept it with the verify

wolfssl/wolfcrypt/settings.h

@@ -4344,11 +4344,9 @@ blinding by defining WC_BLINDING_NO_RNG_ACKNOWLEDGE_WEAKNESS."
     #define OPENSSL_EXTRA_X509_SMALL
 #endif /* OPENSSL_EXTRA */
 
-/* X.509 verify-only profile (placed before DER_TO_PEM/OCSP derivations so they
- * observe it). Drives existing switches so defs and callers stay consistent;
- * WOLFSSL_X509_<f> adds a feature back. */
+/* X.509 verify-only profile. Define WOLFSSL_X509_PEM (or a gen add-back) to keep
+ * PEM parsing, else WOLFSSL_NO_PEM below also disables PEM-to-DER trust anchors. */
 #ifdef WOLFSSL_X509_VERIFY_ONLY
-    /* Cert/key generation add-backs need the PEM helpers, so don't strip PEM. */
     #if !defined(WOLFSSL_X509_PEM) && !defined(WOLFSSL_NO_PEM) && \
         !defined(WOLFSSL_X509_CERT_GEN) && !defined(WOLFSSL_X509_KEY_GEN)
         #define WOLFSSL_NO_PEM