Reject certificates with unhandled critical extensions.

CHANGES

@@ -12,6 +12,15 @@
          *) applies to 0.9.6a/0.9.6b/0.9.6c and 0.9.7
          +) applies to 0.9.7 only
 
+  +) Test for certificates which contain unsupported critical extensions.
+     If such a certificate is found during a verify operation it is 
+     rejected by default: this behaviour can be overridden by either
+     handling the new error X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION or
+     by setting the verify flag X509_V_FLAG_IGNORE_CRITICAL. A new function
+     X509_supported_extension() has also been added which returns 1 if a
+     particular extension is supported.
+     [Steve Henson]
+
   +) New functions/macros
 
           SSL_CTX_set_msg_callback(ctx, cb)

apps/verify.c

@@ -146,6 +146,8 @@ int MAIN(int argc, char **argv)
 				}
 			else if (strcmp(*argv,"-help") == 0)
 				goto end;
+			else if (strcmp(*argv,"-ignore_critical") == 0)
+				vflags |= X509_V_FLAG_IGNORE_CRITICAL;
 			else if (strcmp(*argv,"-issuer_checks") == 0)
 				vflags |= X509_V_FLAG_CB_ISSUER_CHECK;
 			else if (strcmp(*argv,"-crl_check") == 0)
@@ -343,6 +345,7 @@ static int MS_CALLBACK cb(int ok, X509_STORE_CTX *ctx)
 		if (ctx->error == X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT) ok=1;
 		if (ctx->error == X509_V_ERR_CRL_HAS_EXPIRED) ok=1;
 		if (ctx->error == X509_V_ERR_CRL_NOT_YET_VALID) ok=1;
+		if (ctx->error == X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION) ok=1;
 		}
 	if (!v_verbose)
 		ERR_clear_error();

crypto/x509/x509_txt.c

@@ -144,6 +144,9 @@ const char *X509_verify_cert_error_string(long n)
 	case X509_V_ERR_UNABLE_TO_GET_CRL_ISSUER:
 		return("unable to get CRL issuer certificate");
 
+	case X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION:
+		return("unhandled critical extension");
+
 	default:
 		sprintf(buf,"error number %ld",n);
 		return(buf);

crypto/x509/x509_vfy.c

@@ -384,6 +384,15 @@ static int check_chain_purpose(X509_STORE_CTX *ctx)
 	for (i = 0; i < ctx->last_untrusted; i++)
 		{
 		x = sk_X509_value(ctx->chain, i);
+		if (!(ctx->flags & X509_V_FLAG_IGNORE_CRITICAL)
+			&& (x->ex_flags & EXFLAG_CRITICAL))
+			{
+			ctx->error = X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION;
+			ctx->error_depth = i;
+			ctx->current_cert = x;
+			ok=cb(0,ctx);
+			if (!ok) goto end;
+			}
 		if (!X509_check_purpose(x, ctx->purpose, i))
 			{
 			if (i)
@@ -721,8 +730,6 @@ static int internal_verify(X509_STORE_CTX *ctx)
 			if (!ok) goto end;
 			}
 
-		/* CRL CHECK */
-
 		/* The last error (if any) is still in the error value */
 		ctx->current_cert=xs;
 		ok=(*cb)(1,ctx);

crypto/x509/x509_vfy.h

@@ -303,6 +303,7 @@ struct x509_store_ctx_st      /* X509_STORE_CTX */
 #define		X509_V_ERR_KEYUSAGE_NO_CERTSIGN			32
 
 #define		X509_V_ERR_UNABLE_TO_GET_CRL_ISSUER		33
+#define		X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION		34
 
 /* The application is not happy */
 #define		X509_V_ERR_APPLICATION_VERIFICATION		50
@@ -313,6 +314,7 @@ struct x509_store_ctx_st      /* X509_STORE_CTX */
 #define	X509_V_FLAG_USE_CHECK_TIME		0x2	/* Use check time instead of current time */
 #define	X509_V_FLAG_CRL_CHECK			0x4	/* Lookup CRLs */
 #define	X509_V_FLAG_CRL_CHECK_ALL		0x8	/* Lookup CRLs for whole chain */
+#define	X509_V_FLAG_IGNORE_CRITICAL		0x10	/* Ignore unhandled critical extensions */
 
 int X509_OBJECT_idx_by_subject(STACK_OF(X509_OBJECT) *h, int type,
 	     X509_NAME *name);

crypto/x509v3/v3_purp.c

@@ -1,9 +1,9 @@
 /* v3_purp.c */
 /* Written by Dr Stephen N Henson (shenson@bigfoot.com) for the OpenSSL
- * project 1999.
+ * project 2001.
  */
 /* ====================================================================
- * Copyright (c) 1999 The OpenSSL Project.  All rights reserved.
+ * Copyright (c) 1999-2001 The OpenSSL Project.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -266,12 +266,51 @@ int X509_PURPOSE_get_trust(X509_PURPOSE *xp)
 	return xp->trust;
 }
 
+static int nid_cmp(int *a, int *b)
+	{
+	return *a - *b;
+	}
+
+int X509_supported_extension(X509_EXTENSION *ex)
+	{
+	/* This table is a list of the NIDs of supported extensions:
+	 * that is those which are used by the verify process. If
+	 * an extension is critical and doesn't appear in this list
+	 * then the verify process will normally reject the certificate.
+	 * The list must be kept in numerical order because it will be
+	 * searched using bsearch.
+	 */
+
+	static int supported_nids[] = {
+		NID_netscape_cert_type, /* 71 */
+        	NID_key_usage,		/* 83 */
+		NID_subject_alt_name,	/* 85 */
+		NID_basic_constraints,	/* 87 */
+        	NID_ext_key_usage	/* 126 */
+	};
+
+	int ex_nid;
+
+	ex_nid = OBJ_obj2nid(X509_EXTENSION_get_object(ex));
+
+	if (ex_nid == NID_undef) 
+		return 0;
+
+	if (OBJ_bsearch((char *)&ex_nid, (char *)supported_nids,
+		sizeof(supported_nids)/sizeof(int), sizeof(int),
+		(int (*)(const void *, const void *))nid_cmp))
+		return 1;
+	return 0;
+	}
+ 
+
 static void x509v3_cache_extensions(X509 *x)
 {
 	BASIC_CONSTRAINTS *bs;
 	ASN1_BIT_STRING *usage;
 	ASN1_BIT_STRING *ns;
 	EXTENDED_KEY_USAGE *extusage;
+	X509_EXTENSION *ex;
 	
 	int i;
 	if(x->ex_flags & EXFLAG_SET) return;
@@ -352,6 +391,17 @@ static void x509v3_cache_extensions(X509 *x)
 	}
 	x->skid =X509_get_ext_d2i(x, NID_subject_key_identifier, NULL, NULL);
 	x->akid =X509_get_ext_d2i(x, NID_authority_key_identifier, NULL, NULL);
+	for (i = 0; i < X509_get_ext_count(x); i++)
+		{
+		ex = X509_get_ext(x, i);
+		if (!X509_EXTENSION_get_critical(ex))
+			continue;
+		if (!X509_supported_extension(ex))
+			{
+			x->ex_flags |= EXFLAG_CRITICAL;
+			break;
+			}
+		}
 	x->ex_flags |= EXFLAG_SET;
 }
 

crypto/x509v3/x509v3.h

@@ -324,6 +324,7 @@ DECLARE_ASN1_SET_OF(POLICYINFO)
 #define EXFLAG_V1		0x40
 #define EXFLAG_INVALID		0x80
 #define EXFLAG_SET		0x100
+#define EXFLAG_CRITICAL		0x200
 
 #define KU_DIGITAL_SIGNATURE	0x0080
 #define KU_NON_REPUDIATION	0x0040
@@ -528,6 +529,7 @@ int X509V3_EXT_print_fp(FILE *out, X509_EXTENSION *ext, int flag, int indent);
 int X509V3_extensions_print(BIO *out, char *title, STACK_OF(X509_EXTENSION) *exts, unsigned long flag, int indent);
 
 int X509_check_purpose(X509 *x, int id, int ca);
+int X509_supported_extension(X509_EXTENSION *ex);
 int X509_PURPOSE_set(int *p, int purpose);
 int X509_check_issued(X509 *issuer, X509 *subject);
 int X509_PURPOSE_get_count(void);