Added some default limits in the verification of certificate

chains, to avoid denial of service attacks. Also added
gnutls_certificate_set_verify_limits() to override them.

10 files changed, 136 insertions, 21 deletions

diff --git a/NEWS b/NEWS
index 22a70f60a3..d99109d90c 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,9 @@ Version 1.0.17
   latest (yet unreleased) draft. Unfortunately this breaks
   compatibility with previous versions.
 - Changed the makefiles to be more portable.
+- Added some default limits in the verification of certificate
+  chains, to avoid denial of service attacks. Also added 
+  gnutls_certificate_set_verify_limits() to override them.
 
 Version 1.0.16 (10/07/2004)
 - Do not free the SRP (prime and generator) parameters obtained from the 
diff --git a/lib/auth_cert.h b/lib/auth_cert.h
index a27dbffc92..2d4b6cc1eb 100644
--- a/lib/auth_cert.h
+++ b/lib/auth_cert.h
@@ -81,6 +81,8 @@ typedef struct {
 	unsigned int    verify_flags; /* flags to be used at 
 				       * certificate verification.
 				       */
+	unsigned int    verify_depth;
+	unsigned int    verify_bits;
 
 			/* holds a sequence of the
 			 * RDNs of the CAs above.
diff --git a/lib/gnutls.h.in.in b/lib/gnutls.h.in.in
index 114f348bda..41cccb244d 100644
--- a/lib/gnutls.h.in.in
+++ b/lib/gnutls.h.in.in
@@ -363,7 +363,8 @@ void gnutls_certificate_free_crls(gnutls_certificate_credentials sc);
 void gnutls_certificate_set_dh_params(gnutls_certificate_credentials res, gnutls_dh_params);
 void gnutls_certificate_set_rsa_export_params(gnutls_certificate_credentials res, gnutls_rsa_params rsa_params);
 void gnutls_certificate_set_verify_flags(gnutls_certificate_credentials res, unsigned int flags);
-
+void gnutls_certificate_set_verify_limits(gnutls_certificate_credentials res, unsigned int max_bits,
+    unsigned int max_depth);
 
 int gnutls_certificate_set_x509_trust_file( gnutls_certificate_credentials res, const char* CAFILE, 
 	gnutls_x509_crt_fmt);
diff --git a/lib/gnutls_cert.c b/lib/gnutls_cert.c
index 5c1ca58869..81875677ad 100644
--- a/lib/gnutls_cert.c
+++ b/lib/gnutls_cert.c
@@ -227,6 +227,9 @@ int gnutls_certificate_allocate_credentials(gnutls_certificate_credentials * res
 
 	if (*res == NULL)
 		return GNUTLS_E_MEMORY_ERROR;
+		
+	(*res)->verify_bits = DEFAULT_VERIFY_BITS;
+	(*res)->verify_depth = DEFAULT_VERIFY_DEPTH;
 
 	return 0;
 }
@@ -482,6 +485,11 @@ int _gnutls_openpgp_cert_verify_peers(gnutls_session session)
 		return GNUTLS_E_NO_CERTIFICATE_FOUND;
 	}
 	
+	if (info->ncerts > cred->verify_depth) {
+		gnutls_assert();
+		return GNUTLS_E_CONSTRAINT_ERROR;
+	}
+	
 	/* generate a list of gnutls_certs based on the auth info
 	 * raw certs.
 	 */
@@ -509,6 +517,59 @@ int _gnutls_openpgp_cert_verify_peers(gnutls_session session)
 }
 
 /**
+  * gnutls_certificate_verify_peers2 - This function returns the peer's certificate verification status
+  * @session: is a gnutls session
+  * @status: is the output of the verification
+  *
+  * This function will try to verify the peer's certificate and return its status (trusted, invalid etc.).
+  * The value of @status should be one or more of the gnutls_certificate_status_t
+  * enumerated elements bitwise or'd.
+  * However you must also check the peer's name in order to check if the verified certificate belongs to the
+  * actual peer.
+  *
+  * Returns a negative error code on error and zero on success.
+  *
+  * This is the same as gnutls_x509_verify_certificate().
+  *
+  **/
+int gnutls_certificate_verify_peers2(gnutls_session session, unsigned int *status)
+{
+    CERTIFICATE_AUTH_INFO info;
+    int ret;
+    
+    CHECK_AUTH(GNUTLS_CRD_CERTIFICATE, GNUTLS_E_INVALID_REQUEST);
+
+    info = _gnutls_get_auth_info(session);
+    if (info == NULL) {
+	return GNUTLS_E_NO_CERTIFICATE_FOUND;
+    }
+
+    if (info->raw_certificate_list == NULL || info->ncerts == 0)
+	return GNUTLS_E_NO_CERTIFICATE_FOUND;
+
+    switch (gnutls_certificate_type_get(session)) {
+    case GNUTLS_CRT_X509: {
+	ret = _gnutls_x509_cert_verify_peers(session);
+	*status = ret;
+
+	if (ret < 0)
+	    return ret;
+	return 0;
+    }
+    case GNUTLS_CRT_OPENPGP: {
+	ret = _gnutls_openpgp_cert_verify_peers(session);
+	*status = ret;
+
+	if (ret < 0)
+	    return ret;
+	return 0;
+    }
+    default:
+	return GNUTLS_E_INVALID_REQUEST;
+    }
+}
+
+/**
   * gnutls_certificate_verify_peers - This function returns the peer's certificate verification status
   * @session: is a gnutls session
   *
@@ -517,33 +578,20 @@ int _gnutls_openpgp_cert_verify_peers(gnutls_session session)
   * actual peer.
   *
   * The return value should be one or more of the gnutls_certificate_status
-  * enumerated elements bitwise or'd.
+  * enumerated elements bitwise or'd, or a negative error code on error.
   *
   * This is the same as gnutls_x509_verify_certificate().
   *
   **/
 int gnutls_certificate_verify_peers(gnutls_session session)
 {
-	CERTIFICATE_AUTH_INFO info;
-
-	CHECK_AUTH(GNUTLS_CRD_CERTIFICATE, GNUTLS_E_INVALID_REQUEST);
+unsigned int status;
+int ret;
 
-	info = _gnutls_get_auth_info(session);
-	if (info == NULL) {
-		return GNUTLS_E_NO_CERTIFICATE_FOUND;
-	}
+	ret = gnutls_certificate_verify_peers2( session, &status);
+	if (ret < 0) return ret;
 	
-	if (info->raw_certificate_list == NULL || info->ncerts == 0)
-		return GNUTLS_E_NO_CERTIFICATE_FOUND;
-
-	switch( gnutls_certificate_type_get( session)) {
-		case GNUTLS_CRT_X509:
-			return _gnutls_x509_cert_verify_peers( session);
-		case GNUTLS_CRT_OPENPGP:
-			return _gnutls_openpgp_cert_verify_peers( session);
-		default:
-			return GNUTLS_E_INVALID_REQUEST;
-	}
+	return status;
 }
 
 /**
diff --git a/lib/gnutls_errors.c b/lib/gnutls_errors.c
index c68239e28c..734947204d 100644
--- a/lib/gnutls_errors.c
+++ b/lib/gnutls_errors.c
@@ -148,6 +148,7 @@ static gnutls_error_entry error_algorithms[] = {
         ERROR_ENTRY("The PKCS structure's bag type is unknown.", GNUTLS_E_UNKNOWN_PKCS_BAG_TYPE, 1),
         ERROR_ENTRY("The given password contains invalid characters.", GNUTLS_E_INVALID_PASSWORD, 1),
         ERROR_ENTRY("The Message Authentication Code verification failed.", GNUTLS_E_MAC_VERIFY_FAILED, 1),
+        ERROR_ENTRY("Some constraint limits were reached.", GNUTLS_E_CONSTRAINT_ERROR, 1),
 	{NULL, NULL, 0, 0}
 };
 
diff --git a/lib/gnutls_errors_int.h b/lib/gnutls_errors_int.h
index 3f64c626d7..10f7e27f75 100644
--- a/lib/gnutls_errors_int.h
+++ b/lib/gnutls_errors_int.h
@@ -115,6 +115,7 @@
 #define GNUTLS_E_UNKNOWN_PKCS_BAG_TYPE -98
 #define GNUTLS_E_INVALID_PASSWORD -99
 #define GNUTLS_E_MAC_VERIFY_FAILED -100 /* for PKCS #12 MAC */
+#define GNUTLS_E_CONSTRAINT_ERROR -101
 
 #define GNUTLS_E_BASE64_ENCODING_ERROR -201
 #define GNUTLS_E_INCOMPATIBLE_GCRYPT_LIBRARY -202
diff --git a/lib/gnutls_int.h b/lib/gnutls_int.h
index f14d7e5ced..65e072d4af 100644
--- a/lib/gnutls_int.h
+++ b/lib/gnutls_int.h
@@ -92,6 +92,11 @@ typedef void * gnutls_transport_ptr;
 
 #define HANDSHAKE_HEADER_SIZE 4
 
+/* defaults for verification functions
+ */
+#define DEFAULT_VERIFY_DEPTH 5
+#define DEFAULT_VERIFY_BITS 8200
+
 #include <gnutls_mem.h>
 #include <gnutls_ui.h>
 
diff --git a/lib/gnutls_ui.c b/lib/gnutls_ui.c
index b19a4b8499..8a5708a1de 100644
--- a/lib/gnutls_ui.c
+++ b/lib/gnutls_ui.c
@@ -373,7 +373,6 @@ void gnutls_anon_set_params_function(gnutls_anon_server_credentials res,
 	res->params_func = func;
 }
 
-
 /**
   * gnutls_certificate_set_verify_flags - This function will set the flags to be used at certificate verification
   * @res: is a gnutls_certificate_credentials structure
@@ -389,6 +388,24 @@ void gnutls_certificate_set_verify_flags(gnutls_certificate_credentials res, uns
 }
 
 /**
+  * gnutls_certificate_set_verify_limits - This function will set the upper limits to be used at certificate verification
+  * @res: is a gnutls_certificate_credentials structure
+  * @max_bits: is the number of bits of an acceptable certificate (default 8200)
+  * @max_depth: is maximum depth of the verification of a certificate chain (default 5)
+  *
+  * This function will set some upper limits for the default verification function
+  * (gnutls_certificate_verify_peers()) to avoid denial of service attacks.
+  *
+  **/
+void gnutls_certificate_set_verify_limits(gnutls_certificate_credentials res, unsigned int max_bits,
+    unsigned int max_depth)
+{
+	res->verify_depth = max_depth;
+	res->verify_bits = max_bits;
+}
+
+
+/**
   * gnutls_certificate_set_rsa_export_params - This function will set the RSA parameters for a server to use
   * @res: is a gnutls_certificate_credentials structure
   * @rsa_params: is a structure that holds temporary RSA parameters.
diff --git a/lib/gnutls_ui.h b/lib/gnutls_ui.h
index f30f5afae0..0d6f04224b 100644
--- a/lib/gnutls_ui.h
+++ b/lib/gnutls_ui.h
@@ -105,6 +105,7 @@ time_t gnutls_certificate_expiration_time_peers(gnutls_session session);
 
 int gnutls_certificate_client_get_request_status(gnutls_session);
 int gnutls_certificate_verify_peers(gnutls_session);
+int gnutls_certificate_verify_peers2(gnutls_session, unsigned int* status);
 
 int gnutls_pem_base64_encode(const char *header, const gnutls_datum * data,
 	char *result, size_t * result_size);
diff --git a/lib/gnutls_x509.c b/lib/gnutls_x509.c
index 5d7d5484a3..437c945928 100644
--- a/lib/gnutls_x509.c
+++ b/lib/gnutls_x509.c
@@ -53,6 +53,29 @@
  * some x509 certificate parsing functions.
  */
 
+/* Check if the number of bits of the key in the certificate
+ * is unacceptable.
+ */
+inline 
+static int check_bits( gnutls_x509_crt crt, unsigned int max_bits)
+{
+int ret;
+unsigned int bits;
+
+    ret = gnutls_x509_crt_get_pk_algorithm( crt, &bits);
+    if (ret < 0) {
+    	gnutls_assert();
+    	return ret;
+    }
+
+    if ( bits > max_bits) {
+        gnutls_assert();
+        return GNUTLS_E_CONSTRAINT_ERROR;
+    }
+    
+    return 0;
+}
+
 #define CLEAR_CERTS for(x=0;x<peer_certificate_list_size;x++) { \
 	if (peer_certificate_list[x]) \
 		gnutls_x509_crt_deinit(peer_certificate_list[x]); \
@@ -93,6 +116,12 @@ int _gnutls_x509_cert_verify_peers(gnutls_session session)
 
 	if (info->raw_certificate_list == NULL || info->ncerts == 0)
 		return GNUTLS_E_NO_CERTIFICATE_FOUND;
+	
+	if (info->ncerts > cred->verify_depth) {
+		gnutls_assert();
+		return GNUTLS_E_CONSTRAINT_ERROR;
+	}
+		
 
 	/* generate a list of gnutls_certs based on the auth info
 	 * raw certs.
@@ -122,6 +151,13 @@ int _gnutls_x509_cert_verify_peers(gnutls_session session)
 			CLEAR_CERTS;
 			return ret;
 		}
+
+		ret = check_bits( peer_certificate_list[i], cred->verify_bits);
+		if (ret < 0) {
+			gnutls_assert();
+			CLEAR_CERTS;
+			return ret;
+		}
 	}
 
 	/* Verify certificate