Set a compile-time limit to X.509 chain length
diff --git a/ChangeLog b/ChangeLog
index d1a87be..1b6770a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,8 @@
Features
* Add function pk_check_pair() to test if public and private keys match.
* Add x509_crl_parse_der().
+ * Add compile-time option POLARSSL_X509_MAX_INTERMEDIATE_CA to limit the
+ length of an X.509 verification chain.
Bugfix
* User set CFLAGS were ignore by Cmake with gcc (introduced in 1.3.9, found
diff --git a/include/polarssl/config.h b/include/polarssl/config.h
index fa15b37..a0ec2f3 100644
--- a/include/polarssl/config.h
+++ b/include/polarssl/config.h
@@ -2185,6 +2185,9 @@
/* Debug options */
//#define POLARSSL_DEBUG_DFL_MODE POLARSSL_DEBUG_LOG_FULL /**< Default log: Full or Raw */
+/* X509 options */
+//#define POLARSSL_X509_MAX_INTERMEDIATE_CA 8 /**< Maximum number of intermediate CAs in a verification chain. */
+
/* \} name SECTION: Module configuration options */
#include "check_config.h"
diff --git a/include/polarssl/x509.h b/include/polarssl/x509.h
index 9b0bcb7..3fe6820 100644
--- a/include/polarssl/x509.h
+++ b/include/polarssl/x509.h
@@ -45,6 +45,18 @@
* \{
*/
+#if !defined(POLARSSL_X509_MAX_INTERMEDIATE_CA)
+/**
+ * Maximum number of intermediate CAs in a verification chain.
+ * That is, maximum length of the chain, excluding the end-entity certificate
+ * and the trusted root certificate.
+ *
+ * Set this to a low value to prevent an adversary from making you waste
+ * resources verifying an overlong certificate chain.
+ */
+#define POLARSSL_X509_MAX_INTERMEDIATE_CA 8
+#endif
+
/**
* \name X509 Error codes
* \{
diff --git a/library/x509_crt.c b/library/x509_crt.c
index 2d72f6a..4d20889 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -1834,6 +1834,13 @@
x509_crt *grandparent;
const md_info_t *md_info;
+ /* path_cnt is 0 for the first intermediate CA */
+ if( 1 + path_cnt > POLARSSL_X509_MAX_INTERMEDIATE_CA )
+ {
+ *flags |= BADCERT_NOT_TRUSTED;
+ return( POLARSSL_ERR_X509_CERT_VERIFY_FAILED );
+ }
+
if( x509_time_expired( &child->valid_to ) )
*flags |= BADCERT_EXPIRED;
