Allow compile-time configuration of DTLS badmac limit
Introduces MBEDTLS_SSL_CONF_BADMAC_LIMIT to fix the maximum
number of records with bad MAC tolerated in DTLS at compile-time.
Impact on code-size:
| | GCC | ARMC5 | ARMC6 |
| --- | --- | --- | --- |
| `libmbedtls.a` before | 23511 | 24049 | 27903 |
| `libmbedtls.a` after | 23487 | 24025 | 27885 |
| gain in Bytes | 24 | 24 | 18 |
diff --git a/configs/baremetal.h b/configs/baremetal.h
index 2a3e39a..bacc9d1 100644
--- a/configs/baremetal.h
+++ b/configs/baremetal.h
@@ -80,6 +80,7 @@
#define MBEDTLS_SSL_DTLS_CONNECTION_ID
/* Compile-time fixed parts of the SSL configuration */
+#define MBEDTLS_SSL_CONF_BADMAC_LIMIT 0
#define MBEDTLS_SSL_CONF_ANTI_REPLAY MBEDTLS_SSL_ANTI_REPLAY_ENABLED
#define MBEDTLS_SSL_CONF_EXTENDED_MASTER_SECRET \
MBEDTLS_SSL_EXTENDED_MS_ENABLED
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 1ff34dc..ee292c5 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -3450,8 +3450,9 @@
* \{
*/
-/* DTLS Anti replay */
+/* DTLS-specific settings */
//#define MBEDTLS_SSL_CONF_ANTI_REPLAY MBEDTLS_SSL_ANTI_REPLAY_ENABLED
+//#define MBEDTLS_SSL_CONF_BADMAC_LIMIT 0
/* ExtendedMasterSecret extension
* The following two options must be set/unset simultaneously. */
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index fbc6109..dd546b8 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1029,7 +1029,9 @@
#endif
#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
+#if !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
unsigned int badmac_limit; /*!< limit of records with a bad MAC */
+#endif /* !MBEDTLS_SSL_CONF_BADMAC_LIMIT */
#endif
#if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_CLI_C)
@@ -2043,7 +2045,8 @@
void mbedtls_ssl_conf_dtls_anti_replay( mbedtls_ssl_config *conf, char mode );
#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY && !MBEDTLS_SSL_CONF_ANTI_REPLAY */
-#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
+#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT) && \
+ !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
/**
* \brief Set a limit on the number of records with a bad MAC
* before terminating the connection.
@@ -2066,9 +2069,13 @@
* connection. On the other hand, a high limit or no limit
* might make us waste resources checking authentication on
* many bogus packets.
+ *
+ * \note On constrained systems, this option can also be
+ * fixed at compile-time by defining the constant
+ * MBEDTLS_SSL_CONF_BADMAC_LIMIT.
*/
void mbedtls_ssl_conf_dtls_badmac_limit( mbedtls_ssl_config *conf, unsigned limit );
-#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT */
+#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT && !MBEDTLS_SSL_CONF_BADMAC_LIMIT */
#if defined(MBEDTLS_SSL_PROTO_DTLS)
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 092819e..49c6050 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -1085,6 +1085,23 @@
* be fixed at compile time via one of MBEDTLS_SSL_SSL_CONF_XXX.
*/
+#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
+#if !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
+static inline unsigned int mbedtls_ssl_conf_get_badmac_limit(
+ mbedtls_ssl_config const *conf )
+{
+ return( conf->badmac_limit );
+}
+#else /* !MBEDTLS_SSL_CONF_BADMAC_LIMIT */
+static inline unsigned int mbedtls_ssl_conf_get_badmac_limit(
+ mbedtls_ssl_config const *conf )
+{
+ ((void) conf);
+ return( MBEDTLS_SSL_CONF_BADMAC_LIMIT );
+}
+#endif /* MBEDTLS_SSL_CONF_BADMAC_LIMIT */
+#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT */
+
#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
#if !defined(MBEDTLS_SSL_CONF_ANTI_REPLAY)
static inline unsigned int mbedtls_ssl_conf_get_anti_replay(
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c70bc21..a79ce8d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5780,8 +5780,8 @@
}
#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
- if( ssl->conf->badmac_limit != 0 &&
- ++ssl->badmac_seen >= ssl->conf->badmac_limit )
+ if( mbedtls_ssl_conf_get_badmac_limit( ssl->conf ) != 0 &&
+ ++ssl->badmac_seen >= mbedtls_ssl_conf_get_badmac_limit( ssl->conf ) )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "too many records with bad MAC" ) );
return( MBEDTLS_ERR_SSL_INVALID_MAC );
@@ -8068,12 +8068,14 @@
}
#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY && !MBEDTLS_SSL_CONF_ANTI_REPLAY */
-#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
-void mbedtls_ssl_conf_dtls_badmac_limit( mbedtls_ssl_config *conf, unsigned limit )
+#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT) && \
+ !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
+void mbedtls_ssl_conf_dtls_badmac_limit( mbedtls_ssl_config *conf,
+ unsigned limit )
{
conf->badmac_limit = limit;
}
-#endif
+#endif /* MBEDTLS_SSL_DTLS_BADMAC_LIMIT && !MBEDTLS_SSL_CONF_BADMAC_LIMIT */
#if defined(MBEDTLS_SSL_PROTO_DTLS)
diff --git a/programs/ssl/query_config.c b/programs/ssl/query_config.c
index 35b3fe9..2a7ca13 100644
--- a/programs/ssl/query_config.c
+++ b/programs/ssl/query_config.c
@@ -2586,6 +2586,14 @@
}
#endif /* MBEDTLS_SSL_CONF_ANTI_REPLAY */
+#if defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
+ if( strcmp( "MBEDTLS_SSL_CONF_BADMAC_LIMIT", config ) == 0 )
+ {
+ MACRO_EXPANSION_TO_STR( MBEDTLS_SSL_CONF_BADMAC_LIMIT );
+ return( 0 );
+ }
+#endif /* MBEDTLS_SSL_CONF_BADMAC_LIMIT */
+
#if defined(MBEDTLS_SSL_CONF_EXTENDED_MASTER_SECRET)
if( strcmp( "MBEDTLS_SSL_CONF_EXTENDED_MASTER_SECRET", config ) == 0 )
{
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index b76473f..3fcc120 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -325,7 +325,8 @@
#define USAGE_ANTI_REPLAY ""
#endif
-#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
+#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT) && \
+ !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
#define USAGE_BADMAC_LIMIT \
" badmac_limit=%%d default: (library default: disabled)\n"
#else
@@ -1898,12 +1899,14 @@
goto usage;
}
#endif /* !MBEDTLS_SSL_CONF_ANTI_REPLAY */
+#if !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
else if( strcmp( p, "badmac_limit" ) == 0 )
{
opt.badmac_limit = atoi( q );
if( opt.badmac_limit < 0 )
goto usage;
}
+#endif /* !MBEDTLS_SSL_CONF_BADMAC_LIMIT */
else if( strcmp( p, "hs_timeout" ) == 0 )
{
if( ( p = strchr( q, '-' ) ) == NULL )
@@ -2589,7 +2592,8 @@
mbedtls_ssl_conf_dtls_anti_replay( &conf, opt.anti_replay );
#endif
-#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
+#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT) && \
+ !defined(MBEDTLS_SSL_CONF_BADMAC_LIMIT)
if( opt.badmac_limit != DFL_BADMAC_LIMIT )
mbedtls_ssl_conf_dtls_badmac_limit( &conf, opt.badmac_limit );
#endif
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 6d71120..87c1d24 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -549,6 +549,9 @@
check_cmdline_param_compat "anti_replay" \
"MBEDTLS_SSL_CONF_ANTI_REPLAY"
+ # DTLS bad MAC limit
+ check_cmdline_param_compat "badmac_limit" \
+ "MBEDTLS_SSL_CONF_BADMAC_LIMIT"
}
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