Account for additional record expansion when using CIDs
Using the Connection ID extension increases the maximum record expansion
because
- the real record content type is added to the plaintext
- the plaintext may be padded with an arbitrary number of
zero bytes, in order to prevent leakage of information
through package length analysis. Currently, we always
pad the plaintext in a minimal way so that its length
is a multiple of 16 Bytes.
This commit adapts the various parts of the library to account
for that additional source of record expansion.
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index c7668eb..41a1c7f 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -175,10 +175,19 @@
#define MBEDTLS_SSL_PADDING_ADD 0
#endif
+#if defined(MBEDTLS_SSL_CID)
+#define MBEDTLS_SSL_MAX_CID_EXPANSION 16 /* Currently, we pad records
+ * to lengths which are multiples
+ * of 16 Bytes. */
+#else
+#define MBEDTLS_SSL_MAX_CID_EXPANSION 0
+#endif
+
#define MBEDTLS_SSL_PAYLOAD_OVERHEAD ( MBEDTLS_SSL_COMPRESSION_ADD + \
MBEDTLS_MAX_IV_LENGTH + \
MBEDTLS_SSL_MAC_ADD + \
- MBEDTLS_SSL_PADDING_ADD \
+ MBEDTLS_SSL_PADDING_ADD + \
+ MBEDTLS_SSL_MAX_CID_EXPANSION \
)
#define MBEDTLS_SSL_IN_PAYLOAD_LEN ( MBEDTLS_SSL_PAYLOAD_OVERHEAD + \
@@ -231,11 +240,23 @@
implicit sequence number. */
#define MBEDTLS_SSL_HEADER_LEN 13
+#if defined(MBEDTLS_SSL_CID)
#define MBEDTLS_SSL_IN_BUFFER_LEN \
( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) )
+#else
+#define MBEDTLS_SSL_IN_BUFFER_LEN \
+ ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) \
+ + ( MBEDTLS_SSL_CID_IN_LEN_MAX ) )
+#endif
+#if defined(MBEDTLS_SSL_CID)
#define MBEDTLS_SSL_OUT_BUFFER_LEN \
( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN ) )
+#else
+#define MBEDTLS_SSL_OUT_BUFFER_LEN \
+ ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN ) \
+ + ( MBEDTLS_SSL_CID_OUT_LEN_MAX ) )
+#endif
#ifdef MBEDTLS_ZLIB_SUPPORT
/* Compression buffer holds both IN and OUT buffers, so should be size of the larger */
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index ab2ae6f..cce834e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -9261,6 +9261,11 @@
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
+#if defined(MBEDTLS_SSL_CID)
+ if( transform->out_cid_len != 0 )
+ transform_expansion += MBEDTLS_SSL_MAX_CID_EXPANSION;
+#endif /* MBEDTLS_SSL_CID */
+
return( (int)( out_hdr_len + transform_expansion ) );
}