Merge remote-tracking branch 'public/pr/1768' into mbedtls-2.7
diff --git a/ChangeLog b/ChangeLog
index 5e4e764..1e2f9b8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,8 @@
Contributed by fbrosson in #1533.
* Fix a memory leak in mbedtls_x509_csr_parse(), found by catenacyber,
Philippe Antoine.
+ * Clarify documentation for mbedtls_ssl_write() to include 0 as a valid
+ return value. Found by @davidwu2000. #839
= mbed TLS 2.7.4 branch released 2018-06-18
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 42e0dcb..3937d02 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -2504,17 +2504,19 @@
* or MBEDTLS_ERR_SSL_WANT_WRITE or MBEDTLS_ERR_SSL_WANT_READ,
* or another negative error code.
*
- * \note If this function returns something other than a positive
- * value or MBEDTLS_ERR_SSL_WANT_READ/WRITE, the ssl context
- * becomes unusable, and you should either free it or call
- * \c mbedtls_ssl_session_reset() on it before re-using it for
- * a new connection; the current connection must be closed.
+ * \note If this function returns something other than 0, a positive
+ * value or MBEDTLS_ERR_SSL_WANT_READ/WRITE, you must stop
+ * using the SSL context for reading or writing, and either
+ * free it or call \c mbedtls_ssl_session_reset() on it before
+ * re-using it for a new connection; the current connection
+ * must be closed.
*
* \note When this function returns MBEDTLS_ERR_SSL_WANT_WRITE/READ,
* it must be called later with the *same* arguments,
- * until it returns a positive value. When the function returns
- * MBEDTLS_ERR_SSL_WANT_WRITE there may be some partial
- * data in the output buffer, however this is not yet sent.
+ * until it returns a value greater that or equal to 0. When
+ * the function returns MBEDTLS_ERR_SSL_WANT_WRITE there may be
+ * some partial data in the output buffer, however this is not
+ * yet sent.
*
* \note If the requested length is greater than the maximum
* fragment length (either the built-in limit or the one set
@@ -2523,6 +2525,9 @@
* - with DTLS, MBEDTLS_ERR_SSL_BAD_INPUT_DATA is returned.
* \c mbedtls_ssl_get_max_frag_len() may be used to query the
* active maximum fragment length.
+ *
+ * \note Attempting to write 0 bytes will result in an empty TLS
+ * application record being sent.
*/
int mbedtls_ssl_write( mbedtls_ssl_context *ssl, const unsigned char *buf, size_t len );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 6d7ad33..153d745 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -7137,8 +7137,16 @@
}
/*
- * Send application data to be encrypted by the SSL layer,
- * taking care of max fragment length and buffer size
+ * Send application data to be encrypted by the SSL layer, taking care of max
+ * fragment length and buffer size.
+ *
+ * According to RFC 5246 Section 6.2.1:
+ *
+ * Zero-length fragments of Application data MAY be sent as they are
+ * potentially useful as a traffic analysis countermeasure.
+ *
+ * Therefore, it is possible that the input message length is 0 and the
+ * corresponding return code is 0 on success.
*/
static int ssl_write_real( mbedtls_ssl_context *ssl,
const unsigned char *buf, size_t len )
@@ -7166,6 +7174,12 @@
if( ssl->out_left != 0 )
{
+ /*
+ * The user has previously tried to send the data and
+ * MBEDTLS_ERR_SSL_WANT_WRITE or the message was only partially
+ * written. In this case, we expect the high-level write function
+ * (e.g. mbedtls_ssl_write()) to be called with the same parameters
+ */
if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
{
MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flush_output", ret );
@@ -7174,6 +7188,11 @@
}
else
{
+ /*
+ * The user is trying to send a message the first time, so we need to
+ * copy the data into the internal buffers and setup the data structure
+ * to keep track of partial writes
+ */
ssl->out_msglen = len;
ssl->out_msgtype = MBEDTLS_SSL_MSG_APPLICATION_DATA;
memcpy( ssl->out_msg, buf, len );