This commit adds a test to ssl-opt.sh which exercises the behavior
of the library in the situation where a single proper fragment
of a future handshake message is received prior to the next
expected handshake message (concretely, the client receives
the first fragment of the server's Certificate message prior
to the server's ServerHello).
This commit adds two builds to all.sh which use a value of
MBEDTLS_SSL_DTLS_MAX_BUFFERING that allows to run the
reordering tests in ssl-opt.sh introduced in the last commit.
This commit adds tests to ssl-opt.sh which trigger code-paths
responsible for freeing future buffered messages when the buffering
limitations set by MBEDTLS_SSL_DTLS_MAX_BUFFERING don't allow the
next expected message to be reassembled.
These tests only work for very specific ranges of
MBEDTLS_SSL_DTLS_MAX_BUFFERING and will therefore be skipped
on a run of ssl-opt.sh in ordinary configurations.
This commit adds functions requires_config_value_at_most()
and requires_config_value_at_least() which can be used to
only run tests when a numerical value from config.h
(e.g. MBEDTLS_SSL_IN_CONTENT_LEN) is within a certain range.
The negotiated MFL is always the one suggested by the client, even
if the server has a smaller MFL configured locally. Hence, in the test
where the client asks for an MFL of 4096 bytes while the server locally
has an MFL of 512 bytes configured, the client will still send datagrams
of up to ~4K size.
By the standard (RFC 6066, Sect. 4), the Maximum Fragment Length (MFL)
extension limits the maximum record payload size, but not the maximum
datagram size. However, not inferring any limitations on the MTU when
setting the MFL means that a party has no means to dynamically inform
the peer about MTU limitations.
This commit changes the function ssl_get_remaining_payload_in_datagram()
to never return more than
MFL - { Total size of all records within the current datagram }
thereby limiting the MTU to MFL + { Maximum Record Expansion }.
The function ssl_free_buffered_record() frees a future epoch record, if
such is present. Previously, it was called in mbedtls_handshake_free(),
i.e. an unused buffered record would be cleared at the end of the handshake.
This commit moves the call to the function ssl_buffering_free() responsible
for freeing all buffering-related data, and which is called not only at
the end of the handshake, but at the end of every flight. In particular,
future record epochs won't be buffered across flight boundaries anymore,
and they shouldn't.
The previous code appended messages to flights only if their handshake type,
as derived from the first byte in the message, was different from
MBEDTLS_SSL_HS_HELLO_REQUEST. This check should only be performed
for handshake records, while CCS records should immediately be appended.
