In preparation for reworking mbedtls_ssl_prepare_handshake_record(), tweak
the "waiting for more handshake fragments" log message in
ssl_consume_current_message(), and add a similar one in
mbedtls_ssl_prepare_handshake_record(). Assert both.

Signed-off-by: Gilles Peskine <[email protected]>

In preparation for reworking mbedtls_ssl_prepare_handshake_record(),
tweak the "handshake fragment:" log message.

This changes what information is displayed when a record contains data
beyond the expected end of the handshake message. This case is currently
untested and its handling will change in a subsequent commit.

Signed-off-by: Gilles Peskine <[email protected]>

Minor refactoring of the initial checks and preparation when receiving the
first fragment. Use `ssl->in_hsfraglen` to determine whether there is a
pending handshake fragment, for consistency, and possibly for more
robustness in case handshake fragments are mixed with non-handshake
records (although this is not currently supported anyway).

Signed-off-by: Gilles Peskine <[email protected]>

Signed-off-by: Gilles Peskine <[email protected]>

Reassemble handshake fragments incrementally instead of all at the end. That
is, every time we receive a non-initial handshake fragment, append it to the
initial fragment. Since we only have to deal with at most two handshake
fragments at the same time, this simplifies the code (no re-parsing of a
record) and is a little more memory-efficient (no need to store one record
header per record).

This commit also fixes a bug. The previous code did not calculate offsets
correctly when records use an explicit IV, which is the case in TLS 1.2 with
CBC (encrypt-then-MAC or not), GCM and CCM encryption (i.e. all but null and
ChachaPoly). This led to the wrong data when an encrypted handshake message
was fragmented (Finished or renegotiation). The new code handles this
correctly.

Signed-off-by: Gilles Peskine <[email protected]>

Pacify `clang -Wformat-pedantic`.

Signed-off-by: Gilles Peskine <[email protected]>

Signed-off-by: Gilles Peskine <[email protected]>

A handshake record may contain multiple handshake messages, or multiple
fragments (there can be the final fragment of a pending message, then zero
or more whole messages, and an initial fragment of an incomplete message).
This was previously untested, but supported, so don't break it.

Signed-off-by: Gilles Peskine <[email protected]>

There is no longer any different processing at this point, just
near-identical log messages.

Signed-off-by: Gilles Peskine <[email protected]>

Signed-off-by: Gilles Peskine <[email protected]>