tree c4c0771e2fe93968cb73d8b711f77c8b6c910b4c
parent d16bf3421c67c5989aca3db4b3d69bc9a84836be
author David Benjamin <davidben@chromium.org> 1450418481 -0500
committer Adam Langley <agl@google.com> 1450805038 +0000

Rewrite ssl3_send_server_key_exchange to use CBB.

There is some messiness around saving and restoring the CBB, but this is
still significantly clearer.

Note that the BUF_MEM_grow line is gone in favor of a fixed CBB like the
other functions ported thus far. This line was never necessary as
init_buf is initialized to 16k and none of our key exchanges get that
large. (The largest one can get is DHE_RSA. Even so, it'd take a roughly
30k-bit DH group with a 30k-bit RSA key.)

Having such limits and tight assumptions on init_buf's initial size is
poor (but on par for the old code which usually just blindly assumed the
message would not get too large) and the size of the certificate chain
is much less obviously bounded, so those BUF_MEM_grows can't easily go.

My current plan is convert everything but those which legitimately need
BUF_MEM_grow to CBB, then atomically convert the rest, remove init_buf,
and switch everything to non-fixed CBBs. This will hopefully also
simplify async resumption. In the meantime, having a story for
resumption means the future atomic change is smaller and, more
importantly, relieves some complexity budget in the ServerKeyExchange
code for adding Curve25519.

Change-Id: I1de6af9856caaed353453d92a502ba461a938fbd
Reviewed-on: https://boringssl-review.googlesource.com/6770
Reviewed-by: Adam Langley <agl@google.com>