Re: SSL renegotiation

Here's the patch I propose to handle renegotiation cleanly.  I noticed
in testing that SSL_renegotiate_pending() doesn't seem to actually work
--- if I throw an ereport(FATAL) at the point where I expect the
renegotiation to be complete, it always dies; even if I give it
megabytes of extra traffic while waiting for the renegotiation to
complete.  I suspect this is an OpenSSL bug.  Instead, in this patch I
check the internal renegotiation counter: grab its current value when
starting the renegotiation, and consider it complete when the counter
has advanced.  This works fine.

Another thing not covered by the original code snippet I proposed
upthread is to avoid renegotiating when there was a renegotiation in
progress.  This bug has been observed in the field.

Per discussion, I made it close the connection with a FATAL error if the
limit is reached and the renegotiation hasn't taken place.  To do
otherwise is not acceptable for a security PoV.

Sean Chittenden mentioned that when retrying the handshake, we should be
careful to only do it a few times, not forever, to avoid a malfeasant
from grabbing hold of a connection indefinitely.  I've added that too,
hardcoding the number of retries to 20.

Also, I made this code request a renegotiation slightly before the limit
is actually reached.  I noticed that in some cases some traffic can go
by before the renegotiation is actually completed.  The difference
should be pretty minimal.

--
Álvaro Herrera                http://www.2ndQuadrant.com/
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