Hi Christian,
On 04/01/2023 16:55, Christian Mazakas wrote:
Hey everyone,
I'm trying to get libssl to work without using any built-in I/O so for this,
I'm using manually managed BIO pairs.
It seems like I can get a TLS Client Hello written to a user-provided buffer
but I'm having trouble getting the server to parse this data and generate
its own Server Hello in response.
I have a Compiler Explorer link that demonstrates my issue here:
https://godbolt.org/z/ncxezWfqG <https://godbolt.org/z/ncxezWfqG>
Is there something plainly obvious that I'm missing? I've been scouring the
docs so I'm wondering if there's something easy I missed.
Since I am doing something similar (I am wrapping all of my sockets,
some of which may be encrypted using openssl, others not, through one
select() statement and thus can't hand off the sockets to openssl
directly), you'll want something like
...
result = SSL_read_ex (session->cryptoparams->ssl,
(void *) buffer_data_start
(&session->ibuf),
buffer_data_space (&session->ibuf),
&rsize);
if (result) {
log_msg (V_DEBUG3, "crypto: read %zu bytes", rsize);
// ...
} else {
error = SSL_get_error (session->cryptoparams->ssl, result);
switch (error) {
// Not enough data
case SSL_ERROR_WANT_READ:
case SSL_ERROR_WANT_WRITE:
// I am handling writes from server to client outside this; it's part of
a loop
return 0;
// Intended shutdown of TLS session
case SSL_ERROR_ZERO_RETURN:
log_msg (V_INFO, "crypto: TLS session closed");
SSL_shutdown (session->cryptoparams->ssl);
return 1;
// read error: shutdown
default:
log_msg (V_ERROR, "crypto: failed to read: %s",
SSL_reason_error_string (error));
SSL_shutdown (session->cryptoparams->ssl);
return -1;
}
}
...
I am manually handling the SSL_accept() for the server with state
tracking though, with similar error checking & handling. I left some
references to my internal data structures and functions in and hope they
are self explaining.
If you remove the direct I/O handling from openssl, you need to handle
the SSL handshake data exchange, too, and won't be able to only act on
the decrypted data, as data needs to be exchanged between client and
server with potentially extra round trips, which will result in the
SSL_ERROR_WANT_* which are not terminal errors, but you'll need to act
on them. The 16,3,1 is a good start though as it's a TLS 1.0 handshake,
which SHOULD be used up to and including TLS 1.3.
Good luck,
Christian
- Christian
