Implement flushing for TLSv1.3 handshakes.

When we finish sending a flight of records, flush the record layer output.
This effectively means calling BIO_flush() on the wbio.

Some things (such as apache2) have custom BIOs that perform buffering and
do not actually send on BIO_write(). Without BIO_flush() the server thinks
it has sent data and starts receiving records, however the client never
sends records since it never received those that the server should have
sent.

Joint work with tb@

ok tb@

1 files changed, 25 insertions, 1 deletions

diff --git a/src/lib/libssl/tls13_legacy.c b/src/lib/libssl/tls13_legacy.c
index 3368600c60..f668dd4ea3 100644
--- a/src/lib/libssl/tls13_legacy.c
+++ b/src/lib/libssl/tls13_legacy.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: tls13_legacy.c,v 1.30 2021/09/14 14:31:21 tb Exp $ */
+/*      $OpenBSD: tls13_legacy.c,v 1.31 2021/09/16 19:25:30 jsing Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -96,6 +96,30 @@ tls13_legacy_wire_write_cb(const void *buf, size_t n, void *arg)
         return tls13_legacy_wire_write(ctx->ssl, buf, n);
 }
 
+static ssize_t
+tls13_legacy_wire_flush(SSL *ssl)
+{
+        if (BIO_flush(ssl->wbio) <= 0) {
+                if (BIO_should_write(ssl->wbio))
+                        return TLS13_IO_WANT_POLLOUT;
+
+                if (ERR_peek_error() == 0 && errno != 0)
+                        SYSerror(errno);
+
+                return TLS13_IO_FAILURE;
+        }
+
+        return TLS13_IO_SUCCESS;
+}
+
+ssize_t
+tls13_legacy_wire_flush_cb(void *arg)
+{
+        struct tls13_ctx *ctx = arg;
+
+        return tls13_legacy_wire_flush(ctx->ssl);
+}
+
 static void
 tls13_legacy_error(SSL *ssl)
 {