[PATCH 1/3] crypto: Add qcrypto_tls_shutdown()

[Eric Blake <eblake@redhat.com>]

Gnutls documents that applications that want to distinguish between a
clean end-of-communication and a malicious client abruptly tearing the
underlying transport out of under our feet need to use gnutls_bye().
Our channel code is already set up to allow shutdown requests, but we
weren't forwarding those to gnutls.  To make that work, we first need
a new entry point that can isolate the rest of our code from the
gnutls interface.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 qapi/crypto.json            | 15 +++++++++++++++
 include/crypto/tlssession.h | 24 ++++++++++++++++++++++++
 crypto/tlssession.c         | 27 +++++++++++++++++++++++++++
 3 files changed, 66 insertions(+)

diff --git a/qapi/crypto.json b/qapi/crypto.json
index b2a4cff683ff..1df0f4502885 100644
--- a/qapi/crypto.json
+++ b/qapi/crypto.json
@@ -119,6 +119,21 @@
   'prefix': 'QCRYPTO_IVGEN_ALG',
   'data': ['plain', 'plain64', 'essiv']}

+##
+# @QCryptoShutdownMode:
+#
+# The supported modes for requesting shutdown of a crypto
+# communication channel.
+#
+# @shut-wr: No more writes will be sent, but the remote end can still send
+#           data to be read.
+# @shut-rdwr: No more reads or writes should occur.
+# Since: 5.1
+##
+{ 'enum': 'QCryptoShutdownMode',
+  'prefix': 'QCRYPTO',
+  'data': ['shut-wr', 'shut-rdwr']}
+
 ##
 # @QCryptoBlockFormat:
 #
diff --git a/include/crypto/tlssession.h b/include/crypto/tlssession.h
index 15b9cef086cc..10c670e3b6a2 100644
--- a/include/crypto/tlssession.h
+++ b/include/crypto/tlssession.h
@@ -321,4 +321,28 @@ int qcrypto_tls_session_get_key_size(QCryptoTLSSession *sess,
  */
 char *qcrypto_tls_session_get_peer_name(QCryptoTLSSession *sess);

+/**
+ * qcrypto_tls_shutdown:
+ * @sess: the TLS session object
+ * @how: the desired shutdown mode
+ *
+ * Prepare to terminate the session.  If @how is QCRYPTO_SHUT_WR, this
+ * side will no longer write data, but should still process reads
+ * until EOF; if @how is QCRYPTO_SHUT_RDWR, then the entire session
+ * should shut down.  Use of this function is optional, since closing
+ * the session implies QCRYPTO_SHUT_RDWR.  However, using this
+ * function prior to terminating the underlying transport layer makes
+ * it possible for the remote endpoint to distinguish between a
+ * malicious party prematurely terminating the the connection and
+ * normal termination.
+ *
+ * This function should only be used after a successful
+ * qcrypto_tls_session_handshake().
+ *
+ * Returns: 0 for success, or -EAGAIN if more underlying I/O is
+ * required to finish proper session shutdown.
+ */
+int qcrypto_tls_session_shutdown(QCryptoTLSSession *sess,
+                                 QCryptoShutdownMode how);
+
 #endif /* QCRYPTO_TLSSESSION_H */
diff --git a/crypto/tlssession.c b/crypto/tlssession.c
index 33203e8ca711..903301189069 100644
--- a/crypto/tlssession.c
+++ b/crypto/tlssession.c
@@ -521,6 +521,33 @@ qcrypto_tls_session_get_handshake_status(QCryptoTLSSession *session)
 }


+int qcrypto_tls_session_shutdown(QCryptoTLSSession *session,
+                                 QCryptoShutdownMode how)
+{
+    gnutls_close_request_t mode;
+    int ret;
+
+    assert(session->handshakeComplete);
+    switch (how) {
+    case QCRYPTO_SHUT_WR:
+        mode = GNUTLS_SHUT_WR;
+        break;
+    case QCRYPTO_SHUT_RDWR:
+        mode = GNUTLS_SHUT_RDWR;
+        break;
+    default:
+        abort();
+    }
+
+    ret = gnutls_bye(session->handle, mode);
+    if (ret == GNUTLS_E_INTERRUPTED ||
+        ret == GNUTLS_E_AGAIN) {
+        return -EAGAIN;
+    }
+    return 0;
+}
+
+
 int
 qcrypto_tls_session_get_key_size(QCryptoTLSSession *session,
                                  Error **errp)
-- 
2.26.0.rc2