crypto: Implement TLS Pre-Shared Keys (PSK).

Pre-Shared Keys (PSK) is a simpler mechanism for enabling TLS
connections than using certificates.  It requires only a simple secret
key:

  $ mkdir -m 0700 /tmp/keys
  $ psktool -u rjones -p /tmp/keys/keys.psk
  $ cat /tmp/keys/keys.psk
  rjones:d543770c15ad93d76443fb56f501a31969235f47e999720ae8d2336f6a13fcbc

The key can be secretly shared between clients and servers.  Clients
must specify the directory containing the "keys.psk" file and a
username (defaults to "qemu").  Servers must specify only the
directory.

Example NBD client:

  $ qemu-img info \
    --object tls-creds-psk,id=tls0,dir=/tmp/keys,username=rjones,endpoint=client \
    --image-opts \
    file.driver=nbd,file.host=localhost,file.port=10809,file.tls-creds=tls0,file.export=/

Example NBD server using qemu-nbd:

  $ qemu-nbd -t -x / \
    --object tls-creds-psk,id=tls0,endpoint=server,dir=/tmp/keys \
    --tls-creds tls0 \
    image.qcow2

Example NBD server using nbdkit:

  $ nbdkit -n -e / -fv \
    --tls=on --tls-psk=/tmp/keys/keys.psk \
    file file=disk.img

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 54 insertions, 2 deletions

diff --git a/crypto/tlssession.c b/crypto/tlssession.c
index 96a02deb69..66a6fbe19c 100644
--- a/crypto/tlssession.c
+++ b/crypto/tlssession.c
@@ -21,6 +21,7 @@
 #include "qemu/osdep.h"
 #include "crypto/tlssession.h"
 #include "crypto/tlscredsanon.h"
+#include "crypto/tlscredspsk.h"
 #include "crypto/tlscredsx509.h"
 #include "qapi/error.h"
 #include "qemu/acl.h"
@@ -88,6 +89,14 @@ qcrypto_tls_session_pull(void *opaque, void *buf, size_t len)
     return session->readFunc(buf, len, session->opaque);
 }
 
+#define TLS_PRIORITY_ADDITIONAL_ANON "+ANON-DH"
+
+#if GNUTLS_VERSION_MAJOR >= 3
+#define TLS_ECDHE_PSK "+ECDHE-PSK:"
+#else
+#define TLS_ECDHE_PSK ""
+#endif
+#define TLS_PRIORITY_ADDITIONAL_PSK TLS_ECDHE_PSK "+DHE-PSK:+PSK"
 
 QCryptoTLSSession *
 qcrypto_tls_session_new(QCryptoTLSCreds *creds,
@@ -135,9 +144,12 @@ qcrypto_tls_session_new(QCryptoTLSCreds *creds,
         char *prio;
 
         if (creds->priority != NULL) {
-            prio = g_strdup_printf("%s:+ANON-DH", creds->priority);
+            prio = g_strdup_printf("%s:%s",
+                                   creds->priority,
+                                   TLS_PRIORITY_ADDITIONAL_ANON);
         } else {
-            prio = g_strdup(CONFIG_TLS_PRIORITY ":+ANON-DH");
+            prio = g_strdup(CONFIG_TLS_PRIORITY ":"
+                            TLS_PRIORITY_ADDITIONAL_ANON);
         }
 
         ret = gnutls_priority_set_direct(session->handle, prio, NULL);
@@ -163,6 +175,42 @@ qcrypto_tls_session_new(QCryptoTLSCreds *creds,
             goto error;
         }
     } else if (object_dynamic_cast(OBJECT(creds),
+                                   TYPE_QCRYPTO_TLS_CREDS_PSK)) {
+        QCryptoTLSCredsPSK *pcreds = QCRYPTO_TLS_CREDS_PSK(creds);
+        char *prio;
+
+        if (creds->priority != NULL) {
+            prio = g_strdup_printf("%s:%s",
+                                   creds->priority,
+                                   TLS_PRIORITY_ADDITIONAL_PSK);
+        } else {
+            prio = g_strdup(CONFIG_TLS_PRIORITY ":"
+                            TLS_PRIORITY_ADDITIONAL_PSK);
+        }
+
+        ret = gnutls_priority_set_direct(session->handle, prio, NULL);
+        if (ret < 0) {
+            error_setg(errp, "Unable to set TLS session priority %s: %s",
+                       prio, gnutls_strerror(ret));
+            g_free(prio);
+            goto error;
+        }
+        g_free(prio);
+        if (creds->endpoint == QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
+            ret = gnutls_credentials_set(session->handle,
+                                         GNUTLS_CRD_PSK,
+                                         pcreds->data.server);
+        } else {
+            ret = gnutls_credentials_set(session->handle,
+                                         GNUTLS_CRD_PSK,
+                                         pcreds->data.client);
+        }
+        if (ret < 0) {
+            error_setg(errp, "Cannot set session credentials: %s",
+                       gnutls_strerror(ret));
+            goto error;
+        }
+    } else if (object_dynamic_cast(OBJECT(creds),
                                    TYPE_QCRYPTO_TLS_CREDS_X509)) {
         QCryptoTLSCredsX509 *tcreds = QCRYPTO_TLS_CREDS_X509(creds);
         const char *prio = creds->priority;
@@ -354,6 +402,10 @@ qcrypto_tls_session_check_credentials(QCryptoTLSSession *session,
         trace_qcrypto_tls_session_check_creds(session, "nop");
         return 0;
     } else if (object_dynamic_cast(OBJECT(session->creds),
+                            TYPE_QCRYPTO_TLS_CREDS_PSK)) {
+        trace_qcrypto_tls_session_check_creds(session, "nop");
+        return 0;
+    } else if (object_dynamic_cast(OBJECT(session->creds),
                             TYPE_QCRYPTO_TLS_CREDS_X509)) {
         if (session->creds->verifyPeer) {
             int ret = qcrypto_tls_session_check_certificate(session,