[RFC,3/4] migration/multifd: Terminate the TLS connection

Commit Message

Fabiano Rosas Feb. 6, 2025, 5:58 p.m. UTC

The multifd recv side has been getting a TLS error of
GNUTLS_E_PREMATURE_TERMINATION at the end of migration when the send
side closes the sockets without ending the TLS session. This has been
masked by the code not checking the migration error after loadvm.

Start ending the TLS session at multifd_send_shutdown() so the recv
side always sees a clean termination (EOF) and we can start to
differentiate that from an actual premature termination that might
possibly happen in the middle of the migration.

There's nothing to be done if a previous migration error has already
broken the connection, so add a comment explaining it and ignore any
errors coming from gnutls_bye().

This doesn't break compat with older recv-side QEMUs because EOF has
always caused the recv thread to exit cleanly.

Signed-off-by: Fabiano Rosas <[e-mail]>
---
 migration/multifd.c | 34 +++++++++++++++++++++++++++++++++-
 migration/tls.c     |  5 +++++
 migration/tls.h     |  2 +-
 3 files changed, 39 insertions(+), 2 deletions(-)

Patch

diff --git a/migration/multifd.c b/migration/multifd.c
index ab73d6d984..b57cad3bb1 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -490,6 +490,32 @@  void multifd_send_shutdown(void)
         return;
     }
 
+    for (i = 0; i < migrate_multifd_channels(); i++) {
+        MultiFDSendParams *p = &multifd_send_state->params[i];
+
+        /* thread_created implies the TLS handshake has succeeded */
+        if (p->tls_thread_created && p->thread_created) {
+            Error *local_err = NULL;
+            /*
+             * The destination expects the TLS session to always be
+             * properly terminated. This helps to detect a premature
+             * termination in the middle of the stream.  Note that
+             * older QEMUs always break the connection on the source
+             * and the destination always sees
+             * GNUTLS_E_PREMATURE_TERMINATION.
+             */
+            migration_tls_channel_end(p->c, &local_err);
+
+            if (local_err) {
+                /*
+                 * The above can fail with broken pipe due to a
+                 * previous migration error, ignore the error.
+                 */
+                assert(migration_has_failed(migrate_get_current()));
+            }
+        }
+    }
+
     multifd_send_terminate_threads();
 
     for (i = 0; i < migrate_multifd_channels(); i++) {
@@ -1141,7 +1167,13 @@  static void *multifd_recv_thread(void *opaque)
 
             ret = qio_channel_read_all_eof(p->c, (void *)p->packet,
                                            p->packet_len, &local_err);
-            if (ret == 0 || ret == -1) {   /* 0: EOF  -1: Error */
+            if (!ret) {
+                /* EOF */
+                assert(!local_err);
+                break;
+            }
+
+            if (ret == -1) {
                 break;
             }
 
diff --git a/migration/tls.c b/migration/tls.c
index fa03d9136c..5cbf952383 100644
--- a/migration/tls.c
+++ b/migration/tls.c
@@ -156,6 +156,11 @@  void migration_tls_channel_connect(MigrationState *s,
                               NULL);
 }
 
+void migration_tls_channel_end(QIOChannel *ioc, Error **errp)
+{
+    qio_channel_tls_bye(QIO_CHANNEL_TLS(ioc), errp);
+}
+
 bool migrate_channel_requires_tls_upgrade(QIOChannel *ioc)
 {
     if (!migrate_tls()) {
diff --git a/migration/tls.h b/migration/tls.h
index 5797d153cb..58b25e1228 100644
--- a/migration/tls.h
+++ b/migration/tls.h
@@ -36,7 +36,7 @@  void migration_tls_channel_connect(MigrationState *s,
                                    QIOChannel *ioc,
                                    const char *hostname,
                                    Error **errp);
-
+void migration_tls_channel_end(QIOChannel *ioc, Error **errp);
 /* Whether the QIO channel requires further TLS handshake? */
 bool migrate_channel_requires_tls_upgrade(QIOChannel *ioc);