varlink: disconnect varlink link in one more case

Previously we'd possibly see POLLHUP on a varlink link, and continue to
run epoll on it even though we have nothing to read nor write anymore.

Let's fix that, and once we know that there's nothing to write anymore
(or we saw a write error already) we'll disconnect after POLLHUP.

Fixes: #20062

1 files changed, 4 insertions, 3 deletions

diff --git a/src/shared/varlink.c b/src/shared/varlink.c
index c34a08cf57..b31ca108fe 100644
--- a/src/shared/varlink.c
+++ b/src/shared/varlink.c
@@ -416,9 +416,10 @@ static int varlink_test_disconnect(Varlink *v) {
         if (IN_SET(v->state, VARLINK_IDLE_CLIENT) && (v->write_disconnected || v->got_pollhup))
                 goto disconnect;
 
-        /* The server is still expecting to write more, but its write end is disconnected and it got a POLLHUP
-         * (i.e. from a disconnected client), so disconnect. */
-        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE) && v->write_disconnected && v->got_pollhup)
+        /* We are on the server side and still want to send out more replies, but we saw POLLHUP already, and
+         * either got no buffered bytes to write anymore or already saw a write error. In that case we should
+         * shut down the varlink link. */
+        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE) && (v->write_disconnected || v->output_buffer_size == 0) && v->got_pollhup)
                 goto disconnect;
 
         return 0;