From: Jan Beulich <jbeulich@suse.com>
Subject: xen-netback: defer xenvif_mcast_addr_list_free()

In order for the function to legitimately avoid locking/RCU, it needs to
run after all TX/RX processing has finished/stopped: Lookups happen from
xenvif_start_xmit(), while adds/removes happen from xenvif_tx_action()
(called out of xenvif_poll()).

Move the call out of xenvif_disconnect_data() (the call to the function
from connect()'s error path doesn't require any cleaning up there), and
put it past the synchronization point in backend_disconnect().

This is XSA-527 / CVE-2026-100081.

Fixes: b17075d5c198 ("xen-netback: fix race condition on XenBus disconnect")
Reported-by: kerhunt <kerhunt@proton.me>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -812,8 +812,6 @@ void xenvif_disconnect_data(struct xenvi
 
 		xenvif_disconnect_queue(queue);
 	}
-
-	xenvif_mcast_addr_list_free(vif);
 }
 
 void xenvif_disconnect_ctrl(struct xenvif *vif)
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -267,6 +267,8 @@ static void backend_disconnect(struct ba
 		vif->num_queues = 0;
 		synchronize_net();
 
+		xenvif_mcast_addr_list_free(vif);
+
 		for (queue_index = 0; queue_index < num_queues; ++queue_index)
 			xenvif_deinit_queue(&vif->queues[queue_index]);