[PATCH 2/2] net: move backend cleanup to NIC cleanup

["Eugenio Pérez" <eperezma@redhat.com>]

Commit a0d7215e33 ("vhost-vdpa: do not cleanup the vdpa/vhost-net
structures if peer nic is present") effectively delayed the backend
cleanup, allowing the frontend or the guest to access it resources as
long as the frontend is still visible to the guest.

However it does not clean up the resources until the qemu process is
over.  This causes an effective leak if the device is deleted with
device_del, as there is no way to close the vdpa device.  This makes
impossible to re-add that device to this or other QEMU instances until
the first instance of QEMU is finished.

Move the cleanup from qemu_cleanup to the NIC deletion.

Fixes: a0d7215e33 ("vhost-vdpa: do not cleanup the vdpa/vhost-net structures if peer nic is present")
Acked-by: Jason Wang <jasowang@redhat.com>
Reported-by: Lei Yang <leiyang@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
Carring the Acked-by Jason as it was given when I proposed this one year
ago to qemu-security@nongnu.org off list, trying to solve CVE-2023-3301.
---
 net/net.c        | 19 +++++++++++++------
 net/vhost-vdpa.c |  8 --------
 2 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/net/net.c b/net/net.c
index 11e19d3bed..fb6e130c62 100644
--- a/net/net.c
+++ b/net/net.c
@@ -422,7 +422,13 @@ void qemu_del_net_client(NetClientState *nc)
         object_unparent(OBJECT(nf));
     }
 
-    /* If there is a peer NIC, delete and cleanup client, but do not free. */
+    /*
+     * If there is a peer NIC, transfer ownership to it.  Delete the client
+     * from net_client list but do not cleanup nor free.  This way NIC can
+     * still access to members of the backend.
+     *
+     * The cleanup and free will be done when the NIC is free.
+     */
     if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_NIC) {
         NICState *nic = qemu_get_nic(nc->peer);
         if (nic->peer_deleted) {
@@ -432,16 +438,13 @@ void qemu_del_net_client(NetClientState *nc)
 
         for (i = 0; i < queues; i++) {
             ncs[i]->peer->link_down = true;
+            QTAILQ_REMOVE(&net_clients, ncs[i], next);
         }
 
         if (nc->peer->info->link_status_changed) {
             nc->peer->info->link_status_changed(nc->peer);
         }
 
-        for (i = 0; i < queues; i++) {
-            qemu_cleanup_net_client(ncs[i], true);
-        }
-
         return;
     }
 
@@ -459,8 +462,12 @@ void qemu_del_nic(NICState *nic)
 
     for (i = 0; i < queues; i++) {
         NetClientState *nc = qemu_get_subqueue(nic, i);
-        /* If this is a peer NIC and peer has already been deleted, free it now. */
+        /*
+         * If this is a peer NIC and peer has already been deleted, clean it up
+         * and free it now.
+         */
         if (nic->peer_deleted) {
+            qemu_cleanup_net_client(nc->peer, false);
             qemu_free_net_client(nc->peer);
         } else if (nc->peer) {
             /* if there are RX packets pending, complete them */
diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 3726ee5d67..64825136a3 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -221,14 +221,6 @@ static void vhost_vdpa_cleanup(NetClientState *nc)
 {
     VhostVDPAState *s = DO_UPCAST(VhostVDPAState, nc, nc);
 
-    /*
-     * If a peer NIC is attached, do not cleanup anything.
-     * Cleanup will happen as a part of qemu_cleanup() -> net_cleanup()
-     * when the guest is shutting down.
-     */
-    if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_NIC) {
-        return;
-    }
     munmap(s->cvq_cmd_out_buffer, vhost_vdpa_net_cvq_cmd_page_len());
     munmap(s->status, vhost_vdpa_net_cvq_cmd_page_len());
     if (s->vhost_net) {
-- 
2.39.3