vhost-vdpa: do not cleanup the vdpa/vhost-net structures if peer nic is present

When a peer nic is still attached to the vdpa backend, it is too early to free
up the vhost-net and vdpa structures. If these structures are freed here, then
QEMU crashes when the guest is being shut down. The following call chain
would result in an assertion failure since the pointer returned from
vhost_vdpa_get_vhost_net() would be NULL:

do_vm_stop() -> vm_state_notify() -> virtio_set_status() ->
virtio_net_vhost_status() -> get_vhost_net().

Therefore, we defer freeing up the structures until at guest shutdown
time when qemu_cleanup() calls net_cleanup() which then calls
qemu_del_net_client() which would eventually call vhost_vdpa_cleanup()
again to free up the structures. This time, the loop in net_cleanup()
ensures that vhost_vdpa_cleanup() will be called one last time when
all the peer nics are detached and freed.

All unit tests pass with this change.

CC: imammedo@redhat.com
CC: jusual@redhat.com
CC: mst@redhat.com
Fixes: CVE-2023-3301
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2128929
Signed-off-by: Ani Sinha <anisinha@redhat.com>
Message-Id: <20230619065209.442185-1-anisinha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit a0d7215e339b61c7d7a7b3fcf754954d80d93eb8)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: context change for stable-8.0)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 1c3086c892ff0a93b7cb5d0a82201a4d9f352a32..8670dbf23ff737936488bde860e631376fb61b45 100644 (file)
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -184,6 +184,14 @@ 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;
+    }
     qemu_vfree(s->cvq_cmd_out_buffer);
     qemu_vfree(s->status);
     if (s->vhost_net) {