net: Update MemReentrancyGuard for NIC

Recently MemReentrancyGuard was added to DeviceState to record that the
device is engaging in I/O. The network device backend needs to update it
when delivering a packet to a device.

This implementation follows what bottom half does, but it does not add
a tracepoint for the case that the network device backend started
delivering a packet to a device which is already engaging in I/O. This
is because such reentrancy frequently happens for
qemu_flush_queued_packets() and is insignificant.

Fixes: CVE-2023-3019
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Jason Wang <jasowang@redhat.com>

include/net/net.h

@@ -126,6 +126,7 @@ typedef QTAILQ_HEAD(NetClientStateList, NetClientState) NetClientStateList;
 typedef struct NICState {
     NetClientState *ncs;
     NICConf *conf;
+    MemReentrancyGuard *reentrancy_guard;
     void *opaque;
     bool peer_deleted;
 } NICState;

net/net.c

@@ -332,6 +332,7 @@ NICState *qemu_new_nic(NetClientInfo *info,
     nic = g_malloc0(info->size + sizeof(NetClientState) * queues);
     nic->ncs = (void *)nic + info->size;
     nic->conf = conf;
+    nic->reentrancy_guard = reentrancy_guard,
     nic->opaque = opaque;
 
     for (i = 0; i < queues; i++) {
@@ -814,6 +815,7 @@ static ssize_t qemu_deliver_packet_iov(NetClientState *sender,
                                        int iovcnt,
                                        void *opaque)
 {
+    MemReentrancyGuard *owned_reentrancy_guard;
     NetClientState *nc = opaque;
     int ret;
 
@@ -826,12 +828,24 @@ static ssize_t qemu_deliver_packet_iov(NetClientState *sender,
         return 0;
     }
 
+    if (nc->info->type != NET_CLIENT_DRIVER_NIC ||
+        qemu_get_nic(nc)->reentrancy_guard->engaged_in_io) {
+        owned_reentrancy_guard = NULL;
+    } else {
+        owned_reentrancy_guard = qemu_get_nic(nc)->reentrancy_guard;
+        owned_reentrancy_guard->engaged_in_io = true;
+    }
+
     if (nc->info->receive_iov && !(flags & QEMU_NET_PACKET_FLAG_RAW)) {
         ret = nc->info->receive_iov(nc, iov, iovcnt);
     } else {
         ret = nc_sendv_compat(nc, iov, iovcnt, flags);
     }
 
+    if (owned_reentrancy_guard) {
+        owned_reentrancy_guard->engaged_in_io = false;
+    }
+
     if (ret == 0) {
         nc->receive_disabled = 1;
     }