net: introduce qemu_receive_packet()

Some NIC supports loopback mode and this is done by calling
nc->info->receive() directly which in fact suppresses the effort of
reentrancy check that is done in qemu_net_queue_send().

Unfortunately we can't use qemu_net_queue_send() here since for
loopback there's no sender as peer, so this patch introduce a
qemu_receive_packet() which is used for implementing loopback mode
for a NIC with this check.

NIC that supports loopback mode will be converted to this helper.

This is intended to address CVE-2021-3416.

Cc: Prasad J Pandit <ppandit@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 31 insertions, 7 deletions

diff --git a/net/net.c b/net/net.c
index 77b35eafc5..edf9b95418 100644
--- a/net/net.c
+++ b/net/net.c
@@ -529,6 +529,17 @@ int qemu_set_vnet_be(NetClientState *nc, bool is_be)
 #endif
 }
 
+int qemu_can_receive_packet(NetClientState *nc)
+{
+    if (nc->receive_disabled) {
+        return 0;
+    } else if (nc->info->can_receive &&
+               !nc->info->can_receive(nc)) {
+        return 0;
+    }
+    return 1;
+}
+
 int qemu_can_send_packet(NetClientState *sender)
 {
     int vm_running = runstate_is_running();
@@ -541,13 +552,7 @@ int qemu_can_send_packet(NetClientState *sender)
         return 1;
     }
 
-    if (sender->peer->receive_disabled) {
-        return 0;
-    } else if (sender->peer->info->can_receive &&
-               !sender->peer->info->can_receive(sender->peer)) {
-        return 0;
-    }
-    return 1;
+    return qemu_can_receive_packet(sender->peer);
 }
 
 static ssize_t filter_receive_iov(NetClientState *nc,
@@ -680,6 +685,25 @@ ssize_t qemu_send_packet(NetClientState *nc, const uint8_t *buf, int size)
     return qemu_send_packet_async(nc, buf, size, NULL);
 }
 
+ssize_t qemu_receive_packet(NetClientState *nc, const uint8_t *buf, int size)
+{
+    if (!qemu_can_receive_packet(nc)) {
+        return 0;
+    }
+
+    return qemu_net_queue_receive(nc->incoming_queue, buf, size);
+}
+
+ssize_t qemu_receive_packet_iov(NetClientState *nc, const struct iovec *iov,
+                                int iovcnt)
+{
+    if (!qemu_can_receive_packet(nc)) {
+        return 0;
+    }
+
+    return qemu_net_queue_receive_iov(nc->incoming_queue, iov, iovcnt);
+}
+
 ssize_t qemu_send_packet_raw(NetClientState *nc, const uint8_t *buf, int size)
 {
     return qemu_send_packet_async_with_flags(nc, QEMU_NET_PACKET_FLAG_RAW,