virtio-net: Verify page list size before fitting into skb

This patch verifies that the length of a buffer stored in a linked list
of pages is small enough to fit into a skb.

If the size is larger than a max size of a skb, it means that we shouldn't
go ahead building skbs anyway since we won't be able to send the buffer as
the user requested.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: netdev@vger.kernel.org
Cc: kvm@vger.kernel.org
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -195,6 +195,19 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	len -= copy;
 	offset += copy;
 
+	/*
+	 * Verify that we can indeed put this data into a skb.
+	 * This is here to handle cases when the device erroneously
+	 * tries to receive more than is possible. This is usually
+	 * the case of a broken device.
+	 */
+	if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) {
+		if (net_ratelimit())
+			pr_debug("%s: too much data\n", skb->dev->name);
+		dev_kfree_skb(skb);
+		return NULL;
+	}
+
 	while (len) {
 		set_skb_frag(skb, page, offset, &len);
 		page = (struct page *)page->private;