[PATCH v2 2/2] virtio-net: Prevent NULL dereference

[Sasha Levin <levinsasha928@gmail.com>]

This patch prevents a NULL dereference when the user has passed a length
longer than an actual buffer to virtio-net.

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>
---
 drivers/net/virtio_net.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index bde0dec..4a53d2a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -208,12 +208,22 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 		return NULL;
 	}
 
-	while (len) {
+	while (len && page) {
 		set_skb_frag(skb, page, offset, &len);
 		page = (struct page *)page->private;
 		offset = 0;
 	}
 
+	/*
+	 * This is the case where we ran out of pages in our linked list, but
+	 * supposedly have more data to read.
+	 */	
+	if (len > 0) {
+		pr_debug("%s: missing data to assemble skb\n", skb->dev->name);
+		dev_kfree_skb(skb);
+		return NULL;
+	}
+
 	if (page)
 		give_pages(vi, page);
 
-- 
1.7.6.1