Linux Virtualization - Apr 2023 - [PATCH net] virtio_net: bugfix overflow inside xdp_linearize_page()

Here we copy the data from the original buf to the new page. But we
not check that it may be overflow.

As long as the size received(including vnethdr) is greater than 3840
(PAGE_SIZE -VIRTIO_XDP_HEADROOM). Then the memcpy will overflow.

And this is completely possible, as long as the MTU is large, such
as 4096. In our test environment, this will cause crash. Since crash is
caused by the written memory, it is meaningless, so I do not include it.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/net/virtio_net.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 2396c28c0122..ea1bd4bb326d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -814,8 +814,13 @@ static struct page *xdp_linearize_page(struct receive_queue
*rq,
 				       int page_off,
 				       unsigned int *len)
 {
-	struct page *page = alloc_page(GFP_ATOMIC);
+	int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	struct page *page;
+
+	if (page_off + *len + tailroom > PAGE_SIZE)
+		return NULL;
 
+	page = alloc_page(GFP_ATOMIC);
 	if (!page)
 		return NULL;
 
@@ -823,7 +828,6 @@ static struct page *xdp_linearize_page(struct receive_queue
*rq,
 	page_off += *len;
 
 	while (--*num_buf) {
-		int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 		unsigned int buflen;
 		void *buf;
 		int off;
-- 
2.32.0.3.g01195cf9f

On Thu, Apr 13, 2023 at 8:19?PM Xuan Zhuo <xuanzhuo at linux.alibaba.com>
wrote:
>
> Here we copy the data from the original buf to the new page. But we
> not check that it may be overflow.
>
> As long as the size received(including vnethdr) is greater than 3840
> (PAGE_SIZE -VIRTIO_XDP_HEADROOM). Then the memcpy will overflow.
>
> And this is completely possible, as long as the MTU is large, such
> as 4096. In our test environment, this will cause crash. Since crash is
> caused by the written memory, it is meaningless, so I do not include it.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
Missing fixes tag?

Other than this,

Acked-by: Jason Wang <jasowang at redhat.com>

Thanks
> ---
>  drivers/net/virtio_net.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 2396c28c0122..ea1bd4bb326d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -814,8 +814,13 @@ static struct page *xdp_linearize_page(struct
receive_queue *rq,
>                                        int page_off,
>                                        unsigned int *len)
>  {
> -       struct page *page = alloc_page(GFP_ATOMIC);
> +       int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> +       struct page *page;
> +
> +       if (page_off + *len + tailroom > PAGE_SIZE)
> +               return NULL;
>
> +       page = alloc_page(GFP_ATOMIC);
>         if (!page)
>                 return NULL;
>
> @@ -823,7 +828,6 @@ static struct page *xdp_linearize_page(struct
receive_queue *rq,
>         page_off += *len;
>
>         while (--*num_buf) {
> -               int tailroom = SKB_DATA_ALIGN(sizeof(struct
skb_shared_info));
>                 unsigned int buflen;
>                 void *buf;
>                 int off;
> --
> 2.32.0.3.g01195cf9f
>