Linux Virtualization - Apr 2023 - [PATCH net v1] 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.

Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non contiguous
buffers")
Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
Acked-by: Jason Wang <jasowang at redhat.com>
---
v1:  add Fixes tag

 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 Fri, Apr 14, 2023 at 02:08:35PM +0800, Xuan Zhuo
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.
> 
> Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non
contiguous buffers")
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> Acked-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
> v1:  add Fixes tag
> 
>  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