Date: Tue, 22 Aug 2023 10:25:48 -0400
From: Feng Liu <feliu@...dia.com>
To: virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
 "Michael S . Tsirkin" <mst@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, "David S . Miller" <davem@...emloft.net>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Simon Horman <horms@...nel.org>, Bodong Wang <bodong@...dia.com>,
 Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next v3] virtio_net: Introduce skb_vnet_common_hdr to
 avoid typecasting

Hi Jason , MST

Could you help to review this patch ?  Any more comments?

Thanks
Feng

On 2023-08-21 a.m.10:27, Feng Liu wrote:
> The virtio_net driver currently deals with different versions and types
> of virtio net headers, such as virtio_net_hdr_mrg_rxbuf,
> virtio_net_hdr_v1_hash, etc. Due to these variations, the code relies
> on multiple type casts to convert memory between different structures,
> potentially leading to bugs when there are changes in these structures.
> 
> Introduces the "struct skb_vnet_common_hdr" as a unifying header
> structure using a union. With this approach, various virtio net header
> structures can be converted by accessing different members of this
> structure, thus eliminating the need for type casting and reducing the
> risk of potential bugs.
> 
> For example following code:
> static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> 		struct receive_queue *rq,
> 		struct page *page, unsigned int offset,
> 		unsigned int len, unsigned int truesize,
> 		unsigned int headroom)
> {
> [...]
> 	struct virtio_net_hdr_mrg_rxbuf *hdr;
> [...]
> 	hdr_len = vi->hdr_len;
> [...]
> ok:
> 	hdr = skb_vnet_hdr(skb);
> 	memcpy(hdr, hdr_p, hdr_len);
> [...]
> }
> 
> When VIRTIO_NET_F_HASH_REPORT feature is enabled, hdr_len = 20
> But the sizeof(*hdr) is 12,
> memcpy(hdr, hdr_p, hdr_len); will copy 20 bytes to the hdr,
> which make a potential risk of bug. And this risk can be avoided by
> introducing struct skb_vnet_common_hdr.
> 
> Change log
> v1->v2
> feedback from Willem de Bruijn <willemdebruijn.kernel@...il.com>
> feedback from Simon Horman <horms@...nel.org>
> 1. change to use net-next tree.
> 2. move skb_vnet_common_hdr inside kernel file instead of the UAPI header.
> 
> v2->v3
> feedback from Willem de Bruijn <willemdebruijn.kernel@...il.com>
> 1. fix typo in commit message.
> 2. add original struct virtio_net_hdr into union
> 3. remove virtio_net_hdr_mrg_rxbuf variable in receive_buf;
> 
> Signed-off-by: Feng Liu <feliu@...dia.com>
> Reviewed-by: Jiri Pirko <jiri@...dia.com>
> ---
>   drivers/net/virtio_net.c | 27 ++++++++++++++++++---------
>   1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8e9f4cfe941f..8c74bc8cfe68 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -303,6 +303,14 @@ struct padded_vnet_hdr {
>   	char padding[12];
>   };
>   
> +struct virtio_net_common_hdr {
> +	union {
> +		struct virtio_net_hdr hdr;
> +		struct virtio_net_hdr_mrg_rxbuf	mrg_hdr;
> +		struct virtio_net_hdr_v1_hash hash_v1_hdr;
> +	};
> +};
> +
>   static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
>   static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
>   
> @@ -344,9 +352,10 @@ static int rxq2vq(int rxq)
>   	return rxq * 2;
>   }
>   
> -static inline struct virtio_net_hdr_mrg_rxbuf *skb_vnet_hdr(struct sk_buff *skb)
> +static inline struct virtio_net_common_hdr *
> +skb_vnet_common_hdr(struct sk_buff *skb)
>   {
> -	return (struct virtio_net_hdr_mrg_rxbuf *)skb->cb;
> +	return (struct virtio_net_common_hdr *)skb->cb;
>   }
>   
>   /*
> @@ -469,7 +478,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>   				   unsigned int headroom)
>   {
>   	struct sk_buff *skb;
> -	struct virtio_net_hdr_mrg_rxbuf *hdr;
> +	struct virtio_net_common_hdr *hdr;
>   	unsigned int copy, hdr_len, hdr_padded_len;
>   	struct page *page_to_free = NULL;
>   	int tailroom, shinfo_size;
> @@ -554,7 +563,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>   		give_pages(rq, page);
>   
>   ok:
> -	hdr = skb_vnet_hdr(skb);
> +	hdr = skb_vnet_common_hdr(skb);
>   	memcpy(hdr, hdr_p, hdr_len);
>   	if (page_to_free)
>   		put_page(page_to_free);
> @@ -966,7 +975,7 @@ static struct sk_buff *receive_small_build_skb(struct virtnet_info *vi,
>   		return NULL;
>   
>   	buf += header_offset;
> -	memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
> +	memcpy(skb_vnet_common_hdr(skb), buf, vi->hdr_len);
>   
>   	return skb;
>   }
> @@ -1577,7 +1586,7 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>   {
>   	struct net_device *dev = vi->dev;
>   	struct sk_buff *skb;
> -	struct virtio_net_hdr_mrg_rxbuf *hdr;
> +	struct virtio_net_common_hdr *hdr;
>   
>   	if (unlikely(len < vi->hdr_len + ETH_HLEN)) {
>   		pr_debug("%s: short packet %i\n", dev->name, len);
> @@ -1597,9 +1606,9 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
>   	if (unlikely(!skb))
>   		return;
>   
> -	hdr = skb_vnet_hdr(skb);
> +	hdr = skb_vnet_common_hdr(skb);
>   	if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report)
> -		virtio_skb_set_hash((const struct virtio_net_hdr_v1_hash *)hdr, skb);
> +		virtio_skb_set_hash(&hdr->hash_v1_hdr, skb);
>   
>   	if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
>   		skb->ip_summed = CHECKSUM_UNNECESSARY;
> @@ -2105,7 +2114,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
>   	if (can_push)
>   		hdr = (struct virtio_net_hdr_mrg_rxbuf *)(skb->data - hdr_len);
>   	else
> -		hdr = skb_vnet_hdr(skb);
> +		hdr = &skb_vnet_common_hdr(skb)->mrg_hdr;
>   
>   	if (virtio_net_hdr_from_skb(skb, &hdr->hdr,
>   				    virtio_is_little_endian(vi->vdev), false,

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