linux-kernel - Re: [PATCH net-next v3] virtio_net: Introduce skb_vnet_common

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Date:   Mon, 21 Aug 2023 10:46:57 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Feng Liu <feliu@...dia.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        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>, Feng Liu <feliu@...dia.com>,
        Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next v3] virtio_net: Introduce skb_vnet_common_hdr to
 avoid typecasting

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>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>

A similar solution as tpacket_uhdr.