Re: [PATCH net-next v2] virtio_net: Introduce skb_vnet_common_hdr to avoid typecasting
From: Willem de Bruijn
Date: Thu Aug 17 2023 - 14:28:55 EST
On Thu, Aug 17, 2023 at 11:20 AM Feng Liu <feliu@xxxxxxxxxx> 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 virtio_net_hdr_mrg_rxbuf.
You mean virtio_net_common_hdr?
I'm not sure I follow the reasoning. Because then hdr_len might be
sizeof(virtio_net_hdr_mrg_rxbuf), but sizeof(virtio_net_common_hdr) is
larger. So the same issue remains?
Indeed, everywhere this patches replaces the one with the other, you
have to verify that nothing was using sizeof(*hdr). Which would not be
visible from the truncated patch contents itself.
>
> Change log
> v1->v2
> feedback from Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
> feedback from Simon Horman <horms@xxxxxxxxxx>
> 1. change to use net-next tree.
> 2. move skb_vnet_common_hdr inside kernel file instead of the UAPI header.
>
> Signed-off-by: Feng Liu <feliu@xxxxxxxxxx>
> Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 36 +++++++++++++++++++++++-------------
> 1 file changed, 23 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 1270c8d23463..03cf744de512 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -303,6 +303,13 @@ struct padded_vnet_hdr {
> char padding[12];
> };
>
> +struct virtio_net_common_hdr {
> + union {
> + struct virtio_net_hdr_mrg_rxbuf mrg_hdr;
> + struct virtio_net_hdr_v1_hash hash_v1_hdr;
> + };
> +};
Perhaps even add in struct virtio_net_hdr. As that is the original of
the three structs, and all the initial fields overlap.
> +
> 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 +351,10 @@ 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 +477,7 @@ 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 +562,7 @@ 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 +974,7 @@ 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 +1585,8 @@ 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 *common_hdr;
> + struct virtio_net_hdr_mrg_rxbuf *mrg_hdr;
No more need for this second struct now that we have the union. That's
its whole purpose?
>
> if (unlikely(len < vi->hdr_len + ETH_HLEN)) {
> pr_debug("%s: short packet %i\n", dev->name, len);
> @@ -1597,18 +1606,19 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> if (unlikely(!skb))
> return;
>
> - hdr = skb_vnet_hdr(skb);
> + common_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(&common_hdr->hash_v1_hdr, skb);
>
> - if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
> + mrg_hdr = &common_hdr->mrg_hdr;
> + if (mrg_hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
> skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> - if (virtio_net_hdr_to_skb(skb, &hdr->hdr,
> + if (virtio_net_hdr_to_skb(skb, &mrg_hdr->hdr,
> virtio_is_little_endian(vi->vdev))) {
> net_warn_ratelimited("%s: bad gso: type: %u, size: %u\n",
> - dev->name, hdr->hdr.gso_type,
> - hdr->hdr.gso_size);
> + dev->name, mrg_hdr->hdr.gso_type,
> + mrg_hdr->hdr.gso_size);
> goto frame_err;
> }
>
> @@ -2105,7 +2115,7 @@ 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,
> --
> 2.37.1 (Apple Git-137.1)
>