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Date: Thu, 17 Aug 2023 17:52:12 -0400
From: Feng Liu <feliu@...dia.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: 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>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
"David S . Miller" <davem@...emloft.net>, Simon Horman <horms@...nel.org>,
Bodong Wang <bodong@...dia.com>, Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next v2] virtio_net: Introduce skb_vnet_common_hdr to
avoid typecasting
On 2023-08-17 p.m.2:26, Willem de Bruijn wrote:
> External email: Use caution opening links or attachments
>
>
> On Thu, Aug 17, 2023 at 11:20 AM Feng Liu <feliu@...dia.com> 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?
>
It is a typo, will correct it.
> 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?
>
static int virtnet_probe(struct virtio_device *vdev)
{
[...]
if (vi->has_rss_hash_report) {
vi->hdr_len = sizeof(struct virtio_net_hdr_v1_hash); /* hdr_len will
be 20 bytes */
}
else if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF) ||
virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
vi->hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
else
vi->hdr_len = sizeof(struct virtio_net_hdr);
[...]
}
When VIRTIO_NET_F_HASH_REPORT is enabled, hdr_len = 20 (as above); and
the size of virtio_net_hdr_mrg_rxbuf is 12, so virtio_net_hdr_mrg_rxbuf
is wrong, should use struct virtio_net_common_hdr here.
> 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.
>
Have checked. Nothing is using sizeof(*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.
>>
>> Signed-off-by: Feng Liu <feliu@...dia.com>
>> Reviewed-by: Jiri Pirko <jiri@...dia.com>
>> ---
>> 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.
>
But I didn't use virtio_net_hdr in this patch, is it redundant to put it
here？ what do you think?
>> +
>> 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?
Yes, struct virtio_net_hdr_mrg_rxbuf *mrg_hdr is not needed. Writing
mrg_hdr here is just to make the code look more concise, such as
mrg_hdr->hdr.flags, if mrg_hdr is not used, it should be written as
common_hdr->mrg_hdr.hdr.flags, I think it looks too long. what you think?
>>
>> 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)
>>
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