Re: [PATCH net-next v2] virtio_net: Introduce skb_vnet_common_hdr to avoid typecasting
From: Feng Liu
Date: Thu Aug 17 2023 - 17:53:10 EST
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@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?
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@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.
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)