diff mbox series

[net-next,1/2] IPv6/GRO: generic helper to remove temporary HBH/jumbo header in driver

Message ID 20221122232740.3180560-1-lixiaoyan@google.com
State New
Headers
Series [net-next,1/2] IPv6/GRO: generic helper to remove temporary HBH/jumbo header in driver |

Commit Message

Coco Li Nov. 22, 2022, 11:27 p.m. UTC 
  IPv6/TCP and GRO stacks can build big TCP packets with an added
temporary Hop By Hop header.

Is GSO is not involved, then the temporary header needs to be removed in
the driver. This patch provides a generic helper for drivers that need
to modify their headers in place.

Signed-off-by: Coco Li <lixiaoyan@google.com>
---
 include/net/ipv6.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

Comments

Alexander Lobakin Nov. 23, 2022, 4:38 p.m. UTC | #1 
From: Coco Li <lixiaoyan@google.com>
Date: Tue, 22 Nov 2022 15:27:39 -0800

> IPv6/TCP and GRO stacks can build big TCP packets with an added
> temporary Hop By Hop header.
> 
> Is GSO is not involved, then the temporary header needs to be removed in
> the driver. This patch provides a generic helper for drivers that need
> to modify their headers in place.
> 
> Signed-off-by: Coco Li <lixiaoyan@google.com>
> ---
>  include/net/ipv6.h | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> index d383c895592a..a11d58c85c05 100644
> --- a/include/net/ipv6.h
> +++ b/include/net/ipv6.h
> @@ -500,6 +500,39 @@ static inline int ipv6_has_hopopt_jumbo(const struct sk_buff *skb)
>  	return jhdr->nexthdr;
>  }
>  
> +/* Return 0 if HBH header is successfully removed
> + * Or if HBH removal is unnecessary (packet is not big TCP)
> + * Return error to indicate dropping the packet
> + */
> +static inline int ipv6_hopopt_jumbo_remove(struct sk_buff *skb)
> +{
> +	const int hophdr_len = sizeof(struct hop_jumbo_hdr);
> +	int nexthdr = ipv6_has_hopopt_jumbo(skb);
> +	struct ipv6hdr *h6;
> +
> +	if (!nexthdr)
> +		return 0;
> +
> +	if (skb_cow_head(skb, 0))
> +		return -1;

	err = skb_cow_head(skb, 0);
	if (err)
		return err;

Alternatively, if you want to keep it simple, make the function bool
and return false on `if (skb_cow_head(skb, 0)` and true otherwise.

> +
> +	/* Remove the HBH header.
> +	 * Layout: [Ethernet header][IPv6 header][HBH][L4 Header]
> +	 */
> +	memmove(skb->data + hophdr_len,
> +		skb->data,

This can fit into the previous line.

> +		ETH_HLEN + sizeof(struct ipv6hdr));

Not correct at this point. I assume you took the implementation from
ip6_offload.c[0], but ::gso_segment() and ::ndo_start_xmit() are two
different entry points. Here you may have not only Eth header, but
also VLAN, MPLS and whatnot.
Correct way would be:

	memmove(skb_mac_header(skb) + hophdr_len, skb_mac_header(skb),
		ipv6_hdr(skb) - skb_mac_header(skb) +
		sizeof(struct ipv6hdr));

> +
> +	skb->data += hophdr_len;
> +	skb->len -= hophdr_len;
> +	skb->network_header += hophdr_len;

skb->mac_header also needs to be adjusted, the fact that it's equal
to skb->data at the entry of ::ndo_start_xmit() doesn't mean
anything.

> +
> +	h6 = ipv6_hdr(skb);
> +	h6->nexthdr = nexthdr;
> +
> +	return 0;
> +}

Please switch all the places where the same logics is used to your
new helper.

> +
>  static inline bool ipv6_accept_ra(struct inet6_dev *idev)
>  {
>  	/* If forwarding is enabled, RA are not accepted unless the special
> -- 
> 2.38.1.584.g0f3c55d4c2-goog

Thanks,
Olek
Alexander Lobakin Nov. 23, 2022, 6:44 p.m. UTC | #2 
From: Alexander Lobakin <alexandr.lobakin@intel.com>
Date: Wed, 23 Nov 2022 17:38:25 +0100

> From: Coco Li <lixiaoyan@google.com>
> Date: Tue, 22 Nov 2022 15:27:39 -0800
> 
> > IPv6/TCP and GRO stacks can build big TCP packets with an added
> > temporary Hop By Hop header.
> > 
> > Is GSO is not involved, then the temporary header needs to be removed in
> > the driver. This patch provides a generic helper for drivers that need
> > to modify their headers in place.
> > 
> > Signed-off-by: Coco Li <lixiaoyan@google.com>
> > ---
> >  include/net/ipv6.h | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> > 
> > diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> > index d383c895592a..a11d58c85c05 100644
> > --- a/include/net/ipv6.h
> > +++ b/include/net/ipv6.h
> > @@ -500,6 +500,39 @@ static inline int ipv6_has_hopopt_jumbo(const struct sk_buff *skb)
> >  	return jhdr->nexthdr;
> >  }
> >  
> > +/* Return 0 if HBH header is successfully removed
> > + * Or if HBH removal is unnecessary (packet is not big TCP)
> > + * Return error to indicate dropping the packet
> > + */
> > +static inline int ipv6_hopopt_jumbo_remove(struct sk_buff *skb)
> > +{
> > +	const int hophdr_len = sizeof(struct hop_jumbo_hdr);
> > +	int nexthdr = ipv6_has_hopopt_jumbo(skb);
> > +	struct ipv6hdr *h6;
> > +
> > +	if (!nexthdr)
> > +		return 0;
> > +
> > +	if (skb_cow_head(skb, 0))
> > +		return -1;
> 
> 	err = skb_cow_head(skb, 0);
> 	if (err)
> 		return err;
> 
> Alternatively, if you want to keep it simple, make the function bool
> and return false on `if (skb_cow_head(skb, 0)` and true otherwise.
> 
> > +
> > +	/* Remove the HBH header.
> > +	 * Layout: [Ethernet header][IPv6 header][HBH][L4 Header]
> > +	 */
> > +	memmove(skb->data + hophdr_len,
> > +		skb->data,
> 
> This can fit into the previous line.
> 
> > +		ETH_HLEN + sizeof(struct ipv6hdr));
> 
> Not correct at this point. I assume you took the implementation from
> ip6_offload.c[0], but ::gso_segment() and ::ndo_start_xmit() are two

Traditionally forgot to paste the links to the end of the mail. Pls
look at the end of this one for them (if I don't forget to paste
them again :clownface:).

> different entry points. Here you may have not only Eth header, but
> also VLAN, MPLS and whatnot.
> Correct way would be:
> 
> 	memmove(skb_mac_header(skb) + hophdr_len, skb_mac_header(skb),
> 		ipv6_hdr(skb) - skb_mac_header(skb) +
> 		sizeof(struct ipv6hdr));
> 
> > +
> > +	skb->data += hophdr_len;
> > +	skb->len -= hophdr_len;
> > +	skb->network_header += hophdr_len;
> 
> skb->mac_header also needs to be adjusted, the fact that it's equal
> to skb->data at the entry of ::ndo_start_xmit() doesn't mean
> anything.

Also, while I'm here: you should use skb_may_pull() +
{,__}skb_pull() here instead of manual maths. ::network_header and
::mac_header still need to be adjusted manually tho.

> 
> > +
> > +	h6 = ipv6_hdr(skb);
> > +	h6->nexthdr = nexthdr;
> > +
> > +	return 0;
> > +}
> 
> Please switch all the places where the same logics is used to your
> new helper.
> 
> > +
> >  static inline bool ipv6_accept_ra(struct inet6_dev *idev)
> >  {
> >  	/* If forwarding is enabled, RA are not accepted unless the special
> > -- 
> > 2.38.1.584.g0f3c55d4c2-goog
> 
> Thanks,
> Olek

[0] https://elixir.bootlin.com/linux/v6.1-rc6/source/net/ipv6/ip6_offload.c#L92

Thanks,
Olek
diff mbox series

Patch

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index d383c895592a..a11d58c85c05 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -500,6 +500,39 @@  static inline int ipv6_has_hopopt_jumbo(const struct sk_buff *skb)
 	return jhdr->nexthdr;
 }
 
+/* Return 0 if HBH header is successfully removed
+ * Or if HBH removal is unnecessary (packet is not big TCP)
+ * Return error to indicate dropping the packet
+ */
+static inline int ipv6_hopopt_jumbo_remove(struct sk_buff *skb)
+{
+	const int hophdr_len = sizeof(struct hop_jumbo_hdr);
+	int nexthdr = ipv6_has_hopopt_jumbo(skb);
+	struct ipv6hdr *h6;
+
+	if (!nexthdr)
+		return 0;
+
+	if (skb_cow_head(skb, 0))
+		return -1;
+
+	/* Remove the HBH header.
+	 * Layout: [Ethernet header][IPv6 header][HBH][L4 Header]
+	 */
+	memmove(skb->data + hophdr_len,
+		skb->data,
+		ETH_HLEN + sizeof(struct ipv6hdr));
+
+	skb->data += hophdr_len;
+	skb->len -= hophdr_len;
+	skb->network_header += hophdr_len;
+
+	h6 = ipv6_hdr(skb);
+	h6->nexthdr = nexthdr;
+
+	return 0;
+}
+
 static inline bool ipv6_accept_ra(struct inet6_dev *idev)
 {
 	/* If forwarding is enabled, RA are not accepted unless the special