netdev - RE: [PATCH net v5] xen-netback: fix fragment detection in checksum setup

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Date:	Thu, 5 Dec 2013 09:08:15 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Zoltan Kiss <zoltan.kiss@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	"David Miller" <davem@...emloft.net>
Subject: RE: [PATCH net v5] xen-netback: fix fragment detection in checksum
 setup

> -----Original Message-----
> From: annie li [mailto:annie.li@...cle.com]
> Sent: 05 December 2013 06:28
> To: Paul Durrant
> Cc: xen-devel@...ts.xen.org; netdev@...r.kernel.org; Zoltan Kiss; Wei Liu;
> Ian Campbell; David Vrabel; David Miller
> Subject: Re: [PATCH net v5] xen-netback: fix fragment detection in checksum
> setup
> 
> 
> On 2013/12/4 1:39, Paul Durrant wrote:
> 
> >
> > +/* This value should be large enough to cover a tagged ethernet header
> plus
> > + * an IPv6 header, all options, and a maximal TCP or UDP header.
> > + */
> > +#define MAX_IPV6_HDR_LEN 256
> > +
> > +#define OPT_HDR(type, skb, off) \
> > +	(type *)(skb_network_header(skb) + (off))
> > +
> >   static int checksum_setup_ipv6(struct xenvif *vif, struct sk_buff *skb,
> >   			       int recalculate_partial_csum)
> >   {
> > -	int err = -EPROTO;
> > -	struct ipv6hdr *ipv6h = (void *)skb->data;
> > +	int err;
> >   	u8 nexthdr;
> > -	unsigned int header_size;
> >   	unsigned int off;
> > +	unsigned int len;
> >   	bool fragment;
> >   	bool done;
> >
> > +	fragment = false;
> >   	done = false;
> >
> >   	off = sizeof(struct ipv6hdr);
> >
> > -	header_size = skb->network_header + off;
> > -	maybe_pull_tail(skb, header_size);
> > +	err = maybe_pull_tail(skb, off, MAX_IPV6_HDR_LEN);
> > +	if (err < 0)
> > +		goto out;
> >
> > -	nexthdr = ipv6h->nexthdr;
> > +	nexthdr = ipv6_hdr(skb)->nexthdr;
> >
> > -	while ((off <= sizeof(struct ipv6hdr) + ntohs(ipv6h->payload_len))
> &&
> > -	       !done) {
> > +	len = sizeof(struct ipv6hdr) + ntohs(ipv6_hdr(skb)->payload_len);
> > +	while (off <= len && !done) {
> >   		switch (nexthdr) {
> >   		case IPPROTO_DSTOPTS:
> >   		case IPPROTO_HOPOPTS:
> >   		case IPPROTO_ROUTING: {
> > -			struct ipv6_opt_hdr *hp = (void *)(skb->data + off);
> > +			struct ipv6_opt_hdr *hp;
> >
> > -			header_size = skb->network_header +
> > -				off +
> > -				sizeof(struct ipv6_opt_hdr);
> > -			maybe_pull_tail(skb, header_size);
> > +			err = maybe_pull_tail(skb,
> > +					      off +
> > +					      sizeof(struct ipv6_opt_hdr),
> > +					      MAX_IPV6_HDR_LEN);
> > +			if (err < 0)
> > +				goto out;
> >
> > +			hp = OPT_HDR(struct ipv6_opt_hdr, skb, off);
> >   			nexthdr = hp->nexthdr;
> >   			off += ipv6_optlen(hp);
> >   			break;
> >   		}
> >   		case IPPROTO_AH: {
> > -			struct ip_auth_hdr *hp = (void *)(skb->data + off);
> > +			struct ip_auth_hdr *hp;
> > +
> > +			err = maybe_pull_tail(skb,
> > +					      off +
> > +					      sizeof(struct ip_auth_hdr),
> > +					      MAX_IPV6_HDR_LEN);
> > +			if (err < 0)
> > +				goto out;
> > +
> > +			hp = OPT_HDR(struct ip_auth_hdr, skb, off);
> > +			nexthdr = hp->nexthdr;
> > +			off += ipv6_authlen(hp);
> > +			break;
> > +		}
> > +		case IPPROTO_FRAGMENT: {
> > +			struct frag_hdr *hp;
> >
> > -			header_size = skb->network_header +
> > -				off +
> > -				sizeof(struct ip_auth_hdr);
> > -			maybe_pull_tail(skb, header_size);
> > +			err = maybe_pull_tail(skb,
> > +					      off +
> > +					      sizeof(struct frag_hdr),
> > +					      MAX_IPV6_HDR_LEN);
> > +			if (err < 0)
> > +				goto out;
> > +
> > +			hp = OPT_HDR(struct frag_hdr, skb, off);
> > +
> > +			if (hp->frag_off & htons(IP6_OFFSET | IP6_MF))
> > +				fragment = true;
> >
> >   			nexthdr = hp->nexthdr;
> > -			off += (hp->hdrlen+2)<<2;
> > +			off += sizeof(struct frag_hdr);
> >   			break;
> >   		}
> > -		case IPPROTO_FRAGMENT:
> > -			fragment = true;
> > -			/* fall through */
> 
> About IPv6 extension headers, should "Encapsulating Security Payload" be
> processed too?(See rfc2460 and rfc2406) Is there any concern to ignore
> it here?
> 

It's deliberately ignored. If we have an ESP header then the TCP/UDP header and payload will be encrypted so you can't do checksum offload, hence this function should return an error.

  Paul