ipv6.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include	"u.h"
#include	"../port/lib.h"
#include	"mem.h"
#include	"dat.h"
#include	"fns.h"
#include	"../port/error.h"

#include	"ip.h"
#include	"ipv6.h"

enum
{
	IP4HDR		= 20,		/* sizeof(Ip4hdr) */
	IP6HDR		= 40,		/* sizeof(Ip6hdr) */
	IP_HLEN4	= 0x05,		/* Header length in words */
	IP_DF		= 0x4000,	/* Don't fragment */
	IP_MF		= 0x2000,	/* More fragments */
	IP6FHDR		= 8, 		/* sizeof(Fraghdr6) */
	IP_MAX		= (32*1024),	/* Maximum Internet packet size */
};

#define IPV6CLASS(hdr) ((hdr->vcf[0]&0x0F)<<2 | (hdr->vcf[1]&0xF0)>>2)
#define BLKIPVER(xp)	(((Ip6hdr*)((xp)->rp))->vcf[0]&0xF0)
/*
 * This sleazy macro is stolen shamelessly from ip.c, see comment there.
 */
#define BKFG(xp)	((Ipfrag*)((xp)->base))

typedef struct	IP	IP;
typedef struct	Fragment4	Fragment4;
typedef struct	Fragment6	Fragment6;
typedef struct	Ipfrag	Ipfrag;

Block*		ip6reassemble(IP*, int, Block*, Ip6hdr*);
void		ipfragfree6(IP*, Fragment6*);
Fragment6*	ipfragallo6(IP*);
static Block*		procxtns(IP *ip, Block *bp, int doreasm);
int		unfraglen(Block *bp, uchar *nexthdr, int setfh);
Block*		procopts(Block *bp);

/* MIB II counters */
enum
{
	Forwarding,
	DefaultTTL,
	InReceives,
	InHdrErrors,
	InAddrErrors,
	ForwDatagrams,
	InUnknownProtos,
	InDiscards,
	InDelivers,
	OutRequests,
	OutDiscards,
	OutNoRoutes,
	ReasmTimeout,
	ReasmReqds,
	ReasmOKs,
	ReasmFails,
	FragOKs,
	FragFails,
	FragCreates,

	Nstats,
};

static char *statnames[] =
{
[Forwarding]	"Forwarding",
[DefaultTTL]	"DefaultTTL",
[InReceives]	"InReceives",
[InHdrErrors]	"InHdrErrors",
[InAddrErrors]	"InAddrErrors",
[ForwDatagrams]	"ForwDatagrams",
[InUnknownProtos]	"InUnknownProtos",
[InDiscards]	"InDiscards",
[InDelivers]	"InDelivers",
[OutRequests]	"OutRequests",
[OutDiscards]	"OutDiscards",
[OutNoRoutes]	"OutNoRoutes",
[ReasmTimeout]	"ReasmTimeout",
[ReasmReqds]	"ReasmReqds",
[ReasmOKs]	"ReasmOKs",
[ReasmFails]	"ReasmFails",
[FragOKs]	"FragOKs",
[FragFails]	"FragFails",
[FragCreates]	"FragCreates",
};

struct Fragment4
{
	Block*	blist;
	Fragment4*	next;
	ulong 	src;
	ulong 	dst;
	ushort	id;
	ulong 	age;
};

struct Fragment6
{
	Block*	blist;
	Fragment6*	next;
	uchar 	src[IPaddrlen];
	uchar 	dst[IPaddrlen];
	uint	id;
	ulong 	age;
};

struct Ipfrag
{
	ushort	foff;
	ushort	flen;
};

/* an instance of IP */
struct IP
{
	ulong		stats[Nstats];

	QLock		fraglock4;
	Fragment4*	flisthead4;
	Fragment4*	fragfree4;
	Ref		id4;

	QLock		fraglock6;
	Fragment6*	flisthead6;
	Fragment6*	fragfree6;
	Ref		id6;

	int		iprouting;	/* true if we route like a gateway */
};

int
ipoput6(Fs *f, Block *bp, int gating, int ttl, int tos, Conv *c)
{
	int tentative;
	Ipifc *ifc;
	uchar *gate, nexthdr;
	Ip6hdr *eh;
	int medialen, len, chunk, uflen, flen, seglen, lid, offset, fragoff, morefrags, blklen;
	Route *r, *sr;
	Fraghdr6 fraghdr;
	Block *xp, *nb;
	IP *ip;
	int rv = 0;

	ip = f->ip;

	/* Fill out the ip header */
	eh = (Ip6hdr*)(bp->rp);

	ip->stats[OutRequests]++;

	/* Number of uchars in data and ip header to write */
	len = blocklen(bp);
	
	tentative = iptentative(f, eh->src);
	if(tentative){
		netlog(f, Logip, "reject tx of packet with tentative src address\n");
		goto free;
	}

	if(gating){
		chunk = nhgets(eh->ploadlen);
		if(chunk > len){
			ip->stats[OutDiscards]++;
			netlog(f, Logip, "short gated packet\n");
			goto free;
		}
		if(chunk + IPV6HDR_LEN < len)
			len = chunk + IPV6HDR_LEN;
	}

	if(len >= IP_MAX){
//		print("len > IP_MAX, free\n");
		ip->stats[OutDiscards]++;
		netlog(f, Logip, "exceeded ip max size %I\n", eh->dst);
		goto free;
	}

	r = v6lookup(f, eh->dst, c);
	if(r == nil){
//		print("no route for %I, src %I free\n", eh->dst, eh->src);
		ip->stats[OutNoRoutes]++;
		netlog(f, Logip, "no interface %I\n", eh->dst);
		rv = -1;
		goto free;
	}

	ifc = r->ifc;
	if(r->type & (Rifc|Runi))
		gate = eh->dst;
	else
	if(r->type & (Rbcast|Rmulti)) {
		gate = eh->dst;
		sr = v6lookup(f, eh->src, nil);
		if(sr != nil && (sr->type & Runi))
			ifc = sr->ifc;
	}
	else
		gate = r->v6.gate;

	if(!gating)
		eh->vcf[0] = IP_VER6;
	eh->ttl = ttl;
	if(!gating) {
		eh->vcf[0] |= (tos >> 4);
		eh->vcf[1] = (tos << 4);
	}

	if(!canrlock(ifc)) {
		goto free;
	}

	if(waserror()){
		runlock(ifc);
		nexterror();
	}

	if(ifc->m == nil) {
		goto raise;
	}

	/* If we dont need to fragment just send it */
	medialen = ifc->maxtu - ifc->m->hsize;
	if(len <= medialen) {
		hnputs(eh->ploadlen, len-IPV6HDR_LEN);
		ifc->m->bwrite(ifc, bp, V6, gate);
		runlock(ifc);
		poperror();
		return 0;
	}

	if(gating) 
	if(ifc->reassemble <= 0) {

		/* v6 intermediate nodes are not supposed to fragment pkts;
		   we fragment if ifc->reassemble is turned on; an exception
		   needed for nat.
		 */

		ip->stats[OutDiscards]++;
		icmppkttoobig6(f, ifc, bp);
		netlog(f, Logip, "%I: gated pkts not fragmented\n", eh->dst);
		goto raise;
	}
		
	/* start v6 fragmentation */
	uflen = unfraglen(bp, &nexthdr, 1);
	if(uflen > medialen) {
		ip->stats[FragFails]++;
		ip->stats[OutDiscards]++;
		netlog(f, Logip, "%I: unfragmentable part too big\n", eh->dst);
		goto raise;
	}

	flen = len - uflen;
	seglen = (medialen - (uflen + IP6FHDR)) & ~7;
	if(seglen < 8) {
		ip->stats[FragFails]++;
		ip->stats[OutDiscards]++;
		netlog(f, Logip, "%I: seglen < 8\n", eh->dst);
		goto raise;
	}

	lid = incref(&ip->id6);
	fraghdr.nexthdr = nexthdr;
	fraghdr.res = 0;
	hnputl(fraghdr.id, lid);

	xp = bp;
	offset = uflen;
	while (xp != nil && offset && offset >= BLEN(xp)) {
		offset -= BLEN(xp);
		xp = xp->next;
	}
	xp->rp += offset;

	fragoff = 0; 
	morefrags = 1;

	for(; fragoff < flen; fragoff += seglen) {
		nb = allocb(uflen + IP6FHDR + seglen);

		if(fragoff + seglen >= flen) {
			seglen = flen - fragoff;
			morefrags = 0;
		}

		hnputs(eh->ploadlen, seglen+IP6FHDR);
		memmove(nb->wp, eh, uflen);
		nb->wp += uflen;

		hnputs(fraghdr.offsetRM, fragoff); // last 3 bits must be 0
		fraghdr.offsetRM[1] |= morefrags;
		memmove(nb->wp, &fraghdr, IP6FHDR);
		nb->wp += IP6FHDR;

		/* Copy data */
		chunk = seglen;
		while (chunk) {
			if(!xp) {
				ip->stats[OutDiscards]++;
				ip->stats[FragFails]++;
				freeblist(nb);
				netlog(f, Logip, "!xp: chunk in v6%d\n", chunk);
				goto raise;
			}
			blklen = chunk;
			if(BLEN(xp) < chunk)
				blklen = BLEN(xp);
			memmove(nb->wp, xp->rp, blklen);

			nb->wp += blklen;
			xp->rp += blklen;
			chunk -= blklen;
			if(xp->rp == xp->wp)
				xp = xp->next; 
		}

		ifc->m->bwrite(ifc, nb, V6, gate);
		ip->stats[FragCreates]++;
	}
	ip->stats[FragOKs]++;

raise:
	runlock(ifc);
	poperror();
free:
	freeblist(bp);	
	return rv;
}

void
ipiput6(Fs *f, Ipifc *ifc, Block *bp)
{
	int hl;
	int hop, tos;
	uchar proto;
	Ip6hdr *h;
	Proto *p;
	int notforme;
	int tentative;
	uchar v6dst[IPaddrlen];
	IP *ip;
	Route *r, *sr;

	ip = f->ip;
	ip->stats[InReceives]++;

	/*
	 *  Ensure we have all the header info in the first
	 *  block.  Make life easier for other protocols by
	 *  collecting up to the first 64 bytes in the first block.
	 */
	if(BLEN(bp) < 64) {
		hl = blocklen(bp);
		if(hl < IP6HDR)
			hl = IP6HDR;
		if(hl > 64)
			hl = 64;
		bp = pullupblock(bp, hl);
		if(bp == nil)
			return;
	}

	h = (Ip6hdr *)(bp->rp);

	memmove(&v6dst[0], &(h->dst)[0], IPaddrlen);
	notforme = ipforme(f, v6dst) == 0;
	tentative = iptentative(f, v6dst);
  
	if(tentative && (h->proto != ICMPv6)) {
		print("tentative addr, drop\n");
		freeblist(bp);
		return;
	}

	/* Check header version */
	if(BLKIPVER(bp) != IP_VER6) {
		ip->stats[InHdrErrors]++;
		netlog(f, Logip, "ip: bad version %ux\n", (h->vcf[0]&0xF0)>>2);
		freeblist(bp);
		return;
	}

	/* route */
	if(notforme) {
		if(!ip->iprouting){
			freeb(bp);
			return;
		}
		/* don't forward to source's network */
		sr = v6lookup(f, h->src, nil);
		r = v6lookup(f, h->dst, nil);

		if(r == nil || sr == r){
			ip->stats[OutDiscards]++;
			freeblist(bp);
			return;
		}

		/* don't forward if packet has timed out */
		hop = h->ttl;
		if(hop < 1) {
			ip->stats[InHdrErrors]++;
			icmpttlexceeded6(f, ifc, bp);
			freeblist(bp);
			return;
		}

		/* process headers & reassemble if the interface expects it */
		bp = procxtns(ip, bp, r->ifc->reassemble);

		if(bp == nil)
			return;

		ip->stats[ForwDatagrams]++;
		h = (Ip6hdr *) (bp->rp);
		tos = IPV6CLASS(h);
		hop = h->ttl;
		ipoput6(f, bp, 1, hop-1, tos, nil);
		return;
	}

	/* reassemble & process headers if needed */
	bp = procxtns(ip, bp, 1);

	if(bp == nil)
		return;

	h = (Ip6hdr *) (bp->rp);
	proto = h->proto;
	p = Fsrcvpcol(f, proto);
	if(p != nil && p->rcv != nil) {
		ip->stats[InDelivers]++;
		(*p->rcv)(p, ifc, bp);
		return;
	}

	ip->stats[InDiscards]++;
	ip->stats[InUnknownProtos]++;
	freeblist(bp);
}

/*
 * ipfragfree6 - copied from ipfragfree4 - assume hold fraglock6
 */
void
ipfragfree6(IP *ip, Fragment6 *frag)
{
	Fragment6 *fl, **l;

	if(frag->blist)
		freeblist(frag->blist);

	memset(frag->src, 0, IPaddrlen);
	frag->id = 0;
	frag->blist = nil;

	l = &ip->flisthead6;
	for(fl = *l; fl; fl = fl->next) {
		if(fl == frag) {
			*l = frag->next;
			break;
		}
		l = &fl->next;
	}

	frag->next = ip->fragfree6;
	ip->fragfree6 = frag;

}

/*
 * ipfragallo6 - copied from ipfragalloc4
 */
Fragment6*
ipfragallo6(IP *ip)
{
	Fragment6 *f;

	while(ip->fragfree6 == nil) {
		/* free last entry on fraglist */
		for(f = ip->flisthead6; f->next; f = f->next)
			;
		ipfragfree6(ip, f);
	}
	f = ip->fragfree6;
	ip->fragfree6 = f->next;
	f->next = ip->flisthead6;
	ip->flisthead6 = f;
	f->age = NOW + 30000;

	return f;
}

static Block*
procxtns(IP *ip, Block *bp, int doreasm) {

	int offset;
	uchar proto;
	Ip6hdr *h;

	h = (Ip6hdr *) (bp->rp);
	offset = unfraglen(bp, &proto, 0);

	if((proto == FH) && (doreasm != 0)) {
		bp = ip6reassemble(ip, offset, bp, h);
		if(bp == nil) 
			return nil; 
		offset = unfraglen(bp, &proto, 0);
	}

	if(proto == DOH || offset > IP6HDR) 
		bp = procopts(bp);

	return bp;
}


/*	returns length of "Unfragmentable part", i.e., sum of lengths of ipv6 hdr,
 *	hop-by-hop & routing headers if present; *nexthdr is set to nexthdr value
 *	of the last header in the "Unfragmentable part"; if setfh != 0, nexthdr
 *	field of the last header in the "Unfragmentable part" is set to FH.
 */
int
unfraglen(Block *bp, uchar *nexthdr, int setfh)
{
	uchar *p, *q;
	int ufl, hs;

	p = bp->rp;
	q = p+6;	/* proto, = p+sizeof(Ip6hdr.vcf)+sizeof(Ip6hdr.ploadlen) */
	*nexthdr = *q;
	ufl = IP6HDR;
	p += ufl;

	for(;;) {
		if(*nexthdr == HBH || *nexthdr == RH) {
			*nexthdr = *p;
			hs = ((int)*(p+1) + 1) * 8;
			ufl += hs;
			q = p;
			p += hs;
		}
		else
			break;
	}

	if(*nexthdr == FH)
		*q = *p;

	if(setfh)
		*q = FH;

	return ufl;
}

Block*
procopts(Block *bp)
{
	return bp;
}

Block*
ip6reassemble(IP* ip, int uflen, Block* bp, Ip6hdr* ih)
{

	int fend, offset;
	uint id;
	Fragment6 *f, *fnext;
	Fraghdr6 *fraghdr;
	uchar src[IPaddrlen], dst[IPaddrlen];
	Block *bl, **l, *last, *prev;
	int ovlap, len, fragsize, pktposn;

	fraghdr = (Fraghdr6 *) (bp->rp + uflen);
	memmove(src, ih->src, IPaddrlen);
	memmove(dst, ih->dst, IPaddrlen);
	id = nhgetl(fraghdr->id);
	offset = nhgets(fraghdr->offsetRM) & ~7;

	/*
	 *  block lists are too hard, pullupblock into a single block
	 */
	if(bp->next){
		bp = pullupblock(bp, blocklen(bp));
		ih = (Ip6hdr *)(bp->rp);
	}


	qlock(&ip->fraglock6);

	/*
	 *  find a reassembly queue for this fragment
	 */
	for(f = ip->flisthead6; f; f = fnext){
		fnext = f->next;
		if(ipcmp(f->src, src)==0 && ipcmp(f->dst, dst)==0 && f->id == id)
			break;
		if(f->age < NOW){
			ip->stats[ReasmTimeout]++;
			ipfragfree6(ip, f);
		}
	}


	/*
	 *  if this isn't a fragmented packet, accept it
	 *  and get rid of any fragments that might go
	 *  with it.
	 */
	if(nhgets(fraghdr->offsetRM)==0) {	// first frag is also the last
		if(f != nil) {
			ipfragfree6(ip, f);
			ip->stats[ReasmFails]++;
		}
		qunlock(&ip->fraglock6);
		return bp;
	}

	if(bp->base+sizeof(Ipfrag) >= bp->rp){
		bp = padblock(bp, sizeof(Ipfrag));
		bp->rp += sizeof(Ipfrag);
	}

	BKFG(bp)->foff = offset;
	BKFG(bp)->flen = nhgets(ih->ploadlen) + IP6HDR - uflen - IP6FHDR;

	/* First fragment allocates a reassembly queue */
	if(f == nil) {
		f = ipfragallo6(ip);
		f->id = id;
		memmove(f->src, src, IPaddrlen);
		memmove(f->dst, dst, IPaddrlen);

		f->blist = bp;

		qunlock(&ip->fraglock6);
		ip->stats[ReasmReqds]++;
		return nil;
	}

	/*
	 *  find the new fragment's position in the queue
	 */
	prev = nil;
	l = &f->blist;
	bl = f->blist;
	while(bl != nil && BKFG(bp)->foff > BKFG(bl)->foff) {
		prev = bl;
		l = &bl->next;
		bl = bl->next;
	}

	/* Check overlap of a previous fragment - trim away as necessary */
	if(prev) {
		ovlap = BKFG(prev)->foff + BKFG(prev)->flen - BKFG(bp)->foff;
		if(ovlap > 0) {
			if(ovlap >= BKFG(bp)->flen) {
				freeblist(bp);
				qunlock(&ip->fraglock6);
				return nil;
			}
			BKFG(prev)->flen -= ovlap;
		}
	}

	/* Link onto assembly queue */
	bp->next = *l;
	*l = bp;

	/* Check to see if succeeding segments overlap */
	if(bp->next) {
		l = &bp->next;
		fend = BKFG(bp)->foff + BKFG(bp)->flen;

		/* Take completely covered segments out */

		while(*l) {
			ovlap = fend - BKFG(*l)->foff;

			if(ovlap <= 0) 
				break; 
			if(ovlap < BKFG(*l)->flen) {
				BKFG(*l)->flen -= ovlap;
				BKFG(*l)->foff += ovlap;
				/* move up ih hdrs */
				memmove((*l)->rp + ovlap, (*l)->rp, uflen);
				(*l)->rp += ovlap;
				break;
			}
			last = (*l)->next;
			(*l)->next = nil;
			freeblist(*l);
			*l = last;
		}
	}

	/*
	 *  look for a complete packet.  if we get to a fragment
	 *  with the trailing bit of fraghdr->offsetRM[1] set, we're done.
	 */
	pktposn = 0;
	for(bl = f->blist; bl; bl = bl->next) {
		if(BKFG(bl)->foff != pktposn)
			break;
	
		fraghdr = (Fraghdr6 *) (bl->rp + uflen);
		if((fraghdr->offsetRM[1] & 1) == 0) {

			bl = f->blist;

			/* get rid of frag header in first fragment */

			memmove(bl->rp + IP6FHDR, bl->rp, uflen);
			bl->rp += IP6FHDR;
			len = nhgets(((Ip6hdr*)(bl->rp))->ploadlen) - IP6FHDR;
			bl->wp = bl->rp + len + IP6HDR;

			/* Pullup all the fragment headers and
			 * return a complete packet
			 */
			for(bl = bl->next; bl; bl = bl->next) {
				fragsize = BKFG(bl)->flen;
				len += fragsize;
				bl->rp += uflen + IP6FHDR;
				bl->wp = bl->rp + fragsize;
			}

			bl = f->blist;
			f->blist = nil;
			ipfragfree6(ip, f);
			ih = (Ip6hdr*)(bl->rp);
			hnputs(ih->ploadlen, len);
			qunlock(&ip->fraglock6);
			ip->stats[ReasmOKs]++;
			return bl;		
		}
		pktposn += BKFG(bl)->flen;
	}
	qunlock(&ip->fraglock6);
	return nil;
}