slhc.c

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/*
 * Routines to compress and uncompress tcp packets (for transmission
 * over low speed serial lines).
 *
 * Copyright (c) 1989 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *	Van Jacobson ([e-mail]), Dec 31, 1989:
 *	- Initial distribution.
 *
 *
 * modified for KA9Q Internet Software Package by
 * Katie Stevens ([e-mail])
 * University of California, Davis
 * Computing Services
 *	- 01-31-90	initial adaptation (from 1.19)
 *	PPP.05	02-15-90 [ks]
 *	PPP.08	05-02-90 [ks]	use PPP protocol field to signal compression
 *	PPP.15	09-90	 [ks]	improve mbuf handling
 *	PPP.16	11-02	 [karn]	substantially rewritten to use NOS facilities
 *
 *	- Feb 1991	[e-mail]
 *			variable number of conversation slots
 *			allow zero or one slots
 *			separate routines
 *			status display
 *	- Jul 1994	Dmitry Gorodchanin
 *			Fixes for memory leaks.
 *      - Oct 1994      Dmitry Gorodchanin
 *                      Modularization.
 *	- Jan 1995	Bjorn Ekwall
 *			Use ip_fast_csum from ip.h
 *	- July 1995	Christos A. Polyzols 
 *			Spotted bug in tcp option checking
 *
 *
 *	This module is a difficult issue. It's clearly inet code but it's also clearly
 *	driver code belonging close to PPP and SLIP
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <net/slhc_vj.h>

#ifdef CONFIG_INET
/* Entire module is for IP only */
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/termios.h>
#include <linux/in.h>
#include <linux/fcntl.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <net/ip.h>
#include <net/protocol.h>
#include <net/icmp.h>
#include <net/tcp.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/timer.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <net/checksum.h>
#include <asm/unaligned.h>

int last_retran;

static unsigned char *encode(unsigned char *cp, unsigned short n);
static long decode(unsigned char **cpp);
static unsigned char * put16(unsigned char *cp, unsigned short x);
static unsigned short pull16(unsigned char **cpp);

/* Initialize compression data structure
 *	slots must be in range 0 to 255 (zero meaning no compression)
 */
struct slcompress *
slhc_init(int rslots, int tslots)
{
	register short i;
	register struct cstate *ts;
	struct slcompress *comp;

	MOD_INC_USE_COUNT;
	comp = (struct slcompress *)kmalloc(sizeof(struct slcompress),
					    GFP_KERNEL);
	if (! comp)
		goto out_fail;
	memset(comp, 0, sizeof(struct slcompress));

	if ( rslots > 0  &&  rslots < 256 ) {
		size_t rsize = rslots * sizeof(struct cstate);
		comp->rstate = (struct cstate *) kmalloc(rsize, GFP_KERNEL);
		if (! comp->rstate)
			goto out_free;
		memset(comp->rstate, 0, rsize);
		comp->rslot_limit = rslots - 1;
	}

	if ( tslots > 0  &&  tslots < 256 ) {
		size_t tsize = tslots * sizeof(struct cstate);
		comp->tstate = (struct cstate *) kmalloc(tsize, GFP_KERNEL);
		if (! comp->tstate)
			goto out_free2;
		memset(comp->tstate, 0, tsize);
		comp->tslot_limit = tslots - 1;
	}

	comp->xmit_oldest = 0;
	comp->xmit_current = 255;
	comp->recv_current = 255;
	/*
	 * don't accept any packets with implicit index until we get
	 * one with an explicit index.  Otherwise the uncompress code
	 * will try to use connection 255, which is almost certainly
	 * out of range
	 */
	comp->flags |= SLF_TOSS;

	if ( tslots > 0 ) {
		ts = comp->tstate;
		for(i = comp->tslot_limit; i > 0; --i){
			ts[i].cs_this = i;
			ts[i].next = &(ts[i - 1]);
		}
		ts[0].next = &(ts[comp->tslot_limit]);
		ts[0].cs_this = 0;
	}
	return comp;

out_free2:
	kfree((unsigned char *)comp->rstate);
out_free:
	kfree((unsigned char *)comp);
out_fail:
	MOD_DEC_USE_COUNT;
	return NULL;
}


/* Free a compression data structure */
void
slhc_free(struct slcompress *comp)
{
	if ( comp == NULLSLCOMPR )
		return;

	if ( comp->tstate != NULLSLSTATE )
		kfree( comp->tstate );

	if ( comp->rstate != NULLSLSTATE )
		kfree( comp->rstate );

	kfree( comp );
	MOD_DEC_USE_COUNT;
}


/* Put a short in host order into a char array in network order */
static inline unsigned char *
put16(unsigned char *cp, unsigned short x)
{
	*cp++ = x >> 8;
	*cp++ = x;

	return cp;
}


/* Encode a number */
unsigned char *
encode(unsigned char *cp, unsigned short n)
{
	if(n >= 256 || n == 0){
		*cp++ = 0;
		cp = put16(cp,n);
	} else {
		*cp++ = n;
	}
	return cp;
}

/* Pull a 16-bit integer in host order from buffer in network byte order */
static unsigned short
pull16(unsigned char **cpp)
{
	short rval;

	rval = *(*cpp)++;
	rval <<= 8;
	rval |= *(*cpp)++;
	return rval;
}

/* Decode a number */
long
decode(unsigned char **cpp)
{
	register int x;

	x = *(*cpp)++;
	if(x == 0){
		return pull16(cpp) & 0xffff;	/* pull16 returns -1 on error */
	} else {
		return x & 0xff;		/* -1 if PULLCHAR returned error */
	}
}

/*
 * icp and isize are the original packet.
 * ocp is a place to put a copy if necessary.
 * cpp is initially a pointer to icp.  If the copy is used,
 *    change it to ocp.
 */

int
slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
	unsigned char *ocp, unsigned char **cpp, int compress_cid)
{
	register struct cstate *ocs = &(comp->tstate[comp->xmit_oldest]);
	register struct cstate *lcs = ocs;
	register struct cstate *cs = lcs->next;
	register unsigned long deltaS, deltaA;
	register short changes = 0;
	int hlen;
	unsigned char new_seq[16];
	register unsigned char *cp = new_seq;
	struct iphdr *ip;
	struct tcphdr *th, *oth;


	/*
	 *	Don't play with runt packets.
	 */
	 
	if(isize<sizeof(struct iphdr))
		return isize;
		
	ip = (struct iphdr *) icp;

	/* Bail if this packet isn't TCP, or is an IP fragment */
	if(ip->protocol != IPPROTO_TCP || (ntohs(ip->frag_off) & 0x1fff) ||
				       (ip->frag_off & 32)){
		/* Send as regular IP */
		if(ip->protocol != IPPROTO_TCP)
			comp->sls_o_nontcp++;
		else
			comp->sls_o_tcp++;
		return isize;
	}
	/* Extract TCP header */

	th = (struct tcphdr *)(((unsigned char *)ip) + ip->ihl*4);
	hlen = ip->ihl*4 + th->doff*4;

	/*  Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
	 *  some other control bit is set). Also uncompressible if
	 *  its a runt.
	 */
	if(hlen > isize || th->syn || th->fin || th->rst ||
	    ! (th->ack)){
		/* TCP connection stuff; send as regular IP */
		comp->sls_o_tcp++;
		return isize;
	}
	/*
	 * Packet is compressible -- we're going to send either a
	 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way,
	 * we need to locate (or create) the connection state.
	 *
	 * States are kept in a circularly linked list with
	 * xmit_oldest pointing to the end of the list.  The
	 * list is kept in lru order by moving a state to the
	 * head of the list whenever it is referenced.  Since
	 * the list is short and, empirically, the connection
	 * we want is almost always near the front, we locate
	 * states via linear search.  If we don't find a state
	 * for the datagram, the oldest state is (re-)used.
	 */
	for ( ; ; ) {
		if( ip->saddr == cs->cs_ip.saddr
		 && ip->daddr == cs->cs_ip.daddr
		 && th->source == cs->cs_tcp.source
		 && th->dest == cs->cs_tcp.dest)
			goto found;

		/* if current equal oldest, at end of list */
		if ( cs == ocs )
			break;
		lcs = cs;
		cs = cs->next;
		comp->sls_o_searches++;
	};
	/*
	 * Didn't find it -- re-use oldest cstate.  Send an
	 * uncompressed packet that tells the other side what
	 * connection number we're using for this conversation.
	 *
	 * Note that since the state list is circular, the oldest
	 * state points to the newest and we only need to set
	 * xmit_oldest to update the lru linkage.
	 */
	comp->sls_o_misses++;
	comp->xmit_oldest = lcs->cs_this;
	goto uncompressed;

found:
	/*
	 * Found it -- move to the front on the connection list.
	 */
	if(lcs == ocs) {
 		/* found at most recently used */
	} else if (cs == ocs) {
		/* found at least recently used */
		comp->xmit_oldest = lcs->cs_this;
	} else {
		/* more than 2 elements */
		lcs->next = cs->next;
		cs->next = ocs->next;
		ocs->next = cs;
	}

	/*
	 * Make sure that only what we expect to change changed.
	 * Check the following:
	 * IP protocol version, header length & type of service.
	 * The "Don't fragment" bit.
	 * The time-to-live field.
	 * The TCP header length.
	 * IP options, if any.
	 * TCP options, if any.
	 * If any of these things are different between the previous &
	 * current datagram, we send the current datagram `uncompressed'.
	 */
	oth = &cs->cs_tcp;

	if(last_retran
	 || ip->version != cs->cs_ip.version || ip->ihl != cs->cs_ip.ihl
	 || ip->tos != cs->cs_ip.tos
	 || (ip->frag_off & 64) != (cs->cs_ip.frag_off & 64)
	 || ip->ttl != cs->cs_ip.ttl
	 || th->doff != cs->cs_tcp.doff
	 || (ip->ihl > 5 && memcmp(ip+1,cs->cs_ipopt,((ip->ihl)-5)*4) != 0)
	 || (th->doff > 5 && memcmp(th+1,cs->cs_tcpopt,((th->doff)-5)*4) != 0)){
		goto uncompressed;
	}

	/*
	 * Figure out which of the changing fields changed.  The
	 * receiver expects changes in the order: urgent, window,
	 * ack, seq (the order minimizes the number of temporaries
	 * needed in this section of code).
	 */
	if(th->urg){
		deltaS = ntohs(th->urg_ptr);
		cp = encode(cp,deltaS);
		changes |= NEW_U;
	} else if(th->urg_ptr != oth->urg_ptr){
		/* argh! URG not set but urp changed -- a sensible
		 * implementation should never do this but RFC793
		 * doesn't prohibit the change so we have to deal
		 * with it. */
		goto uncompressed;
	}
	if((deltaS = ntohs(th->window) - ntohs(oth->window)) != 0){
		cp = encode(cp,deltaS);
		changes |= NEW_W;
	}
	if((deltaA = ntohl(th->ack_seq) - ntohl(oth->ack_seq)) != 0L){
		if(deltaA > 0x0000ffff)
			goto uncompressed;
		cp = encode(cp,deltaA);
		changes |= NEW_A;
	}
	if((deltaS = ntohl(th->seq) - ntohl(oth->seq)) != 0L){
		if(deltaS > 0x0000ffff)
			goto uncompressed;
		cp = encode(cp,deltaS);
		changes |= NEW_S;
	}

	switch(changes){
	case 0:	/* Nothing changed. If this packet contains data and the
		 * last one didn't, this is probably a data packet following
		 * an ack (normal on an interactive connection) and we send