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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 (van@helios.ee.lbl.gov), Dec 31, 1989:

 *      - Initial distribution.

 *

 *

 * modified for KA9Q Internet Software Package by

 * Katie Stevens (dkstevens@ucdavis.edu)

 * 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      Bill_Simpson@um.cc.umich.edu

 *                      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>

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) & 0x3fff)) {

                /* 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(ip->version != cs->cs_ip.version || ip->ihl != cs->cs_ip.ihl

         || ip->tos != cs->cs_ip.tos

         || (ip->frag_off & htons(0x4000)) != (cs->cs_ip.frag_off & htons(0x4000))

         || 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

                 * it compressed.  Otherwise it's probably a retransmit,

                 * retransmitted ack or window probe.  Send it uncompressed

                 * in case the other side missed the compressed version.

                 */

                if(ip->tot_len != cs->cs_ip.tot_len &&

                   ntohs(cs->cs_ip.tot_len) == hlen)

                        break;

                goto uncompressed;

                break;

        case SPECIAL_I:

        case SPECIAL_D:

                /* actual changes match one of our special case encodings --

                 * send packet uncompressed.

                 */

                goto uncompressed;

        case NEW_S|NEW_A:

                if(deltaS == deltaA &&

                    deltaS == ntohs(cs->cs_ip.tot_len) - hlen){

                        /* special case for echoed terminal traffic */

                        changes = SPECIAL_I;

                        cp = new_seq;

                }

                break;

        case NEW_S:

                if(deltaS == ntohs(cs->cs_ip.tot_len) - hlen){

                        /* special case for data xfer */

                        changes = SPECIAL_D;

                        cp = new_seq;

                }

                break;

        }

        deltaS = ntohs(ip->id) - ntohs(cs->cs_ip.id);

        if(deltaS != 1){

                cp = encode(cp,deltaS);

                changes |= NEW_I;

        }

        if(th->psh)

                changes |= TCP_PUSH_BIT;

        /* Grab the cksum before we overwrite it below.  Then update our

         * state with this packet's header.

         */

        deltaA = ntohs(th->check);

        memcpy(&cs->cs_ip,ip,20);

        memcpy(&cs->cs_tcp,th,20);

        /* We want to use the original packet as our compressed packet.

         * (cp - new_seq) is the number of bytes we need for compressed

         * sequence numbers.  In addition we need one byte for the change

         * mask, one for the connection id and two for the tcp checksum.

         * So, (cp - new_seq) + 4 bytes of header are needed.

         */

        deltaS = cp - new_seq;

        if(compress_cid == 0 || comp->xmit_current != cs->cs_this){

                cp = ocp;

                *cpp = ocp;

                *cp++ = changes | NEW_C;

                *cp++ = cs->cs_this;

                comp->xmit_current = cs->cs_this;

        } else {

                cp = ocp;

                *cpp = ocp;

                *cp++ = changes;

        }

        cp = put16(cp,(short)deltaA);   /* Write TCP checksum */

/* deltaS is now the size of the change section of the compressed header */

        memcpy(cp,new_seq,deltaS);      /* Write list of deltas */

        memcpy(cp+deltaS,icp+hlen,isize-hlen);

        comp->sls_o_compressed++;

        ocp[0] |= SL_TYPE_COMPRESSED_TCP;

        return isize - hlen + deltaS + (cp - ocp);

        /* Update connection state cs & send uncompressed packet (i.e.,

         * a regular ip/tcp packet but with the 'conversation id' we hope

         * to use on future compressed packets in the protocol field).

         */

uncompressed:

        memcpy(&cs->cs_ip,ip,20);

        memcpy(&cs->cs_tcp,th,20);

        if (ip->ihl > 5)

          memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);

        if (th->doff > 5)

          memcpy(cs->cs_tcpopt, th+1, ((th->doff) - 5) * 4);

        comp->xmit_current = cs->cs_this;

        comp->sls_o_uncompressed++;

        memcpy(ocp, icp, isize);

        *cpp = ocp;

        ocp[9] = cs->cs_this;

        ocp[0] |= SL_TYPE_UNCOMPRESSED_TCP;

        return isize;

}

int

slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)

{

        register int changes;

        long x;

        register struct tcphdr *thp;

        register struct iphdr *ip;

        register struct cstate *cs;

        int len, hdrlen;

        unsigned char *cp = icp;

        /* We've got a compressed packet; read the change byte */

        comp->sls_i_compressed++;

        if(isize < 3){

                comp->sls_i_error++;

                return 0;

        }

        changes = *cp++;

        if(changes & NEW_C){

                /* Make sure the state index is in range, then grab the state.

                 * If we have a good state index, clear the 'discard' flag.

                 */

                x = *cp++;      /* Read conn index */

                if(x < 0 || x > comp->rslot_limit)

                        goto bad;

                comp->flags &=~ SLF_TOSS;

                comp->recv_current = x;

        } else {

                /* this packet has an implicit state index.  If we've

                 * had a line error since the last time we got an

                 * explicit state index, we have to toss the packet. */

                if(comp->flags & SLF_TOSS){

                        comp->sls_i_tossed++;

                        return 0;

                }

        }

        cs = &comp->rstate[comp->recv_current];

        thp = &cs->cs_tcp;

        ip = &cs->cs_ip;

        if((x = pull16(&cp)) == -1) {   /* Read the TCP checksum */

                goto bad;

        }

        thp->check = htons(x);

        thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;

/*

 * we can use the same number for the length of the saved header and

 * the current one, because the packet wouldn't have been sent

 * as compressed unless the options were the same as the previous one

 */

        hdrlen = ip->ihl * 4 + thp->doff * 4;

        switch(changes & SPECIALS_MASK){

        case SPECIAL_I:         /* Echoed terminal traffic */

                {

                register short i;

                i = ntohs(ip->tot_len) - hdrlen;

                thp->ack_seq = htonl( ntohl(thp->ack_seq) + i);

                thp->seq = htonl( ntohl(thp->seq) + i);

                }

                break;

        case SPECIAL_D:                 /* Unidirectional data */

                thp->seq = htonl( ntohl(thp->seq) +

                                  ntohs(ip->tot_len) - hdrlen);

                break;

        default:

                if(changes & NEW_U){

                        thp->urg = 1;

                        if((x = decode(&cp)) == -1) {

                                goto bad;

                        }

                        thp->urg_ptr = htons(x);

                } else

                        thp->urg = 0;

                if(changes & NEW_W){

                        if((x = decode(&cp)) == -1) {

                                goto bad;

                        }

                        thp->window = htons( ntohs(thp->window) + x);

                }

                if(changes & NEW_A){

                        if((x = decode(&cp)) == -1) {

                                goto bad;

                        }

                        thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);

                }

                if(changes & NEW_S){

                        if((x = decode(&cp)) == -1) {

                                goto bad;

                        }

                        thp->seq = htonl( ntohl(thp->seq) + x);

                }

                break;

        }

        if(changes & NEW_I){

                if((x = decode(&cp)) == -1) {

                        goto bad;

                }

                ip->id = htons (ntohs (ip->id) + x);

        } else

                ip->id = htons (ntohs (ip->id) + 1);

        /*

         * At this point, cp points to the first byte of data in the

         * packet.  Put the reconstructed TCP and IP headers back on the

         * packet.  Recalculate IP checksum (but not TCP checksum).

         */

        len = isize - (cp - icp);

        if (len < 0)

                goto bad;

        len += hdrlen;

        ip->tot_len = htons(len);

        ip->check = 0;

        memmove(icp + hdrlen, cp, len - hdrlen);

        cp = icp;

        memcpy(cp, ip, 20);

        cp += 20;

        if (ip->ihl > 5) {

          memcpy(cp, cs->cs_ipopt, (ip->ihl - 5) * 4);

          cp += (ip->ihl - 5) * 4;

        }

        put_unaligned(ip_fast_csum(icp, ip->ihl),

                      &((struct iphdr *)icp)->check);

        memcpy(cp, thp, 20);

        cp += 20;

        if (thp->doff > 5) {

          memcpy(cp, cs->cs_tcpopt, ((thp->doff) - 5) * 4);

          cp += ((thp->doff) - 5) * 4;

        }

        return len;

bad:

        comp->sls_i_error++;

        return slhc_toss( comp );

}

int

slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)

{

        register struct cstate *cs;

        unsigned ihl;

        unsigned char index;

        if(isize < 20) {

                /* The packet is shorter than a legal IP header */

                comp->sls_i_runt++;

                return slhc_toss( comp );

        }

        /* Peek at the IP header's IHL field to find its length */

        ihl = icp[0] & 0xf;

        if(ihl < 20 / 4){

                /* The IP header length field is too small */

                comp->sls_i_runt++;

                return slhc_toss( comp );

        }

        index = icp[9];

        icp[9] = IPPROTO_TCP;

        if (ip_fast_csum(icp, ihl)) {

                /* Bad IP header checksum; discard */

                comp->sls_i_badcheck++;

                return slhc_toss( comp );

        }

        if(index > comp->rslot_limit) {