/*
 * 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/module.h>
#include <linux/slab.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/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 <linux/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);

/* Allocate compression data structure
 *      slots must be in range 0 to 255 (zero meaning no compression)
 * Returns pointer to structure or ERR_PTR() on error.
 */
struct slcompress *
slhc_init(int rslots, int tslots)
{
        register short i;
        register struct cstate *ts;
        struct slcompress *comp;

        if (rslots < 0 || rslots > 255 || tslots < 0 || tslots > 255)
                return ERR_PTR(-EINVAL);

        comp = kzalloc(sizeof(struct slcompress), GFP_KERNEL);
        if (! comp)
                goto out_fail;

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

        if (tslots > 0) {
                size_t tsize = tslots * sizeof(struct cstate);
                comp->tstate = kzalloc(tsize, GFP_KERNEL);
                if (! comp->tstate)
                        goto out_free2;
                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(comp->rstate);
out_free:
        kfree(comp);
out_fail:
        return ERR_PTR(-ENOMEM);
}


/* 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 );
}


/* 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 */
static 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 */
static 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;
        __sum16 csum;


        /*
         *      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
         *  it's 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;
        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.
         */
        csum = 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;
        }
        *(__sum16 *)cp = csum;
        cp += 2;
/* 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;

                /* Check if the cstate is initialized */
                if (!comp->rstate[x].initialized)
                        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;

        thp->check = *(__sum16 *)cp;
        cp += 2;

        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) {
                comp->sls_i_error++;
                return slhc_toss(comp);
        }

        /* Update local state */
        cs = &comp->rstate[comp->recv_current = index];
        comp->flags &=~ SLF_TOSS;
        memcpy(&cs->cs_ip,icp,20);
        memcpy(&cs->cs_tcp,icp + ihl*4,20);
        if (ihl > 5)
          memcpy(cs->cs_ipopt, icp + sizeof(struct iphdr), (ihl - 5) * 4);
        if (cs->cs_tcp.doff > 5)
          memcpy(cs->cs_tcpopt, icp + ihl*4 + sizeof(struct tcphdr), (cs->cs_tcp.doff - 5) * 4);
        cs->cs_hsize = ihl*2 + cs->cs_tcp.doff*2;
        cs->initialized = true;
        /* Put headers back on packet
         * Neither header checksum is recalculated
         */
        comp->sls_i_uncompressed++;
        return isize;
}

int
slhc_toss(struct slcompress *comp)
{
        if ( comp == NULLSLCOMPR )
                return 0;

        comp->flags |= SLF_TOSS;
        return 0;
}

#else /* CONFIG_INET */

int
slhc_toss(struct slcompress *comp)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_toss");
  return -EINVAL;
}
int
slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_uncompress");
  return -EINVAL;
}
int
slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
        unsigned char *ocp, unsigned char **cpp, int compress_cid)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_compress");
  return -EINVAL;
}

int
slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_remember");
  return -EINVAL;
}

void
slhc_free(struct slcompress *comp)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_free");
}
struct slcompress *
slhc_init(int rslots, int tslots)
{
  printk(KERN_DEBUG "Called IP function on non IP-system: slhc_init");
  return NULL;
}

#endif /* CONFIG_INET */

/* VJ header compression */
EXPORT_SYMBOL(slhc_init);
EXPORT_SYMBOL(slhc_free);
EXPORT_SYMBOL(slhc_remember);
EXPORT_SYMBOL(slhc_compress);
EXPORT_SYMBOL(slhc_uncompress);
EXPORT_SYMBOL(slhc_toss);

MODULE_LICENSE("Dual BSD/GPL");