slhc.c

Go to the documentation of this file.

/*
 * 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 ([email protected]), Dec 31, 1989:
 *  - Initial distribution.
 *
 *
 * modified for KA9Q Internet Software Package by
 * Katie Stevens ([email protected])
 * 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  [email protected]
 *          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 <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;

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

    if ( rslots > 0  &&  rslots < 256 ) {
        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  &&  tslots < 256 ) {
        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 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 );
}


/* 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;
        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.
     */
    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;

        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;
    /* 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");