/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1989, 1993, 1994
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)slcompress.c 8.2 (Berkeley) 4/16/94
* $FreeBSD$
*/
/*
* Routines to compress and uncompess tcp packets (for transmission
* over low speed serial lines.
*
* Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
* - Initial distribution.
*
*/
#include <sys/param.h>
#include <sys/mbuf.h>
#include <sys/systm.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <net/slcompress.h>
#ifndef SL_NO_STATS
#define INCR(counter) ++comp->counter;
#else
#define INCR(counter)
#endif
#define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n))
#define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
void
sl_compress_init(struct slcompress *comp, int max_state)
{
u_int i;
struct cstate *tstate = comp->tstate;
if (max_state == -1) {
max_state = MAX_STATES - 1;
bzero((char *)comp, sizeof(*comp));
} else {
/* Don't reset statistics */
bzero((char *)comp->tstate, sizeof(comp->tstate));
bzero((char *)comp->rstate, sizeof(comp->rstate));
}
for (i = max_state; i > 0; --i) {
tstate[i].cs_id = i;
tstate[i].cs_next = &tstate[i - 1];
}
tstate[0].cs_next = &tstate[max_state];
tstate[0].cs_id = 0;
comp->last_cs = &tstate[0];
comp->last_recv = 255;
comp->last_xmit = 255;
comp->flags = SLF_TOSS;
}
/* ENCODE encodes a number that is known to be non-zero. ENCODEZ
* checks for zero (since zero has to be encoded in the long, 3 byte
* form).
*/
#define ENCODE(n) { \
if ((u_int16_t)(n) >= 256) { \
*cp++ = 0; \
cp[1] = (n); \
cp[0] = (n) >> 8; \
cp += 2; \
} else { \
*cp++ = (n); \
} \
}
#define ENCODEZ(n) { \
if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
*cp++ = 0; \
cp[1] = (n); \
cp[0] = (n) >> 8; \
cp += 2; \
} else { \
*cp++ = (n); \
} \
}
#define DECODEL(f) { \
if (*cp == 0) {\
(f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
cp += 3; \
} else { \
(f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
} \
}
#define DECODES(f) { \
if (*cp == 0) {\
(f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
cp += 3; \
} else { \
(f) = htons(ntohs(f) + (u_int32_t)*cp++); \
} \
}
#define DECODEU(f) { \
if (*cp == 0) {\
(f) = htons((cp[1] << 8) | cp[2]); \
cp += 3; \
} else { \
(f) = htons((u_int32_t)*cp++); \
} \
}
/*
* Attempt to compress an outgoing TCP packet and return the type of
* the result. The caller must have already verified that the protocol
* is TCP. The first mbuf must contain the complete IP and TCP headers,
* and "ip" must be == mtod(m, struct ip *). "comp" supplies the
* compression state, and "compress_cid" tells us whether it is OK
* to leave out the CID field when feasible.
*
* The caller is responsible for adjusting m->m_pkthdr.len upon return,
* if m is an M_PKTHDR mbuf.
*/
u_int
sl_compress_tcp(struct mbuf *m, struct ip *ip, struct slcompress *comp,
int compress_cid)
{
struct cstate *cs = comp->last_cs->cs_next;
u_int hlen = ip->ip_hl;
struct tcphdr *oth;
struct tcphdr *th;
u_int deltaS, deltaA;
u_int changes = 0;
u_char new_seq[16];
u_char *cp = new_seq;
/*
* Bail if this is an IP fragment or if the TCP packet isn't
* `compressible' (i.e., ACK isn't set or some other control bit is
* set). (We assume that the caller has already made sure the
* packet is IP proto TCP).
*/
if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40)
return (TYPE_IP);
th = (struct tcphdr *)&((int32_t *)ip)[hlen];
if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
return (TYPE_IP);
/*
* 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. Special case the
* most recently used connection since it's most likely to be used
* again & we don't have to do any reordering if it's used.
*/
INCR(sls_packets)
if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
*(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
/*
* Wasn't the first -- search for it.
*
* States are kept in a circularly linked list with
* last_cs 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.
*/
struct cstate *lcs;
struct cstate *lastcs = comp->last_cs;
do {
lcs = cs; cs = cs->cs_next;
INCR(sls_searches)
if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
&& ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
&& *(int32_t *)th ==
((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl])
goto found;
} while (cs != lastcs);
/*
* 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
* last_cs to update the lru linkage.
*/
INCR(sls_misses)
comp->last_cs = lcs;
hlen += th->th_off;
hlen <<= 2;
if (hlen > m->m_len)
return TYPE_IP;
goto uncompressed;
found:
/*
* Found it -- move to the front on the connection list.
*/
if (cs == lastcs)
comp->last_cs = lcs;
else {
lcs->cs_next = cs->cs_next;
cs->cs_next = lastcs->cs_next;
lastcs->cs_next = cs;
}
}
/*
* Make sure that only what we expect to change changed. The first
* line of the `if' checks the IP protocol version, header length &
* type of service. The 2nd line checks the "Don't fragment" bit.
* The 3rd line checks the time-to-live and protocol (the protocol
* check is unnecessary but costless). The 4th line checks the TCP
* header length. The 5th line checks IP options, if any. The 6th
* line checks TCP options, if any. If any of these things are
* different between the previous & current datagram, we send the
* current datagram `uncompressed'.
*/
oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen];
deltaS = hlen;
hlen += th->th_off;
hlen <<= 2;
if (hlen > m->m_len)
return TYPE_IP;
if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||
((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||
((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] ||
th->th_off != oth->th_off ||
(deltaS > 5 &&
BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
(th->th_off > 5 &&
BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
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->th_flags & TH_URG) {
deltaS = ntohs(th->th_urp);
ENCODEZ(deltaS);
changes |= NEW_U;
} else if (th->th_urp != oth->th_urp)
/* 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;
deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));
if (deltaS) {
ENCODE(deltaS);
changes |= NEW_W;
}
deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
if (deltaA) {
if (deltaA > 0xffff)
goto uncompressed;
ENCODE(deltaA);
changes |= NEW_A;
}
deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
if (deltaS) {
if (deltaS > 0xffff)
goto uncompressed;
ENCODE(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->ip_len != cs->cs_ip.ip_len &&
ntohs(cs->cs_ip.ip_len) == hlen)
break;
/* FALLTHROUGH */
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.ip_len) - hlen) {
/* special case for echoed terminal traffic */
changes = SPECIAL_I;
cp = new_seq;
}
break;
case NEW_S:
if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
/* special case for data xfer */
changes = SPECIAL_D;
cp = new_seq;
}
break;
}
deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
if (deltaS != 1) {
ENCODEZ(deltaS);
changes |= NEW_I;
}
if (th->th_flags & TH_PUSH)
changes |= TCP_PUSH_BIT;
/*
* Grab the cksum before we overwrite it below. Then update our
* state with this packet's header.
*/
deltaA = ntohs(th->th_sum);
BCOPY(ip, &cs->cs_ip, hlen);
/*
* 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. hlen is how
* many bytes of the original packet to toss so subtract the two to
* get the new packet size.
*/
deltaS = cp - new_seq;
cp = (u_char *)ip;
if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
comp->last_xmit = cs->cs_id;
hlen -= deltaS + 4;
cp += hlen;
*cp++ = changes | NEW_C;
*cp++ = cs->cs_id;
} else {
hlen -= deltaS + 3;
cp += hlen;
*cp++ = changes;
}
m->m_len -= hlen;
m->m_data += hlen;
*cp++ = deltaA >> 8;
*cp++ = deltaA;
BCOPY(new_seq, cp, deltaS);
INCR(sls_compressed)
return (TYPE_COMPRESSED_TCP);
/*
* Update connection state cs & send uncompressed packet ('uncompressed'
* means a regular ip/tcp packet but with the 'conversation id' we hope
* to use on future compressed packets in the protocol field).
*/
uncompressed:
BCOPY(ip, &cs->cs_ip, hlen);
ip->ip_p = cs->cs_id;
comp->last_xmit = cs->cs_id;
return (TYPE_UNCOMPRESSED_TCP);
}
int
sl_uncompress_tcp(u_char **bufp, int len, u_int type, struct slcompress *comp)
{
u_char *hdr, *cp;
int hlen, vjlen;
cp = bufp? *bufp: NULL;
vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);
if (vjlen < 0)
return (0); /* error */
if (vjlen == 0)
return (len); /* was uncompressed already */
cp += vjlen;
len -= vjlen;
/*
* At this point, cp points to the first byte of data in the
* packet. If we're not aligned on a 4-byte boundary, copy the
* data down so the ip & tcp headers will be aligned. Then back up
* cp by the tcp/ip header length to make room for the reconstructed
* header (we assume the packet we were handed has enough space to
* prepend 128 bytes of header).
*/
if ((intptr_t)cp & 3) {
if (len > 0)
BCOPY(cp, ((intptr_t)cp &~ 3), len);
cp = (u_char *)((intptr_t)cp &~ 3);
}
cp -= hlen;
len += hlen;
BCOPY(hdr, cp, hlen);
*bufp = cp;
return (len);
}
/*
* Uncompress a packet of total length total_len. The first buflen
* bytes are at buf; this must include the entire (compressed or
* uncompressed) TCP/IP header. This procedure returns the length
* of the VJ header, with a pointer to the uncompressed IP header
* in *hdrp and its length in *hlenp.
*/
int
sl_uncompress_tcp_core(u_char *buf, int buflen, int total_len, u_int type,
struct slcompress *comp, u_char **hdrp, u_int *hlenp)
{
u_char *cp;
u_int hlen, changes;
struct tcphdr *th;
struct cstate *cs;
struct ip *ip;
u_int16_t *bp;
u_int vjlen;
switch (type) {
case TYPE_UNCOMPRESSED_TCP:
ip = (struct ip *) buf;
if (ip->ip_p >= MAX_STATES)
goto bad;
cs = &comp->rstate[comp->last_recv = ip->ip_p];
comp->flags &=~ SLF_TOSS;
ip->ip_p = IPPROTO_TCP;
/*
* Calculate the size of the TCP/IP header and make sure that
* we don't overflow the space we have available for it.
*/
hlen = ip->ip_hl << 2;
if (hlen + sizeof(struct tcphdr) > buflen)
goto bad;
hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;
if (hlen > MAX_HDR || hlen > buflen)
goto bad;
BCOPY(ip, &cs->cs_ip, hlen);
cs->cs_hlen = hlen;
INCR(sls_uncompressedin)
*hdrp = (u_char *) &cs->cs_ip;
*hlenp = hlen;
return (0);
default:
goto bad;
case TYPE_COMPRESSED_TCP:
break;
}
/* We've got a compressed packet. */
INCR(sls_compressedin)
cp = buf;
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. */
if (*cp >= MAX_STATES)
goto bad;
comp->flags &=~ SLF_TOSS;
comp->last_recv = *cp++;
} 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) {
INCR(sls_tossed)
return (-1);
}
}
cs = &comp->rstate[comp->last_recv];
hlen = cs->cs_ip.ip_hl << 2;
th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
th->th_sum = htons((*cp << 8) | cp[1]);
cp += 2;
if (changes & TCP_PUSH_BIT)
th->th_flags |= TH_PUSH;
else
th->th_flags &=~ TH_PUSH;
switch (changes & SPECIALS_MASK) {
case SPECIAL_I:
{
u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
th->th_ack = htonl(ntohl(th->th_ack) + i);
th->th_seq = htonl(ntohl(th->th_seq) + i);
}
break;
case SPECIAL_D:
th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
- cs->cs_hlen);
break;
default:
if (changes & NEW_U) {
th->th_flags |= TH_URG;
DECODEU(th->th_urp)
} else
th->th_flags &=~ TH_URG;
if (changes & NEW_W)
DECODES(th->th_win)
if (changes & NEW_A)
DECODEL(th->th_ack)
if (changes & NEW_S)
DECODEL(th->th_seq)
break;
}
if (changes & NEW_I) {
DECODES(cs->cs_ip.ip_id)
} else
cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
/*
* At this point, cp points to the first byte of data in the
* packet. Fill in the IP total length and update the IP
* header checksum.
*/
vjlen = cp - buf;
buflen -= vjlen;
if (buflen < 0)
/* we must have dropped some characters (crc should detect
* this but the old slip framing won't) */
goto bad;
total_len += cs->cs_hlen - vjlen;
cs->cs_ip.ip_len = htons(total_len);
/* recompute the ip header checksum */
bp = (u_int16_t *) &cs->cs_ip;
cs->cs_ip.ip_sum = 0;
for (changes = 0; hlen > 0; hlen -= 2)
changes += *bp++;
changes = (changes & 0xffff) + (changes >> 16);
changes = (changes & 0xffff) + (changes >> 16);
cs->cs_ip.ip_sum = ~ changes;
*hdrp = (u_char *) &cs->cs_ip;
*hlenp = cs->cs_hlen;
return vjlen;
bad:
comp->flags |= SLF_TOSS;
INCR(sls_errorin)
return (-1);
}
