ref: 84076e37167a9329d70104a39ea398a9f676009d
dir: /sys/src/9/ip/tcp.c/
#include "u.h"
#include "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "../port/error.h"
#include "ip.h"
enum
{
QMAX = 64*1024-1,
IP_TCPPROTO = 6,
TCP4_IPLEN = 8,
TCP4_PHDRSIZE = 12,
TCP4_HDRSIZE = 20,
TCP4_TCBPHDRSZ = 40,
TCP4_PKT = TCP4_IPLEN+TCP4_PHDRSIZE,
TCP6_IPLEN = 0,
TCP6_PHDRSIZE = 40,
TCP6_HDRSIZE = 20,
TCP6_TCBPHDRSZ = 60,
TCP6_PKT = TCP6_IPLEN+TCP6_PHDRSIZE,
TcptimerOFF = 0,
TcptimerON = 1,
TcptimerDONE = 2,
MAX_TIME = (1<<20), /* Forever */
TCP_ACK = 50, /* Timed ack sequence in ms */
MAXBACKMS = 9*60*1000, /* longest backoff time (ms) before hangup */
URG = 0x20, /* Data marked urgent */
ACK = 0x10, /* Acknowledge is valid */
PSH = 0x08, /* Whole data pipe is pushed */
RST = 0x04, /* Reset connection */
SYN = 0x02, /* Pkt. is synchronise */
FIN = 0x01, /* Start close down */
EOLOPT = 0,
NOOPOPT = 1,
MSSOPT = 2,
MSS_LENGTH = 4, /* Maximum segment size */
WSOPT = 3,
WS_LENGTH = 3, /* Bits to scale window size by */
MSL2 = 10,
MSPTICK = 50, /* Milliseconds per timer tick */
DEF_MSS = 1460, /* Default maximum segment */
DEF_MSS6 = 1220, /* Default maximum segment (min) for v6 */
DEF_RTT = 500, /* Default round trip */
DEF_KAT = 120000, /* Default time (ms) between keep alives */
TCP_LISTEN = 0, /* Listen connection */
TCP_CONNECT = 1, /* Outgoing connection */
SYNACK_RXTIMER = 250, /* ms between SYNACK retransmits */
TCPREXMTTHRESH = 3, /* dupack threshhold for rxt */
FORCE = 1,
CLONE = 2,
RETRAN = 4,
ACTIVE = 8,
SYNACK = 16,
LOGAGAIN = 3,
LOGDGAIN = 2,
Closed = 0, /* Connection states */
Listen,
Syn_sent,
Syn_received,
Established,
Finwait1,
Finwait2,
Close_wait,
Closing,
Last_ack,
Time_wait,
Maxlimbo = 1000, /* maximum procs waiting for response to SYN ACK */
NLHT = 256, /* hash table size, must be a power of 2 */
LHTMASK = NLHT-1,
/*
* window is 64kb · 2ⁿ
* these factors determine the ultimate bandwidth-delay product.
* 64kb · 2⁵ = 2mb, or 2x overkill for 100mbps · 70ms.
*/
Maxqscale = 4, /* maximum queuing scale */
Defadvscale = 4, /* default advertisement */
};
/* Must correspond to the enumeration above */
char *tcpstates[] =
{
"Closed", "Listen", "Syn_sent", "Syn_received",
"Established", "Finwait1", "Finwait2", "Close_wait",
"Closing", "Last_ack", "Time_wait"
};
typedef struct Tcptimer Tcptimer;
struct Tcptimer
{
Tcptimer *next;
Tcptimer *prev;
Tcptimer *readynext;
int state;
int start;
int count;
void (*func)(void*);
void *arg;
};
/*
* v4 and v6 pseudo headers used for
* checksuming tcp
*/
typedef struct Tcp4hdr Tcp4hdr;
struct Tcp4hdr
{
uchar vihl; /* Version and header length */
uchar tos; /* Type of service */
uchar length[2]; /* packet length */
uchar id[2]; /* Identification */
uchar frag[2]; /* Fragment information */
uchar Unused;
uchar proto;
uchar tcplen[2];
uchar tcpsrc[4];
uchar tcpdst[4];
uchar tcpsport[2];
uchar tcpdport[2];
uchar tcpseq[4];
uchar tcpack[4];
uchar tcpflag[2];
uchar tcpwin[2];
uchar tcpcksum[2];
uchar tcpurg[2];
/* Options segment */
uchar tcpopt[1];
};
typedef struct Tcp6hdr Tcp6hdr;
struct Tcp6hdr
{
uchar vcf[4];
uchar ploadlen[2];
uchar proto;
uchar ttl;
uchar tcpsrc[IPaddrlen];
uchar tcpdst[IPaddrlen];
uchar tcpsport[2];
uchar tcpdport[2];
uchar tcpseq[4];
uchar tcpack[4];
uchar tcpflag[2];
uchar tcpwin[2];
uchar tcpcksum[2];
uchar tcpurg[2];
/* Options segment */
uchar tcpopt[1];
};
/*
* this represents the control info
* for a single packet. It is derived from
* a packet in ntohtcp{4,6}() and stuck into
* a packet in htontcp{4,6}().
*/
typedef struct Tcp Tcp;
struct Tcp
{
ushort source;
ushort dest;
ulong seq;
ulong ack;
uchar flags;
uchar update;
ushort ws; /* window scale option */
ulong wnd; /* prescaled window*/
ushort urg;
ushort mss; /* max segment size option (if not zero) */
ushort len; /* size of data */
};
/*
* this header is malloc'd to thread together fragments
* waiting to be coalesced
*/
typedef struct Reseq Reseq;
struct Reseq
{
Reseq *next;
Tcp seg;
Block *bp;
ushort length;
};
/*
* the qlock in the Conv locks this structure
*/
typedef struct Tcpctl Tcpctl;
struct Tcpctl
{
uchar state; /* Connection state */
uchar type; /* Listening or active connection */
uchar code; /* Icmp code */
struct {
ulong una; /* Unacked data pointer */
ulong nxt; /* Next sequence expected */
ulong ptr; /* Data pointer */
ulong wnd; /* Tcp send window */
ulong urg; /* Urgent data pointer */
ulong wl2;
uint scale; /* how much to right shift window in xmitted packets */
/* to implement tahoe and reno TCP */
ulong dupacks; /* number of duplicate acks rcvd */
ulong partialack;
int recovery; /* loss recovery flag */
int retransmit; /* retransmit 1 packet @ una flag */
int rto;
ulong rxt; /* right window marker for recovery "recover" rfc3782 */
} snd;
struct {
ulong nxt; /* Receive pointer to next uchar slot */
ulong wnd; /* Receive window incoming */
ulong wsnt; /* Last wptr sent. important to track for large bdp */
ulong wptr;
ulong urg; /* Urgent pointer */
ulong ackptr; /* last acked sequence */
int blocked;
uint scale; /* how much to left shift window in rcv'd packets */
} rcv;
ulong iss; /* Initial sequence number */
ulong cwind; /* Congestion window */
ulong abcbytes; /* appropriate byte counting rfc 3465 */
uint scale; /* desired snd.scale */
ulong ssthresh; /* Slow start threshold */
int resent; /* Bytes just resent */
int irs; /* Initial received squence */
ushort mss; /* Maximum segment size */
int rerecv; /* Overlap of data rerecevived */
ulong window; /* Our receive window (queue) */
uint qscale; /* Log2 of our receive window (queue) */
uchar backoff; /* Exponential backoff counter */
int backedoff; /* ms we've backed off for rexmits */
uchar flags; /* State flags */
Reseq *reseq; /* Resequencing queue */
int nreseq;
int reseqlen;
Tcptimer timer; /* Activity timer */
Tcptimer acktimer; /* Acknowledge timer */
Tcptimer rtt_timer; /* Round trip timer */
Tcptimer katimer; /* keep alive timer */
ulong rttseq; /* Round trip sequence */
int srtt; /* Smoothed round trip */
int mdev; /* Mean deviation of round trip */
int kacounter; /* count down for keep alive */
uint sndsyntime; /* time syn sent */
ulong time; /* time Finwait2 or Syn_received was sent */
ulong timeuna; /* snd.una when time was set */
int nochecksum; /* non-zero means don't send checksums */
int flgcnt; /* number of flags in the sequence (FIN,SEQ) */
union {
Tcp4hdr tcp4hdr;
Tcp6hdr tcp6hdr;
} protohdr; /* prototype header */
};
/*
* New calls are put in limbo rather than having a conversation structure
* allocated. Thus, a SYN attack results in lots of limbo'd calls but not
* any real Conv structures mucking things up. Calls in limbo rexmit their
* SYN ACK every SYNACK_RXTIMER ms up to 4 times, i.e., they disappear after 1 second.
*
* In particular they aren't on a listener's queue so that they don't figure
* in the input queue limit.
*
* If 1/2 of a T3 was attacking SYN packets, we'ld have a permanent queue
* of 70000 limbo'd calls. Not great for a linear list but doable. Therefore
* there is no hashing of this list.
*/
typedef struct Limbo Limbo;
struct Limbo
{
Limbo *next;
uchar laddr[IPaddrlen];
uchar raddr[IPaddrlen];
ushort lport;
ushort rport;
ulong irs; /* initial received sequence */
ulong iss; /* initial sent sequence */
ushort mss; /* mss from the other end */
ushort rcvscale; /* how much to scale rcvd windows */
ushort sndscale; /* how much to scale sent windows */
ulong lastsend; /* last time we sent a synack */
uchar version; /* v4 or v6 */
uchar rexmits; /* number of retransmissions */
};
int tcp_irtt = DEF_RTT; /* Initial guess at round trip time */
enum {
/* MIB stats */
MaxConn,
Mss,
ActiveOpens,
PassiveOpens,
EstabResets,
CurrEstab,
InSegs,
OutSegs,
RetransSegs,
RetransSegsSent,
RetransTimeouts,
InErrs,
OutRsts,
/* non-MIB stats */
CsumErrs,
HlenErrs,
LenErrs,
Resequenced,
OutOfOrder,
ReseqBytelim,
ReseqPktlim,
Delayack,
Wopenack,
Recovery,
RecoveryDone,
RecoveryRTO,
RecoveryNoSeq,
RecoveryCwind,
RecoveryPA,
Nstats
};
static char *statnames[Nstats] =
{
[MaxConn] "MaxConn",
[Mss] "MaxSegment",
[ActiveOpens] "ActiveOpens",
[PassiveOpens] "PassiveOpens",
[EstabResets] "EstabResets",
[CurrEstab] "CurrEstab",
[InSegs] "InSegs",
[OutSegs] "OutSegs",
[RetransSegs] "RetransSegs",
[RetransSegsSent] "RetransSegsSent",
[RetransTimeouts] "RetransTimeouts",
[InErrs] "InErrs",
[OutRsts] "OutRsts",
[CsumErrs] "CsumErrs",
[HlenErrs] "HlenErrs",
[LenErrs] "LenErrs",
[OutOfOrder] "OutOfOrder",
[Resequenced] "Resequenced",
[ReseqBytelim] "ReseqBytelim",
[ReseqPktlim] "ReseqPktlim",
[Delayack] "Delayack",
[Wopenack] "Wopenack",
[Recovery] "Recovery",
[RecoveryDone] "RecoveryDone",
[RecoveryRTO] "RecoveryRTO",
[RecoveryNoSeq] "RecoveryNoSeq",
[RecoveryCwind] "RecoveryCwind",
[RecoveryPA] "RecoveryPA",
};
typedef struct Tcppriv Tcppriv;
struct Tcppriv
{
/* List of active timers */
QLock tl;
Tcptimer *timers;
/* hash table for matching conversations */
Ipht ht;
/* calls in limbo waiting for an ACK to our SYN ACK */
int nlimbo;
Limbo *lht[NLHT];
/* for keeping track of tcpackproc */
QLock apl;
int ackprocstarted;
uvlong stats[Nstats];
};
/*
* Setting tcpporthogdefense to non-zero enables Dong Lin's
* solution to hijacked systems staking out port's as a form
* of DoS attack.
*
* To avoid stateless Conv hogs, we pick a sequence number at random. If
* that number gets acked by the other end, we shut down the connection.
* Look for tcpporthogdefense in the code.
*/
int tcpporthogdefense = 0;
static int addreseq(Fs*, Tcpctl*, Tcppriv*, Tcp*, Block*, ushort);
static int dumpreseq(Tcpctl*);
static void getreseq(Tcpctl*, Tcp*, Block**, ushort*);
static void limbo(Conv*, uchar*, uchar*, Tcp*, int);
static void limborexmit(Proto*);
static void localclose(Conv*, char*);
static void procsyn(Conv*, Tcp*);
static void tcpacktimer(void*);
static void tcpiput(Proto*, Ipifc*, Block*);
static void tcpkeepalive(void*);
static void tcpoutput(Conv*);
static void tcprcvwin(Conv*);
static void tcprxmit(Conv*);
static void tcpsetkacounter(Tcpctl*);
static void tcpsetscale(Conv*, Tcpctl*, ushort, ushort);
static void tcpsettimer(Tcpctl*);
static void tcpsndsyn(Conv*, Tcpctl*);
static void tcpstart(Conv*, int);
static void tcpsynackrtt(Conv*);
static void tcptimeout(void*);
static int tcptrim(Tcpctl*, Tcp*, Block**, ushort*);
static void
tcpsetstate(Conv *s, uchar newstate)
{
Tcpctl *tcb;
uchar oldstate;
Tcppriv *tpriv;
tpriv = s->p->priv;
tcb = (Tcpctl*)s->ptcl;
oldstate = tcb->state;
if(oldstate == newstate)
return;
if(oldstate == Established)
tpriv->stats[CurrEstab]--;
if(newstate == Established)
tpriv->stats[CurrEstab]++;
switch(newstate) {
case Closed:
qclose(s->rq);
qclose(s->wq);
qclose(s->eq);
break;
case Close_wait: /* Remote closes */
qhangup(s->rq, nil);
break;
}
tcb->state = newstate;
if(oldstate == Syn_sent && newstate != Closed)
Fsconnected(s, nil);
}
static char*
tcpconnect(Conv *c, char **argv, int argc)
{
char *e;
Tcpctl *tcb;
tcb = (Tcpctl*)(c->ptcl);
if(tcb->state != Closed)
return Econinuse;
e = Fsstdconnect(c, argv, argc);
if(e != nil)
return e;
tcpstart(c, TCP_CONNECT);
return nil;
}
static int
tcpstate(Conv *c, char *state, int n)
{
Tcpctl *s;
s = (Tcpctl*)(c->ptcl);
return snprint(state, n,
"%s qin %d qout %d rq %d.%d srtt %d mdev %d sst %lud cwin %lud swin %lud>>%d rwin %lud>>%d qscale %d timer.start %d timer.count %d rerecv %d katimer.start %d katimer.count %d\n",
tcpstates[s->state],
c->rq ? qlen(c->rq) : 0,
c->wq ? qlen(c->wq) : 0,
s->nreseq, s->reseqlen,
s->srtt, s->mdev, s->ssthresh,
s->cwind, s->snd.wnd, s->snd.scale, s->rcv.wnd, s->rcv.scale,
s->qscale,
s->timer.start, s->timer.count, s->rerecv,
s->katimer.start, s->katimer.count);
}
static int
tcpinuse(Conv *c)
{
Tcpctl *s;
s = (Tcpctl*)(c->ptcl);
return s->state != Closed;
}
static char*
tcpannounce(Conv *c, char **argv, int argc)
{
char *e;
Tcpctl *tcb;
tcb = (Tcpctl*)(c->ptcl);
if(tcb->state != Closed)
return Econinuse;
e = Fsstdannounce(c, argv, argc);
if(e != nil)
return e;
tcpstart(c, TCP_LISTEN);
Fsconnected(c, nil);
return nil;
}
/*
* tcpclose is always called with the q locked
*/
static void
tcpclose(Conv *c)
{
Tcpctl *tcb;
tcb = (Tcpctl*)c->ptcl;
qhangup(c->rq, nil);
qhangup(c->wq, nil);
qhangup(c->eq, nil);
qflush(c->rq);
switch(tcb->state) {
case Listen:
/*
* reset any incoming calls to this listener
*/
Fsconnected(c, "Hangup");
localclose(c, nil);
break;
case Closed:
case Syn_sent:
localclose(c, nil);
break;
case Syn_received:
case Established:
tcb->flgcnt++;
tcb->snd.nxt++;
tcpsetstate(c, Finwait1);
tcpoutput(c);
break;
case Close_wait:
tcb->flgcnt++;
tcb->snd.nxt++;
tcpsetstate(c, Last_ack);
tcpoutput(c);
break;
}
}
static void
tcpkick(void *x)
{
Conv *s = x;
Tcpctl *tcb;
tcb = (Tcpctl*)s->ptcl;
if(waserror()){
qunlock(s);
nexterror();
}
qlock(s);
switch(tcb->state) {
case Syn_sent:
case Syn_received:
case Established:
case Close_wait:
/*
* Push data
*/
tcpoutput(s);
break;
default:
localclose(s, "Hangup");
break;
}
qunlock(s);
poperror();
}
static int seq_lt(ulong, ulong);
static void
tcprcvwin(Conv *s) /* Call with tcb locked */
{
int w;
Tcpctl *tcb;
tcb = (Tcpctl*)s->ptcl;
w = tcb->window - qlen(s->rq);
if(w < 0)
w = 0;
/* RFC 1122 § 4.2.2.17 do not move right edge of window left */
if(seq_lt(tcb->rcv.nxt + w, tcb->rcv.wptr))
w = tcb->rcv.wptr - tcb->rcv.nxt;
if(w != tcb->rcv.wnd)
if(w>>tcb->rcv.scale == 0 || tcb->window > 4*tcb->mss && w < tcb->mss/4){
tcb->rcv.blocked = 1;
netlog(s->p->f, Logtcp, "tcprcvwin: window %lud qlen %d ws %ud lport %d\n",
tcb->window, qlen(s->rq), tcb->rcv.scale, s->lport);
}
tcb->rcv.wnd = w;
tcb->rcv.wptr = tcb->rcv.nxt + w;
}
static void
tcpacktimer(void *v)
{
Tcpctl *tcb;
Conv *s;
s = v;
tcb = (Tcpctl*)s->ptcl;
if(waserror()){
qunlock(s);
nexterror();
}
qlock(s);
if(tcb->state != Closed){
tcb->flags |= FORCE;
tcpoutput(s);
}
qunlock(s);
poperror();
}
static void
tcpcongestion(Tcpctl *tcb)
{
ulong inflight;
inflight = tcb->snd.nxt - tcb->snd.una;
if(inflight > tcb->cwind)
inflight = tcb->cwind;
tcb->ssthresh = inflight / 2;
if(tcb->ssthresh < 2*tcb->mss)
tcb->ssthresh = 2*tcb->mss;
}
enum {
L = 2, /* aggressive slow start; legal values ∈ (1.0, 2.0) */
};
static void
tcpabcincr(Tcpctl *tcb, uint acked)
{
uint limit;
tcb->abcbytes += acked;
if(tcb->cwind < tcb->ssthresh){
/* slow start */
if(tcb->snd.rto)
limit = 1*tcb->mss;
else
limit = L*tcb->mss;
tcb->cwind += MIN(tcb->abcbytes, limit);
tcb->abcbytes = 0;
}
else{
tcb->snd.rto = 0;
/* avoidance */
if(tcb->abcbytes >= tcb->cwind){
tcb->abcbytes -= tcb->cwind;
tcb->cwind += tcb->mss;
}
}
}
static void
tcpcreate(Conv *c)
{
c->rq = qopen(QMAX, Qcoalesce, tcpacktimer, c);
c->wq = qopen(QMAX, Qkick, tcpkick, c);
}
static void
timerstate(Tcppriv *priv, Tcptimer *t, int newstate)
{
if(newstate != TcptimerON){
if(t->state == TcptimerON){
/* unchain */
if(priv->timers == t){
priv->timers = t->next;
if(t->prev != nil)
panic("timerstate1");
}
if(t->next)
t->next->prev = t->prev;
if(t->prev)
t->prev->next = t->next;
t->next = t->prev = nil;
}
} else {
if(t->state != TcptimerON){
/* chain */
if(t->prev != nil || t->next != nil)
panic("timerstate2");
t->prev = nil;
t->next = priv->timers;
if(t->next)
t->next->prev = t;
priv->timers = t;
}
}
t->state = newstate;
}
static void
tcpackproc(void *a)
{
Tcptimer *t, *tp, *timeo;
Proto *tcp;
Tcppriv *priv;
int loop;
tcp = a;
priv = tcp->priv;
while(waserror())
;
for(;;) {
tsleep(&up->sleep, return0, 0, MSPTICK);
qlock(&priv->tl);
timeo = nil;
loop = 0;
for(t = priv->timers; t != nil; t = tp) {
if(loop++ > 10000)
panic("tcpackproc1");
tp = t->next;
if(t->state == TcptimerON) {
t->count--;
if(t->count == 0) {
timerstate(priv, t, TcptimerDONE);
t->readynext = timeo;
timeo = t;
}
}
}
qunlock(&priv->tl);
loop = 0;
for(t = timeo; t != nil; t = t->readynext) {
if(loop++ > 10000)
panic("tcpackproc2");
if(t->state == TcptimerDONE && t->func != nil && !waserror()){
(*t->func)(t->arg);
poperror();
}
}
limborexmit(tcp);
}
}
static void
tcpgo(Tcppriv *priv, Tcptimer *t)
{
if(t == nil || t->start == 0)
return;
qlock(&priv->tl);
t->count = t->start;
timerstate(priv, t, TcptimerON);
qunlock(&priv->tl);
}
static void
tcphalt(Tcppriv *priv, Tcptimer *t)
{
if(t == nil)
return;
qlock(&priv->tl);
timerstate(priv, t, TcptimerOFF);
qunlock(&priv->tl);
}
static int
backoff(int n)
{
return 1 << n;
}
static void
localclose(Conv *s, char *reason) /* called with tcb locked */
{
Tcpctl *tcb;
Tcppriv *tpriv;
tpriv = s->p->priv;
tcb = (Tcpctl*)s->ptcl;
iphtrem(&tpriv->ht, s);
tcphalt(tpriv, &tcb->timer);
tcphalt(tpriv, &tcb->rtt_timer);
tcphalt(tpriv, &tcb->acktimer);
tcphalt(tpriv, &tcb->katimer);
/* Flush reassembly queue; nothing more can arrive */
dumpreseq(tcb);
if(tcb->state == Syn_sent)
Fsconnected(s, reason);
if(s->state == Announced)
wakeup(&s->listenr);
qhangup(s->rq, reason);
qhangup(s->wq, reason);
tcpsetstate(s, Closed);
}
/* mtu (- TCP + IP hdr len) of 1st hop */
static int
tcpmtu(Route *r, int version, uint *scale)
{
Ipifc *ifc;
int mtu;
/*
* set the ws. it doesn't commit us to anything.
* ws is the ultimate limit to the bandwidth-delay product.
*/
*scale = Defadvscale;
/*
* currently we do not implement path MTU discovery
* so use interface MTU *only* if directly reachable
* or when we use V4 which allows routers to fragment.
* otherwise, we use the default MSS which assumes a
* safe minimum MTU of 1280 bytes for V6.
*/
if(r != nil && (ifc = r->ifc) != nil){
mtu = ifc->maxtu - ifc->m->hsize;
if(version == V4)
return mtu - (TCP4_PKT + TCP4_HDRSIZE);
mtu -= TCP6_PKT + TCP6_HDRSIZE;
if((r->type & (Rifc|Runi)) != 0 || mtu <= DEF_MSS6)
return mtu;
}
if(version == V6)
return DEF_MSS6;
else
return DEF_MSS;
}
static void
inittcpctl(Conv *s, int mode)
{
Tcpctl *tcb;
Tcp4hdr* h4;
Tcp6hdr* h6;
Tcppriv *tpriv;
int mss;
tcb = (Tcpctl*)s->ptcl;
memset(tcb, 0, sizeof(Tcpctl));
tcb->ssthresh = QMAX; /* reset by tcpsetscale() */
tcb->srtt = tcp_irtt<<LOGAGAIN;
tcb->mdev = 0;
/* setup timers */
tcb->timer.start = tcp_irtt / MSPTICK;
tcb->timer.func = tcptimeout;
tcb->timer.arg = s;
tcb->rtt_timer.start = MAX_TIME;
tcb->acktimer.start = TCP_ACK / MSPTICK;
tcb->acktimer.func = tcpacktimer;
tcb->acktimer.arg = s;
tcb->katimer.start = DEF_KAT / MSPTICK;
tcb->katimer.func = tcpkeepalive;
tcb->katimer.arg = s;
mss = DEF_MSS;
/* create a prototype(pseudo) header */
if(mode != TCP_LISTEN){
if(ipcmp(s->laddr, IPnoaddr) == 0)
findlocalip(s->p->f, s->laddr, s->raddr);
switch(s->ipversion){
case V4:
h4 = &tcb->protohdr.tcp4hdr;
memset(h4, 0, sizeof(*h4));
h4->proto = IP_TCPPROTO;
hnputs(h4->tcpsport, s->lport);
hnputs(h4->tcpdport, s->rport);
v6tov4(h4->tcpsrc, s->laddr);
v6tov4(h4->tcpdst, s->raddr);
break;
case V6:
h6 = &tcb->protohdr.tcp6hdr;
memset(h6, 0, sizeof(*h6));
h6->proto = IP_TCPPROTO;
hnputs(h6->tcpsport, s->lport);
hnputs(h6->tcpdport, s->rport);
ipmove(h6->tcpsrc, s->laddr);
ipmove(h6->tcpdst, s->raddr);
mss = DEF_MSS6;
break;
default:
panic("inittcpctl: version %d", s->ipversion);
}
}
tcb->mss = tcb->cwind = mss;
tcb->abcbytes = 0;
tpriv = s->p->priv;
tpriv->stats[Mss] = tcb->mss;
/* default is no window scaling */
tcpsetscale(s, tcb, 0, 0);
}
/*
* called with s qlocked
*/
static void
tcpstart(Conv *s, int mode)
{
Tcpctl *tcb;
Tcppriv *tpriv;
char kpname[KNAMELEN];
tpriv = s->p->priv;
if(tpriv->ackprocstarted == 0){
qlock(&tpriv->apl);
if(tpriv->ackprocstarted == 0){
snprint(kpname, sizeof(kpname), "#I%dtcpack", s->p->f->dev);
kproc(kpname, tcpackproc, s->p);
tpriv->ackprocstarted = 1;
}
qunlock(&tpriv->apl);
}
tcb = (Tcpctl*)s->ptcl;
inittcpctl(s, mode);
iphtadd(&tpriv->ht, s);
switch(mode) {
case TCP_LISTEN:
tpriv->stats[PassiveOpens]++;
tcb->flags |= CLONE;
tcpsetstate(s, Listen);
break;
case TCP_CONNECT:
tpriv->stats[ActiveOpens]++;
tcb->flags |= ACTIVE;
tcpsndsyn(s, tcb);
tcpsetstate(s, Syn_sent);
tcpoutput(s);
break;
}
}
static char*
tcpflag(char *buf, char *e, ushort flag)
{
char *p;
p = seprint(buf, e, "%d", flag>>10); /* Head len */
if(flag & URG)
p = seprint(p, e, " URG");
if(flag & ACK)
p = seprint(p, e, " ACK");
if(flag & PSH)
p = seprint(p, e, " PSH");
if(flag & RST)
p = seprint(p, e, " RST");
if(flag & SYN)
p = seprint(p, e, " SYN");
if(flag & FIN)
p = seprint(p, e, " FIN");
USED(p);
return buf;
}
static Block*
htontcp6(Tcp *tcph, Block *data, Tcp6hdr *ph, Tcpctl *tcb)
{
int dlen;
Tcp6hdr *h;
ushort csum;
ushort hdrlen, optpad = 0;
uchar *opt;
hdrlen = TCP6_HDRSIZE;
if(tcph->flags & SYN){
if(tcph->mss)
hdrlen += MSS_LENGTH;
if(tcph->ws)
hdrlen += WS_LENGTH;
optpad = hdrlen & 3;
if(optpad)
optpad = 4 - optpad;
hdrlen += optpad;
}
if(data) {
dlen = blocklen(data);
data = padblock(data, hdrlen + TCP6_PKT);
}
else {
dlen = 0;
data = allocb(hdrlen + TCP6_PKT + 64); /* the 64 pad is to meet mintu's */
data->wp += hdrlen + TCP6_PKT;
}
/* copy in pseudo ip header plus port numbers */
h = (Tcp6hdr *)(data->rp);
memmove(h, ph, TCP6_TCBPHDRSZ);
/* compose pseudo tcp header, do cksum calculation */
hnputl(h->vcf, hdrlen + dlen);
h->ploadlen[0] = h->ploadlen[1] = h->proto = 0;
h->ttl = ph->proto;
/* copy in variable bits */
hnputl(h->tcpseq, tcph->seq);
hnputl(h->tcpack, tcph->ack);
hnputs(h->tcpflag, (hdrlen<<10) | tcph->flags);
hnputs(h->tcpwin, tcph->wnd>>(tcb != nil ? tcb->snd.scale : 0));
hnputs(h->tcpurg, tcph->urg);
if(tcph->flags & SYN){
opt = h->tcpopt;
if(tcph->mss != 0){
*opt++ = MSSOPT;
*opt++ = MSS_LENGTH;
hnputs(opt, tcph->mss);
opt += 2;
}
if(tcph->ws != 0){
*opt++ = WSOPT;
*opt++ = WS_LENGTH;
*opt++ = tcph->ws;
}
while(optpad-- > 0)
*opt++ = NOOPOPT;
}
if(tcb != nil && tcb->nochecksum){
h->tcpcksum[0] = h->tcpcksum[1] = 0;
} else {
csum = ptclcsum(data, TCP6_IPLEN, hdrlen+dlen+TCP6_PHDRSIZE);
hnputs(h->tcpcksum, csum);
}
/* move from pseudo header back to normal ip header */
memset(h->vcf, 0, 4);
h->vcf[0] = IP_VER6;
hnputs(h->ploadlen, hdrlen+dlen);
h->proto = ph->proto;
return data;
}
static Block*
htontcp4(Tcp *tcph, Block *data, Tcp4hdr *ph, Tcpctl *tcb)
{
int dlen;
Tcp4hdr *h;
ushort csum;
ushort hdrlen, optpad = 0;
uchar *opt;
hdrlen = TCP4_HDRSIZE;
if(tcph->flags & SYN){
if(tcph->mss)
hdrlen += MSS_LENGTH;
if(1)
hdrlen += WS_LENGTH;
optpad = hdrlen & 3;
if(optpad)
optpad = 4 - optpad;
hdrlen += optpad;
}
if(data) {
dlen = blocklen(data);
data = padblock(data, hdrlen + TCP4_PKT);
}
else {
dlen = 0;
data = allocb(hdrlen + TCP4_PKT + 64); /* the 64 pad is to meet mintu's */
data->wp += hdrlen + TCP4_PKT;
}
/* copy in pseudo ip header plus port numbers */
h = (Tcp4hdr *)(data->rp);
memmove(h, ph, TCP4_TCBPHDRSZ);
/* copy in variable bits */
hnputs(h->tcplen, hdrlen + dlen);
hnputl(h->tcpseq, tcph->seq);
hnputl(h->tcpack, tcph->ack);
hnputs(h->tcpflag, (hdrlen<<10) | tcph->flags);
hnputs(h->tcpwin, tcph->wnd>>(tcb != nil ? tcb->snd.scale : 0));
hnputs(h->tcpurg, tcph->urg);
if(tcph->flags & SYN){
opt = h->tcpopt;
if(tcph->mss != 0){
*opt++ = MSSOPT;
*opt++ = MSS_LENGTH;
hnputs(opt, tcph->mss);
opt += 2;
}
/* always offer. rfc1323 §2.2 */
if(1){
*opt++ = WSOPT;
*opt++ = WS_LENGTH;
*opt++ = tcph->ws;
}
while(optpad-- > 0)
*opt++ = NOOPOPT;
}
if(tcb != nil && tcb->nochecksum){
h->tcpcksum[0] = h->tcpcksum[1] = 0;
} else {
csum = ptclcsum(data, TCP4_IPLEN, hdrlen+dlen+TCP4_PHDRSIZE);
hnputs(h->tcpcksum, csum);
}
return data;
}
static int
ntohtcp6(Tcp *tcph, Block **bpp)
{
Tcp6hdr *h;
uchar *optr;
ushort hdrlen;
ushort optlen;
int n;
*bpp = pullupblock(*bpp, TCP6_PKT+TCP6_HDRSIZE);
if(*bpp == nil)
return -1;
h = (Tcp6hdr *)((*bpp)->rp);
tcph->source = nhgets(h->tcpsport);
tcph->dest = nhgets(h->tcpdport);
tcph->seq = nhgetl(h->tcpseq);
tcph->ack = nhgetl(h->tcpack);
hdrlen = (h->tcpflag[0]>>2) & ~3;
if(hdrlen < TCP6_HDRSIZE) {
freeblist(*bpp);
return -1;
}
tcph->flags = h->tcpflag[1];
tcph->wnd = nhgets(h->tcpwin);
tcph->urg = nhgets(h->tcpurg);
tcph->mss = 0;
tcph->ws = 0;
tcph->update = 0;
tcph->len = nhgets(h->ploadlen) - hdrlen;
*bpp = pullupblock(*bpp, hdrlen+TCP6_PKT);
if(*bpp == nil)
return -1;
optr = h->tcpopt;
n = hdrlen - TCP6_HDRSIZE;
while(n > 0 && *optr != EOLOPT) {
if(*optr == NOOPOPT) {
n--;
optr++;
continue;
}
optlen = optr[1];
if(optlen < 2 || optlen > n)
break;
switch(*optr) {
case MSSOPT:
if(optlen == MSS_LENGTH)
tcph->mss = nhgets(optr+2);
break;
case WSOPT:
if(optlen == WS_LENGTH && *(optr+2) <= 14)
tcph->ws = *(optr+2);
break;
}
n -= optlen;
optr += optlen;
}
return hdrlen;
}
static int
ntohtcp4(Tcp *tcph, Block **bpp)
{
Tcp4hdr *h;
uchar *optr;
ushort hdrlen;
ushort optlen;
int n;
*bpp = pullupblock(*bpp, TCP4_PKT+TCP4_HDRSIZE);
if(*bpp == nil)
return -1;
h = (Tcp4hdr *)((*bpp)->rp);
tcph->source = nhgets(h->tcpsport);
tcph->dest = nhgets(h->tcpdport);
tcph->seq = nhgetl(h->tcpseq);
tcph->ack = nhgetl(h->tcpack);
hdrlen = (h->tcpflag[0]>>2) & ~3;
if(hdrlen < TCP4_HDRSIZE) {
freeblist(*bpp);
return -1;
}
tcph->flags = h->tcpflag[1];
tcph->wnd = nhgets(h->tcpwin);
tcph->urg = nhgets(h->tcpurg);
tcph->mss = 0;
tcph->ws = 0;
tcph->update = 0;
tcph->len = nhgets(h->length) - (hdrlen + TCP4_PKT);
*bpp = pullupblock(*bpp, hdrlen+TCP4_PKT);
if(*bpp == nil)
return -1;
optr = h->tcpopt;
n = hdrlen - TCP4_HDRSIZE;
while(n > 0 && *optr != EOLOPT) {
if(*optr == NOOPOPT) {
n--;
optr++;
continue;
}
optlen = optr[1];
if(optlen < 2 || optlen > n)
break;
switch(*optr) {
case MSSOPT:
if(optlen == MSS_LENGTH)
tcph->mss = nhgets(optr+2);
break;
case WSOPT:
if(optlen == WS_LENGTH && *(optr+2) <= 14)
tcph->ws = *(optr+2);
break;
}
n -= optlen;
optr += optlen;
}
return hdrlen;
}
/*
* For outgoing calls, generate an initial sequence
* number and put a SYN on the send queue
*/
static void
tcpsndsyn(Conv *s, Tcpctl *tcb)
{
Tcppriv *tpriv;
tcb->iss = (nrand(1<<16)<<16)|nrand(1<<16);
tcb->rttseq = tcb->iss;
tcb->snd.wl2 = tcb->iss;
tcb->snd.una = tcb->iss;
tcb->snd.rxt = tcb->iss;
tcb->snd.ptr = tcb->rttseq;
tcb->snd.nxt = tcb->rttseq;
tcb->flgcnt++;
tcb->flags |= FORCE;
tcb->sndsyntime = NOW;
/* set desired mss and scale */
tcb->mss = tcpmtu(v6lookup(s->p->f, s->raddr, s->laddr, s), s->ipversion, &tcb->scale);
tpriv = s->p->priv;
tpriv->stats[Mss] = tcb->mss;
}
void
sndrst(Proto *tcp, uchar *source, uchar *dest, ushort length, Tcp *seg, uchar version, char *reason)
{
Block *hbp;
uchar rflags;
Tcppriv *tpriv;
Tcp4hdr ph4;
Tcp6hdr ph6;
netlog(tcp->f, Logtcp, "sndrst: %s\n", reason);
tpriv = tcp->priv;
if(seg->flags & RST)
return;
/* make pseudo header */
switch(version) {
case V4:
memset(&ph4, 0, sizeof(ph4));
ph4.vihl = IP_VER4;
v6tov4(ph4.tcpsrc, dest);
v6tov4(ph4.tcpdst, source);
ph4.proto = IP_TCPPROTO;
hnputs(ph4.tcplen, TCP4_HDRSIZE);
hnputs(ph4.tcpsport, seg->dest);
hnputs(ph4.tcpdport, seg->source);
break;
case V6:
memset(&ph6, 0, sizeof(ph6));
ph6.vcf[0] = IP_VER6;
ipmove(ph6.tcpsrc, dest);
ipmove(ph6.tcpdst, source);
ph6.proto = IP_TCPPROTO;
hnputs(ph6.ploadlen, TCP6_HDRSIZE);
hnputs(ph6.tcpsport, seg->dest);
hnputs(ph6.tcpdport, seg->source);
break;
default:
panic("sndrst: version %d", version);
}
tpriv->stats[OutRsts]++;
rflags = RST;
/* convince the other end that this reset is in band */
if(seg->flags & ACK) {
seg->seq = seg->ack;
seg->ack = 0;
}
else {
rflags |= ACK;
seg->ack = seg->seq;
seg->seq = 0;
if(seg->flags & SYN)
seg->ack++;
seg->ack += length;
if(seg->flags & FIN)
seg->ack++;
}
seg->flags = rflags;
seg->wnd = 0;
seg->urg = 0;
seg->mss = 0;
seg->ws = 0;
switch(version) {
case V4:
hbp = htontcp4(seg, nil, &ph4, nil);
if(hbp == nil)
return;
ipoput4(tcp->f, hbp, 0, MAXTTL, DFLTTOS, nil);
break;
case V6:
hbp = htontcp6(seg, nil, &ph6, nil);
if(hbp == nil)
return;
ipoput6(tcp->f, hbp, 0, MAXTTL, DFLTTOS, nil);
break;
default:
panic("sndrst2: version %d", version);
}
}
/*
* send a reset to the remote side and close the conversation
* called with s qlocked
*/
static char*
tcphangup(Conv *s)
{
Tcp seg;
Tcpctl *tcb;
Block *hbp;
tcb = (Tcpctl*)s->ptcl;
if(waserror())
return commonerror();
if(ipcmp(s->raddr, IPnoaddr) != 0) {
if(!waserror()){
memset(&seg, 0, sizeof seg);
seg.flags = RST | ACK;
seg.ack = tcb->rcv.nxt;
tcb->rcv.ackptr = seg.ack;
seg.seq = tcb->snd.ptr;
seg.wnd = 0;
seg.urg = 0;
seg.mss = 0;
seg.ws = 0;
switch(s->ipversion) {
case V4:
tcb->protohdr.tcp4hdr.vihl = IP_VER4;
hbp = htontcp4(&seg, nil, &tcb->protohdr.tcp4hdr, tcb);
ipoput4(s->p->f, hbp, 0, s->ttl, s->tos, s);
break;
case V6:
tcb->protohdr.tcp6hdr.vcf[0] = IP_VER6;
hbp = htontcp6(&seg, nil, &tcb->protohdr.tcp6hdr, tcb);
ipoput6(s->p->f, hbp, 0, s->ttl, s->tos, s);
break;
default:
panic("tcphangup: version %d", s->ipversion);
}
poperror();
}
}
localclose(s, nil);
poperror();
return nil;
}
/*
* (re)send a SYN ACK
*/
static int
sndsynack(Proto *tcp, Limbo *lp)
{
Block *hbp;
Tcp4hdr ph4;
Tcp6hdr ph6;
Tcp seg;
uint scale;
/* make pseudo header */
switch(lp->version) {
case V4:
memset(&ph4, 0, sizeof(ph4));
ph4.vihl = IP_VER4;
v6tov4(ph4.tcpsrc, lp->laddr);
v6tov4(ph4.tcpdst, lp->raddr);
ph4.proto = IP_TCPPROTO;
hnputs(ph4.tcplen, TCP4_HDRSIZE);
hnputs(ph4.tcpsport, lp->lport);
hnputs(ph4.tcpdport, lp->rport);
break;
case V6:
memset(&ph6, 0, sizeof(ph6));
ph6.vcf[0] = IP_VER6;
ipmove(ph6.tcpsrc, lp->laddr);
ipmove(ph6.tcpdst, lp->raddr);
ph6.proto = IP_TCPPROTO;
hnputs(ph6.ploadlen, TCP6_HDRSIZE);
hnputs(ph6.tcpsport, lp->lport);
hnputs(ph6.tcpdport, lp->rport);
break;
default:
panic("sndrst: version %d", lp->version);
}
memset(&seg, 0, sizeof seg);
seg.seq = lp->iss;
seg.ack = lp->irs+1;
seg.flags = SYN|ACK;
seg.urg = 0;
seg.mss = tcpmtu(v6lookup(tcp->f, lp->raddr, lp->laddr, nil), lp->version, &scale);
seg.wnd = QMAX;
/* if the other side set scale, we should too */
if(lp->rcvscale){
seg.ws = scale;
lp->sndscale = scale;
} else {
seg.ws = 0;
lp->sndscale = 0;
}
switch(lp->version) {
case V4:
hbp = htontcp4(&seg, nil, &ph4, nil);
if(hbp == nil)
return -1;
ipoput4(tcp->f, hbp, 0, MAXTTL, DFLTTOS, nil);
break;
case V6:
hbp = htontcp6(&seg, nil, &ph6, nil);
if(hbp == nil)
return -1;
ipoput6(tcp->f, hbp, 0, MAXTTL, DFLTTOS, nil);
break;
default:
panic("sndsnack: version %d", lp->version);
}
lp->lastsend = NOW;
return 0;
}
#define hashipa(a, p) ( ( (a)[IPaddrlen-2] + (a)[IPaddrlen-1] + p )&LHTMASK )
/*
* put a call into limbo and respond with a SYN ACK
*
* called with proto locked
*/
static void
limbo(Conv *s, uchar *source, uchar *dest, Tcp *seg, int version)
{
Limbo *lp, **l;
Tcppriv *tpriv;
int h;
tpriv = s->p->priv;
h = hashipa(source, seg->source);
for(l = &tpriv->lht[h]; *l != nil; l = &lp->next){
lp = *l;
if(lp->lport != seg->dest || lp->rport != seg->source || lp->version != version)
continue;
if(ipcmp(lp->raddr, source) != 0)
continue;
if(ipcmp(lp->laddr, dest) != 0)
continue;
/* each new SYN restarts the retransmits */
lp->irs = seg->seq;
break;
}
lp = *l;
if(lp == nil){
if(tpriv->nlimbo >= Maxlimbo && tpriv->lht[h]){
lp = tpriv->lht[h];
tpriv->lht[h] = lp->next;
lp->next = nil;
} else {
lp = malloc(sizeof(*lp));
if(lp == nil)
return;
tpriv->nlimbo++;
}
*l = lp;
lp->version = version;
ipmove(lp->laddr, dest);
ipmove(lp->raddr, source);
lp->lport = seg->dest;
lp->rport = seg->source;
lp->mss = seg->mss;
lp->rcvscale = seg->ws;
lp->irs = seg->seq;
lp->iss = (nrand(1<<16)<<16)|nrand(1<<16);
}
if(sndsynack(s->p, lp) < 0){
*l = lp->next;
tpriv->nlimbo--;
free(lp);
}
}
/*
* resend SYN ACK's once every SYNACK_RXTIMER ms.
*/
static void
limborexmit(Proto *tcp)
{
Tcppriv *tpriv;
Limbo **l, *lp;
int h;
int seen;
ulong now;
tpriv = tcp->priv;
if(!canqlock(tcp))
return;
seen = 0;
now = NOW;
for(h = 0; h < NLHT && seen < tpriv->nlimbo; h++){
for(l = &tpriv->lht[h]; *l != nil && seen < tpriv->nlimbo; ){
lp = *l;
seen++;
if(now - lp->lastsend < (lp->rexmits+1)*SYNACK_RXTIMER)
continue;
/* time it out after 1 second */
if(++(lp->rexmits) > 5){
tpriv->nlimbo--;
*l = lp->next;
free(lp);
continue;
}
/* if we're being attacked, don't bother resending SYN ACK's */
if(tpriv->nlimbo > 100)
continue;
if(sndsynack(tcp, lp) < 0){
tpriv->nlimbo--;
*l = lp->next;
free(lp);
continue;
}
l = &lp->next;
}
}
qunlock(tcp);
}
/*
* lookup call in limbo. if found, throw it out.
*
* called with proto locked
*/
static void
limborst(Conv *s, Tcp *segp, uchar *src, uchar *dst, uchar version)
{
Limbo *lp, **l;
int h;
Tcppriv *tpriv;
tpriv = s->p->priv;
/* find a call in limbo */
h = hashipa(src, segp->source);
for(l = &tpriv->lht[h]; *l != nil; l = &lp->next){
lp = *l;
if(lp->lport != segp->dest || lp->rport != segp->source || lp->version != version)
continue;
if(ipcmp(lp->laddr, dst) != 0)
continue;
if(ipcmp(lp->raddr, src) != 0)
continue;
/* RST can only follow the SYN */
if(segp->seq == lp->irs+1){
tpriv->nlimbo--;
*l = lp->next;
free(lp);
}
break;
}
}
static void
initialwindow(Tcpctl *tcb)
{
/* RFC 3390 initial window */
if(tcb->mss < 1095)
tcb->cwind = 4*tcb->mss;
else if(tcb->mss < 2190)
tcb->cwind = 4380;
else
tcb->cwind = 2*tcb->mss;
}
/*
* come here when we finally get an ACK to our SYN-ACK.
* lookup call in limbo. if found, create a new conversation
*
* called with proto locked
*/
static Conv*
tcpincoming(Conv *s, Tcp *segp, uchar *src, uchar *dst, uchar version)
{
Conv *new;
Tcpctl *tcb;
Tcppriv *tpriv;
Tcp4hdr *h4;
Tcp6hdr *h6;
Limbo *lp, **l;
int h;
/* unless it's just an ack, it can't be someone coming out of limbo */
if((segp->flags & SYN) || (segp->flags & ACK) == 0)
return nil;
tpriv = s->p->priv;
/* find a call in limbo */
h = hashipa(src, segp->source);
for(l = &tpriv->lht[h]; (lp = *l) != nil; l = &lp->next){
netlog(s->p->f, Logtcp, "tcpincoming s %I!%ud/%I!%ud d %I!%ud/%I!%ud v %d/%d\n",
src, segp->source, lp->raddr, lp->rport,
dst, segp->dest, lp->laddr, lp->lport,
version, lp->version
);
if(lp->lport != segp->dest || lp->rport != segp->source || lp->version != version)
continue;
if(ipcmp(lp->laddr, dst) != 0)
continue;
if(ipcmp(lp->raddr, src) != 0)
continue;
/* we're assuming no data with the initial SYN */
if(segp->seq != lp->irs+1 || segp->ack != lp->iss+1){
netlog(s->p->f, Logtcp, "tcpincoming s %lux/%lux a %lux %lux\n",
segp->seq, lp->irs+1, segp->ack, lp->iss+1);
lp = nil;
} else {
tpriv->nlimbo--;
*l = lp->next;
}
break;
}
if(lp == nil)
return nil;
new = Fsnewcall(s, src, segp->source, dst, segp->dest, version);
if(new == nil)
return nil;
memmove(new->ptcl, s->ptcl, sizeof(Tcpctl));
tcb = (Tcpctl*)new->ptcl;
tcb->flags &= ~CLONE;
tcb->timer.arg = new;
tcb->timer.state = TcptimerOFF;
tcb->acktimer.arg = new;
tcb->acktimer.state = TcptimerOFF;
tcb->katimer.arg = new;
tcb->katimer.state = TcptimerOFF;
tcb->rtt_timer.arg = new;
tcb->rtt_timer.state = TcptimerOFF;
tcb->irs = lp->irs;
tcb->rcv.nxt = tcb->irs+1;
tcb->rcv.wptr = tcb->rcv.nxt;
tcb->rcv.wsnt = 0;
tcb->rcv.urg = tcb->rcv.nxt;
tcb->iss = lp->iss;
tcb->rttseq = tcb->iss;
tcb->snd.wl2 = tcb->iss;
tcb->snd.una = tcb->iss+1;
tcb->snd.ptr = tcb->iss+1;
tcb->snd.nxt = tcb->iss+1;
tcb->snd.rxt = tcb->iss+1;
tcb->flgcnt = 0;
tcb->flags |= SYNACK;
/* set desired mss and scale */
tcb->mss = tcpmtu(v6lookup(s->p->f, src, dst, s), version, &tcb->scale);
/* our sending max segment size cannot be bigger than what he asked for */
if(lp->mss != 0 && lp->mss < tcb->mss)
tcb->mss = lp->mss;
tpriv->stats[Mss] = tcb->mss;
/* window scaling */
tcpsetscale(new, tcb, lp->rcvscale, lp->sndscale);
/* congestion window */
tcb->snd.wnd = segp->wnd;
initialwindow(tcb);
/* set initial round trip time */
tcb->sndsyntime = lp->lastsend+lp->rexmits*SYNACK_RXTIMER;
tcpsynackrtt(new);
free(lp);
/* set up proto header */
switch(version){
case V4:
h4 = &tcb->protohdr.tcp4hdr;
memset(h4, 0, sizeof(*h4));
h4->proto = IP_TCPPROTO;
hnputs(h4->tcpsport, new->lport);
hnputs(h4->tcpdport, new->rport);
v6tov4(h4->tcpsrc, dst);
v6tov4(h4->tcpdst, src);
break;
case V6:
h6 = &tcb->protohdr.tcp6hdr;
memset(h6, 0, sizeof(*h6));
h6->proto = IP_TCPPROTO;
hnputs(h6->tcpsport, new->lport);
hnputs(h6->tcpdport, new->rport);
ipmove(h6->tcpsrc, dst);
ipmove(h6->tcpdst, src);
break;
default:
panic("tcpincoming: version %d", new->ipversion);
}
tcpsetstate(new, Established);
iphtadd(&tpriv->ht, new);
return new;
}
static int
seq_within(ulong x, ulong low, ulong high)
{
if(low <= high){
if(low <= x && x <= high)
return 1;
}
else {
if(x >= low || x <= high)
return 1;
}
return 0;
}
static int
seq_lt(ulong x, ulong y)
{
return (int)(x-y) < 0;
}
static int
seq_le(ulong x, ulong y)
{
return (int)(x-y) <= 0;
}
static int
seq_gt(ulong x, ulong y)
{
return (int)(x-y) > 0;
}
static int
seq_ge(ulong x, ulong y)
{
return (int)(x-y) >= 0;
}
/*
* use the time between the first SYN and it's ack as the
* initial round trip time
*/
static void
tcpsynackrtt(Conv *s)
{
Tcpctl *tcb;
int delta;
Tcppriv *tpriv;
tcb = (Tcpctl*)s->ptcl;
tpriv = s->p->priv;
delta = NOW - tcb->sndsyntime;
tcb->srtt = delta<<LOGAGAIN;
tcb->mdev = delta<<LOGDGAIN;
/* halt round trip timer */
tcphalt(tpriv, &tcb->rtt_timer);
}
static void
update(Conv *s, Tcp *seg)
{
int rtt, delta;
Tcpctl *tcb;
ulong acked;
Tcppriv *tpriv;
if(seg->update)
return;
seg->update = 1;
tpriv = s->p->priv;
tcb = (Tcpctl*)s->ptcl;
/* catch zero-window updates, update window & recover */
if(tcb->snd.wnd == 0 && seg->wnd > 0)
if(seq_lt(seg->ack, tcb->snd.ptr)){
netlog(s->p->f, Logtcp, "tcp: zwu ack %lud una %lud ptr %lud win %lud\n",
seg->ack, tcb->snd.una, tcb->snd.ptr, seg->wnd);
tcb->snd.wnd = seg->wnd;
goto recovery;
}
/* newreno fast retransmit */
if(seg->ack == tcb->snd.una)
if(tcb->snd.una != tcb->snd.nxt)
if(++tcb->snd.dupacks == 3){
recovery:
if(tcb->snd.recovery){
tpriv->stats[RecoveryCwind]++;
tcb->cwind += tcb->mss;
}else if(seq_le(tcb->snd.rxt, seg->ack)){
tpriv->stats[Recovery]++;
tcb->abcbytes = 0;
tcb->snd.recovery = 1;
tcb->snd.partialack = 0;
tcb->snd.rxt = tcb->snd.nxt;
tcpcongestion(tcb);
tcb->cwind = tcb->ssthresh + 3*tcb->mss;
netlog(s->p->f, Logtcpwin, "recovery inflate %ld ss %ld @%lud\n",
tcb->cwind, tcb->ssthresh, tcb->snd.rxt);
tcprxmit(s);
}else{
tpriv->stats[RecoveryNoSeq]++;
netlog(s->p->f, Logtcpwin, "!recov %lud not ≤ %lud %ld\n",
tcb->snd.rxt, seg->ack, tcb->snd.rxt - seg->ack);
/* do not enter fast retransmit */
/* do not change ssthresh */
}
}else if(tcb->snd.recovery){
tpriv->stats[RecoveryCwind]++;
tcb->cwind += tcb->mss;
}
/*
* update window
*/
if(seq_gt(seg->ack, tcb->snd.wl2)
|| (tcb->snd.wl2 == seg->ack && seg->wnd > tcb->snd.wnd)){
/* clear dupack if we advance wl2 */
if(tcb->snd.wl2 != seg->ack)
tcb->snd.dupacks = 0;
tcb->snd.wnd = seg->wnd;
tcb->snd.wl2 = seg->ack;
}
if(!seq_gt(seg->ack, tcb->snd.una)){
/*
* don't let us hangup if sending into a closed window and
* we're still getting acks
*/
if((tcb->flags&RETRAN) && tcb->snd.wnd == 0)
tcb->backedoff = MAXBACKMS/4;
return;
}
/* Compute the new send window size */
acked = seg->ack - tcb->snd.una;
/* avoid slow start and timers for SYN acks */
if((tcb->flags & SYNACK) == 0) {
tcb->flags |= SYNACK;
acked--;
tcb->flgcnt--;
goto done;
}
/*
* congestion control
*/
if(tcb->snd.recovery){
if(seq_ge(seg->ack, tcb->snd.rxt)){
/* recovery finished; deflate window */
tpriv->stats[RecoveryDone]++;
tcb->snd.dupacks = 0;
tcb->snd.recovery = 0;
tcb->cwind = (tcb->snd.nxt - tcb->snd.una) + tcb->mss;
if(tcb->ssthresh < tcb->cwind)
tcb->cwind = tcb->ssthresh;
netlog(s->p->f, Logtcpwin, "recovery deflate %ld %ld\n",
tcb->cwind, tcb->ssthresh);
} else {
/* partial ack; we lost more than one segment */
tpriv->stats[RecoveryPA]++;
if(tcb->cwind > acked)
tcb->cwind -= acked;
else{
netlog(s->p->f, Logtcpwin, "partial ack neg\n");
tcb->cwind = tcb->mss;
}
netlog(s->p->f, Logtcpwin, "partial ack %ld left %ld cwind %ld\n",
acked, tcb->snd.rxt - seg->ack, tcb->cwind);
if(acked >= tcb->mss)
tcb->cwind += tcb->mss;
tcb->snd.partialack++;
}
} else
tcpabcincr(tcb, acked);
/* Adjust the timers according to the round trip time */
/* todo: fix sloppy treatment of overflow cases here. */
if(tcb->rtt_timer.state == TcptimerON && seq_ge(seg->ack, tcb->rttseq)) {
tcphalt(tpriv, &tcb->rtt_timer);
if((tcb->flags&RETRAN) == 0) {
tcb->backoff = 0;
tcb->backedoff = 0;
rtt = tcb->rtt_timer.start - tcb->rtt_timer.count;
if(rtt == 0)
rtt = 1; /* otherwise all close systems will rexmit in 0 time */
rtt *= MSPTICK;
if(tcb->srtt == 0) {
tcb->srtt = rtt << LOGAGAIN;
tcb->mdev = rtt << LOGDGAIN;
} else {
delta = rtt - (tcb->srtt>>LOGAGAIN);
tcb->srtt += delta;
if(tcb->srtt <= 0)
tcb->srtt = 1;
delta = abs(delta) - (tcb->mdev>>LOGDGAIN);
tcb->mdev += delta;
if(tcb->mdev <= 0)
tcb->mdev = 1;
}
tcpsettimer(tcb);
}
}
done:
if(qdiscard(s->wq, acked) < acked)
tcb->flgcnt--;
tcb->snd.una = seg->ack;
/* newreno fast recovery */
if(tcb->snd.recovery)
tcprxmit(s);
if(seq_gt(seg->ack, tcb->snd.urg))
tcb->snd.urg = seg->ack;
if(tcb->snd.una != tcb->snd.nxt){
/* “impatient” variant */
if(!tcb->snd.recovery || tcb->snd.partialack == 1){
tcb->time = NOW;
tcb->timeuna = tcb->snd.una;
tcpgo(tpriv, &tcb->timer);
}
}
else
tcphalt(tpriv, &tcb->timer);
if(seq_lt(tcb->snd.ptr, tcb->snd.una))
tcb->snd.ptr = tcb->snd.una;
if(!tcb->snd.recovery)
tcb->flags &= ~RETRAN;
tcb->backoff = 0;
tcb->backedoff = 0;
}
static void
tcpiput(Proto *tcp, Ipifc*, Block *bp)
{
Tcp seg;
Tcp4hdr *h4;
Tcp6hdr *h6;
int hdrlen;
Tcpctl *tcb;
ushort length, csum;
uchar source[IPaddrlen], dest[IPaddrlen];
Conv *s;
Fs *f;
Tcppriv *tpriv;
uchar version;
f = tcp->f;
tpriv = tcp->priv;
tpriv->stats[InSegs]++;
h4 = (Tcp4hdr*)(bp->rp);
h6 = (Tcp6hdr*)(bp->rp);
if((h4->vihl&0xF0)==IP_VER4) {
version = V4;
length = nhgets(h4->length);
v4tov6(dest, h4->tcpdst);
v4tov6(source, h4->tcpsrc);
h4->Unused = 0;
hnputs(h4->tcplen, length-TCP4_PKT);
if(!(bp->flag & Btcpck) && (h4->tcpcksum[0] || h4->tcpcksum[1]) &&
ptclcsum(bp, TCP4_IPLEN, length-TCP4_IPLEN)) {
tpriv->stats[CsumErrs]++;
tpriv->stats[InErrs]++;
netlog(f, Logtcp, "bad tcp proto cksum\n");
freeblist(bp);
return;
}
hdrlen = ntohtcp4(&seg, &bp);
if(hdrlen < 0){
tpriv->stats[HlenErrs]++;
tpriv->stats[InErrs]++;
netlog(f, Logtcp, "bad tcp hdr len\n");
return;
}
/* trim the packet to the size claimed by the datagram */
length -= hdrlen+TCP4_PKT;
bp = trimblock(bp, hdrlen+TCP4_PKT, length);
if(bp == nil){
tpriv->stats[LenErrs]++;
tpriv->stats[InErrs]++;
netlog(f, Logtcp, "tcp len < 0 after trim\n");
return;
}
}
else {
int ttl = h6->ttl;
int proto = h6->proto;
version = V6;
length = nhgets(h6->ploadlen);
ipmove(dest, h6->tcpdst);
ipmove(source, h6->tcpsrc);
h6->ploadlen[0] = h6->ploadlen[1] = h6->proto = 0;
h6->ttl = proto;
hnputl(h6->vcf, length);
if((h6->tcpcksum[0] || h6->tcpcksum[1]) &&
(csum = ptclcsum(bp, TCP6_IPLEN, length+TCP6_PHDRSIZE)) != 0) {
tpriv->stats[CsumErrs]++;
tpriv->stats[InErrs]++;
netlog(f, Logtcp,
"bad tcpv6 proto cksum: got %#ux, computed %#ux\n",
h6->tcpcksum[0]<<8 | h6->tcpcksum[1], csum);
freeblist(bp);
return;
}
h6->ttl = ttl;
h6->proto = proto;
hnputs(h6->ploadlen, length);
hdrlen = ntohtcp6(&seg, &bp);
if(hdrlen < 0){
tpriv->stats[HlenErrs]++;
tpriv->stats[InErrs]++;
netlog(f, Logtcp, "bad tcpv6 hdr len\n");
return;
}
/* trim the packet to the size claimed by the datagram */
length -= hdrlen;
bp = trimblock(bp, hdrlen+TCP6_PKT, length);
if(bp == nil){
tpriv->stats[LenErrs]++;
tpriv->stats[InErrs]++;
netlog(f, Logtcp, "tcpv6 len < 0 after trim\n");
return;
}
}
/* lock protocol while searching for a conversation */
qlock(tcp);
/* Look for a matching conversation */
s = iphtlook(&tpriv->ht, source, seg.source, dest, seg.dest);
if(s == nil){
netlog(f, Logtcp, "iphtlook(src %I!%d, dst %I!%d) failed\n",
source, seg.source, dest, seg.dest);
reset:
qunlock(tcp);
sndrst(tcp, source, dest, length, &seg, version, "no conversation");
freeblist(bp);
return;
}
/* if it's a listener, look for the right flags and get a new conv */
tcb = (Tcpctl*)s->ptcl;
if(tcb->state == Listen){
if(seg.flags & RST){
limborst(s, &seg, source, dest, version);
qunlock(tcp);
freeblist(bp);
return;
}
/* if this is a new SYN, put the call into limbo */
if((seg.flags & SYN) && (seg.flags & ACK) == 0){
limbo(s, source, dest, &seg, version);
qunlock(tcp);
freeblist(bp);
return;
}
/*
* if there's a matching call in limbo, tcpincoming will
* return it in state Syn_received
*/
s = tcpincoming(s, &seg, source, dest, version);
if(s == nil)
goto reset;
}
/* The rest of the input state machine is run with the control block
* locked and implements the state machine directly out of the RFC.
* Out-of-band data is ignored - it was always a bad idea.
*/
tcb = (Tcpctl*)s->ptcl;
if(waserror()){
qunlock(s);
nexterror();
}
qlock(s);
qunlock(tcp);
/* fix up window */
seg.wnd <<= tcb->rcv.scale;
/* every input packet in puts off the keep alive time out */
tcpsetkacounter(tcb);
switch(tcb->state) {
case Closed:
sndrst(tcp, source, dest, length, &seg, version, "sending to Closed");
goto raise;
case Syn_sent:
if(seg.flags & ACK) {
if(!seq_within(seg.ack, tcb->iss+1, tcb->snd.nxt)) {
sndrst(tcp, source, dest, length, &seg, version,
"bad seq in Syn_sent");
goto raise;
}
}
if(seg.flags & RST) {
if(seg.flags & ACK)
localclose(s, Econrefused);
goto raise;
}
if(seg.flags & SYN) {
procsyn(s, &seg);
if(seg.flags & ACK){
update(s, &seg);
tcpsynackrtt(s);
tcpsetstate(s, Established);
tcpsetscale(s, tcb, seg.ws, tcb->scale);
}
else {
tcb->time = NOW;
tcpsetstate(s, Syn_received); /* DLP - shouldn't this be a reset? */
}
if(length != 0 || (seg.flags & FIN))
break;
freeblist(bp);
goto output;
}
else
freeblist(bp);
qunlock(s);
poperror();
return;
case Syn_received:
/* doesn't matter if it's the correct ack, we're just trying to set timing */
if(seg.flags & ACK)
tcpsynackrtt(s);
break;
}
/*
* One DOS attack is to open connections to us and then forget about them,
* thereby tying up a conv at no long term cost to the attacker.
* This is an attempt to defeat these stateless DOS attacks. See
* corresponding code in tcpsendka().
*/
if(tcb->state != Syn_received && (seg.flags & RST) == 0){
if(tcpporthogdefense
&& seq_within(seg.ack, tcb->snd.una-(1<<31), tcb->snd.una-(1<<29))){
print("stateless hog %I.%d->%I.%d f %ux %lux - %lux - %lux\n",
source, seg.source, dest, seg.dest, seg.flags,
tcb->snd.una-(1<<31), seg.ack, tcb->snd.una-(1<<29));
localclose(s, "stateless hog");
}
}
/* Cut the data to fit the receive window */
tcprcvwin(s);
if(tcptrim(tcb, &seg, &bp, &length) == -1) {
if(seg.seq+1 != tcb->rcv.nxt || length != 1)
netlog(f, Logtcp, "tcp: trim: !inwind: seq %lud-%lud win %lud-%lud l %d from %I\n",
seg.seq, seg.seq + length - 1,
tcb->rcv.nxt, tcb->rcv.nxt + tcb->rcv.wnd-1, length, s->raddr);
update(s, &seg);
if(qlen(s->wq)+tcb->flgcnt == 0 && tcb->state == Closing) {
tcphalt(tpriv, &tcb->rtt_timer);
tcphalt(tpriv, &tcb->acktimer);
tcphalt(tpriv, &tcb->katimer);
tcpsetstate(s, Time_wait);
tcb->timer.start = MSL2*(1000 / MSPTICK);
tcpgo(tpriv, &tcb->timer);
}
if(!(seg.flags & RST)) {
tcb->flags |= FORCE;
goto output;
}
qunlock(s);
poperror();
return;
}
/* Cannot accept so answer with a rst */
if(length && tcb->state == Closed) {
sndrst(tcp, source, dest, length, &seg, version, "sending to Closed");
goto raise;
}
/* The segment is beyond the current receive pointer so
* queue the data in the resequence queue
*/
if(seg.seq != tcb->rcv.nxt)
if(length != 0 || (seg.flags & (SYN|FIN))) {
update(s, &seg);
if(addreseq(f, tcb, tpriv, &seg, bp, length) < 0)
print("reseq %I.%d -> %I.%d\n", s->raddr, s->rport, s->laddr, s->lport);
tcb->flags |= FORCE; /* force duplicate ack; RFC 5681 §3.2 */
goto output;
}
if(tcb->nreseq > 0)
tcb->flags |= FORCE; /* filled hole in sequence space; RFC 5681 §3.2 */
/*
* keep looping till we've processed this packet plus any
* adjacent packets in the resequence queue
*/
for(;;) {
if(seg.flags & RST) {
if(tcb->state == Established) {
tpriv->stats[EstabResets]++;
if(tcb->rcv.nxt != seg.seq)
print("out of order RST rcvd: %I.%d -> %I.%d, rcv.nxt %lux seq %lux\n", s->raddr, s->rport, s->laddr, s->lport, tcb->rcv.nxt, seg.seq);
}
localclose(s, Econrefused);
goto raise;
}
if((seg.flags&ACK) == 0)
goto raise;
switch(tcb->state) {
case Syn_received:
if(!seq_within(seg.ack, tcb->snd.una+1, tcb->snd.nxt)){
sndrst(tcp, source, dest, length, &seg, version,
"bad seq in Syn_received");
goto raise;
}
update(s, &seg);
tcpsetstate(s, Established);
case Established:
case Close_wait:
update(s, &seg);
break;
case Finwait1:
update(s, &seg);
if(qlen(s->wq)+tcb->flgcnt == 0){
tcphalt(tpriv, &tcb->rtt_timer);
tcphalt(tpriv, &tcb->acktimer);
tcpsetkacounter(tcb);
tcb->time = NOW;
tcpsetstate(s, Finwait2);
tcb->katimer.start = MSL2 * (1000 / MSPTICK);
tcpgo(tpriv, &tcb->katimer);
}
break;
case Finwait2:
update(s, &seg);
break;
case Closing:
update(s, &seg);
if(qlen(s->wq)+tcb->flgcnt == 0) {
tcphalt(tpriv, &tcb->rtt_timer);
tcphalt(tpriv, &tcb->acktimer);
tcphalt(tpriv, &tcb->katimer);
tcpsetstate(s, Time_wait);
tcb->timer.start = MSL2*(1000 / MSPTICK);
tcpgo(tpriv, &tcb->timer);
}
break;
case Last_ack:
update(s, &seg);
if(qlen(s->wq)+tcb->flgcnt == 0) {
localclose(s, nil);
goto raise;
}
case Time_wait:
if(seg.flags & FIN)
tcb->flags |= FORCE;
if(tcb->timer.state != TcptimerON)
tcpgo(tpriv, &tcb->timer);
}
if((seg.flags&URG) && seg.urg) {
if(seq_gt(seg.urg + seg.seq, tcb->rcv.urg)) {
tcb->rcv.urg = seg.urg + seg.seq;
pullblock(&bp, seg.urg);
}
}
else
if(seq_gt(tcb->rcv.nxt, tcb->rcv.urg))
tcb->rcv.urg = tcb->rcv.nxt;
if(length == 0) {
if(bp != nil)
freeblist(bp);
}
else {
switch(tcb->state){
default:
/* Ignore segment text */
if(bp != nil)
freeblist(bp);
break;
case Syn_received:
case Established:
case Finwait1:
/* If we still have some data place on
* receive queue
*/
if(bp) {
qpassnolim(s->rq, packblock(bp));
bp = nil;
}
tcb->rcv.nxt += length;
/*
* turn on the acktimer if there's something
* to ack
*/
if(tcb->acktimer.state != TcptimerON)
tcpgo(tpriv, &tcb->acktimer);
break;
case Finwait2:
/* no process to read the data, send a reset */
if(bp != nil)
freeblist(bp);
sndrst(tcp, source, dest, length, &seg, version,
"send to Finwait2");
qunlock(s);
poperror();
return;
}
}
if(seg.flags & FIN) {
tcb->flags |= FORCE;
switch(tcb->state) {
case Syn_received:
case Established:
tcb->rcv.nxt++;
tcpsetstate(s, Close_wait);
break;
case Finwait1:
tcb->rcv.nxt++;
if(qlen(s->wq)+tcb->flgcnt == 0) {
tcphalt(tpriv, &tcb->rtt_timer);
tcphalt(tpriv, &tcb->acktimer);
tcphalt(tpriv, &tcb->katimer);
tcpsetstate(s, Time_wait);
tcb->timer.start = MSL2*(1000/MSPTICK);
tcpgo(tpriv, &tcb->timer);
}
else
tcpsetstate(s, Closing);
break;
case Finwait2:
tcb->rcv.nxt++;
tcphalt(tpriv, &tcb->rtt_timer);
tcphalt(tpriv, &tcb->acktimer);
tcphalt(tpriv, &tcb->katimer);
tcpsetstate(s, Time_wait);
tcb->timer.start = MSL2 * (1000/MSPTICK);
tcpgo(tpriv, &tcb->timer);
break;
case Close_wait:
case Closing:
case Last_ack:
break;
case Time_wait:
tcpgo(tpriv, &tcb->timer);
break;
}
}
/*
* get next adjacent segment from the resequence queue.
* dump/trim any overlapping segments
*/
for(;;) {
if(tcb->reseq == nil)
goto output;
if(seq_ge(tcb->rcv.nxt, tcb->reseq->seg.seq) == 0)
goto output;
getreseq(tcb, &seg, &bp, &length);
tcprcvwin(s);
if(tcptrim(tcb, &seg, &bp, &length) == 0){
tcb->flags |= FORCE;
break;
}
}
}
output:
tcpoutput(s);
qunlock(s);
poperror();
return;
raise:
qunlock(s);
poperror();
freeblist(bp);
tcpkick(s);
}
/*
* always enters and exits with the s locked. We drop
* the lock to ipoput the packet so some care has to be
* taken by callers.
*/
static void
tcpoutput(Conv *s)
{
Tcp seg;
uint msgs;
Tcpctl *tcb;
Block *hbp, *bp;
int sndcnt;
ulong ssize, dsize, sent;
Fs *f;
Tcppriv *tpriv;
uchar version;
f = s->p->f;
tpriv = s->p->priv;
version = s->ipversion;
tcb = (Tcpctl*)s->ptcl;
/* force ack every 2*mss */
if((tcb->flags & FORCE) == 0)
if(tcb->rcv.nxt - tcb->rcv.ackptr >= 2*tcb->mss){
tpriv->stats[Delayack]++;
tcb->flags |= FORCE;
}
/* force ack if window opening */
if(0)
if((tcb->flags & FORCE) == 0){
tcprcvwin(s);
if((int)(tcb->rcv.wptr - tcb->rcv.wsnt) >= 2*tcb->mss){
tpriv->stats[Wopenack]++;
tcb->flags |= FORCE;
}
}
for(msgs = 0; msgs < 100; msgs++) {
switch(tcb->state) {
case Listen:
case Closed:
case Finwait2:
return;
}
/* Don't send anything else until our SYN has been acked */
if(tcb->snd.ptr != tcb->iss && (tcb->flags & SYNACK) == 0)
break;
/* force an ack when a window has opened up */
tcprcvwin(s);
if(tcb->rcv.blocked && tcb->rcv.wnd > 0){
tcb->rcv.blocked = 0;
tcb->flags |= FORCE;
}
sndcnt = qlen(s->wq)+tcb->flgcnt;
sent = tcb->snd.ptr - tcb->snd.una;
ssize = sndcnt;
if(tcb->snd.wnd == 0){
/* zero window probe */
if(sent > 0)
if(!(tcb->flags & FORCE))
break; /* already probing, rto re-probes */
if(ssize < sent)
ssize = 0;
else{
ssize -= sent;
if(ssize > 0)
ssize = 1;
}
} else {
/* calculate usable segment size */
if(ssize > tcb->cwind)
ssize = tcb->cwind;
if(ssize > tcb->snd.wnd)
ssize = tcb->snd.wnd;
if(ssize < sent)
ssize = 0;
else {
ssize -= sent;
if(ssize > tcb->mss)
ssize = tcb->mss;
}
}
dsize = ssize;
seg.urg = 0;
if(!(tcb->flags & FORCE)){
if(ssize == 0)
break;
if(ssize < tcb->mss)
if(tcb->snd.nxt == tcb->snd.ptr)
if(sent > TCPREXMTTHRESH*tcb->mss)
break;
}
tcb->flags &= ~FORCE;
/* By default we will generate an ack */
tcphalt(tpriv, &tcb->acktimer);
seg.source = s->lport;
seg.dest = s->rport;
seg.flags = ACK;
seg.mss = 0;
seg.ws = 0;
seg.update = 0;
switch(tcb->state){
case Syn_sent:
seg.flags = 0;
if(tcb->snd.ptr == tcb->iss){
seg.flags |= SYN;
dsize--;
seg.mss = tcb->mss;
seg.ws = tcb->scale;
}
break;
case Syn_received:
/*
* don't send any data with a SYN/ACK packet
* because Linux rejects the packet in its
* attempt to solve the SYN attack problem
*/
if(tcb->snd.ptr == tcb->iss){
seg.flags |= SYN;
dsize = 0;
ssize = 1;
seg.mss = tcb->mss;
seg.ws = tcb->scale;
}
break;
}
seg.seq = tcb->snd.ptr;
seg.ack = tcb->rcv.nxt;
seg.wnd = tcb->rcv.wnd;
/* Pull out data to send */
bp = nil;
if(dsize != 0) {
bp = qcopy(s->wq, dsize, sent);
if(BLEN(bp) != dsize) {
seg.flags |= FIN;
dsize--;
}
}
if(sent+dsize == sndcnt && dsize)
seg.flags |= PSH;
tcb->snd.ptr += ssize;
/* Pull up the send pointer so we can accept acks
* for this window
*/
if(seq_gt(tcb->snd.ptr,tcb->snd.nxt))
tcb->snd.nxt = tcb->snd.ptr;
/* Build header, link data and compute cksum */
switch(version){
case V4:
tcb->protohdr.tcp4hdr.vihl = IP_VER4;
hbp = htontcp4(&seg, bp, &tcb->protohdr.tcp4hdr, tcb);
if(hbp == nil) {
freeblist(bp);
return;
}
break;
case V6:
tcb->protohdr.tcp6hdr.vcf[0] = IP_VER6;
hbp = htontcp6(&seg, bp, &tcb->protohdr.tcp6hdr, tcb);
if(hbp == nil) {
freeblist(bp);
return;
}
break;
default:
hbp = nil; /* to suppress a warning */
panic("tcpoutput: version %d", version);
}
/* Start the transmission timers if there is new data and we
* expect acknowledges
*/
if(ssize != 0){
if(tcb->timer.state != TcptimerON){
tcb->time = NOW;
tcb->timeuna = tcb->snd.una;
tcpgo(tpriv, &tcb->timer);
}
/* If round trip timer isn't running, start it.
* measure the longest packet only in case the
* transmission time dominates RTT
*/
if(tcb->snd.retransmit == 0)
if(tcb->rtt_timer.state != TcptimerON)
if(ssize == tcb->mss) {
tcpgo(tpriv, &tcb->rtt_timer);
tcb->rttseq = tcb->snd.ptr;
}
}
tpriv->stats[OutSegs]++;
if(tcb->snd.retransmit)
tpriv->stats[RetransSegsSent]++;
tcb->rcv.ackptr = seg.ack;
tcb->rcv.wsnt = tcb->rcv.wptr;
/* put off the next keep alive */
tcpgo(tpriv, &tcb->katimer);
switch(version){
case V4:
if(ipoput4(f, hbp, 0, s->ttl, s->tos, s) < 0){
/* a negative return means no route */
localclose(s, "no route");
}
break;
case V6:
if(ipoput6(f, hbp, 0, s->ttl, s->tos, s) < 0){
/* a negative return means no route */
localclose(s, "no route");
}
break;
default:
panic("tcpoutput2: version %d", version);
}
if((msgs%4) == 3){
qunlock(s);
qlock(s);
}
}
}
/*
* the BSD convention (hack?) for keep alives. resend last uchar acked.
*/
static void
tcpsendka(Conv *s)
{
Tcp seg;
Tcpctl *tcb;
Block *hbp,*dbp;
tcb = (Tcpctl*)s->ptcl;
dbp = nil;
memset(&seg, 0, sizeof seg);
seg.urg = 0;
seg.source = s->lport;
seg.dest = s->rport;
seg.flags = ACK|PSH;
seg.mss = 0;
seg.ws = 0;
if(tcpporthogdefense)
seg.seq = tcb->snd.una-(1<<30)-nrand(1<<20);
else
seg.seq = tcb->snd.una-1;
seg.ack = tcb->rcv.nxt;
tcb->rcv.ackptr = seg.ack;
tcprcvwin(s);
seg.wnd = tcb->rcv.wnd;
if(tcb->state == Finwait2){
seg.flags |= FIN;
} else {
dbp = allocb(1);
dbp->wp++;
}
if(isv4(s->raddr)) {
/* Build header, link data and compute cksum */
tcb->protohdr.tcp4hdr.vihl = IP_VER4;
hbp = htontcp4(&seg, dbp, &tcb->protohdr.tcp4hdr, tcb);
if(hbp == nil) {
freeblist(dbp);
return;
}
ipoput4(s->p->f, hbp, 0, s->ttl, s->tos, s);
}
else {
/* Build header, link data and compute cksum */
tcb->protohdr.tcp6hdr.vcf[0] = IP_VER6;
hbp = htontcp6(&seg, dbp, &tcb->protohdr.tcp6hdr, tcb);
if(hbp == nil) {
freeblist(dbp);
return;
}
ipoput6(s->p->f, hbp, 0, s->ttl, s->tos, s);
}
}
/*
* set connection to time out after 12 minutes
*/
static void
tcpsetkacounter(Tcpctl *tcb)
{
tcb->kacounter = (12 * 60 * 1000) / (tcb->katimer.start*MSPTICK);
if(tcb->kacounter < 3)
tcb->kacounter = 3;
}
/*
* if we've timed out, close the connection
* otherwise, send a keepalive and restart the timer
*/
static void
tcpkeepalive(void *v)
{
Tcpctl *tcb;
Conv *s;
s = v;
tcb = (Tcpctl*)s->ptcl;
if(waserror()){
qunlock(s);
nexterror();
}
qlock(s);
if(tcb->state != Closed){
if(--(tcb->kacounter) <= 0) {
localclose(s, Etimedout);
} else {
tcpsendka(s);
tcpgo(s->p->priv, &tcb->katimer);
}
}
qunlock(s);
poperror();
}
/*
* start keepalive timer
*/
static char*
tcpstartka(Conv *s, char **f, int n)
{
Tcpctl *tcb;
int x;
tcb = (Tcpctl*)s->ptcl;
if(tcb->state != Established)
return "connection must be in Establised state";
if(n > 1){
x = atoi(f[1]);
if(x >= MSPTICK)
tcb->katimer.start = x/MSPTICK;
}
tcpsetkacounter(tcb);
tcpgo(s->p->priv, &tcb->katimer);
return nil;
}
/*
* turn checksums on/off
*/
static char*
tcpsetchecksum(Conv *s, char **f, int)
{
Tcpctl *tcb;
tcb = (Tcpctl*)s->ptcl;
tcb->nochecksum = !atoi(f[1]);
return nil;
}
/*
* retransmit (at most) one segment at snd.una.
* preserve cwind & snd.ptr
*/
static void
tcprxmit(Conv *s)
{
Tcpctl *tcb;
Tcppriv *tpriv;
ulong tcwind, tptr;
tcb = (Tcpctl*)s->ptcl;
tcb->flags |= RETRAN|FORCE;
tptr = tcb->snd.ptr;
tcwind = tcb->cwind;
tcb->snd.ptr = tcb->snd.una;
tcb->cwind = tcb->mss;
tcb->snd.retransmit = 1;
tcpoutput(s);
tcb->snd.retransmit = 0;
tcb->cwind = tcwind;
tcb->snd.ptr = tptr;
tpriv = s->p->priv;
tpriv->stats[RetransSegs]++;
}
/*
* todo: RFC 4138 F-RTO
*/
static void
tcptimeout(void *arg)
{
Conv *s;
Tcpctl *tcb;
int maxback;
Tcppriv *tpriv;
s = (Conv*)arg;
tpriv = s->p->priv;
tcb = (Tcpctl*)s->ptcl;
if(waserror()){
qunlock(s);
nexterror();
}
qlock(s);
switch(tcb->state){
default:
tcb->backoff++;
if(tcb->state == Syn_sent)
maxback = MAXBACKMS/2;
else
maxback = MAXBACKMS;
tcb->backedoff += tcb->timer.start * MSPTICK;
if(tcb->backedoff >= maxback) {
localclose(s, Etimedout);
break;
}
netlog(s->p->f, Logtcprxmt, "rxm %d/%d %ldms %lud rto %d %lud %s\n",
tcb->srtt, tcb->mdev, NOW-tcb->time,
tcb->snd.una-tcb->timeuna, tcb->snd.rto, tcb->snd.ptr,
tcpstates[s->state]);
tcpsettimer(tcb);
if(tcb->snd.rto == 0)
tcpcongestion(tcb);
tcprxmit(s);
tcb->snd.ptr = tcb->snd.una;
tcb->cwind = tcb->mss;
tcb->snd.rto = 1;
tpriv->stats[RetransTimeouts]++;
if(tcb->snd.recovery){
tcb->snd.dupacks = 0; /* reno rto */
tcb->snd.recovery = 0;
tpriv->stats[RecoveryRTO]++;
tcb->snd.rxt = tcb->snd.nxt;
netlog(s->p->f, Logtcpwin,
"rto recovery rxt @%lud\n", tcb->snd.nxt);
}
tcb->abcbytes = 0;
break;
case Time_wait:
localclose(s, nil);
break;
case Closed:
break;
}
qunlock(s);
poperror();
}
static int
inwindow(Tcpctl *tcb, int seq)
{
return seq_within(seq, tcb->rcv.nxt, tcb->rcv.nxt+tcb->rcv.wnd-1);
}
/*
* set up state for a received SYN (or SYN ACK) packet
*/
static void
procsyn(Conv *s, Tcp *seg)
{
Tcpctl *tcb;
Tcppriv *tpriv;
tcb = (Tcpctl*)s->ptcl;
tcb->flags |= FORCE;
tcb->rcv.nxt = seg->seq + 1;
tcb->rcv.wptr = tcb->rcv.nxt;
tcb->rcv.wsnt = 0;
tcb->rcv.urg = tcb->rcv.nxt;
tcb->irs = seg->seq;
/* our sending max segment size cannot be bigger than what he asked for */
if(seg->mss != 0 && seg->mss < tcb->mss) {
tcb->mss = seg->mss;
tpriv = s->p->priv;
tpriv->stats[Mss] = tcb->mss;
}
/* if the server does not support ws option, disable window scaling */
if(seg->ws == 0){
tcb->scale = 0;
tcb->snd.scale = 0;
}
tcb->snd.wnd = seg->wnd;
initialwindow(tcb);
}
static int
dumpreseq(Tcpctl *tcb)
{
Reseq *r, *next;
for(r = tcb->reseq; r != nil; r = next){
next = r->next;
freeblist(r->bp);
free(r);
}
tcb->reseq = nil;
tcb->nreseq = 0;
tcb->reseqlen = 0;
return -1;
}
static void
logreseq(Fs *f, Reseq *r, ulong n)
{
char *s;
for(; r != nil; r = r->next){
s = nil;
if(r->next == nil && r->seg.seq != n)
s = "hole/end";
else if(r->next == nil)
s = "end";
else if(r->seg.seq != n)
s = "hole";
if(s != nil)
netlog(f, Logtcp, "%s %lud-%lud (%ld) %#ux\n", s,
n, r->seg.seq, r->seg.seq-n, r->seg.flags);
n = r->seg.seq + r->seg.len;
}
}
static int
addreseq(Fs *f, Tcpctl *tcb, Tcppriv *tpriv, Tcp *seg, Block *bp, ushort length)
{
Reseq *rp, **rr;
int qmax;
rp = malloc(sizeof(Reseq));
if(rp == nil){
freeblist(bp); /* bp always consumed by addreseq */
return 0;
}
rp->seg = *seg;
rp->bp = bp;
rp->length = length;
tcb->reseqlen += length;
tcb->nreseq++;
/* Place on reassembly list sorting by starting seq number */
for(rr = &tcb->reseq;; rr = &(*rr)->next)
if(*rr == nil || seq_lt(seg->seq, (*rr)->seg.seq)){
rp->next = *rr;
*rr = rp;
tpriv->stats[Resequenced]++;
if(rp->next != nil)
tpriv->stats[OutOfOrder]++;
break;
}
qmax = tcb->window;
if(tcb->reseqlen > qmax){
netlog(f, Logtcp, "tcp: reseq: queue > window: %d > %d; %d packets\n", tcb->reseqlen, qmax, tcb->nreseq);
logreseq(f, tcb->reseq, tcb->rcv.nxt);
tpriv->stats[ReseqBytelim]++;
return dumpreseq(tcb);
}
qmax = tcb->window / tcb->mss; /* ~190 for qscale==2, 390 for qscale=3 */
if(tcb->nreseq > qmax){
netlog(f, Logtcp, "resequence queue > packets: %d %d; %d bytes\n", tcb->nreseq, qmax, tcb->reseqlen);
logreseq(f, tcb->reseq, tcb->rcv.nxt);
tpriv->stats[ReseqPktlim]++;
return dumpreseq(tcb);
}
return 0;
}
static void
getreseq(Tcpctl *tcb, Tcp *seg, Block **bp, ushort *length)
{
Reseq *rp;
rp = tcb->reseq;
if(rp == nil)
return;
tcb->reseq = rp->next;
*seg = rp->seg;
*bp = rp->bp;
*length = rp->length;
tcb->nreseq--;
tcb->reseqlen -= rp->length;
free(rp);
}
static int
tcptrim(Tcpctl *tcb, Tcp *seg, Block **bp, ushort *length)
{
ushort len;
uchar accept;
int dupcnt, excess;
accept = 0;
len = *length;
if(seg->flags & SYN)
len++;
if(seg->flags & FIN)
len++;
if(tcb->rcv.wnd == 0) {
if(len == 0 && seg->seq == tcb->rcv.nxt)
return 0;
}
else {
/* Some part of the segment should be in the window */
if(inwindow(tcb,seg->seq))
accept++;
else
if(len != 0) {
if(inwindow(tcb, seg->seq+len-1) ||
seq_within(tcb->rcv.nxt, seg->seq,seg->seq+len-1))
accept++;
}
}
if(!accept) {
freeblist(*bp);
return -1;
}
dupcnt = tcb->rcv.nxt - seg->seq;
if(dupcnt > 0){
tcb->rerecv += dupcnt;
if(seg->flags & SYN){
seg->flags &= ~SYN;
seg->seq++;
if(seg->urg > 1)
seg->urg--;
else
seg->flags &= ~URG;
dupcnt--;
}
if(dupcnt > 0){
pullblock(bp, (ushort)dupcnt);
seg->seq += dupcnt;
*length -= dupcnt;
if(seg->urg > dupcnt)
seg->urg -= dupcnt;
else {
seg->flags &= ~URG;
seg->urg = 0;
}
}
}
excess = seg->seq + *length - (tcb->rcv.nxt + tcb->rcv.wnd);
if(excess > 0) {
tcb->rerecv += excess;
*length -= excess;
*bp = trimblock(*bp, 0, *length);
if(*bp == nil)
panic("presotto is a boofhead");
seg->flags &= ~FIN;
}
return 0;
}
static void
tcpadvise(Proto *tcp, Block *bp, char *msg)
{
Tcp4hdr *h4;
Tcp6hdr *h6;
Tcpctl *tcb;
uchar source[IPaddrlen];
uchar dest[IPaddrlen];
ushort psource, pdest;
Conv *s, **p;
h4 = (Tcp4hdr*)(bp->rp);
h6 = (Tcp6hdr*)(bp->rp);
if((h4->vihl&0xF0)==IP_VER4) {
v4tov6(dest, h4->tcpdst);
v4tov6(source, h4->tcpsrc);
psource = nhgets(h4->tcpsport);
pdest = nhgets(h4->tcpdport);
} else {
ipmove(dest, h6->tcpdst);
ipmove(source, h6->tcpsrc);
psource = nhgets(h6->tcpsport);
pdest = nhgets(h6->tcpdport);
}
/* Look for a connection */
qlock(tcp);
for(p = tcp->conv; (s = *p) != nil; p++) {
tcb = (Tcpctl*)s->ptcl;
if(s->rport == pdest)
if(s->lport == psource)
if(tcb->state != Closed)
if(ipcmp(s->raddr, dest) == 0)
if(ipcmp(s->laddr, source) == 0){
if(s->ignoreadvice)
break;
qlock(s);
qunlock(tcp);
switch(tcb->state){
case Syn_sent:
localclose(s, msg);
break;
}
qunlock(s);
freeblist(bp);
return;
}
}
qunlock(tcp);
freeblist(bp);
}
static char*
tcpporthogdefensectl(char *val)
{
if(strcmp(val, "on") == 0)
tcpporthogdefense = 1;
else if(strcmp(val, "off") == 0)
tcpporthogdefense = 0;
else
return "unknown value for tcpporthogdefense";
return nil;
}
/* called with c qlocked */
static char*
tcpctl(Conv* c, char** f, int n)
{
if(n == 1 && strcmp(f[0], "close") == 0)
return tcpclose(c), nil;
if(n == 1 && strcmp(f[0], "hangup") == 0)
return tcphangup(c);
if(n >= 1 && strcmp(f[0], "keepalive") == 0)
return tcpstartka(c, f, n);
if(n >= 1 && strcmp(f[0], "checksum") == 0)
return tcpsetchecksum(c, f, n);
if(n >= 1 && strcmp(f[0], "tcpporthogdefense") == 0)
return tcpporthogdefensectl(f[1]);
return "unknown control request";
}
static int
tcpstats(Proto *tcp, char *buf, int len)
{
Tcppriv *priv;
char *p, *e;
int i;
priv = tcp->priv;
p = buf;
e = p+len;
for(i = 0; i < Nstats; i++)
p = seprint(p, e, "%s: %llud\n", statnames[i], priv->stats[i]);
return p - buf;
}
/*
* garbage collect any stale conversations:
* - SYN received but no SYN-ACK after 5 seconds (could be the SYN attack)
* - Finwait2 after 5 minutes
*
* this is called whenever we run out of channels. Both checks are
* of questionable validity so we try to use them only when we're
* up against the wall.
*/
static int
tcpgc(Proto *tcp)
{
Conv *c, **pp, **ep;
int n;
Tcpctl *tcb;
n = 0;
ep = &tcp->conv[tcp->nc];
for(pp = tcp->conv; pp < ep; pp++) {
c = *pp;
if(c == nil)
break;
if(!canqlock(c))
continue;
tcb = (Tcpctl*)c->ptcl;
switch(tcb->state){
case Syn_received:
if(NOW - tcb->time > 5000){
localclose(c, Etimedout);
n++;
}
break;
case Finwait2:
if(NOW - tcb->time > 5*60*1000){
localclose(c, Etimedout);
n++;
}
break;
}
qunlock(c);
}
return n;
}
static void
tcpsettimer(Tcpctl *tcb)
{
int x;
/* round trip dependency */
x = backoff(tcb->backoff) *
(tcb->mdev + (tcb->srtt>>LOGAGAIN) + MSPTICK) / MSPTICK;
/* bounded twixt 0.3 and 64 seconds */
if(x < 300/MSPTICK)
x = 300/MSPTICK;
else if(x > (64000/MSPTICK))
x = 64000/MSPTICK;
tcb->timer.start = x;
}
void
tcpinit(Fs *fs)
{
Proto *tcp;
Tcppriv *tpriv;
tcp = smalloc(sizeof(Proto));
tpriv = tcp->priv = smalloc(sizeof(Tcppriv));
tcp->name = "tcp";
tcp->connect = tcpconnect;
tcp->announce = tcpannounce;
tcp->ctl = tcpctl;
tcp->state = tcpstate;
tcp->create = tcpcreate;
tcp->close = tcpclose;
tcp->rcv = tcpiput;
tcp->advise = tcpadvise;
tcp->stats = tcpstats;
tcp->inuse = tcpinuse;
tcp->gc = tcpgc;
tcp->ipproto = IP_TCPPROTO;
tcp->nc = scalednconv();
tcp->ptclsize = sizeof(Tcpctl);
tpriv->stats[MaxConn] = tcp->nc;
Fsproto(fs, tcp);
}
static void
tcpsetscale(Conv *s, Tcpctl *tcb, ushort rcvscale, ushort sndscale)
{
/*
* guess at reasonable queue sizes. there's no current way
* to know how many nic receive buffers we can safely tie up in the
* tcp stack, and we don't adjust our queues to maximize throughput
* and minimize bufferbloat. n.b. the offer (rcvscale) needs to be
* respected, but we still control our own buffer commitment by
* keeping a seperate qscale.
*/
tcb->rcv.scale = rcvscale & 0xff;
tcb->snd.scale = sndscale & 0xff;
tcb->qscale = rcvscale & 0xff;
if(rcvscale > Maxqscale)
tcb->qscale = Maxqscale;
if(rcvscale != tcb->rcv.scale)
netlog(s->p->f, Logtcp, "tcpsetscale: window %lud qlen %d >> window %ud lport %d\n",
tcb->window, qlen(s->rq), QMAX<<tcb->qscale, s->lport);
tcb->window = QMAX<<tcb->qscale;
tcb->ssthresh = tcb->window;
/*
* it's important to set wq large enough to cover the full
* bandwidth-delay product. it's possible to be in loss
* recovery with a big window, and we need to keep sending
* into the inflated window. the difference can be huge
* for even modest (70ms) ping times.
*/
qsetlimit(s->rq, QMAX<<tcb->qscale);
qsetlimit(s->wq, QMAX<<tcb->qscale);
tcprcvwin(s);
}