smtpd.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

		rejectcount++;
		reply("503 Start by saying HELO, please\r\n");
		return;
	}
	if(senders.last)
		sender = s_to_c(senders.last->p);
	else
		sender = "<unknown>";

	if(!recipok(s_to_c(path))){
		rejectcount++;
		syslog(0, "smtpd",
		 "Disallowed %s (%s/%s) to blocked, unknown or invalid name %s",
			sender, him, nci->rsys, s_to_c(path));
		reply("550 %s ... user unknown\r\n", s_to_c(path));
		return;
	}
	rcpt = s_to_c(path);
	if (!senderok(rcpt)) {
		rejectcount++;
		syslog(0, "smtpd", "Disallowed sending IP of %s (%s/%s) to %s",
				sender, him, nci->rsys, rcpt);
		reply("550 %s ... sending system not allowed\r\n", rcpt);
		return;
	}

	logged = 0;
		/* forwarding() can modify 'path' on loopback request */
	if(filterstate == ACCEPT && (fflag && !authenticated) && forwarding(path)) {
		syslog(0, "smtpd", "Bad Forward %s (%s/%s) (%s)",
			s_to_c(senders.last->p), him, nci->rsys, s_to_c(path));
		rejectcount++;
		reply("550 we don't relay.  send to your-path@[] for loopback.\r\n");
		return;
	}
	listadd(&rcvers, path);
	reply("250 receiver is %s\r\n", s_to_c(path));
}

void
quit(void)
{
	reply("221 Successful termination\r\n");
	close(0);
	exits(0);
}

void
turn(void)
{
	if(rejectcheck())
		return;
	reply("502 TURN unimplemented\r\n");
}

void
noop(void)
{
	if(rejectcheck())
		return;
	reply("250 Stop wasting my time!\r\n");
}

void
help(String *cmd)
{
	if(rejectcheck())
		return;
	if(cmd)
		s_free(cmd);
	reply("250 Read rfc821 and stop wasting my time\r\n");
}

void
verify(String *path)
{
	char *p, *q;
	char *av[4];

	if(rejectcheck())
		return;
	if(shellchars(s_to_c(path))){
		reply("503 Bad character in address %s.\r\n", s_to_c(path));
		return;
	}
	av[0] = s_to_c(mailer);
	av[1] = "-x";
	av[2] = s_to_c(path);
	av[3] = 0;

	pp = noshell_proc_start(av, (stream *)0, outstream(),  (stream *)0, 1, 0);
	if (pp == 0) {
		reply("450 We're busy right now, try later\r\n");
		return;
	}

	p = Brdline(pp->std[1]->fp, '\n');
	if(p == 0){
		reply("550 String does not match anything.\r\n");
	} else {
		p[Blinelen(pp->std[1]->fp)-1] = 0;
		if(strchr(p, ':'))
			reply("550 String does not match anything.\r\n");
		else{
			q = strrchr(p, '!');
			if(q)
				p = q+1;
			reply("250 %s <%s@%s>\r\n", s_to_c(path), p, dom);
		}
	}
	proc_wait(pp);
	proc_free(pp);
	pp = 0;
}

/*
 *  get a line that ends in crnl or cr, turn terminating crnl into a nl
 *
 *  return 0 on EOF
 */
static int
getcrnl(String *s, Biobuf *fp)
{
	int c;

	for(;;){
		c = Bgetc(fp);
		if(debug) {
			seek(2, 0, 2);
			fprint(2, "%c", c);
		}
		switch(c){
		case -1:
			goto out;
		case '\r':
			c = Bgetc(fp);
			if(c == '\n'){
				if(debug) {
					seek(2, 0, 2);
					fprint(2, "%c", c);
				}
				s_putc(s, '\n');
				goto out;
			}
			Bungetc(fp);
			s_putc(s, '\r');
			break;
		case '\n':
			s_putc(s, c);
			goto out;
		default:
			s_putc(s, c);
			break;
		}
	}
out:
	s_terminate(s);
	return s_len(s);
}

void
logcall(int nbytes)
{
	Link *l;
	String *to, *from;

	to = s_new();
	from = s_new();
	for(l = senders.first; l; l = l->next){
		if(l != senders.first)
			s_append(from, ", ");
		s_append(from, s_to_c(l->p));
	}
	for(l = rcvers.first; l; l = l->next){
		if(l != rcvers.first)
			s_append(to, ", ");
		s_append(to, s_to_c(l->p));
	}
	syslog(0, "smtpd", "[%s/%s] %s sent %d bytes to %s", him, nci->rsys,
		s_to_c(from), nbytes, s_to_c(to));
	s_free(to);
	s_free(from);
}

static void
logmsg(char *action)
{
	Link *l;

	if(logged)
		return;

	logged = 1;
	for(l = rcvers.first; l; l = l->next)
		syslog(0, "smtpd", "%s %s (%s/%s) (%s)", action,
			s_to_c(senders.last->p), him, nci->rsys, s_to_c(l->p));
}

static int
optoutall(int filterstate)
{
	Link *l;

	switch(filterstate){
	case ACCEPT:
	case TRUSTED:
		return filterstate;
	}

	for(l = rcvers.first; l; l = l->next)
		if(!optoutofspamfilter(s_to_c(l->p)))
			return filterstate;

	return ACCEPT;
}

String*
startcmd(void)
{
	int n;
	Link *l;
	char **av;
	String *cmd;
	char *filename;

	/*
	 *  ignore the filterstate if the all the receivers prefer it.
	 */
	filterstate = optoutall(filterstate);

	switch (filterstate){
	case BLOCKED:
	case DELAY:
		rejectcount++;
		logmsg("Blocked");
		filename = dumpfile(s_to_c(senders.last->p));
		cmd = s_new();
		s_append(cmd, "cat > ");
		s_append(cmd, filename);
		pp = proc_start(s_to_c(cmd), instream(), 0, outstream(), 0, 0);
		break;
	case DIALUP:
		logmsg("Dialup");
		rejectcount++;
		reply("554 We don't accept mail from dial-up ports.\r\n");
		/*
		 * we could exit here, because we're never going to accept mail from this
		 * ip address, but it's unclear that RFC821 allows that.  Instead we set
		 * the hardreject flag and go stupid.
		 */
		hardreject = 1;
		return 0;
	case DENIED:
		logmsg("Denied");
		rejectcount++;
		reply("554-We don't accept mail from %s.\r\n", s_to_c(senders.last->p));
		reply("554 Contact postmaster@%s for more information.\r\n", dom);
		return 0;
	case REFUSED:
		logmsg("Refused");
		rejectcount++;
		reply("554 Sender domain must exist: %s\r\n", s_to_c(senders.last->p));
		return 0;
	default:
	case NONE:
		logmsg("Confused");
		rejectcount++;
		reply("554-We have had an internal mailer error classifying your message.\r\n");
		reply("554-Filterstate is %d\r\n", filterstate);
		reply("554 Contact postmaster@%s for more information.\r\n", dom);
		return 0;
	case ACCEPT:
	case TRUSTED:
		/*
		 * now that all other filters have been passed,
		 * do grey-list processing.
		 */
		if(gflag)
			vfysenderhostok();

		/*
		 *  set up mail command
		 */
		cmd = s_clone(mailer);
		n = 3;
		for(l = rcvers.first; l; l = l->next)
			n++;
		av = malloc(n*sizeof(char*));
		if(av == nil){
			reply("450 We're busy right now, try later\n");
			s_free(cmd);
			return 0;
		}

			n = 0;
		av[n++] = s_to_c(cmd);
		av[n++] = "-r";
		for(l = rcvers.first; l; l = l->next)
			av[n++] = s_to_c(l->p);
		av[n] = 0;
		/*
		 *  start mail process
		 */
		pp = noshell_proc_start(av, instream(), outstream(), outstream(), 0, 0);
		free(av);
		break;
	}
	if(pp == 0) {
		reply("450 We're busy right now, try later\n");
		s_free(cmd);
		return 0;
	}
	return cmd;
}

/*
 *  print out a header line, expanding any domainless addresses into
 *  address@him
 */
char*
bprintnode(Biobuf *b, Node *p)
{
	if(p->s){
		if(p->addr && strchr(s_to_c(p->s), '@') == nil){
			if(Bprint(b, "%s@%s", s_to_c(p->s), him) < 0)
				return nil;
		} else {
			if(Bwrite(b, s_to_c(p->s), s_len(p->s)) < 0)
				return nil;
		}
	}else{
		if(Bputc(b, p->c) < 0)
			return nil;
	}
	if(p->white)
		if(Bwrite(b, s_to_c(p->white), s_len(p->white)) < 0)
			return nil;
	return p->end+1;
}

static String*
getaddr(Node *p)
{
	for(; p; p = p->next)
		if(p->s && p->addr)
			return p->s;
	return nil;
}

/*
 *  add waring headers of the form
 *	X-warning: <reason>
 *  for any headers that looked like they might be forged.
 *
 *  return byte count of new headers
 */
static int
forgedheaderwarnings(void)
{
	int nbytes;
	Field *f;

	nbytes = 0;

	/* warn about envelope sender */
	if(strcmp(s_to_c(senders.last->p), "/dev/null") != 0 && masquerade(senders.last->p, nil))
		nbytes += Bprint(pp->std[0]->fp, "X-warning: suspect envelope domain\n");

	/*
	 *  check Sender: field.  If it's OK, ignore the others because this is an
	 *  exploded mailing list.
	 */
	for(f = firstfield; f; f = f->next){
		if(f->node->c == SENDER){
			if(masquerade(getaddr(f->node), him))
				nbytes += Bprint(pp->std[0]->fp, "X-warning: suspect Sender: domain\n");
			else
				return nbytes;
		}
	}

	/* check From: */
	for(f = firstfield; f; f = f->next){
		if(f->node->c == FROM && masquerade(getaddr(f->node), him))
			nbytes += Bprint(pp->std[0]->fp, "X-warning: suspect From: domain\n");
	}
	return nbytes;
}

/*
 *  pipe message to mailer with the following transformations:
 *	- change \r\n into \n.
 *	- add sender's domain to any addrs with no domain
 *	- add a From: if none of From:, Sender:, or Replyto: exists
 *	- add a Received: line
 */
int
pipemsg(int *byteswritten)
{
	int status;
	char *cp;
	String *line;
	String *hdr;
	int n, nbytes;
	int sawdot;
	Field *f;
	Node *p;
	Link *l;

	pipesig(&status);	/* set status to 1 on write to closed pipe */
	sawdot = 0;
	status = 0;

	/*
	 *  add a 'From ' line as envelope
	 */
	nbytes = 0;
	nbytes += Bprint(pp->std[0]->fp, "From %s %s remote from \n",
			s_to_c(senders.first->p), thedate());

	/*
	 *  add our own Received: stamp
	 */
	nbytes += Bprint(pp->std[0]->fp, "Received: from %s ", him);
	if(nci->rsys)
		nbytes += Bprint(pp->std[0]->fp, "([%s]) ", nci->rsys);
	nbytes += Bprint(pp->std[0]->fp, "by %s; %s\n", me, thedate());

	/*
	 *  read first 16k obeying '.' escape.  we're assuming
	 *  the header will all be there.
	 */
	line = s_new();
	hdr = s_new();
	while(sawdot == 0 && s_len(hdr) < 16*1024){
		n = getcrnl(s_reset(line), &bin);

		/* eof or error ends the message */
		if(n <= 0)
			break;

		/* a line with only a '.' ends the message */
		cp = s_to_c(line);
		if(n == 2 && *cp == '.' && *(cp+1) == '\n'){
			sawdot = 1;
			break;
		}

		s_append(hdr, *cp == '.' ? cp+1 : cp);
	}

	/*
 	 *  parse header
	 */
	yyinit(s_to_c(hdr), s_len(hdr));
	yyparse();

	/*
 	 *  Look for masquerades.  Let Sender: trump From: to allow mailing list
	 *  forwarded messages.
	 */
	if(fflag)
		nbytes += forgedheaderwarnings();

	/*
	 *  add an orginator and/or destination if either is missing
	 */
	if(originator == 0){
		if(senders.last == nil)
			Bprint(pp->std[0]->fp, "From: /dev/null@%s\n", him);
		else
			Bprint(pp->std[0]->fp, "From: %s\n", s_to_c(senders.last->p));
	}
	if(destination == 0){
		Bprint(pp->std[0]->fp, "To: ");
		for(l = rcvers.first; l; l = l->next){
			if(l != rcvers.first)
				Bprint(pp->std[0]->fp, ", ");
			Bprint(pp->std[0]->fp, "%s", s_to_c(l->p));
		}
		Bprint(pp->std[0]->fp, "\n");
	}

	/*
	 *  add sender's domain to any domainless addresses
	 *  (to avoid forging local addresses)
	 */
	cp = s_to_c(hdr);
	for(f = firstfield; cp != nil && f; f = f->next){
		for(p = f->node; cp != 0 && p; p = p->next)
			cp = bprintnode(pp->std[0]->fp, p);
		if(status == 0 && Bprint(pp->std[0]->fp, "\n") < 0){
			piperror = "write error";
			status = 1;
		}
	}
	if(cp == nil){
		piperror = "sender domain";
		status = 1;
	}

	/* write anything we read following the header */
	if(status == 0 && Bwrite(pp->std[0]->fp, cp, s_to_c(hdr) + s_len(hdr) - cp) < 0){
		piperror = "write error 2";
		status = 1;
	}
	s_free(hdr);

	/*