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

	 *  pass rest of message to mailer.  take care of '.'
	 *  escapes.
	 */
	while(sawdot == 0){
		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;
		}
		nbytes += n;
		if(status == 0 && Bwrite(pp->std[0]->fp, *cp == '.' ? cp+1 : cp, n) < 0){
			piperror = "write error 3";
			status = 1;
		}
	}
	s_free(line);
	if(sawdot == 0){
		/* message did not terminate normally */
		snprint(pipbuf, sizeof pipbuf, "network eof: %r");
		piperror = pipbuf;
		syskillpg(pp->pid);
		status = 1;
	}

	if(status == 0 && Bflush(pp->std[0]->fp) < 0){
		piperror = "write error 4";
		status = 1;
	}
	stream_free(pp->std[0]);
	pp->std[0] = 0;
	*byteswritten = nbytes;
	pipesigoff();
	if(status && !piperror)
		piperror = "write on closed pipe";
	return status;
}

char*
firstline(char *x)
{
	static char buf[128];
	char *p;

	strncpy(buf, x, sizeof(buf));
	buf[sizeof(buf)-1] = 0;
	p = strchr(buf, '\n');
	if(p)
		*p = 0;
	return buf;
}

int
sendermxcheck(void)
{
	char *cp, *senddom, *user;
	char *who;
	int pid;
	Waitmsg *w;

	who = s_to_c(senders.first->p);
	if(strcmp(who, "/dev/null") == 0){
		/* /dev/null can only send to one rcpt at a time */
		if(rcvers.first != rcvers.last){
			werrstr("rejected: /dev/null sending to multiple recipients");
			return -1;
		}
		return 0;
	}

	if(access("/mail/lib/validatesender", AEXEC) < 0)
		return 0;

	senddom = strdup(who);
	if((cp = strchr(senddom, '!')) == nil){
		werrstr("rejected: domainless sender %s", who);
		free(senddom);
		return -1;
	}
	*cp++ = 0;
	user = cp;

	switch(pid = fork()){
	case -1:
		werrstr("deferred: fork: %r");
		return -1;
	case 0:
		/*
		 * Could add an option with the remote IP address
		 * to allow validatesender to implement SPF eventually.
		 */
		execl("/mail/lib/validatesender", "validatesender", 
			"-n", nci->root, senddom, user, nil);
		_exits("exec validatesender: %r");
	default:
		break;
	}

	free(senddom);
	w = wait();
	if(w == nil){
		werrstr("deferred: wait failed: %r");
		return -1;
	}
	if(w->pid != pid){
		werrstr("deferred: wait returned wrong pid %d != %d", w->pid, pid);
		free(w);
		return -1;
	}
	if(w->msg[0] == 0){
		free(w);
		return 0;
	}
	/*
	 * skip over validatesender 143123132: prefix from rc.
	 */
	cp = strchr(w->msg, ':');
	if(cp && *(cp+1) == ' ')
		werrstr("%s", cp+2);
	else
		werrstr("%s", w->msg);
	free(w);
	return -1;
}

void
data(void)
{
	String *cmd;
	String *err;
	int status, nbytes;
	char *cp, *ep;
	char errx[ERRMAX];
	Link *l;

	if(rejectcheck())
		return;
	if(senders.last == 0){
		reply("503 Data without MAIL FROM:\r\n");
		rejectcount++;
		return;
	}
	if(rcvers.last == 0){
		reply("503 Data without RCPT TO:\r\n");
		rejectcount++;
		return;
	}
	if(!trusted && sendermxcheck()){
		rerrstr(errx, sizeof errx);
		if(strncmp(errx, "rejected:", 9) == 0)
			reply("554 %s\r\n", errx);
		else
			reply("450 %s\r\n", errx);
		for(l=rcvers.first; l; l=l->next)
			syslog(0, "smtpd", "[%s/%s] %s -> %s sendercheck: %s",
					him, nci->rsys, s_to_c(senders.first->p), 
					s_to_c(l->p), errx);
		rejectcount++;
		return;
	}

	cmd = startcmd();
	if(cmd == 0)
		return;

	reply("354 Input message; end with <CRLF>.<CRLF>\r\n");

	/*
	 *  allow 145 more minutes to move the data
	 */
	alarm(145*60*1000);

	status = pipemsg(&nbytes);

	/*
	 *  read any error messages
	 */
	err = s_new();
	while(s_read_line(pp->std[2]->fp, err))
		;

	alarm(0);
	atnotify(catchalarm, 0);

	status |= proc_wait(pp);
	if(debug){
		seek(2, 0, 2);
		fprint(2, "%d status %ux\n", getpid(), status);
		if(*s_to_c(err))
			fprint(2, "%d error %s\n", getpid(), s_to_c(err));
	}

	/*
	 *  if process terminated abnormally, send back error message
	 */
	if(status){
		int code;

		if(strstr(s_to_c(err), "mail refused")){
			syslog(0, "smtpd", "++[%s/%s] %s %s refused: %s", him, nci->rsys,
				s_to_c(senders.first->p), s_to_c(cmd), firstline(s_to_c(err)));
			code = 554;
		} else {
			syslog(0, "smtpd", "++[%s/%s] %s %s %s%s%sreturned %#q %s", him, nci->rsys,
				s_to_c(senders.first->p), s_to_c(cmd), 
				piperror ? "error during pipemsg: " : "",
				piperror ? piperror : "",
				piperror ? "; " : "",
				pp->waitmsg->msg, firstline(s_to_c(err)));
			code = 450;
		}
		for(cp = s_to_c(err); ep = strchr(cp, '\n'); cp = ep){
			*ep++ = 0;
			reply("%d-%s\r\n", code, cp);
		}
		reply("%d mail process terminated abnormally\r\n", code);
	} else {
		/*
		 * if a message appeared on stderr, despite good status,
		 * log it.  this can happen if rewrite.in contains a bad
		 * r.e., for example.
		 */
		if(*s_to_c(err))
			syslog(0, "smtpd",
				"%s returned good status, but said: %s",
				s_to_c(mailer), s_to_c(err));

		if(filterstate == BLOCKED)
			reply("554 we believe this is spam.  we don't accept it.\r\n");
		else
		if(filterstate == DELAY)
			reply("554 There will be a delay in delivery of this message.\r\n");
		else {
			reply("250 sent\r\n");
			logcall(nbytes);
		}
	}
	proc_free(pp);
	pp = 0;
	s_free(cmd);
	s_free(err);

	listfree(&senders);
	listfree(&rcvers);
}

/*
 * when we have blocked a transaction based on IP address, there is nothing
 * that the sender can do to convince us to take the message.  after the
 * first rejection, some spammers continually RSET and give a new MAIL FROM:
 * filling our logs with rejections.  rejectcheck() limits the retries and
 * swiftly rejects all further commands after the first 500-series message
 * is issued.
 */
int
rejectcheck(void)
{

	if(rejectcount > MAXREJECTS){
		syslog(0, "smtpd", "Rejected (%s/%s)", him, nci->rsys);
		reply("554 too many errors.  transaction failed.\r\n");
		exits("errcount");
	}
	if(hardreject){
		rejectcount++;
		reply("554 We don't accept mail from dial-up ports.\r\n");
	}
	return hardreject;
}

/*
 *  create abs path of the mailer
 */
String*
mailerpath(char *p)
{
	String *s;

	if(p == nil)
		return nil;
	if(*p == '/')
		return s_copy(p);
	s = s_new();
	s_append(s, UPASBIN);
	s_append(s, "/");
	s_append(s, p);
	return s;
}

String *
s_dec64(String *sin)
{
	String *sout;
	int lin, lout;
	lin = s_len(sin);

	/*
	 * if the string is coming from smtpd.y, it will have no nl.
	 * if it is coming from getcrnl below, it will have an nl.
	 */
	if (*(s_to_c(sin)+lin-1) == '\n')
		lin--;
	sout = s_newalloc(lin+1);
	lout = dec64((uchar *)s_to_c(sout), lin, s_to_c(sin), lin);
	if (lout < 0) {
		s_free(sout);
		return nil;
	}
	sout->ptr = sout->base + lout;
	s_terminate(sout);
	return sout;
}

void
starttls(void)
{
	uchar *cert;
	int certlen, fd;
	TLSconn *conn;

	if (tlscert == nil) {
		reply("454 TLS not available\r\n");
		return;
	}
	conn = mallocz(sizeof *conn, 1);
	cert = readcert(tlscert, &certlen);
	if (conn == nil || cert == nil) {
		if (conn != nil)
			free(conn);
		reply("454 TLS not available\r\n");
		return;
	}
	reply("220 Go ahead make my day\r\n");
	conn->cert = cert;
	conn->certlen = certlen;
	fd = tlsServer(Bfildes(&bin), conn);
	if (fd < 0) {
		free(cert);
		free(conn);
		syslog(0, "smtpd", "TLS start-up failed with %s", him);

		/* force the client to hang up */
		close(Bfildes(&bin));		/* probably fd 0 */
		close(1);
		exits("tls failed");
	}
	Bterm(&bin);
	Binit(&bin, fd, OREAD);
	if (dup(fd, 1) < 0)
		fprint(2, "dup of %d failed: %r\n", fd);
	passwordinclear = 1;
	syslog(0, "smtpd", "started TLS with %s", him);
}

void
auth(String *mech, String *resp)
{
	Chalstate *chs = nil;
	AuthInfo *ai = nil;
	String *s_resp1_64 = nil;
	String *s_resp2_64 = nil;
	String *s_resp1 = nil;
	String *s_resp2 = nil;
	char *scratch = nil;
	char *user, *pass;

	if (rejectcheck())
		goto bomb_out;

 	syslog(0, "smtpd", "auth(%s, %s) from %s", s_to_c(mech),
		"(protected)", him);

	if (authenticated) {
	bad_sequence:
		rejectcount++;
		reply("503 Bad sequence of commands\r\n");
		goto bomb_out;
	}
	if (cistrcmp(s_to_c(mech), "plain") == 0) {

		if (!passwordinclear) {
			rejectcount++;
			reply("538 Encryption required for requested authentication mechanism\r\n");
			goto bomb_out;
		}
		s_resp1_64 = resp;
		if (s_resp1_64 == nil) {
			reply("334 \r\n");
			s_resp1_64 = s_new();
			if (getcrnl(s_resp1_64, &bin) <= 0) {
				goto bad_sequence;
			}
		}
		s_resp1 = s_dec64(s_resp1_64);
		if (s_resp1 == nil) {
			rejectcount++;
			reply("501 Cannot decode base64\r\n");
			goto bomb_out;
		}
		memset(s_to_c(s_resp1_64), 'X', s_len(s_resp1_64));
		user = (s_to_c(s_resp1) + strlen(s_to_c(s_resp1)) + 1);
		pass = user + (strlen(user) + 1);
		ai = auth_userpasswd(user, pass);
		authenticated = ai != nil;
		memset(pass, 'X', strlen(pass));
		goto windup;
	}
	else if (cistrcmp(s_to_c(mech), "login") == 0) {

		if (!passwordinclear) {
			rejectcount++;
			reply("538 Encryption required for requested authentication mechanism\r\n");
			goto bomb_out;
		}
		if (resp == nil) {
			reply("334 VXNlcm5hbWU6\r\n");
			s_resp1_64 = s_new();
			if (getcrnl(s_resp1_64, &bin) <= 0)
				goto bad_sequence;
		}
		reply("334 UGFzc3dvcmQ6\r\n");
		s_resp2_64 = s_new();
		if (getcrnl(s_resp2_64, &bin) <= 0)
			goto bad_sequence;
		s_resp1 = s_dec64(s_resp1_64);
		s_resp2 = s_dec64(s_resp2_64);
		memset(s_to_c(s_resp2_64), 'X', s_len(s_resp2_64));
		if (s_resp1 == nil || s_resp2 == nil) {
			rejectcount++;
			reply("501 Cannot decode base64\r\n");
			goto bomb_out;
		}
		ai = auth_userpasswd(s_to_c(s_resp1), s_to_c(s_resp2));
		authenticated = ai != nil;
		memset(s_to_c(s_resp2), 'X', s_len(s_resp2));
	windup:
		if (authenticated)
			reply("235 Authentication successful\r\n");
		else {
			rejectcount++;
			reply("535 Authentication failed\r\n");
		}
		goto bomb_out;
	}
	else if (cistrcmp(s_to_c(mech), "cram-md5") == 0) {
		char *resp;
		int chal64n;
		char *t;

		chs = auth_challenge("proto=cram role=server");
		if (chs == nil) {
			rejectcount++;
			reply("501 Couldn't get CRAM-MD5 challenge\r\n");
			goto bomb_out;
		}
		scratch = malloc(chs->nchal * 2 + 1);
		chal64n = enc64(scratch, chs->nchal * 2, (uchar *)chs->chal, chs->nchal);
		scratch[chal64n] = 0;
		reply("334 %s\r\n", scratch);
		s_resp1_64 = s_new();
		if (getcrnl(s_resp1_64, &bin) <= 0)
			goto bad_sequence;
		s_resp1 = s_dec64(s_resp1_64);
		if (s_resp1 == nil) {
			rejectcount++;
			reply("501 Cannot decode base64\r\n");
			goto bomb_out;
		}
		/* should be of form <user><space><response> */
		resp = s_to_c(s_resp1);
		t = strchr(resp, ' ');
		if (t == nil) {
			rejectcount++;
			reply("501 Poorly formed CRAM-MD5 response\r\n");
			goto bomb_out;
		}
		*t++ = 0;
		chs->user = resp;
		chs->resp = t;
		chs->nresp = strlen(t);
		ai = auth_response(chs);
		authenticated = ai != nil;
		goto windup;
	}
	rejectcount++;
	reply("501 Unrecognised authentication type %s\r\n", s_to_c(mech));
bomb_out:
	if (ai)
		auth_freeAI(ai);
	if (chs)
		auth_freechal(chs);
	if (scratch)
		free(scratch);
	if (s_resp1)
		s_free(s_resp1);
	if (s_resp2)
		s_free(s_resp2);
	if (s_resp1_64)
		s_free(s_resp1_64);
	if (s_resp2_64)
		s_free(s_resp2_64);
}