auth.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

#include "vnc.h"
#include <libsec.h>
#include <auth.h>

char *serveraddr;

/*
 * Encrypt n bytes using the password
 * as key, padded with zeros to 8 bytes.
 */
enum
{
	VerLen	= 12
};

static char version[VerLen+1] = "RFB 003.003\n";

static uchar tab[256];

/* VNC reverses the bits of each byte before using as a des key */
static void
mktab(void)
{
	int i, j, k;
	static int once;

	if(once)
		return;
	once = 1;

	for(i=0; i<256; i++){
		j=i;
		tab[i] = 0;
		for(k=0; k<8; k++){
			tab[i] = (tab[i]<<1) | (j&1);
			j >>= 1;
		}
	}
}

static void
vncencrypt(uchar *buf, int n, char *pw)
{
	uchar *p;
	uchar key[9];
	DESstate s;

	mktab();
	memset(key, 0, sizeof key);
	strncpy((char*)key, pw, 8);
	for(p=key; *p; p++)
		*p = tab[*p];

	setupDESstate(&s, key, nil);
	desECBencrypt(buf, n, &s);
}

static int
readln(char *prompt, char *line, int len)
{
	char *p;
	int fd, ctl, n, nr;

	fd = open("/dev/cons", ORDWR);
	if(fd < 0)
		sysfatal("couldn't open cons");
	ctl = open("/dev/consctl", OWRITE);
	if(ctl < 0)
		sysfatal("couldn't open consctl");
	write(ctl, "rawon", 5);
	fprint(fd, "%s", prompt);
	nr = 0;
	p = line;
	for(;;){
		n = read(fd, p, 1);
		if(n < 0){
			close(fd);
			close(ctl);
			return -1;
		}
		if(n == 0 || *p == '\n' || *p == '\r'){
			*p = '\0';
			write(fd, "\n", 1);
			close(fd);
			close(ctl);
			return nr;
		}
		if(*p == '\b'){
			if(nr > 0){
				nr--;
				p--;
			}
		}else if(*p == 21){		/* cntrl-u */
			fprint(fd, "\n%s", prompt);
			nr = 0;
			p = line;
		}else{
			nr++;
			p++;
		}
		if(nr == len){
			fprint(fd, "line too long; try again\n%s", prompt);
			nr = 0;
			p = line;
		}
	}
}

int
vncsrvhandshake(Vnc *v)
{
	char msg[VerLen+1];

	strecpy(msg, msg+sizeof msg, version);
	if(verbose)
		fprint(2, "server version: %s", msg);
	vncwrbytes(v, msg, VerLen);
	vncflush(v);

	vncrdbytes(v, msg, VerLen);
	if(verbose)
		fprint(2, "client version: %s", msg);
	return 0;
}

int
vnchandshake(Vnc *v)
{
	char msg[VerLen+1];

	msg[VerLen] = 0;
	vncrdbytes(v, msg, VerLen);
	if(strncmp(msg, "RFB ", 4) != 0){
		werrstr("bad rfb version \"%s\"", msg);
		return -1;
	}
	if(verbose)
		fprint(2, "server version: %s", msg);
	strcpy(msg, version);
	vncwrbytes(v, msg, VerLen);
	vncflush(v);
	return 0;
}

int
vncauth(Vnc *v, char *keypattern)
{
	char pw[128], *reason;
	uchar chal[VncChalLen];
	ulong auth;
	char *p, *server;

	if(keypattern == nil)
		keypattern = "";
	auth = vncrdlong(v);
	switch(auth){
	default:
		werrstr("unknown auth type 0x%lux", auth);
		if(verbose)
			fprint(2, "unknown auth type 0x%lux", auth);
		return -1;

	case AFailed:
		reason = vncrdstring(v);
		werrstr("%s", reason);
		if(verbose)
			fprint(2, "auth failed: %s\n", reason);
		return -1;

	case ANoAuth:
		if(verbose)
			fprint(2, "no auth needed");
		break;

	case AVncAuth:
		vncrdbytes(v, chal, VncChalLen);
		server = strdup(serveraddr);
		p = strrchr(server, ':');
		if(p)
			*p = 0;
		if(auth_respond(chal, VncChalLen, nil, 0, chal, VncChalLen, auth_getkey,
			"proto=vnc role=client server=%s %s", server, keypattern) != VncChalLen){
			/* BUG This is for drawterm users who don't start their own factotums */
			readln("password: ", pw, sizeof(pw));
			vncencrypt(chal, VncChalLen, pw);
			memset(pw, 0, sizeof pw);
		}
		free(server);
		vncwrbytes(v, chal, VncChalLen);
		vncflush(v);

		auth = vncrdlong(v);
		switch(auth){
		default:
			werrstr("unknown server response 0x%lux", auth);
			return -1;
		case VncAuthFailed:
			werrstr("server says authentication failed");
			return -1;
		case VncAuthTooMany:
			werrstr("server says too many tries");
			return -1;
		case VncAuthOK:
			break;
		}
		break;
	}
	return 0;
}

int
vncsrvauth(Vnc *v)
{
	Chalstate *c;
	AuthInfo *ai;

	if((c = auth_challenge("proto=vnc role=server user=%q", getuser()))==nil)
		sysfatal("vncchal: %r");
	if(c->nchal != VncChalLen)
		sysfatal("vncchal got %d bytes wanted %d", c->nchal, VncChalLen);
	vncwrlong(v, AVncAuth);
	vncwrbytes(v, c->chal, VncChalLen);
	vncflush(v);

	vncrdbytes(v, c->chal, VncChalLen);
	c->resp = c->chal;
	c->nresp = VncChalLen;
	ai = auth_response(c);
	auth_freechal(c);
	if(ai == nil){
		fprint(2, "vnc auth failed: server factotum: %r\n");
		vncwrlong(v, VncAuthFailed);
		vncflush(v);
		return -1;
	}
	auth_freeAI(ai);
	vncwrlong(v, VncAuthOK);
	vncflush(v);

	return 0;
}