secureidcheck.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

/*
	This code uses RADIUS as a portable way to validate tokens such as SecurID.
	It is relatively simple to send a UDP packet and get a response, but various
	things can go wrong.  Speaking the proprietary ACE protocol would allow
	handling "next token code" and other error messages.  More importantly, the
	timeout threshold is inherently hard to pick.  We observe responses taking
	longer than 10 seconds in normal times.  That is a long time to wait before
	retrying on a second server.  Moreover, if the UDP response is lost, retrying
	on a second server will also fail because the valid token code may be
	presented only once.  This whole approach is flawed, but best we can do.
*/
/* RFC2138 */
#include <u.h>
#include <libc.h>
#include <ip.h>
#include <ctype.h>
#include <mp.h>
#include <libsec.h>
#include <bio.h>
#include <ndb.h>
#define AUTHLOG "auth"

enum{	R_AccessRequest=1,	/* Packet code */
	R_AccessAccept=2,
	R_AccessReject=3,
	R_AccessChallenge=11,
	R_UserName=1,
	R_UserPassword=2,
	R_NASIPAddress=4,
	R_ReplyMessage=18,
	R_State=24,
	R_NASIdentifier=32
};

typedef struct Secret{
	uchar *s;
	int len;
} Secret;

typedef struct Attribute{
	struct Attribute *next;
	uchar type;
	uchar len;	// number of bytes in value
	uchar val[256];
} Attribute;

typedef struct Packet{
	uchar code, ID;
	uchar authenticator[16];
	Attribute first;
} Packet;

// assumes pass is at most 16 chars
void
hide(Secret *shared, uchar *auth, Secret *pass, uchar *x)
{
	DigestState *M;
	int i, n = pass->len;

	M = md5(shared->s, shared->len, nil, nil);
	md5(auth, 16, x, M);
	if(n > 16)
		n = 16;
	for(i = 0; i < n; i++)
		x[i] ^= (pass->s)[i];
}

int
authcmp(Secret *shared, uchar *buf, int m, uchar *auth)
{
	DigestState *M;
	uchar x[16];

	M = md5(buf, 4, nil, nil); // Code+ID+Length
	M = md5(auth, 16, nil, M); // RequestAuth
	M = md5(buf+20, m-20, nil, M); // Attributes
	md5(shared->s, shared->len, x, M);
	return memcmp(x, buf+4, 16);
}

Packet*
newRequest(uchar *auth)
{
	static uchar ID = 0;
	Packet *p;

	p = (Packet*)malloc(sizeof(*p));
	if(p == nil)
		return nil;
	p->code = R_AccessRequest;
	p->ID = ++ID;
	memmove(p->authenticator, auth, 16);
	p->first.next = nil;
	p->first.type = 0;
	return p;
}

void
freePacket(Packet *p)
{
	Attribute *a, *x;

	if(!p)
		return;
	a = p->first.next;
	while(a){
		x = a;
		a = a->next;
		free(x);
	}
	free(p);
}

int
ding(void*, char *msg)
{
	syslog(0, AUTHLOG, "ding %s", msg);
	if(strstr(msg, "alarm"))
		return 1;
	return 0;
}

Packet *
rpc(char *dest, Secret *shared, Packet *req)
{
	uchar buf[4096], buf2[4096], *b, *e;
	Packet *resp;
	Attribute *a;
	int m, n, fd, try;

	// marshal request
	e = buf + sizeof buf;
	buf[0] = req->code;
	buf[1] = req->ID;
	memmove(buf+4, req->authenticator, 16);
	b = buf+20;
	for(a = &req->first; a; a = a->next){
		if(b + 2 + a->len > e)
			return nil;
		*b++ = a->type;
		*b++ = 2 + a->len;
		memmove(b, a->val, a->len);
		b += a->len;
	}
	n = b-buf;
	buf[2] = n>>8;
	buf[3] = n;

	// send request, wait for reply
	fd = dial(dest, 0, 0, 0);
	if(fd < 0){
		syslog(0, AUTHLOG, "%s: rpc can't get udp channel", dest);
		return nil;
	}
	atnotify(ding, 1);
	m = -1;
	for(try = 0; try < 2; try++){
		/* increased timeout from 4sec to 15sec because corporate server really takes that long */
		alarm(15000);
		m = write(fd, buf, n);
		if(m != n){
			syslog(0, AUTHLOG, "%s: rpc write err %d %d: %r", dest, m, n);
			m = -1;
			break;
		}
		m = read(fd, buf2, sizeof buf2);
		alarm(0);
		if(m < 0){
			syslog(0, AUTHLOG, "%s rpc read err %d: %r", dest, m);
			break; // failure
		}
		if(m == 0 || buf2[1] != buf[1]){  // need matching ID
			syslog(0, AUTHLOG, "%s unmatched reply %d", dest, m);
			continue;
		}
		if(authcmp(shared, buf2, m, buf+4) == 0)
			break;
		syslog(0, AUTHLOG, "%s bad rpc chksum", dest);
	}
	close(fd);
	if(m <= 0)
		return nil;

	// unmarshal reply
	b = buf2;
	e = buf2+m;
	resp = (Packet*)malloc(sizeof(*resp));
	if(resp == nil)
		return nil;
	resp->code = *b++;
	resp->ID = *b++;
	n = *b++;
	n = (n<<8) | *b++;
	if(m != n){
		syslog(0, AUTHLOG, "rpc got %d bytes, length said %d", m, n);
		if(m > n)
			e = buf2+n;
	}
	memmove(resp->authenticator, b, 16);
	b += 16;
	a = &resp->first;
	a->type = 0;
	for(;;){
		if(b >= e){
			a->next = nil;
			break;			// exit loop
		}
		a->type = *b++;
		a->len = (*b++) - 2;
		if(b + a->len > e){ // corrupt packet
			a->next = nil;
			freePacket(resp);
			return nil;
		}
		memmove(a->val, b, a->len);
		b += a->len;
		if(b < e){  // any more attributes?
			a->next = (Attribute*)malloc(sizeof(*a));
			if(a->next == nil){
				free(req);
				return nil;
			}
			a = a->next;
		}
	}
	return resp;
}

int
setAttribute(Packet *p, uchar type, uchar *s, int n)
{
	Attribute *a;

	a = &p->first;
	if(a->type != 0){
		a = (Attribute*)malloc(sizeof(*a));
		if(a == nil)
			return -1;
		a->next = p->first.next;
		p->first.next = a;
	}
	a->type = type;
	a->len = n;
	if(a->len > 253 )  // RFC2138, section 5
		a->len = 253;
	memmove(a->val, s, a->len);
	return 0;
}

/* return a reply message attribute string */
char*
replymsg(Packet *p)
{
	Attribute *a;
	static char buf[255];

	for(a = &p->first; a; a = a->next){
		if(a->type == R_ReplyMessage){
			if(a->len >= sizeof buf)
				a->len = sizeof(buf)-1;
			memmove(buf, a->val, a->len);
			buf[a->len] = 0;
		}
	}
	return buf;
}

/* for convenience while debugging */
char *replymess;
Attribute *stateattr;

void
logPacket(Packet *p)
{
	Attribute *a;
	char buf[255];
	char pbuf[4*1024];
	uchar *au = p->authenticator;
	int i;
	char *np, *e;

	e = pbuf + sizeof(pbuf);

	np = seprint(pbuf, e, "Packet ID=%d auth=%x %x %x... ", p->ID, au[0], au[1], au[2]);
	switch(p->code){
	case R_AccessRequest:
		np = seprint(np, e, "request\n");
		break;
	case R_AccessAccept:
		np = seprint(np, e, "accept\n");
		break;
	case R_AccessReject:
		np = seprint(np, e, "reject\n");
		break;
	case R_AccessChallenge:
		np = seprint(np, e, "challenge\n");
		break;
	default:
		np = seprint(np, e, "code=%d\n", p->code);
		break;
	}
	replymess = "0000000";
	for(a = &p->first; a; a = a->next){
		if(a->len > 253 )
			a->len = 253;
		memmove(buf, a->val, a->len);
		np = seprint(np, e, " [%d]", a->type);
		for(i = 0; i<a->len; i++)
			if(isprint(a->val[i]))
				np = seprint(np, e, "%c", a->val[i]);
			else
				np = seprint(np, e, "\\%o", a->val[i]);
		np = seprint(np, e, "\n");
		buf[a->len] = 0;
		if(a->type == R_ReplyMessage)
			replymess = strdup(buf);
		else if(a->type == R_State)
			stateattr = a;
	}

	syslog(0, AUTHLOG, "%s", pbuf);
}

static uchar*
getipv4addr(void)
{
	Ipifc *nifc;
	Iplifc *lifc;
	static Ipifc *ifc;

	ifc = readipifc("/net", ifc, -1);
	for(nifc = ifc; nifc; nifc = nifc->next)
		for(lifc = nifc->lifc; lifc; lifc = lifc->next)
			if(ipcmp(lifc->ip, IPnoaddr) != 0 && ipcmp(lifc->ip, v4prefix) != 0)
				return lifc->ip;
	return nil;
}

extern Ndb *db;

/* returns 0 on success, error message on failure */
char*
secureidcheck(char *user, char *response)
{
	Packet *req = nil, *resp = nil;
	ulong u[4];
	uchar x[16];
	char *radiussecret;
	char ruser[ 64];
	char dest[3*IPaddrlen+20];
	Secret shared, pass;
	char *rv = "authentication failed";
	Ndbs s;
	Ndbtuple *t, *nt, *tt;
	uchar *ip;
	static Ndb *netdb;

	if(netdb == nil)
		netdb = ndbopen(0);

	/* bad responses make them disable the fob, avoid silly checks */
	if(strlen(response) < 4 || strpbrk(response,"abcdefABCDEF") != nil)
		goto out;

	/* get radius secret */
	radiussecret = ndbgetvalue(db, &s, "radius", "lra-radius", "secret", &t);
	if(radiussecret == nil){
		syslog(0, AUTHLOG, "secureidcheck: nil radius secret: %r");
		goto out;
	}

	/* translate user name if we have to */
	strcpy(ruser, user);
	for(nt = t; nt; nt = nt->entry){
		if(strcmp(nt->attr, "uid") == 0 && strcmp(nt->val, user) == 0)
			for(tt = nt->line; tt != nt; tt = tt->line)
				if(strcmp(tt->attr, "rid") == 0){
					strcpy(ruser, tt->val);
					break;
				}
	}
	ndbfree(t);

	u[0] = fastrand();
	u[1] = fastrand();
	u[2] = fastrand();
	u[3] = fastrand();
	req = newRequest((uchar*)u);
	if(req == nil)
		goto out;
	shared.s = (uchar*)radiussecret;
	shared.len = strlen(radiussecret);
	ip = getipv4addr();
	if(ip == nil){
		syslog(0, AUTHLOG, "no interfaces: %r\n");
		goto out;
	}
	if(setAttribute(req, R_NASIPAddress, ip + IPv4off, 4) < 0)
		goto out;

	if(setAttribute(req, R_UserName, (uchar*)ruser, strlen(ruser)) < 0)
		goto out;
	pass.s = (uchar*)response;
	pass.len = strlen(response);
	hide(&shared, req->authenticator, &pass, x);
	if(setAttribute(req, R_UserPassword, x, 16) < 0)
		goto out;

	t = ndbsearch(netdb, &s, "sys", "lra-radius");
	if(t == nil){
		syslog(0, AUTHLOG, "secureidcheck: nil radius sys search: %r\n");
		goto out;
	}
	for(nt = t; nt; nt = nt->entry){
		if(strcmp(nt->attr, "ip") != 0)
			continue;

		snprint(dest,sizeof dest,"udp!%s!oradius", nt->val);
		resp = rpc(dest, &shared, req);
		if(resp == nil){
			syslog(0, AUTHLOG, "%s nil response", dest);
			continue;
		}
		if(resp->ID != req->ID){
			syslog(0, AUTHLOG, "%s mismatched ID  req=%d resp=%d",
				dest, req->ID, resp->ID);
			freePacket(resp);
			resp = nil;
			continue;
		}
	
		switch(resp->code){
		case R_AccessAccept:
			syslog(0, AUTHLOG, "%s accepted ruser=%s", dest, ruser);
			rv = nil;
			break;
		case R_AccessReject:
			syslog(0, AUTHLOG, "%s rejected ruser=%s %s", dest, ruser, replymsg(resp));
			rv = "secureid failed";
			break;
		case R_AccessChallenge:
			syslog(0, AUTHLOG, "%s challenge ruser=%s %s", dest, ruser, replymsg(resp));
			rv = "secureid out of sync";
			break;
		default:
			syslog(0, AUTHLOG, "%s code=%d ruser=%s %s", dest, resp->code, ruser, replymsg(resp));
			break;
		}
		break; // we have a proper reply, no need to ask again
	}
	ndbfree(t);
	free(radiussecret);
out:
	freePacket(req);
	freePacket(resp);
	return rv;
}