* This code uses RADIUS as a portable way to validate tokens such as SecurID.

/*
* 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 <ctype.h>
#include <bio.h>
#include <ip.h>
#include <ndb.h>
#include <libsec.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)
{
int i;
char *np, *e;
char buf[255], pbuf[4*1024];
uchar *au = p->authenticator;
Attribute *a;

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)
{
char *radiussecret = nil;
char *rv = "authentication failed";
char dest[3*IPaddrlen+20], ruser[64];
uchar *ip;
uchar x[16];
ulong u[4];
Ndbs s;
Ndbtuple *t = nil, *nt, *tt;
Packet *req = nil, *resp = nil;
Secret shared, pass;
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);
t = nil;

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");
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");
goto out;
}
for(nt = t; nt; nt = nt->entry){
if(strcmp(nt->attr, "ip") != 0)
continue;

snprint(dest, sizeof dest, "udp!%s!radius", 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 */
}
out:
if (t)
ndbfree(t);
free(radiussecret);
freePacket(req);
freePacket(resp);
return rv;
}