packet.c

/*
 * $Id: packet.c,v 1.22 2009-03-18 21:09:26 heas Exp $
 *
 * Copyright (c) 1995-1998 by Cisco systems, Inc.
 *
 * Permission to use, copy, modify, and distribute this software for
 * any purpose and without fee is hereby granted, provided that this
 * copyright and permission notice appear on all copies of the
 * software and supporting documentation, the name of Cisco Systems,
 * Inc. not be used in advertising or publicity pertaining to
 * distribution of the program without specific prior permission, and
 * notice be given in supporting documentation that modification,
 * copying and distribution is by permission of Cisco Systems, Inc.
 *
 * Cisco Systems, Inc. makes no representations about the suitability
 * of this software for any purpose.  THIS SOFTWARE IS PROVIDED ``AS
 * IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
 * WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE.
 */

#include "tac_plus.h"
#include <poll.h>
#include <netdb.h>
#include <signal.h>
#include <time.h>

#pragma	weak	get_authen_continue
#pragma	weak	read_packet
#pragma	weak	send_acct_reply
#pragma	weak	send_authen_error
#pragma	weak	send_authen_reply
#pragma	weak	send_author_reply
#pragma	weak	send_error_reply

/* Everything to do with reading and writing packets */
static int sockread(int, u_char *, int, int);
static int sockwrite(int, u_char *, int, int);
static int write_packet(u_char *);

/* read an authentication GETDATA packet from a NAS.  Return NULL on failure */
u_char *
get_authen_continue(void)
{
    HDR *hdr;
    u_char *pak;
    struct authen_cont *cont;
    char msg[NI_MAXHOST + 256];

    pak = read_packet();
    if (!pak)
	return(NULL);
    hdr = (HDR *)pak;
    cont = (struct authen_cont *)(pak + TAC_PLUS_HDR_SIZE);

    if ((hdr->type != TAC_PLUS_AUTHEN) || (hdr->seq_no <= 1)) {
	if (snprintf(msg, sizeof(msg), "%s: Bad packet type=%d/seq no=%d "
		     "when expecting authentication cont", session.peer,
		     hdr->type, hdr->seq_no) == -1)
	    strcpy(msg, "");
	report(LOG_ERR, msg);
	send_authen_error(msg);
	return(NULL);
    }

    cont->user_msg_len  = ntohs(cont->user_msg_len);
    cont->user_data_len = ntohs(cont->user_data_len);

    if ((TAC_AUTHEN_CONT_FIXED_FIELDS_SIZE + cont->user_msg_len +
	 cont->user_data_len) != ntohl(hdr->datalength)) {
	char *m = "Illegally sized authentication cont packet";
	report(LOG_ERR, "%s: %s", session.peer, m);
	send_authen_error(m);
	return(NULL);
    }

    if (debug & DEBUG_PACKET_FLAG)
	dump_nas_pak(pak);

    return(pak);
}

/*
 * read a packet from the wire, and decrypt it.  Increment the global
 * seq_no return NULL on failure
 */
u_char *
read_packet(void)
{
    HDR		hdr;
    u_char	*pkt, *data;
    int		len;
    char	*tkey;

    if (debug & DEBUG_PACKET_FLAG)
	report(LOG_DEBUG, "Waiting for packet");

    /* read a packet header */
    len = sockread(session.sock, (u_char *)&hdr,
		   TAC_PLUS_HDR_SIZE, TAC_PLUS_READ_TIMEOUT);
    if (len != TAC_PLUS_HDR_SIZE) {
	report(LOG_DEBUG, "Read %d bytes from %s %s, expecting %d",
	       len, session.peer, session.port, TAC_PLUS_HDR_SIZE);
	return(NULL);
    }
    session.peerflags = hdr.flags;

    if ((hdr.version & TAC_PLUS_MAJOR_VER_MASK) != TAC_PLUS_MAJOR_VER) {
	report(LOG_ERR, "%s: Illegal major version specified: found %d wanted "
	       "%d\n", session.peer, hdr.version, TAC_PLUS_MAJOR_VER);
	return(NULL);
    }

    /* get memory for the packet */
    len = TAC_PLUS_HDR_SIZE + ntohl(hdr.datalength);
    if ((ntohl(hdr.datalength) & ~0xffffUL) ||
	(len < TAC_PLUS_HDR_SIZE) || (len > 0x10000)) {
	report(LOG_ERR, "%s: Illegal data size: %lu\n", session.peer,
	       (unsigned long)ntohl(hdr.datalength));
	return(NULL);
    }
    pkt = (u_char *)tac_malloc(len);

    /* initialise the packet */
    memcpy(pkt, &hdr, TAC_PLUS_HDR_SIZE);

    /* the data start here */
    data = pkt + TAC_PLUS_HDR_SIZE;

    /* read the rest of the packet data */
    if (sockread(session.sock, data, ntohl(hdr.datalength),
		 TAC_PLUS_READ_TIMEOUT) != ntohl(hdr.datalength)) {
	report(LOG_ERR, "%s: start_session: bad socket read", session.peer);
	free(pkt);
	return(NULL);
    }
    session.seq_no++;		/* should now equal that of incoming packet */
    session.last_exch = time(NULL);

    if (session.seq_no != hdr.seq_no) {
	report(LOG_ERR, "%s: Illegal session seq #, expecting %d, received %d",
	       session.peer, session.seq_no, hdr.seq_no);
	free(pkt);
	return(NULL);
    }

    /* decrypt the data portion */
    tkey = cfg_get_host_key(session.peerip);
    if (tkey == NULL && !STREQ(session.peer, session.peerip)) {
	tkey = cfg_get_host_prompt(session.peer);
    }
    if (tkey == NULL)
	tkey = session.key;
    if (md5_xor((HDR *)pkt, data, tkey)) {
	report(LOG_ERR, "%s: start_session error decrypting data",
	       session.peer);
	free(pkt);
	return(NULL);
    }

    if (debug & DEBUG_PACKET_FLAG)
	report(LOG_DEBUG, "Read %s size=%d",
	       summarise_incoming_packet_type(pkt), len);

    session.version = hdr.version;

    return(pkt);
}

/* send an accounting response packet */
void
send_acct_reply(u_char status, char *msg, char *data)
{
    u_char *pak, *p;
    HDR *hdr;
    int len;
    struct acct_reply *reply;
    int msg_len, data_len;

    msg_len = msg ? strlen(msg) : 0;
    data_len = data ? strlen(data) : 0;

    len = TAC_PLUS_HDR_SIZE + TAC_ACCT_REPLY_FIXED_FIELDS_SIZE + msg_len +
	  data_len;

    pak = (u_char *)tac_malloc(len);
    reply = (struct acct_reply *)(pak + TAC_PLUS_HDR_SIZE);
    hdr = (HDR *)pak;

    memset(pak, 0, len);

    hdr->version = TAC_PLUS_VER_0;
    hdr->type = TAC_PLUS_ACCT;
    hdr->seq_no = ++session.seq_no;
    hdr->flags = TAC_PLUS_UNENCRYPTED;
    if (!(session.flags & SESS_NO_SINGLECONN))
	hdr->flags |= (session.peerflags & TAC_PLUS_SINGLE_CONNECT_FLAG);
    hdr->session_id = htonl(session.session_id);
    hdr->datalength = htonl(len - TAC_PLUS_HDR_SIZE);

    reply->status = status;
    reply->msg_len  = msg_len;
    reply->data_len = data_len;

    p = pak + TAC_PLUS_HDR_SIZE + TAC_ACCT_REPLY_FIXED_FIELDS_SIZE;
    memcpy(p, msg, msg_len);
    p += msg_len;

    memcpy(p, data, data_len);

    if (debug & DEBUG_PACKET_FLAG) {
	report(LOG_DEBUG, "Writing %s size=%d",
	       summarise_outgoing_packet_type(pak), len);
	dump_tacacs_pak(pak);
    }

    reply->msg_len = ntohs(reply->msg_len);
    reply->data_len = ntohs(reply->data_len);

    write_packet(pak);
    free(pak);

    return;
}

/*
 * Send an authentication reply packet indicating an error has occurred.
 * msg is a null terminated character string
 */
void
send_authen_error(char *msg)
{
    char buf[NI_MAXHOST + 256];

    if (snprintf(buf, sizeof(buf), "%s %s: %s", session.peer, session.port,
		 msg) == -1)
	strcpy(buf, "");
    report(LOG_ERR, buf);
    send_authen_reply(TAC_PLUS_AUTHEN_STATUS_ERROR, buf, strlen(buf), NULL, 0,
		      0);
}

/* create and send an authentication reply packet from tacacs+ to a NAS */
void
send_authen_reply(int status, char *msg, u_short msg_len, char *data,
		  u_short data_len, u_char flags)
{
    u_char *pak, *p;
    HDR *hdr;
    struct authen_reply *reply;
    int len;

    len = TAC_PLUS_HDR_SIZE + TAC_AUTHEN_REPLY_FIXED_FIELDS_SIZE + msg_len +
	  data_len;

    pak = (u_char *)tac_malloc(len);
    memset(pak, 0, len);

    hdr = (HDR *)pak;
    reply = (struct authen_reply *)(pak + TAC_PLUS_HDR_SIZE);

    hdr->version = session.version;
    hdr->type = TAC_PLUS_AUTHEN;
    hdr->seq_no = ++session.seq_no;
    hdr->flags = TAC_PLUS_UNENCRYPTED;
    if (!(session.flags & SESS_NO_SINGLECONN))
	hdr->flags |= (session.peerflags & TAC_PLUS_SINGLE_CONNECT_FLAG);
    hdr->session_id = htonl(session.session_id);
    hdr->datalength = htonl(TAC_AUTHEN_REPLY_FIXED_FIELDS_SIZE + msg_len +
			    data_len);

    reply->status = status;
    reply->msg_len = msg_len;
    reply->data_len = data_len;
    reply->flags = flags;

    p = pak + TAC_PLUS_HDR_SIZE + TAC_AUTHEN_REPLY_FIXED_FIELDS_SIZE;

    memcpy(p, msg, msg_len);
    p += msg_len;
    memcpy(p, data, data_len);

    if (debug & DEBUG_PACKET_FLAG) {
	report(LOG_DEBUG, "Writing %s size=%d",
	       summarise_outgoing_packet_type(pak), len);
	dump_tacacs_pak(pak);
    }

    reply->msg_len = htons(reply->msg_len);
    reply->data_len = htons(reply->data_len);

    write_packet(pak);
    free(pak);

    return;
}

/* send an authorization reply packet */
void
send_author_reply(u_char status, char *msg, char *data, int arg_cnt,
		  char **args)
{
    u_char *pak, *p;
    HDR *hdr;
    struct author_reply *reply;
    int msg_len;
    int len;
    int data_len;
    int i;

    data_len = (data ? strlen(data) : 0);
    msg_len  = (msg  ? strlen(msg)  : 0);

    /* start calculating final packet size */
    len = TAC_PLUS_HDR_SIZE + TAC_AUTHOR_REPLY_FIXED_FIELDS_SIZE + msg_len +
	  data_len;

    for (i = 0; i < arg_cnt; i++) {
	/* space for the arg and its length */
	len += strlen(args[i]) + 1;
    }

    pak = (u_char *)tac_malloc(len);

    memset(pak, 0, len);

    hdr = (HDR *)pak;

    reply = (struct author_reply *) (pak + TAC_PLUS_HDR_SIZE);

    hdr->version = TAC_PLUS_VER_0;
    hdr->type = TAC_PLUS_AUTHOR;
    hdr->seq_no = ++session.seq_no;
    hdr->flags = TAC_PLUS_UNENCRYPTED;
    if (!(session.flags & SESS_NO_SINGLECONN))
	hdr->flags |= (session.peerflags & TAC_PLUS_SINGLE_CONNECT_FLAG);
    hdr->session_id = htonl(session.session_id);
    hdr->datalength = htonl(len - TAC_PLUS_HDR_SIZE);

    reply->status   = status;
    reply->msg_len  = msg_len;
    reply->data_len = data_len;
    reply->arg_cnt  = arg_cnt;

    p = pak + TAC_PLUS_HDR_SIZE + TAC_AUTHOR_REPLY_FIXED_FIELDS_SIZE;

    /* place arg sizes into packet  */
    for (i = 0; i < arg_cnt; i++) {
	*p++ = strlen(args[i]);
    }

    memcpy(p, msg, msg_len);
    p += msg_len;

    memcpy(p, data, data_len);
    p += data_len;

    /* copy arg bodies into packet */
    for (i = 0; i < arg_cnt; i++) {
	int arglen = strlen(args[i]);

	memcpy(p, args[i], arglen);
	p += arglen;
    }

    if (debug & DEBUG_PACKET_FLAG) {
	report(LOG_DEBUG, "Writing %s size=%d",
	       summarise_outgoing_packet_type(pak), len);
	dump_tacacs_pak(pak);
    }

    reply->msg_len  = htons(reply->msg_len);
    reply->data_len = htons(reply->data_len);

    write_packet(pak);
    free(pak);

    return;
}

void
send_error_reply(int type, char *msg)
{
    switch (type) {
    case TAC_PLUS_AUTHEN:
	send_authen_error(msg);
	break;

    case TAC_PLUS_AUTHOR:
	send_author_reply(AUTHOR_STATUS_ERROR, msg, NULL, 0, NULL);
	break;

    case TAC_PLUS_ACCT:
	send_acct_reply(TAC_PLUS_ACCT_STATUS_ERROR, msg, NULL);
	break;

    default:
	report(LOG_ERR, "Illegal type %d for send_error_reply", type);
	break;
    }

    return;
}

/*
 * Read n bytes from descriptor fd into array ptr with timeout t seconds.
 * Note the timeout is applied to each read, not for the overall operation.
 *
 * Return -1 on error, eof or timeout. Otherwise return number of bytes read.
 */
static int
sockread(int fd, u_char *ptr, int nbytes, int timeout)
{
    int nleft, nread;
    struct pollfd pfds;

    pfds.fd = fd;
    pfds.events = POLLIN | POLLERR | POLLHUP | POLLNVAL;
    nleft = nbytes;

    while (nleft > 0) {
	int status = poll(&pfds, 1, timeout * 1000);

	if (status == 0) {
	    report(LOG_DEBUG, "%s: timeout reading fd %d", session.peer, fd);
	    return(-1);
	}
	if (status < 0) {
	    if (errno == EINTR)
		continue;
	    status = errno;
	    report(LOG_DEBUG, "%s: error in poll %s fd %d", session.peer,
		   strerror(errno), fd);
	    errno = status;
	    return(-1);
	}
	if (pfds.revents & (POLLERR | POLLHUP | POLLNVAL)) {
	    status = errno;
	    report(LOG_DEBUG, "%s: exception on fd %d", session.peer, fd);
	    errno = status;
	    return(-1);
	}
	if (!(pfds.revents & POLLIN)) {
	    status = errno;
	    report(LOG_DEBUG, "%s: spurious return from poll", session.peer);
	    errno = status;
	    continue;
	}
    again:
	nread = read(fd, ptr, nleft);

	if (nread < 0) {
	    if (errno == EINTR)
		goto again;
	    status = errno;
	    report(LOG_DEBUG, "%s %s: error reading fd %d nread=%d %s",
		   session.peer, session.port, fd, nread, strerror(errno));
	    errno = status;
	    return(-1);		/* error */

	} else if (nread == 0) {
	    report(LOG_DEBUG, "%s %s: fd %d eof (connection closed)",
		   session.peer, session.port, fd);
	    errno = 0;
	    return(-1);		/* eof */
	}
	nleft -= nread;
	if (nleft)
	    ptr += nread;
    }
    return(nbytes - nleft);
}

/*
 * Write n bytes to descriptor fd from array ptr with timeout t seconds.
 * Note the timeout is applied to each write, not for the overall operation.
 *
 * Return -1 on error, eof or timeout.  Otherwise return number of bytes
 * written.
 */
static int
sockwrite(int fd, u_char *ptr, int bytes, int timeout)
{
    int remaining, sent;
    struct pollfd pfds;

    pfds.fd = fd;
    pfds.events = POLLOUT | POLLERR | POLLHUP | POLLNVAL;
    sent = 0;

    remaining = bytes;

    while (remaining > 0) {
	int status = poll(&pfds, 1, timeout * 1000);

	if (status == 0) {
	    status = errno;
	    report(LOG_DEBUG, "%s: timeout writing to fd %d", session.peer, fd);
	    errno = status;
	    return(-1);
	}
	if (status < 0) {
	    status = errno;
	    report(LOG_DEBUG, "%s: error in poll fd %d", session.peer, fd);
	    errno = status;
	    return(-1);
	}
	if (pfds.revents & (POLLERR | POLLHUP | POLLNVAL)) {
	    status = errno;
	    report(LOG_DEBUG, "%s: exception on fd %d", session.peer, fd);
	    errno = status;
	    return(-1);	/* error */
	}
	if (!(pfds.revents & POLLOUT)) {
	    report(LOG_DEBUG, "%s: spurious return from poll", session.peer);
	    continue;
	}
	sent = write(fd, ptr, remaining);

	if (sent <= 0) {
	    status = errno;
	    report(LOG_DEBUG, "%s: error writing fd %d sent=%d", session.peer,
		   fd, sent);
	    errno = status;
	    return(sent);	/* error */
	}
	remaining -= sent;
	ptr += sent;
    }
    return(bytes - remaining);
}

/* write a packet to the wire, encrypting it */
static int
write_packet(u_char *pak)
{
    HDR		*hdr = (HDR *)pak;
    u_char	*data;
    int		len;
    char	*tkey;

    len = TAC_PLUS_HDR_SIZE + ntohl(hdr->datalength);

    /* the data start here */
    data = pak + TAC_PLUS_HDR_SIZE;

    /* encrypt the data portion */
    tkey = cfg_get_host_key(session.peerip);
    if (tkey == NULL && !STREQ(session.peer, session.peerip)) {
	tkey = cfg_get_host_prompt(session.peer);
    }
    if (tkey == NULL)
	tkey = session.key;
    if (md5_xor((HDR *)pak, data, tkey)) {
	report(LOG_ERR, "%s: write_packet: error encrypting data",
	       session.peer);
	return(-1);
    }

    if (sockwrite(session.sock, pak, len, TAC_PLUS_WRITE_TIMEOUT) != len) {
	return(-1);
    }
    session.last_exch = time(NULL);

    return(0);
}