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radmsg.c

/*
 * Copyright (C) 2006-2008 Stig Venaas <venaas@uninett.no>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 */

#ifdef SYS_SOLARIS9
#include <sys/inttypes.h>
#else
#include <stdint.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include "list.h"
#include "tlv11.h"
#include "radmsg.h"
#include "debug.h"
#include <pthread.h>
#include <openssl/hmac.h>
#include <openssl/rand.h>

#define RADLEN(x) ntohs(((uint16_t *)(x))[1])

void radmsg_free(struct radmsg *msg) {
    if (msg) {
        freetlvlist(msg->attrs);
        free(msg);
    }
}

struct radmsg *radmsg_init(uint8_t code, uint8_t id, uint8_t *auth) {
    struct radmsg *msg;
    
    msg = malloc(sizeof(struct radmsg));
    if (!msg)
        return NULL;
    memset(msg, 0, sizeof(struct radmsg));
    msg->attrs = list_create();
    if (!msg->attrs) {
      free(msg);
        return NULL;
    } 
    msg->code = code;
    msg->id = id;
    if (auth)
      memcpy(msg->auth, auth, 16);
    else if (!RAND_bytes(msg->auth, 16)) {
      free(msg);
      return NULL;
    } 
    return msg;
}

int radmsg_add(struct radmsg *msg, struct tlv *attr) {
    if (!msg || !msg->attrs)
        return 1;
    if (!attr)
        return 0;
    return list_push(msg->attrs, attr);
}

/* returns first tlv of the given type */
struct tlv *radmsg_gettype(struct radmsg *msg, uint8_t type) {
    struct list_node *node;
    struct tlv *tlv;

    if (!msg)
        return NULL;
    for (node = list_first(msg->attrs); node; node = list_next(node)) {
        tlv = (struct tlv *)node->data;
        if (tlv->t == type)
            return tlv;
    }
    return NULL;
}

int _checkmsgauth(unsigned char *rad, uint8_t *authattr, uint8_t *secret) {
    static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
    static unsigned char first = 1;
    static HMAC_CTX hmacctx;
    unsigned int md_len;
    uint8_t auth[16], hash[EVP_MAX_MD_SIZE];
    
    pthread_mutex_lock(&lock);
    if (first) {
      HMAC_CTX_init(&hmacctx);
      first = 0;
    }

    memcpy(auth, authattr, 16);
    memset(authattr, 0, 16);
    md_len = 0;
    HMAC_Init_ex(&hmacctx, secret, strlen((char *)secret), EVP_md5(), NULL);
    HMAC_Update(&hmacctx, rad, RADLEN(rad));
    HMAC_Final(&hmacctx, hash, &md_len);
    memcpy(authattr, auth, 16);
    if (md_len != 16) {
      debug(DBG_WARN, "message auth computation failed");
      pthread_mutex_unlock(&lock);
      return 0;
    }

    if (memcmp(auth, hash, 16)) {
      debug(DBG_WARN, "message authenticator, wrong value");
      pthread_mutex_unlock(&lock);
      return 0;
    } 
      
    pthread_mutex_unlock(&lock);
    return 1;
}

int _validauth(unsigned char *rad, unsigned char *reqauth, unsigned char *sec) {
    static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
    static unsigned char first = 1;
    static EVP_MD_CTX mdctx;
    unsigned char hash[EVP_MAX_MD_SIZE];
    unsigned int len;
    int result;
    
    pthread_mutex_lock(&lock);
    if (first) {
      EVP_MD_CTX_init(&mdctx);
      first = 0;
    }

    len = RADLEN(rad);
    
    result = (EVP_DigestInit_ex(&mdctx, EVP_md5(), NULL) &&
            EVP_DigestUpdate(&mdctx, rad, 4) &&
            EVP_DigestUpdate(&mdctx, reqauth, 16) &&
            (len <= 20 || EVP_DigestUpdate(&mdctx, rad + 20, len - 20)) &&
            EVP_DigestUpdate(&mdctx, sec, strlen((char *)sec)) &&
            EVP_DigestFinal_ex(&mdctx, hash, &len) &&
            len == 16 &&
            !memcmp(hash, rad + 4, 16));
    pthread_mutex_unlock(&lock);
    return result;
}

int _createmessageauth(unsigned char *rad, unsigned char *authattrval, uint8_t *secret) {
    static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
    static unsigned char first = 1;
    static HMAC_CTX hmacctx;
    unsigned int md_len;

    if (!authattrval)
      return 1;
    
    pthread_mutex_lock(&lock);
    if (first) {
      HMAC_CTX_init(&hmacctx);
      first = 0;
    }

    memset(authattrval, 0, 16);
    md_len = 0;
    HMAC_Init_ex(&hmacctx, secret, strlen((char *)secret), EVP_md5(), NULL);
    HMAC_Update(&hmacctx, rad, RADLEN(rad));
    HMAC_Final(&hmacctx, authattrval, &md_len);
    if (md_len != 16) {
      debug(DBG_WARN, "message auth computation failed");
      pthread_mutex_unlock(&lock);
      return 0;
    }
    pthread_mutex_unlock(&lock);
    return 1;
}

int _radsign(unsigned char *rad, unsigned char *sec) {
    static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
    static unsigned char first = 1;
    static EVP_MD_CTX mdctx;
    unsigned int md_len;
    int result;

    pthread_mutex_lock(&lock);
    if (first) {
      EVP_MD_CTX_init(&mdctx);
      first = 0;
    }

    result = (EVP_DigestInit_ex(&mdctx, EVP_md5(), NULL) &&
            EVP_DigestUpdate(&mdctx, rad, RADLEN(rad)) &&
            EVP_DigestUpdate(&mdctx, sec, strlen((char *)sec)) &&
            EVP_DigestFinal_ex(&mdctx, rad + 4, &md_len) &&
            md_len == 16);
    pthread_mutex_unlock(&lock);
    return result;
}

uint8_t *radmsg2buf(struct radmsg *msg, uint8_t *secret) {
    struct list_node *node;
    struct tlv *tlv;
    int size;
    uint8_t *buf, *p, *msgauth = NULL;

    if (!msg || !msg->attrs)
        return NULL;
    size = 20;
    for (node = list_first(msg->attrs); node; node = list_next(node))
        size += 2 + ((struct tlv *)node->data)->l;
    if (size > 65535)
        return NULL;
    buf = malloc(size);
    if (!buf)
        return NULL;
    
    p = buf;
    *p++ = msg->code;
    *p++ = msg->id;
    *(uint16_t *)p = htons(size);
    p += 2;
    memcpy(p, msg->auth, 16);
    p += 16;

    for (node = list_first(msg->attrs); node; node = list_next(node)) {
        tlv = (struct tlv *)node->data;
        p = tlv2buf(p, tlv);
      p[-1] += 2;
      if (tlv->t == RAD_Attr_Message_Authenticator && secret)
          msgauth = p;
        p += tlv->l;
    }
    if (msgauth && !_createmessageauth(buf, msgauth, secret)) {
      free(buf);
      return NULL;
    }
    if (secret) {
      if ((msg->code == RAD_Access_Accept || msg->code == RAD_Access_Reject || msg->code == RAD_Access_Challenge || msg->code == RAD_Accounting_Response || msg->code == RAD_Accounting_Request) && !_radsign(buf, secret)) {
          free(buf);
          return NULL;
      }
      if (msg->code == RAD_Accounting_Request)
          memcpy(msg->auth, buf + 4, 16);
    }
    return buf;
}

/* if secret set we also validate message authenticator if present */
struct radmsg *buf2radmsg(uint8_t *buf, uint8_t *secret, uint8_t *rqauth) {
    struct radmsg *msg;
    uint8_t t, l, *v = NULL, *p, auth[16];
    uint16_t len;
    struct tlv *attr;
    
    len = RADLEN(buf);
    if (len < 20)
      return NULL;

    if (secret && buf[0] == RAD_Accounting_Request) {
      memset(auth, 0, 16);
      if (!_validauth(buf, auth, secret)) {
          debug(DBG_WARN, "buf2radmsg: Accounting-Request message authentication failed");
          return NULL;
      }
    }

    if (rqauth && !_validauth(buf, rqauth, secret)) {
      debug(DBG_WARN, "buf2radmsg: Invalid auth, ignoring reply");
      return NULL;
    }
      
    msg = radmsg_init(buf[0], buf[1], (uint8_t *)buf + 4);
    if (!msg)
        return NULL;

    p = buf + 20;
    while (p - buf + 2 <= len) {
      t = *p++;
        l = *p++;
      if (l < 2) {
          debug(DBG_WARN, "buf2radmsg: invalid attribute length %d", l);
          radmsg_free(msg);
          return NULL;
      }
      l -= 2;
        if (l) {
            if (p - buf + l > len) {
            debug(DBG_WARN, "buf2radmsg: attribute length %d exceeds packet length", l + 2);
            radmsg_free(msg);
            return NULL;
          }
            v = p;
            p += l;
        }
      
      if (t == RAD_Attr_Message_Authenticator && secret) {
          if (rqauth)
            memcpy(buf + 4, rqauth, 16);
          if (l != 16 || !_checkmsgauth(buf, v, secret)) {
            debug(DBG_WARN, "buf2radmsg: message authentication failed");
            if (rqauth)
                memcpy(buf + 4, msg->auth, 16);
            radmsg_free(msg);
            return NULL;
          }
          if (rqauth)
            memcpy(buf + 4, msg->auth, 16);
          debug(DBG_DBG, "buf2radmsg: message auth ok");
      }

        attr = maketlv(t, l, v);
        if (!attr || !radmsg_add(msg, attr)) {
            freetlv(attr);
          radmsg_free(msg);
          return NULL;
        }
    }
    return msg;
}

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