path: root/sys/netinet/ip_esp_old.c

/*	$OpenBSD: ip_esp_old.c,v 1.2 1997/07/14 08:48:46 provos Exp $	*/

/*
 * The author of this code is John Ioannidis, ji@tla.org,
 * 	(except when noted otherwise).
 *
 * This code was written for BSD/OS in Athens, Greece, in November 1995.
 *
 * Ported to OpenBSD and NetBSD, with additional transforms, in December 1996,
 * by Angelos D. Keromytis, kermit@forthnet.gr.
 *
 * Copyright (C) 1995, 1996, 1997 by John Ioannidis and Angelos D. Keromytis.
 *	
 * Permission to use, copy, and modify this software without fee
 * is hereby granted, provided that this entire notice is included in
 * all copies of any software which is or includes a copy or
 * modification of this software.
 *
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTY. IN PARTICULAR, NEITHER AUTHOR MAKES ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
 * MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
 * PURPOSE.
 */

/*
 * DES-CBC
 * Per RFCs 1829/1851 (Metzger & Simpson)
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <machine/cpu.h>

#include <net/if.h>
#include <net/route.h>
#include <net/netisr.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>

#include <sys/socketvar.h>
#include <net/raw_cb.h>
#include <net/encap.h>

#include <netinet/ip_icmp.h>
#include <netinet/ip_ipsp.h>
#include <netinet/ip_esp.h>
#include <dev/rndvar.h>
#include <sys/syslog.h>

extern void des_ecb3_encrypt(caddr_t, caddr_t, caddr_t, caddr_t, caddr_t, int);
extern void des_ecb_encrypt(caddr_t, caddr_t, caddr_t, int);
extern void des_set_key(caddr_t, caddr_t);

int
esp_old_attach()
{
#ifdef ENCDEBUG
    if (encdebug)
      printf("esp_old_attach(): setting up\n");
#endif /* ENCDEBUG */
    return 0;
}

/*
 * esp_old_init() is called when an SPI is being set up. It interprets the
 * encap_msghdr present in m, and sets up the transformation data, in
 * this case, the encryption and decryption key schedules
 */

int
esp_old_init(struct tdb *tdbp, struct xformsw *xsp, struct mbuf *m)
{
    struct esp_old_xdata *xd;
    struct esp_old_xencap xenc;
    struct encap_msghdr *em;
    u_int32_t rk[6];

    if (m->m_len < ENCAP_MSG_FIXED_LEN)
    {
	if ((m = m_pullup(m, ENCAP_MSG_FIXED_LEN)) == NULL)
	{
#ifdef ENCDEBUG
	    if (encdebug)
	      printf("esp_old_init(): m_pullup failed\n");
#endif /* ENCDEBUG */
	    return ENOBUFS;
	}
    }

    em = mtod(m, struct encap_msghdr *);
    if (em->em_msglen - EMT_SETSPI_FLEN <= ESP_OLD_XENCAP_LEN)
    {
	log(LOG_WARNING, "esp_old_init(): initialization failed");
	return EINVAL;
    }

    /* Just copy the standard fields */
    m_copydata(m, EMT_SETSPI_FLEN, ESP_OLD_XENCAP_LEN, (caddr_t) &xenc);

    /* Check whether the encryption algorithm is supported */
    switch (xenc.edx_enc_algorithm)
    {
        case ALG_ENC_DES:
        case ALG_ENC_3DES:
#ifdef ENCDEBUG
            if (encdebug)
              printf("esp_old_init(): initialized TDB with enc algorithm %d\n",
                     xenc.edx_enc_algorithm);
#endif /* ENCDEBUG */
            break;

        default:
            log(LOG_WARNING, "esp_old_init(): unsupported encryption algorithm %d specified", xenc.edx_enc_algorithm);
            return EINVAL;
    }

    if (xenc.edx_ivlen + xenc.edx_keylen + EMT_SETSPI_FLEN +
	ESP_OLD_XENCAP_LEN != em->em_msglen)
    {
	log(LOG_WARNING, "esp_old_init(): message length (%d) doesn't match",
	    em->em_msglen);
	return EINVAL;
    }

    switch (xenc.edx_enc_algorithm)
    {
	case ALG_ENC_DES:
	    if ((xenc.edx_ivlen != 4) && (xenc.edx_ivlen != 8))
	    {
	       	log(LOG_WARNING, "esp_old_init(): unsupported IV length %d",
		    xenc.edx_ivlen);
		return EINVAL;
	    }

	    if (xenc.edx_keylen != 8)
	    {
		log(LOG_WARNING, "esp_old_init(): bad key length",
		    xenc.edx_keylen);
		return EINVAL;
	    }

	    break;

	case ALG_ENC_3DES:
            if ((xenc.edx_ivlen != 4) && (xenc.edx_ivlen != 8))
            {
                log(LOG_WARNING, "esp_old_init(): unsupported IV length %d",
                    xenc.edx_ivlen);
                return EINVAL;
            }

            if (xenc.edx_keylen != 24)
            {
                log(LOG_WARNING, "esp_old_init(): bad key length",
                    xenc.edx_keylen);
                return EINVAL;
            }

            break;
    }

    MALLOC(tdbp->tdb_xdata, caddr_t, sizeof(struct esp_old_xdata),
	   M_XDATA, M_WAITOK);
    if (tdbp->tdb_xdata == NULL)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_init(): MALLOC() failed\n");
#endif /* ENCDEBUG */
      	return ENOBUFS;
    }

    bzero(tdbp->tdb_xdata, sizeof(struct esp_old_xdata));
    xd = (struct esp_old_xdata *) tdbp->tdb_xdata;

    /* Pointer to the transform */
    tdbp->tdb_xform = xsp;

    xd->edx_ivlen = xenc.edx_ivlen;
    xd->edx_enc_algorithm = xenc.edx_enc_algorithm;

    /* Copy the IV */
    m_copydata(m, EMT_SETSPI_FLEN + ESP_OLD_XENCAP_LEN, xd->edx_ivlen,
	       (caddr_t) xd->edx_iv);

    /* Copy the key material */
    m_copydata(m, EMT_SETSPI_FLEN + ESP_OLD_XENCAP_LEN + xd->edx_ivlen,
	       xenc.edx_keylen, (caddr_t) rk);

    switch (xd->edx_enc_algorithm)
    {
	case ALG_ENC_DES:
	    des_set_key((caddr_t) rk, (caddr_t) (xd->edx_eks[0]));
	    break;

	case ALG_ENC_3DES:
	    des_set_key((caddr_t) rk, (caddr_t) (xd->edx_eks[0]));
	    des_set_key((caddr_t) rk + 2, (caddr_t) (xd->edx_eks[1]));
	    des_set_key((caddr_t) rk + 4, (caddr_t) (xd->edx_eks[2]));
	    break;
    }

    bzero(rk, 6 * sizeof(u_int32_t));		/* paranoid */

    bzero(ipseczeroes, IPSEC_ZEROES_SIZE);	/* paranoid */

    return 0;
}

/* Free the memory */
int
esp_old_zeroize(struct tdb *tdbp)
{
#ifdef ENCDEBUG
    if (encdebug)
      printf("esp_old_zeroize(): freeing memory\n");
#endif /* ENCDEBUG */
    FREE(tdbp->tdb_xdata, M_XDATA);
    return 0;
}

/*
 * esp_old_input() gets called to decrypt an input packet
 */
struct mbuf *
esp_old_input(struct mbuf *m, struct tdb *tdb)
{
    struct esp_old_xdata *xd;
    struct ip *ip, ipo;
    u_char iv[ESP_3DES_IVS], niv[ESP_3DES_IVS], blk[ESP_3DES_BLKS], opts[40];
    u_char *idat, *odat;
    struct esp_old *esp;
    struct ifnet *rcvif;
    int ohlen, plen, ilen, olen, i, blks;
    struct mbuf *mi, *mo;

    xd = (struct esp_old_xdata *) tdb->tdb_xdata;

    switch (xd->edx_enc_algorithm)
    {
	case ALG_ENC_DES:
	    blks = ESP_DES_BLKS;
	    break;

	case ALG_ENC_3DES:
	    blks = ESP_3DES_BLKS;
	    break;

	default:
            log(LOG_ALERT,
                "esp_old_input(): unsupported algorithm %d in SA %x/%08x",
                xd->edx_enc_algorithm, tdb->tdb_dst, tdb->tdb_spi);
            m_freem(m);
            return NULL;
    }

    rcvif = m->m_pkthdr.rcvif;
    if (rcvif == NULL)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_input(): receive interface is NULL!!!\n");
#endif /* ENCDEBUG */
	rcvif = &enc_softc;
    }

    if (m->m_len < sizeof(struct ip))
    {
	if ((m = m_pullup(m, sizeof(struct ip))) == NULL)
	{
#ifdef ENCDEBUG
	    if (encdebug)
	      printf("esp_old_input(): m_pullup() failed\n");
#endif /* ENCDEBUG */
	    espstat.esps_hdrops++;
	    return NULL;
	}
    }

    ip = mtod(m, struct ip *);
    ohlen = (ip->ip_hl << 2) + ESP_OLD_FLENGTH;

    /* Make sure the IP header, any IP options, and the ESP header are here */
    if (m->m_len < ohlen + blks)
    {
	if ((m = m_pullup(m, ohlen + blks)) == NULL)
	{
#ifdef ENCDEBUG
            if (encdebug)
              printf("esp_old_input(): m_pullup() failed\n");
#endif /* ENCDEBUG */
            espstat.esps_hdrops++;
            return NULL;
	}

	ip = mtod(m, struct ip *);
	esp = (struct esp_old *) ((u_int8_t *) ip + (ip->ip_hl << 2));
    }
    else
      esp = (struct esp_old *) (ip + 1);

    ipo = *ip;

    /* Skip the IP header, IP options, SPI and IV */
    plen = m->m_pkthdr.len - (ip->ip_hl << 2) - sizeof(u_int32_t) -
	   xd->edx_ivlen;
    if (plen & (blks - 1))
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_input(): payload not a multiple of %d octets for packet from %x to %x, spi %08x\n", blks, ipo.ip_src, ipo.ip_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
	espstat.esps_badilen++;
	m_freem(m);
	return NULL;
    }

    ilen = m->m_len - (ip->ip_hl << 2) - sizeof(u_int32_t) - 4;
    idat = mtod(m, unsigned char *) + (ip->ip_hl << 2) + sizeof(u_int32_t) + 4;

    /* Get the IV */
    iv[0] = esp->esp_iv[0];
    iv[1] = esp->esp_iv[1];
    iv[2] = esp->esp_iv[2];
    iv[3] = esp->esp_iv[3];
    if (xd->edx_ivlen == 4)		/* Half-IV */
    {
	iv[4] = ~esp->esp_iv[0];
	iv[5] = ~esp->esp_iv[1];
	iv[6] = ~esp->esp_iv[2];
	iv[7] = ~esp->esp_iv[3];
    }
    else
    {
	iv[4] = esp->esp_iv[4];
	iv[5] = esp->esp_iv[5];
	iv[6] = esp->esp_iv[6];
	iv[7] = esp->esp_iv[7];

	/* Adjust the lengths accordingly */
	ilen -= 4;
	idat += 4;
    }

    olen = ilen;
    odat = idat;
    mi = mo = m;
    i = 0;

    /*
     * At this point:
     *   plen is # of encapsulated payload octets
     *   ilen is # of octets left in this mbuf
     *   idat is first encapsulated payload octed in this mbuf
     *   same for olen and odat
     *   iv contains the IV.
     *   mi and mo point to the first mbuf
     *
     * From now on until the end of the mbuf chain:
     *   . move the next eight octets of the chain into blk[]
     *     (ilen, idat, and mi are adjusted accordingly)
     *     and save it back into iv[]
     *   . decrypt blk[], xor with iv[], put back into chain
     *     (olen, odat, amd mo are adjusted accordingly)
     *   . repeat
     */

    while (plen > 0)		/* while not done */
    {
	while (ilen == 0)	/* we exhausted previous mbuf */
	{
	    mi = mi->m_next;
	    if (mi == NULL)
	      panic("esp_old_input(): bad chain (i)\n");

	    ilen = mi->m_len;
	    idat = (u_char *) mi->m_data;
	}

	blk[i] = niv[i] = *idat++;
	i++;
	ilen--;

	if (i == blks)
	{
	    switch (xd->edx_enc_algorithm)
	    {
		case ALG_ENC_DES:
	    	    des_ecb_encrypt(blk, blk, (caddr_t) (xd->edx_eks[0]), 0);
		    break;

		case ALG_ENC_3DES:
		    des_ecb3_encrypt(blk, blk, (caddr_t) (xd->edx_eks[2]),
                             	     (caddr_t) (xd->edx_eks[1]),
                             	     (caddr_t) (xd->edx_eks[0]), 0);
		    break;
	    }

	    for (i = 0; i < blks; i++)
	    {
		while (olen == 0)
		{
		    mo = mo->m_next;
		    if (mo == NULL)
		      panic("esp_old_input(): bad chain (o)\n");

		    olen = mo->m_len;
		    odat = (u_char *) mo->m_data;
		}

		*odat = blk[i] ^ iv[i];
		iv[i] = niv[i];
		blk[i] = *odat++; /* needed elsewhere */
		olen--;
	    }

	    i = 0;
	}

	plen--;
    }

    /* Save the options */
    m_copydata(m, sizeof(struct ip), (ipo.ip_hl << 2) - sizeof(struct ip),
	       (caddr_t) opts);

    /*
     * Now, the entire chain has been decrypted. As a side effect,
     * blk[7] contains the next protocol, and blk[6] contains the
     * amount of padding the original chain had. Chop off the
     * appropriate parts of the chain, and return.
     */

    m_adj(m, -blk[6] - 2);
    m_adj(m, 4 + xd->edx_ivlen);

    if (m->m_len < (ipo.ip_hl << 2))
    {
	m = m_pullup(m, (ipo.ip_hl << 2));
	if (m == NULL)
	{
#ifdef ENCDEBUG
	    if (encdebug)
	      printf("esp_old_input(): m_pullup() failed for packet from %x to %x, SA %x/%08x\n", ipo.ip_src, ipo.ip_dst, tdb->tdb_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
	    return NULL;
	}
    }

    ip = mtod(m, struct ip *);
    ipo.ip_p = blk[7];
    ipo.ip_id = htons(ipo.ip_id);
    ipo.ip_off = 0;
    ipo.ip_len += (ipo.ip_hl << 2) - sizeof(u_int32_t) - xd->edx_ivlen -
		  blk[6] - 2;
    ipo.ip_len = htons(ipo.ip_len);
    ipo.ip_sum = 0;
    *ip = ipo;

    /* Copy the options back */
    m_copyback(m, sizeof(struct ip), (ipo.ip_hl << 2) - sizeof(struct ip),
	       (caddr_t) opts);

    ip->ip_sum = in_cksum(m, (ip->ip_hl << 2));

    /* Update the counters */
    tdb->tdb_cur_packets++;
    tdb->tdb_cur_bytes += ntohs(ip->ip_len) - (ip->ip_hl << 2) + blk[6] + 2;
    espstat.esps_ibytes += ntohs(ip->ip_len) - (ip->ip_hl << 2) + blk[6] + 2;

    return m;
}

int
esp_old_output(struct mbuf *m, struct sockaddr_encap *gw, struct tdb *tdb,
	      struct mbuf **mp)
{
    struct esp_old_xdata *xd;
    struct ip *ip, ipo;
    int i, ilen, olen, ohlen, nh, rlen, plen, padding;
    u_int32_t spi;
    struct mbuf *mi, *mo;
    u_char *pad, *idat, *odat;
    u_char iv[ESP_3DES_IVS], blk[ESP_3DES_IVS], opts[40];
    int iphlen, blks;

    xd = (struct esp_old_xdata *) tdb->tdb_xdata;

    switch (xd->edx_enc_algorithm)
    {
        case ALG_ENC_DES:
            blks = ESP_DES_BLKS;
            break;

        case ALG_ENC_3DES:
            blks = ESP_3DES_BLKS;
            break;

        default:
            log(LOG_ALERT,
                "esp_old_output(): unsupported algorithm %d in SA %x/%08x",
                xd->edx_enc_algorithm, tdb->tdb_dst, tdb->tdb_spi);
            m_freem(m);
            return NULL;
    }

    espstat.esps_output++;

    m = m_pullup(m, sizeof(struct ip));
    if (m == NULL)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_output(): m_pullup() failed for SA %x/%08x\n",
		 tdb->tdb_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
        return ENOBUFS;
    }

    ip = mtod(m, struct ip *);
    spi = tdb->tdb_spi;
    iphlen = (ip->ip_hl << 2);

    /*
     * If options are present, pullup the IP header and the options.
     */
    if (iphlen != sizeof(struct ip))
    {
	m = m_pullup(m, iphlen);
	if (m == NULL)
        {
#ifdef ENCDEBUG
	    if (encdebug)
	      printf("esp_old_output(): m_pullup() failed for SA %x/%08x\n",
		     tdb->tdb_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
	    return ENOBUFS;
	}

	ip = mtod(m, struct ip *);

	/* Keep the options */
	m_copydata(m, sizeof(struct ip), iphlen - sizeof(struct ip),
		   (caddr_t) opts);
    }
    
    ilen = ntohs(ip->ip_len);
    ohlen = sizeof(u_int32_t) + xd->edx_ivlen;

    ipo = *ip;
    nh = ipo.ip_p;

    rlen = ilen - iphlen; /* raw payload length  */
    padding = ((blks - ((rlen + 2) % blks)) % blks) + 2;

    pad = (u_char *) m_pad(m, padding);
    if (pad == NULL)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_output(): m_pad() failed for SA %x/%08x\n",
		 tdb->tdb_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
      	return ENOBUFS;
    }

    pad[padding - 2] = padding - 2;
    pad[padding - 1] = nh;

    plen = rlen + padding;
    mi = mo = m;
    ilen = olen = m->m_len - iphlen;
    idat = odat = mtod(m, u_char *) + iphlen;
    i = 0;

    /*
     * We are now ready to encrypt the payload. 
     */

    iv[0] = xd->edx_iv[0];
    iv[1] = xd->edx_iv[1];
    iv[2] = xd->edx_iv[2];
    iv[3] = xd->edx_iv[3];

    if (xd->edx_ivlen == 4)	/* Half-IV */
    {
	iv[4] = ~xd->edx_iv[0];
	iv[5] = ~xd->edx_iv[1];
	iv[6] = ~xd->edx_iv[2];
	iv[7] = ~xd->edx_iv[3];
    }
    else
    {
	iv[4] = xd->edx_iv[4];
	iv[5] = xd->edx_iv[5];
	iv[6] = xd->edx_iv[6];
	iv[7] = xd->edx_iv[7];
    }

    while (plen > 0)		/* while not done */
    {
	while (ilen == 0)	/* we exhausted previous mbuf */
	{
	    mi = mi->m_next;
	    if (mi == NULL)
	      panic("esp_old_output(): bad chain (i)\n");

	    ilen = mi->m_len;
	    idat = (u_char *) mi->m_data;
	}

	blk[i] = *idat++ ^ iv[i];
		
	i++;
	ilen--;

	if (i == blks)
	{
	    switch (xd->edx_enc_algorithm)
	    {
		case ALG_ENC_DES:
	    	    des_ecb_encrypt(blk, blk, (caddr_t) (xd->edx_eks[0]), 1);
		    break;

		case ALG_ENC_3DES:
                    des_ecb3_encrypt(blk, blk, (caddr_t) (xd->edx_eks[0]),
                            	     (caddr_t) (xd->edx_eks[1]),
                             	     (caddr_t) (xd->edx_eks[2]), 1);
		    break;
	    }

	    for (i = 0; i < blks; i++)
	    {
		while (olen == 0)
		{
		    mo = mo->m_next;
		    if (mo == NULL)
		      panic("esp_old_output(): bad chain (o)\n");

		    olen = mo->m_len;
		    odat = (u_char *) mo->m_data;
		}

		*odat++ = blk[i];
		iv[i] = blk[i];
		olen--;
	    }

	    i = 0;
	}

	plen--;
    }

    /*
     * Done with encryption. Let's wedge in the ESP header
     * and send it out.
     */

    M_PREPEND(m, ohlen, M_DONTWAIT);
    if (m == NULL)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_output(): M_PREPEND failed, SA %x/%08x\n",
		 tdb->tdb_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
        return ENOBUFS;
    }

    m = m_pullup(m, iphlen + ohlen);
    if (m == NULL)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("esp_old_output(): m_pullup() failed, SA %x/%08x\n",
		 tdb->tdb_dst, tdb->tdb_spi);
#endif /* ENCDEBUG */
        return ENOBUFS;
    }

    ipo.ip_len = htons(iphlen + ohlen + rlen + padding);
    ipo.ip_p = IPPROTO_ESP;

    iv[0] = xd->edx_iv[0];
    iv[1] = xd->edx_iv[1];
    iv[2] = xd->edx_iv[2];
    iv[3] = xd->edx_iv[3];

    if (xd->edx_ivlen == 8)
    {
	iv[4] = xd->edx_iv[4];
	iv[5] = xd->edx_iv[5];
	iv[6] = xd->edx_iv[6];
	iv[7] = xd->edx_iv[7];
    }

    /* Save the last encrypted block, to be used as the next IV */
    bcopy(blk, xd->edx_iv, xd->edx_ivlen);

    m_copyback(m, 0, sizeof(struct ip), (caddr_t) &ipo);

    /* Copy options, if existing */
    if (iphlen != sizeof(struct ip))
      m_copyback(m, sizeof(struct ip), iphlen - sizeof(struct ip),
		 (caddr_t) opts);

    m_copyback(m, iphlen, sizeof(u_int32_t), (caddr_t) &spi);
    m_copyback(m, iphlen + sizeof(u_int32_t), xd->edx_ivlen, (caddr_t) iv);
	
    *mp = m;

    /* Update the counters */
    tdb->tdb_cur_packets++;
    tdb->tdb_cur_bytes += rlen + padding;
    espstat.esps_obytes += rlen + padding;

    return 0;
}	
	
/*
 *
 *
 * m_pad(m, n) pads <m> with <n> bytes at the end. The packet header
 * length is updated, and a pointer to the first byte of the padding
 * (which is guaranteed to be all in one mbuf) is returned.
 *
 */

caddr_t
m_pad(struct mbuf *m, int n)
{
    register struct mbuf *m0, *m1;
    register int len, pad;
    caddr_t retval;
    u_int8_t dat;
	
    if (n <= 0)			/* no stupid arguments */
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("m_pad(): pad length invalid (%d)\n", n);
#endif /* ENCDEBUG */
        return NULL;
    }

    len = m->m_pkthdr.len;
    pad = n;

    m0 = m;

    while (m0->m_len < len)
    {
	len -= m0->m_len;
	m0 = m0->m_next;
    }

    if (m0->m_len != len)
    {
#ifdef ENCDEBUG
	if (encdebug)
	  printf("m_pad(): length mismatch (should be %d instead of %d)\n",
		 m->m_pkthdr.len, m->m_pkthdr.len + m0->m_len - len);
#endif /* ENCDEBUG */
	m_freem(m);
	return NULL;
    }

    if ((m0->m_flags & M_EXT) ||
	(m0->m_data + m0->m_len + pad >= &(m0->m_dat[MLEN])))
    {
	/*
	 * Add an mbuf to the chain
	 */

	MGET(m1, M_DONTWAIT, MT_DATA);
	if (m1 == 0)
	{
	    m_freem(m0);
#ifdef ENCDEBUG
	    if (encdebug)
	      printf("m_pad(): cannot append\n");
#endif /* ENCDEBUG */
	    return NULL;
	}

	m0->m_next = m1;
	m0 = m1;
	m0->m_len = 0;
    }

    retval = m0->m_data + m0->m_len;
    m0->m_len += pad;
    m->m_pkthdr.len += pad;

    for (len = 0; len < n; len++)
    {
	get_random_bytes((void *) &dat, sizeof(u_int8_t));
	retval[len] = len + dat;
    }

    return retval;
}