gss_krb5_crypto.c

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/*
 *  linux/net/sunrpc/gss_krb5_crypto.c
 *
 *  Copyright (c) 2000-2008 The Regents of the University of Michigan.
 *  All rights reserved.
 *
 *  Andy Adamson   <[email protected]>
 *  Bruce Fields   <[email protected]>
 */

/*
 * Copyright (C) 1998 by the FundsXpress, INC.
 *
 * All rights reserved.
 *
 * Export of this software from the United States of America may require
 * a specific license from the United States Government.  It is the
 * responsibility of any person or organization contemplating export to
 * obtain such a license before exporting.
 *
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of FundsXpress. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  FundsXpress makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <linux/err.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/scatterlist.h>
#include <linux/crypto.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/random.h>
#include <linux/sunrpc/gss_krb5.h>
#include <linux/sunrpc/xdr.h>

#ifdef RPC_DEBUG
# define RPCDBG_FACILITY        RPCDBG_AUTH
#endif

u32
krb5_encrypt(
    struct crypto_blkcipher *tfm,
    void * iv,
    void * in,
    void * out,
    int length)
{
    u32 ret = -EINVAL;
    struct scatterlist sg[1];
    u8 local_iv[GSS_KRB5_MAX_BLOCKSIZE] = {0};
    struct blkcipher_desc desc = { .tfm = tfm, .info = local_iv };

    if (length % crypto_blkcipher_blocksize(tfm) != 0)
        goto out;

    if (crypto_blkcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
        dprintk("RPC:       gss_k5encrypt: tfm iv size too large %d\n",
            crypto_blkcipher_ivsize(tfm));
        goto out;
    }

    if (iv)
        memcpy(local_iv, iv, crypto_blkcipher_ivsize(tfm));

    memcpy(out, in, length);
    sg_init_one(sg, out, length);

    ret = crypto_blkcipher_encrypt_iv(&desc, sg, sg, length);
out:
    dprintk("RPC:       krb5_encrypt returns %d\n", ret);
    return ret;
}

u32
krb5_decrypt(
     struct crypto_blkcipher *tfm,
     void * iv,
     void * in,
     void * out,
     int length)
{
    u32 ret = -EINVAL;
    struct scatterlist sg[1];
    u8 local_iv[GSS_KRB5_MAX_BLOCKSIZE] = {0};
    struct blkcipher_desc desc = { .tfm = tfm, .info = local_iv };

    if (length % crypto_blkcipher_blocksize(tfm) != 0)
        goto out;

    if (crypto_blkcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
        dprintk("RPC:       gss_k5decrypt: tfm iv size too large %d\n",
            crypto_blkcipher_ivsize(tfm));
        goto out;
    }
    if (iv)
        memcpy(local_iv,iv, crypto_blkcipher_ivsize(tfm));

    memcpy(out, in, length);
    sg_init_one(sg, out, length);

    ret = crypto_blkcipher_decrypt_iv(&desc, sg, sg, length);
out:
    dprintk("RPC:       gss_k5decrypt returns %d\n",ret);
    return ret;
}

static int
checksummer(struct scatterlist *sg, void *data)
{
    struct hash_desc *desc = data;

    return crypto_hash_update(desc, sg, sg->length);
}

static int
arcfour_hmac_md5_usage_to_salt(unsigned int usage, u8 salt[4])
{
    unsigned int ms_usage;

    switch (usage) {
    case KG_USAGE_SIGN:
        ms_usage = 15;
        break;
    case KG_USAGE_SEAL:
        ms_usage = 13;
        break;
    default:
        return -EINVAL;
    }
    salt[0] = (ms_usage >> 0) & 0xff;
    salt[1] = (ms_usage >> 8) & 0xff;
    salt[2] = (ms_usage >> 16) & 0xff;
    salt[3] = (ms_usage >> 24) & 0xff;

    return 0;
}

static u32
make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
               struct xdr_buf *body, int body_offset, u8 *cksumkey,
               unsigned int usage, struct xdr_netobj *cksumout)
{
    struct hash_desc                desc;
    struct scatterlist              sg[1];
    int err;
    u8 checksumdata[GSS_KRB5_MAX_CKSUM_LEN];
    u8 rc4salt[4];
    struct crypto_hash *md5;
    struct crypto_hash *hmac_md5;

    if (cksumkey == NULL)
        return GSS_S_FAILURE;

    if (cksumout->len < kctx->gk5e->cksumlength) {
        dprintk("%s: checksum buffer length, %u, too small for %s\n",
            __func__, cksumout->len, kctx->gk5e->name);
        return GSS_S_FAILURE;
    }

    if (arcfour_hmac_md5_usage_to_salt(usage, rc4salt)) {
        dprintk("%s: invalid usage value %u\n", __func__, usage);
        return GSS_S_FAILURE;
    }

    md5 = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(md5))
        return GSS_S_FAILURE;

    hmac_md5 = crypto_alloc_hash(kctx->gk5e->cksum_name, 0,
                     CRYPTO_ALG_ASYNC);
    if (IS_ERR(hmac_md5)) {
        crypto_free_hash(md5);
        return GSS_S_FAILURE;
    }

    desc.tfm = md5;
    desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;

    err = crypto_hash_init(&desc);
    if (err)
        goto out;
    sg_init_one(sg, rc4salt, 4);
    err = crypto_hash_update(&desc, sg, 4);
    if (err)
        goto out;

    sg_init_one(sg, header, hdrlen);
    err = crypto_hash_update(&desc, sg, hdrlen);
    if (err)
        goto out;
    err = xdr_process_buf(body, body_offset, body->len - body_offset,
                  checksummer, &desc);
    if (err)
        goto out;
    err = crypto_hash_final(&desc, checksumdata);
    if (err)
        goto out;

    desc.tfm = hmac_md5;
    desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;

    err = crypto_hash_init(&desc);
    if (err)
        goto out;
    err = crypto_hash_setkey(hmac_md5, cksumkey, kctx->gk5e->keylength);
    if (err)
        goto out;

    sg_init_one(sg, checksumdata, crypto_hash_digestsize(md5));
    err = crypto_hash_digest(&desc, sg, crypto_hash_digestsize(md5),
                 checksumdata);
    if (err)
        goto out;

    memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
    cksumout->len = kctx->gk5e->cksumlength;
out:
    crypto_free_hash(md5);
    crypto_free_hash(hmac_md5);
    return err ? GSS_S_FAILURE : 0;
}

/*
 * checksum the plaintext data and hdrlen bytes of the token header
 * The checksum is performed over the first 8 bytes of the
 * gss token header and then over the data body
 */
u32
make_checksum(struct krb5_ctx *kctx, char *header, int hdrlen,
          struct xdr_buf *body, int body_offset, u8 *cksumkey,
          unsigned int usage, struct xdr_netobj *cksumout)
{
    struct hash_desc                desc;
    struct scatterlist              sg[1];
    int err;
    u8 checksumdata[GSS_KRB5_MAX_CKSUM_LEN];
    unsigned int checksumlen;

    if (kctx->gk5e->ctype == CKSUMTYPE_HMAC_MD5_ARCFOUR)
        return make_checksum_hmac_md5(kctx, header, hdrlen,
                          body, body_offset,
                          cksumkey, usage, cksumout);

    if (cksumout->len < kctx->gk5e->cksumlength) {
        dprintk("%s: checksum buffer length, %u, too small for %s\n",
            __func__, cksumout->len, kctx->gk5e->name);
        return GSS_S_FAILURE;
    }

    desc.tfm = crypto_alloc_hash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(desc.tfm))
        return GSS_S_FAILURE;
    desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;

    checksumlen = crypto_hash_digestsize(desc.tfm);

    if (cksumkey != NULL) {
        err = crypto_hash_setkey(desc.tfm, cksumkey,
                     kctx->gk5e->keylength);
        if (err)
            goto out;
    }

    err = crypto_hash_init(&desc);
    if (err)
        goto out;
    sg_init_one(sg, header, hdrlen);
    err = crypto_hash_update(&desc, sg, hdrlen);
    if (err)
        goto out;
    err = xdr_process_buf(body, body_offset, body->len - body_offset,
                  checksummer, &desc);
    if (err)
        goto out;
    err = crypto_hash_final(&desc, checksumdata);
    if (err)
        goto out;

    switch (kctx->gk5e->ctype) {
    case CKSUMTYPE_RSA_MD5:
        err = kctx->gk5e->encrypt(kctx->seq, NULL, checksumdata,
                      checksumdata, checksumlen);
        if (err)
            goto out;
        memcpy(cksumout->data,
               checksumdata + checksumlen - kctx->gk5e->cksumlength,
               kctx->gk5e->cksumlength);
        break;
    case CKSUMTYPE_HMAC_SHA1_DES3:
        memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
        break;
    default:
        BUG();
        break;
    }
    cksumout->len = kctx->gk5e->cksumlength;
out:
    crypto_free_hash(desc.tfm);
    return err ? GSS_S_FAILURE : 0;
}

/*
 * checksum the plaintext data and hdrlen bytes of the token header
 * Per rfc4121, sec. 4.2.4, the checksum is performed over the data
 * body then over the first 16 octets of the MIC token
 * Inclusion of the header data in the calculation of the
 * checksum is optional.
 */
u32
make_checksum_v2(struct krb5_ctx *kctx, char *header, int hdrlen,
         struct xdr_buf *body, int body_offset, u8 *cksumkey,
         unsigned int usage, struct xdr_netobj *cksumout)
{
    struct hash_desc desc;
    struct scatterlist sg[1];
    int err;
    u8 checksumdata[GSS_KRB5_MAX_CKSUM_LEN];
    unsigned int checksumlen;

    if (kctx->gk5e->keyed_cksum == 0) {
        dprintk("%s: expected keyed hash for %s\n",
            __func__, kctx->gk5e->name);
        return GSS_S_FAILURE;
    }
    if (cksumkey == NULL) {
        dprintk("%s: no key supplied for %s\n",
            __func__, kctx->gk5e->name);
        return GSS_S_FAILURE;
    }

    desc.tfm = crypto_alloc_hash(kctx->gk5e->cksum_name, 0,
                            CRYPTO_ALG_ASYNC);
    if (IS_ERR(desc.tfm))
        return GSS_S_FAILURE;
    checksumlen = crypto_hash_digestsize(desc.tfm);
    desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;

    err = crypto_hash_setkey(desc.tfm, cksumkey, kctx->gk5e->keylength);
    if (err)
        goto out;

    err = crypto_hash_init(&desc);
    if (err)
        goto out;
    err = xdr_process_buf(body, body_offset, body->len - body_offset,
                  checksummer, &desc);
    if (err)
        goto out;
    if (header != NULL) {
        sg_init_one(sg, header, hdrlen);
        err = crypto_hash_update(&desc, sg, hdrlen);
        if (err)
            goto out;
    }
    err = crypto_hash_final(&desc, checksumdata);
    if (err)
        goto out;

    cksumout->len = kctx->gk5e->cksumlength;

    switch (kctx->gk5e->ctype) {
    case CKSUMTYPE_HMAC_SHA1_96_AES128:
    case CKSUMTYPE_HMAC_SHA1_96_AES256:
        /* note that this truncates the hash */
        memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
        break;
    default:
        BUG();
        break;
    }
out:
    crypto_free_hash(desc.tfm);
    return err ? GSS_S_FAILURE : 0;
}

struct encryptor_desc {
    u8 iv[GSS_KRB5_MAX_BLOCKSIZE];
    struct blkcipher_desc desc;
    int pos;
    struct xdr_buf *outbuf;
    struct page **pages;
    struct scatterlist infrags[4];
    struct scatterlist outfrags[4];
    int fragno;
    int fraglen;
};

static int
encryptor(struct scatterlist *sg, void *data)
{
    struct encryptor_desc *desc = data;
    struct xdr_buf *outbuf = desc->outbuf;
    struct page *in_page;
    int thislen = desc->fraglen + sg->length;
    int fraglen, ret;
    int page_pos;

    /* Worst case is 4 fragments: head, end of page 1, start
     * of page 2, tail.  Anything more is a bug. */
    BUG_ON(desc->fragno > 3);

    page_pos = desc->pos - outbuf->head[0].iov_len;
    if (page_pos >= 0 && page_pos < outbuf->page_len) {
        /* pages are not in place: */
        int i = (page_pos + outbuf->page_base) >> PAGE_CACHE_SHIFT;
        in_page = desc->pages[i];
    } else {
        in_page = sg_page(sg);
    }
    sg_set_page(&desc->infrags[desc->fragno], in_page, sg->length,
            sg->offset);
    sg_set_page(&desc->outfrags[desc->fragno], sg_page(sg), sg->length,
            sg->offset);
    desc->fragno++;
    desc->fraglen += sg->length;
    desc->pos += sg->length;

    fraglen = thislen & (crypto_blkcipher_blocksize(desc->desc.tfm) - 1);
    thislen -= fraglen;

    if (thislen == 0)
        return 0;

    sg_mark_end(&desc->infrags[desc->fragno - 1]);
    sg_mark_end(&desc->outfrags[desc->fragno - 1]);

    ret = crypto_blkcipher_encrypt_iv(&desc->desc, desc->outfrags,
                      desc->infrags, thislen);
    if (ret)
        return ret;

    sg_init_table(desc->infrags, 4);
    sg_init_table(desc->outfrags, 4);

    if (fraglen) {
        sg_set_page(&desc->outfrags[0], sg_page(sg), fraglen,
                sg->offset + sg->length - fraglen);
        desc->infrags[0] = desc->outfrags[0];
        sg_assign_page(&desc->infrags[0], in_page);
        desc->fragno = 1;
        desc->fraglen = fraglen;
    } else {
        desc->fragno = 0;
        desc->fraglen = 0;
    }
    return 0;
}

int
gss_encrypt_xdr_buf(struct crypto_blkcipher *tfm, struct xdr_buf *buf,
            int offset, struct page **pages)
{
    int ret;
    struct encryptor_desc desc;

    BUG_ON((buf->len - offset) % crypto_blkcipher_blocksize(tfm) != 0);

    memset(desc.iv, 0, sizeof(desc.iv));
    desc.desc.tfm = tfm;
    desc.desc.info = desc.iv;
    desc.desc.flags = 0;
    desc.pos = offset;
    desc.outbuf = buf;
    desc.pages = pages;
    desc.fragno = 0;
    desc.fraglen = 0;

    sg_init_table(desc.infrags, 4);
    sg_init_table(desc.outfrags, 4);

    ret = xdr_process_buf(buf, offset, buf->len - offset, encryptor, &desc);
    return ret;
}

struct decryptor_desc {
    u8 iv[GSS_KRB5_MAX_BLOCKSIZE];
    struct blkcipher_desc desc;
    struct scatterlist frags[4];
    int fragno;
    int fraglen;
};

static int
decryptor(struct scatterlist *sg, void *data)
{
    struct decryptor_desc *desc = data;
    int thislen = desc->fraglen + sg->length;
    int fraglen, ret;

    /* Worst case is 4 fragments: head, end of page 1, start
     * of page 2, tail.  Anything more is a bug. */
    BUG_ON(desc->fragno > 3);
    sg_set_page(&desc->frags[desc->fragno], sg_page(sg), sg->length,
            sg->offset);
    desc->fragno++;
    desc->fraglen += sg->length;

    fraglen = thislen & (crypto_blkcipher_blocksize(desc->desc.tfm) - 1);
    thislen -= fraglen;

    if (thislen == 0)
        return 0;

    sg_mark_end(&desc->frags[desc->fragno - 1]);

    ret = crypto_blkcipher_decrypt_iv(&desc->desc, desc->frags,
                      desc->frags, thislen);
    if (ret)
        return ret;

    sg_init_table(desc->frags, 4);

    if (fraglen) {
        sg_set_page(&desc->frags[0], sg_page(sg), fraglen,
                sg->offset + sg->length - fraglen);
        desc->fragno = 1;
        desc->fraglen = fraglen;
    } else {
        desc->fragno = 0;
        desc->fraglen = 0;
    }
    return 0;
}

int
gss_decrypt_xdr_buf(struct crypto_blkcipher *tfm, struct xdr_buf *buf,
            int offset)
{
    struct decryptor_desc desc;

    /* XXXJBF: */
    BUG_ON((buf->len - offset) % crypto_blkcipher_blocksize(tfm) != 0);

    memset(desc.iv, 0, sizeof(desc.iv));
    desc.desc.tfm = tfm;
    desc.desc.info = desc.iv;
    desc.desc.flags = 0;
    desc.fragno = 0;
    desc.fraglen = 0;

    sg_init_table(desc.frags, 4);

    return xdr_process_buf(buf, offset, buf->len - offset, decryptor, &desc);
}

/*
 * This function makes the assumption that it was ultimately called
 * from gss_wrap().
 *
 * The client auth_gss code moves any existing tail data into a
 * separate page before calling gss_wrap.
 * The server svcauth_gss code ensures that both the head and the
 * tail have slack space of RPC_MAX_AUTH_SIZE before calling gss_wrap.
 *
 * Even with that guarantee, this function may be called more than
 * once in the processing of gss_wrap().  The best we can do is
 * verify at compile-time (see GSS_KRB5_SLACK_CHECK) that the
 * largest expected shift will fit within RPC_MAX_AUTH_SIZE.
 * At run-time we can verify that a single invocation of this
 * function doesn't attempt to use more the RPC_MAX_AUTH_SIZE.
 */

int
xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
{
    u8 *p;

    if (shiftlen == 0)
        return 0;

    BUILD_BUG_ON(GSS_KRB5_MAX_SLACK_NEEDED > RPC_MAX_AUTH_SIZE);
    BUG_ON(shiftlen > RPC_MAX_AUTH_SIZE);

    p = buf->head[0].iov_base + base;

    memmove(p + shiftlen, p, buf->head[0].iov_len - base);

    buf->head[0].iov_len += shiftlen;
    buf->len += shiftlen;

    return 0;
}

static u32
gss_krb5_cts_crypt(struct crypto_blkcipher *cipher, struct xdr_buf *buf,
           u32 offset, u8 *iv, struct page **pages, int encrypt)
{
    u32 ret;
    struct scatterlist sg[1];
    struct blkcipher_desc desc = { .tfm = cipher, .info = iv };
    u8 data[GSS_KRB5_MAX_BLOCKSIZE * 2];
    struct page **save_pages;
    u32 len = buf->len - offset;

    if (len > ARRAY_SIZE(data)) {
        WARN_ON(0);
        return -ENOMEM;
    }

    /*
     * For encryption, we want to read from the cleartext
     * page cache pages, and write the encrypted data to
     * the supplied xdr_buf pages.
     */
    save_pages = buf->pages;
    if (encrypt)
        buf->pages = pages;

    ret = read_bytes_from_xdr_buf(buf, offset, data, len);
    buf->pages = save_pages;
    if (ret)
        goto out;

    sg_init_one(sg, data, len);

    if (encrypt)
        ret = crypto_blkcipher_encrypt_iv(&desc, sg, sg, len);
    else
        ret = crypto_blkcipher_decrypt_iv(&desc, sg, sg, len);

    if (ret)
        goto out;

    ret = write_bytes_to_xdr_buf(buf, offset, data, len);

out:
    return ret;
}

u32
gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
             struct xdr_buf *buf, int ec, struct page **pages)
{
    u32 err;
    struct xdr_netobj hmac;
    u8 *cksumkey;
    u8 *ecptr;
    struct crypto_blkcipher *cipher, *aux_cipher;
    int blocksize;
    struct page **save_pages;
    int nblocks, nbytes;
    struct encryptor_desc desc;
    u32 cbcbytes;
    unsigned int usage;

    if (kctx->initiate) {
        cipher = kctx->initiator_enc;
        aux_cipher = kctx->initiator_enc_aux;
        cksumkey = kctx->initiator_integ;
        usage = KG_USAGE_INITIATOR_SEAL;
    } else {
        cipher = kctx->acceptor_enc;
        aux_cipher = kctx->acceptor_enc_aux;
        cksumkey = kctx->acceptor_integ;
        usage = KG_USAGE_ACCEPTOR_SEAL;
    }
    blocksize = crypto_blkcipher_blocksize(cipher);

    /* hide the gss token header and insert the confounder */
    offset += GSS_KRB5_TOK_HDR_LEN;
    if (xdr_extend_head(buf, offset, kctx->gk5e->conflen))
        return GSS_S_FAILURE;
    gss_krb5_make_confounder(buf->head[0].iov_base + offset, kctx->gk5e->conflen);
    offset -= GSS_KRB5_TOK_HDR_LEN;

    if (buf->tail[0].iov_base != NULL) {
        ecptr = buf->tail[0].iov_base + buf->tail[0].iov_len;
    } else {
        buf->tail[0].iov_base = buf->head[0].iov_base
                            + buf->head[0].iov_len;
        buf->tail[0].iov_len = 0;
        ecptr = buf->tail[0].iov_base;
    }

    memset(ecptr, 'X', ec);
    buf->tail[0].iov_len += ec;
    buf->len += ec;

    /* copy plaintext gss token header after filler (if any) */
    memcpy(ecptr + ec, buf->head[0].iov_base + offset,
                        GSS_KRB5_TOK_HDR_LEN);
    buf->tail[0].iov_len += GSS_KRB5_TOK_HDR_LEN;
    buf->len += GSS_KRB5_TOK_HDR_LEN;

    /* Do the HMAC */
    hmac.len = GSS_KRB5_MAX_CKSUM_LEN;
    hmac.data = buf->tail[0].iov_base + buf->tail[0].iov_len;

    /*
     * When we are called, pages points to the real page cache
     * data -- which we can't go and encrypt!  buf->pages points
     * to scratch pages which we are going to send off to the
     * client/server.  Swap in the plaintext pages to calculate
     * the hmac.
     */
    save_pages = buf->pages;
    buf->pages = pages;

    err = make_checksum_v2(kctx, NULL, 0, buf,
                   offset + GSS_KRB5_TOK_HDR_LEN,
                   cksumkey, usage, &hmac);
    buf->pages = save_pages;
    if (err)
        return GSS_S_FAILURE;

    nbytes = buf->len - offset - GSS_KRB5_TOK_HDR_LEN;
    nblocks = (nbytes + blocksize - 1) / blocksize;
    cbcbytes = 0;
    if (nblocks > 2)
        cbcbytes = (nblocks - 2) * blocksize;

    memset(desc.iv, 0, sizeof(desc.iv));

    if (cbcbytes) {
        desc.pos = offset + GSS_KRB5_TOK_HDR_LEN;
        desc.fragno = 0;
        desc.fraglen = 0;
        desc.pages = pages;
        desc.outbuf = buf;
        desc.desc.info = desc.iv;
        desc.desc.flags = 0;
        desc.desc.tfm = aux_cipher;

        sg_init_table(desc.infrags, 4);
        sg_init_table(desc.outfrags, 4);

        err = xdr_process_buf(buf, offset + GSS_KRB5_TOK_HDR_LEN,
                      cbcbytes, encryptor, &desc);
        if (err)
            goto out_err;
    }

    /* Make sure IV carries forward from any CBC results. */
    err = gss_krb5_cts_crypt(cipher, buf,
                 offset + GSS_KRB5_TOK_HDR_LEN + cbcbytes,
                 desc.iv, pages, 1);
    if (err) {
        err = GSS_S_FAILURE;
        goto out_err;
    }

    /* Now update buf to account for HMAC */
    buf->tail[0].iov_len += kctx->gk5e->cksumlength;
    buf->len += kctx->gk5e->cksumlength;

out_err:
    if (err)
        err = GSS_S_FAILURE;
    return err;
}

u32
gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, struct xdr_buf *buf,
             u32 *headskip, u32 *tailskip)
{
    struct xdr_buf subbuf;
    u32 ret = 0;
    u8 *cksum_key;
    struct crypto_blkcipher *cipher, *aux_cipher;
    struct xdr_netobj our_hmac_obj;
    u8 our_hmac[GSS_KRB5_MAX_CKSUM_LEN];
    u8 pkt_hmac[GSS_KRB5_MAX_CKSUM_LEN];
    int nblocks, blocksize, cbcbytes;
    struct decryptor_desc desc;
    unsigned int usage;

    if (kctx->initiate) {
        cipher = kctx->acceptor_enc;
        aux_cipher = kctx->acceptor_enc_aux;
        cksum_key = kctx->acceptor_integ;
        usage = KG_USAGE_ACCEPTOR_SEAL;
    } else {
        cipher = kctx->initiator_enc;
        aux_cipher = kctx->initiator_enc_aux;
        cksum_key = kctx->initiator_integ;
        usage = KG_USAGE_INITIATOR_SEAL;
    }
    blocksize = crypto_blkcipher_blocksize(cipher);


    /* create a segment skipping the header and leaving out the checksum */
    xdr_buf_subsegment(buf, &subbuf, offset + GSS_KRB5_TOK_HDR_LEN,
                    (buf->len - offset - GSS_KRB5_TOK_HDR_LEN -
                     kctx->gk5e->cksumlength));

    nblocks = (subbuf.len + blocksize - 1) / blocksize;

    cbcbytes = 0;
    if (nblocks > 2)
        cbcbytes = (nblocks - 2) * blocksize;

    memset(desc.iv, 0, sizeof(desc.iv));

    if (cbcbytes) {
        desc.fragno = 0;
        desc.fraglen = 0;
        desc.desc.info = desc.iv;
        desc.desc.flags = 0;
        desc.desc.tfm = aux_cipher;

        sg_init_table(desc.frags, 4);

        ret = xdr_process_buf(&subbuf, 0, cbcbytes, decryptor, &desc);
        if (ret)
            goto out_err;
    }

    /* Make sure IV carries forward from any CBC results. */
    ret = gss_krb5_cts_crypt(cipher, &subbuf, cbcbytes, desc.iv, NULL, 0);
    if (ret)
        goto out_err;


    /* Calculate our hmac over the plaintext data */
    our_hmac_obj.len = sizeof(our_hmac);
    our_hmac_obj.data = our_hmac;

    ret = make_checksum_v2(kctx, NULL, 0, &subbuf, 0,
                   cksum_key, usage, &our_hmac_obj);
    if (ret)
        goto out_err;

    /* Get the packet's hmac value */
    ret = read_bytes_from_xdr_buf(buf, buf->len - kctx->gk5e->cksumlength,
                      pkt_hmac, kctx->gk5e->cksumlength);
    if (ret)
        goto out_err;

    if (memcmp(pkt_hmac, our_hmac, kctx->gk5e->cksumlength) != 0) {
        ret = GSS_S_BAD_SIG;
        goto out_err;
    }
    *headskip = kctx->gk5e->conflen;
    *tailskip = kctx->gk5e->cksumlength;
out_err:
    if (ret && ret != GSS_S_BAD_SIG)
        ret = GSS_S_FAILURE;
    return ret;
}

/*
 * Compute Kseq given the initial session key and the checksum.
 * Set the key of the given cipher.
 */
int
krb5_rc4_setup_seq_key(struct krb5_ctx *kctx, struct crypto_blkcipher *cipher,
               unsigned char *cksum)
{
    struct crypto_hash *hmac;
    struct hash_desc desc;
    struct scatterlist sg[1];
    u8 Kseq[GSS_KRB5_MAX_KEYLEN];
    u32 zeroconstant = 0;
    int err;

    dprintk("%s: entered\n", __func__);

    hmac = crypto_alloc_hash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(hmac)) {
        dprintk("%s: error %ld, allocating hash '%s'\n",
            __func__, PTR_ERR(hmac), kctx->gk5e->cksum_name);
        return PTR_ERR(hmac);
    }

    desc.tfm = hmac;
    desc.flags = 0;

    err = crypto_hash_init(&desc);
    if (err)
        goto out_err;

    /* Compute intermediate Kseq from session key */
    err = crypto_hash_setkey(hmac, kctx->Ksess, kctx->gk5e->keylength);
    if (err)
        goto out_err;

    sg_init_table(sg, 1);
    sg_set_buf(sg, &zeroconstant, 4);

    err = crypto_hash_digest(&desc, sg, 4, Kseq);
    if (err)
        goto out_err;

    /* Compute final Kseq from the checksum and intermediate Kseq */
    err = crypto_hash_setkey(hmac, Kseq, kctx->gk5e->keylength);
    if (err)
        goto out_err;

    sg_set_buf(sg, cksum, 8);

    err = crypto_hash_digest(&desc, sg, 8, Kseq);
    if (err)
        goto out_err;

    err = crypto_blkcipher_setkey(cipher, Kseq, kctx->gk5e->keylength);
    if (err)
        goto out_err;

    err = 0;

out_err:
    crypto_free_hash(hmac);
    dprintk("%s: returning %d\n", __func__, err);
    return err;
}

/*
 * Compute Kcrypt given the initial session key and the plaintext seqnum.
 * Set the key of cipher kctx->enc.
 */
int
krb5_rc4_setup_enc_key(struct krb5_ctx *kctx, struct crypto_blkcipher *cipher,
               s32 seqnum)
{
    struct crypto_hash *hmac;
    struct hash_desc desc;
    struct scatterlist sg[1];
    u8 Kcrypt[GSS_KRB5_MAX_KEYLEN];
    u8 zeroconstant[4] = {0};
    u8 seqnumarray[4];
    int err, i;

    dprintk("%s: entered, seqnum %u\n", __func__, seqnum);

    hmac = crypto_alloc_hash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(hmac)) {
        dprintk("%s: error %ld, allocating hash '%s'\n",
            __func__, PTR_ERR(hmac), kctx->gk5e->cksum_name);
        return PTR_ERR(hmac);
    }

    desc.tfm = hmac;
    desc.flags = 0;

    err = crypto_hash_init(&desc);
    if (err)
        goto out_err;

    /* Compute intermediate Kcrypt from session key */
    for (i = 0; i < kctx->gk5e->keylength; i++)
        Kcrypt[i] = kctx->Ksess[i] ^ 0xf0;

    err = crypto_hash_setkey(hmac, Kcrypt, kctx->gk5e->keylength);
    if (err)
        goto out_err;

    sg_init_table(sg, 1);
    sg_set_buf(sg, zeroconstant, 4);

    err = crypto_hash_digest(&desc, sg, 4, Kcrypt);
    if (err)
        goto out_err;

    /* Compute final Kcrypt from the seqnum and intermediate Kcrypt */
    err = crypto_hash_setkey(hmac, Kcrypt, kctx->gk5e->keylength);
    if (err)
        goto out_err;

    seqnumarray[0] = (unsigned char) ((seqnum >> 24) & 0xff);
    seqnumarray[1] = (unsigned char) ((seqnum >> 16) & 0xff);
    seqnumarray[2] = (unsigned char) ((seqnum >> 8) & 0xff);
    seqnumarray[3] = (unsigned char) ((seqnum >> 0) & 0xff);

    sg_set_buf(sg, seqnumarray, 4);

    err = crypto_hash_digest(&desc, sg, 4, Kcrypt);
    if (err)
        goto out_err;

    err = crypto_blkcipher_setkey(cipher, Kcrypt, kctx->gk5e->keylength);
    if (err)
        goto out_err;

    err = 0;

out_err:
    crypto_free_hash(hmac);
    dprintk("%s: returning %d\n", __func__, err);
    return err;
}