net/sunrpc/auth_gss/gss_krb5_crypto.c - linux - Git at Google

 /*
  *  linux/net/sunrpc/gss_krb5_crypto.c
  *
  *  Copyright (c) 2000 The Regents of the University of Michigan.
  *  All rights reserved.
  *
  *  Andy Adamson   <andros@umich.edu>
  *  Bruce Fields   <bfields@umich.edu>
  */

 /*
  * 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/slab.h>
 #include <linux/scatterlist.h>
 #include <linux/crypto.h>
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
 #include <linux/sunrpc/gss_krb5.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[16] = {0};
 	struct blkcipher_desc desc = { .tfm = tfm, .info = local_iv };

 	dprintk("RPC:      krb5_encrypt: input data:\n");
 	print_hexl((u32 *)in, length, 0);

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

 	if (crypto_blkcipher_ivsize(tfm) > 16) {
 		dprintk("RPC:      gss_k5encrypt: tfm iv size to large %d\n",
 		         crypto_blkcipher_ivsize(tfm));
 		goto out;
 	}

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

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

 	ret = crypto_blkcipher_encrypt_iv(&desc, sg, sg, length);

 	dprintk("RPC:      krb5_encrypt: output data:\n");
 	print_hexl((u32 *)out, length, 0);
 out:
 	dprintk("RPC:      krb5_encrypt returns %d\n",ret);
 	return(ret);
 }

 EXPORT_SYMBOL(krb5_encrypt);

 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[16] = {0};
 	struct blkcipher_desc desc = { .tfm = tfm, .info = local_iv };

 	dprintk("RPC:      krb5_decrypt: input data:\n");
 	print_hexl((u32 *)in, length, 0);

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

 	if (crypto_blkcipher_ivsize(tfm) > 16) {
 		dprintk("RPC:      gss_k5decrypt: tfm iv size to large %d\n",
 			crypto_blkcipher_ivsize(tfm));
 		goto out;
 	}
 	if (iv)
 		memcpy(local_iv,iv, crypto_blkcipher_ivsize(tfm));

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

 	ret = crypto_blkcipher_decrypt_iv(&desc, sg, sg, length);

 	dprintk("RPC:      krb5_decrypt: output_data:\n");
 	print_hexl((u32 *)out, length, 0);
 out:
 	dprintk("RPC:      gss_k5decrypt returns %d\n",ret);
 	return(ret);
 }

 EXPORT_SYMBOL(krb5_decrypt);

 static int
 process_xdr_buf(struct xdr_buf *buf, int offset, int len,
 		int (*actor)(struct scatterlist *, void *), void *data)
 {
 	int i, page_len, thislen, page_offset, ret = 0;
 	struct scatterlist	sg[1];

 	if (offset >= buf->head[0].iov_len) {
 		offset -= buf->head[0].iov_len;
 	} else {
 		thislen = buf->head[0].iov_len - offset;
 		if (thislen > len)
 			thislen = len;
 		sg_set_buf(sg, buf->head[0].iov_base + offset, thislen);
 		ret = actor(sg, data);
 		if (ret)
 			goto out;
 		offset = 0;
 		len -= thislen;
 	}
 	if (len == 0)
 		goto out;

 	if (offset >= buf->page_len) {
 		offset -= buf->page_len;
 	} else {
 		page_len = buf->page_len - offset;
 		if (page_len > len)
 			page_len = len;
 		len -= page_len;
 		page_offset = (offset + buf->page_base) & (PAGE_CACHE_SIZE - 1);
 		i = (offset + buf->page_base) >> PAGE_CACHE_SHIFT;
 		thislen = PAGE_CACHE_SIZE - page_offset;
 		do {
 			if (thislen > page_len)
 				thislen = page_len;
 			sg->page = buf->pages[i];
 			sg->offset = page_offset;
 			sg->length = thislen;
 			ret = actor(sg, data);
 			if (ret)
 				goto out;
 			page_len -= thislen;
 			i++;
 			page_offset = 0;
 			thislen = PAGE_CACHE_SIZE;
 		} while (page_len != 0);
 		offset = 0;
 	}
 	if (len == 0)
 		goto out;

 	if (offset < buf->tail[0].iov_len) {
 		thislen = buf->tail[0].iov_len - offset;
 		if (thislen > len)
 			thislen = len;
 		sg_set_buf(sg, buf->tail[0].iov_base + offset, thislen);
 		ret = actor(sg, data);
 		len -= thislen;
 	}
 	if (len != 0)
 		ret = -EINVAL;
 out:
 	return ret;
 }

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

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

 /* checksum the plaintext data and hdrlen bytes of the token header */
 s32
 make_checksum(s32 cksumtype, char *header, int hdrlen, struct xdr_buf *body,
 		   int body_offset, struct xdr_netobj *cksum)
 {
 	char                            *cksumname;
 	struct hash_desc                desc; /* XXX add to ctx? */
 	struct scatterlist              sg[1];
 	int err;

 	switch (cksumtype) {
 		case CKSUMTYPE_RSA_MD5:
 			cksumname = "md5";
 			break;
 		default:
 			dprintk("RPC:      krb5_make_checksum:"
 				" unsupported checksum %d", cksumtype);
 			return GSS_S_FAILURE;
 	}
 	desc.tfm = crypto_alloc_hash(cksumname, 0, CRYPTO_ALG_ASYNC);
 	if (IS_ERR(desc.tfm))
 		return GSS_S_FAILURE;
 	cksum->len = crypto_hash_digestsize(desc.tfm);
 	desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;

 	err = crypto_hash_init(&desc);
 	if (err)
 		goto out;
 	sg_set_buf(sg, header, hdrlen);
 	err = crypto_hash_update(&desc, sg, hdrlen);
 	if (err)
 		goto out;
 	err = process_xdr_buf(body, body_offset, body->len - body_offset,
 			      checksummer, &desc);
 	if (err)
 		goto out;
 	err = crypto_hash_final(&desc, cksum->data);

 out:
 	crypto_free_hash(desc.tfm);
 	return err ? GSS_S_FAILURE : 0;
 }

 EXPORT_SYMBOL(make_checksum);

 struct encryptor_desc {
 	u8 iv[8]; /* XXX hard-coded 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);
 	desc->infrags[desc->fragno] = *sg;
 	desc->outfrags[desc->fragno] = *sg;

 	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;
 	}
 	desc->infrags[desc->fragno].page = in_page;
 	desc->fragno++;
 	desc->fraglen += sg->length;
 	desc->pos += sg->length;

 	fraglen = thislen & 7; /* XXX hardcoded blocksize */
 	thislen -= fraglen;

 	if (thislen == 0)
 		return 0;

 	ret = crypto_blkcipher_encrypt_iv(&desc->desc, desc->outfrags,
 					  desc->infrags, thislen);
 	if (ret)
 		return ret;
 	if (fraglen) {
 		desc->outfrags[0].page = sg->page;
 		desc->outfrags[0].offset = sg->offset + sg->length - fraglen;
 		desc->outfrags[0].length = fraglen;
 		desc->infrags[0] = desc->outfrags[0];
 		desc->infrags[0].page = 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;

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

 EXPORT_SYMBOL(gss_encrypt_xdr_buf);

 struct decryptor_desc {
 	u8 iv[8]; /* XXX hard-coded 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);
 	desc->frags[desc->fragno] = *sg;
 	desc->fragno++;
 	desc->fraglen += sg->length;

 	fraglen = thislen & 7; /* XXX hardcoded blocksize */
 	thislen -= fraglen;

 	if (thislen == 0)
 		return 0;

 	ret = crypto_blkcipher_decrypt_iv(&desc->desc, desc->frags,
 					  desc->frags, thislen);
 	if (ret)
 		return ret;
 	if (fraglen) {
 		desc->frags[0].page = sg->page;
 		desc->frags[0].offset = sg->offset + sg->length - fraglen;
 		desc->frags[0].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;
 	return process_xdr_buf(buf, offset, buf->len - offset, decryptor, &desc);
 }

 EXPORT_SYMBOL(gss_decrypt_xdr_buf);
	/*
	* linux/net/sunrpc/gss_krb5_crypto.c
	*
	* Copyright (c) 2000 The Regents of the University of Michigan.
	* All rights reserved.
	*
	* Andy Adamson <andros@umich.edu>
	* Bruce Fields <bfields@umich.edu>
	*/

	/*
	* 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/slab.h>
	#include <linux/scatterlist.h>
	#include <linux/crypto.h>
	#include <linux/highmem.h>
	#include <linux/pagemap.h>
	#include <linux/sunrpc/gss_krb5.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[16] = {0};
	struct blkcipher_desc desc = { .tfm = tfm, .info = local_iv };

	dprintk("RPC: krb5_encrypt: input data:\n");
	print_hexl((u32 *)in, length, 0);

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

	if (crypto_blkcipher_ivsize(tfm) > 16) {
	dprintk("RPC: gss_k5encrypt: tfm iv size to large %d\n",
	crypto_blkcipher_ivsize(tfm));
	goto out;
	}

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

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

	ret = crypto_blkcipher_encrypt_iv(&desc, sg, sg, length);

	dprintk("RPC: krb5_encrypt: output data:\n");
	print_hexl((u32 *)out, length, 0);
	out:
	dprintk("RPC: krb5_encrypt returns %d\n",ret);
	return(ret);
	}

	EXPORT_SYMBOL(krb5_encrypt);

	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[16] = {0};
	struct blkcipher_desc desc = { .tfm = tfm, .info = local_iv };

	dprintk("RPC: krb5_decrypt: input data:\n");
	print_hexl((u32 *)in, length, 0);

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

	if (crypto_blkcipher_ivsize(tfm) > 16) {
	dprintk("RPC: gss_k5decrypt: tfm iv size to large %d\n",
	crypto_blkcipher_ivsize(tfm));
	goto out;
	}
	if (iv)
	memcpy(local_iv,iv, crypto_blkcipher_ivsize(tfm));

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

	ret = crypto_blkcipher_decrypt_iv(&desc, sg, sg, length);

	dprintk("RPC: krb5_decrypt: output_data:\n");
	print_hexl((u32 *)out, length, 0);
	out:
	dprintk("RPC: gss_k5decrypt returns %d\n",ret);
	return(ret);
	}

	EXPORT_SYMBOL(krb5_decrypt);

	static int
	process_xdr_buf(struct xdr_buf *buf, int offset, int len,
	int (actor)(struct scatterlist , void ), void data)
	{
	int i, page_len, thislen, page_offset, ret = 0;
	struct scatterlist sg[1];

	if (offset >= buf->head[0].iov_len) {
	offset -= buf->head[0].iov_len;
	} else {
	thislen = buf->head[0].iov_len - offset;
	if (thislen > len)
	thislen = len;
	sg_set_buf(sg, buf->head[0].iov_base + offset, thislen);
	ret = actor(sg, data);
	if (ret)
	goto out;
	offset = 0;
	len -= thislen;
	}
	if (len == 0)
	goto out;

	if (offset >= buf->page_len) {
	offset -= buf->page_len;
	} else {
	page_len = buf->page_len - offset;
	if (page_len > len)
	page_len = len;
	len -= page_len;
	page_offset = (offset + buf->page_base) & (PAGE_CACHE_SIZE - 1);
	i = (offset + buf->page_base) >> PAGE_CACHE_SHIFT;
	thislen = PAGE_CACHE_SIZE - page_offset;
	do {
	if (thislen > page_len)
	thislen = page_len;
	sg->page = buf->pages[i];
	sg->offset = page_offset;
	sg->length = thislen;
	ret = actor(sg, data);
	if (ret)
	goto out;
	page_len -= thislen;
	i++;
	page_offset = 0;
	thislen = PAGE_CACHE_SIZE;
	} while (page_len != 0);
	offset = 0;
	}
	if (len == 0)
	goto out;

	if (offset < buf->tail[0].iov_len) {
	thislen = buf->tail[0].iov_len - offset;
	if (thislen > len)
	thislen = len;
	sg_set_buf(sg, buf->tail[0].iov_base + offset, thislen);
	ret = actor(sg, data);
	len -= thislen;
	}
	if (len != 0)
	ret = -EINVAL;
	out:
	return ret;
	}

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

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

	/* checksum the plaintext data and hdrlen bytes of the token header */
	s32
	make_checksum(s32 cksumtype, char header, int hdrlen, struct xdr_buf body,
	int body_offset, struct xdr_netobj *cksum)
	{
	char *cksumname;
	struct hash_desc desc; /* XXX add to ctx? */
	struct scatterlist sg[1];
	int err;

	switch (cksumtype) {
	case CKSUMTYPE_RSA_MD5:
	cksumname = "md5";
	break;
	default:
	dprintk("RPC: krb5_make_checksum:"
	" unsupported checksum %d", cksumtype);
	return GSS_S_FAILURE;
	}
	desc.tfm = crypto_alloc_hash(cksumname, 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(desc.tfm))
	return GSS_S_FAILURE;
	cksum->len = crypto_hash_digestsize(desc.tfm);
	desc.flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	err = crypto_hash_init(&desc);
	if (err)
	goto out;
	sg_set_buf(sg, header, hdrlen);
	err = crypto_hash_update(&desc, sg, hdrlen);
	if (err)
	goto out;
	err = process_xdr_buf(body, body_offset, body->len - body_offset,
	checksummer, &desc);
	if (err)
	goto out;
	err = crypto_hash_final(&desc, cksum->data);

	out:
	crypto_free_hash(desc.tfm);
	return err ? GSS_S_FAILURE : 0;
	}

	EXPORT_SYMBOL(make_checksum);

	struct encryptor_desc {
	u8 iv[8]; /* XXX hard-coded 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);
	desc->infrags[desc->fragno] = *sg;
	desc->outfrags[desc->fragno] = *sg;

	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;
	}
	desc->infrags[desc->fragno].page = in_page;
	desc->fragno++;
	desc->fraglen += sg->length;
	desc->pos += sg->length;

	fraglen = thislen & 7; /* XXX hardcoded blocksize */
	thislen -= fraglen;

	if (thislen == 0)
	return 0;

	ret = crypto_blkcipher_encrypt_iv(&desc->desc, desc->outfrags,
	desc->infrags, thislen);
	if (ret)
	return ret;
	if (fraglen) {
	desc->outfrags[0].page = sg->page;
	desc->outfrags[0].offset = sg->offset + sg->length - fraglen;
	desc->outfrags[0].length = fraglen;
	desc->infrags[0] = desc->outfrags[0];
	desc->infrags[0].page = 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;

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

	EXPORT_SYMBOL(gss_encrypt_xdr_buf);

	struct decryptor_desc {
	u8 iv[8]; /* XXX hard-coded 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);
	desc->frags[desc->fragno] = *sg;
	desc->fragno++;
	desc->fraglen += sg->length;

	fraglen = thislen & 7; /* XXX hardcoded blocksize */
	thislen -= fraglen;

	if (thislen == 0)
	return 0;

	ret = crypto_blkcipher_decrypt_iv(&desc->desc, desc->frags,
	desc->frags, thislen);
	if (ret)
	return ret;
	if (fraglen) {
	desc->frags[0].page = sg->page;
	desc->frags[0].offset = sg->offset + sg->length - fraglen;
	desc->frags[0].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;
	return process_xdr_buf(buf, offset, buf->len - offset, decryptor, &desc);
	}

	EXPORT_SYMBOL(gss_decrypt_xdr_buf);