[PATCH 12/13: eCryptfs] Crypto functions

[Phillip Hellewell]

This is the 12th patch in a series of 13 constituting the kernel
components of the eCryptfs cryptographic filesystem.

eCryptfs crypto functions. Scatterlist abstraction functions. Page
encryption/decryption functions. Inode cryptographic context
initialization functions. Header region manipulation
functions. Functions in which filename and xattr encoding/decoding can
be easily implemented.

Signed-off-by: Phillip Hellewell <phillip@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Halcrow <mhalcrow@xxxxxxxxxx>

---

 crypto.c | 1508 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 1508 insertions(+)

Index: linux-2.6.17-rc3-mm1-ecryptfs/fs/ecryptfs/crypto.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.17-rc3-mm1-ecryptfs/fs/ecryptfs/crypto.c	2006-05-12 20:00:25.000000000 -0600
@@ -0,0 +1,1508 @@
+/**
+ * eCryptfs: Linux filesystem encryption layer
+ *
+ * Copyright (C) 1997-2004 Erez Zadok
+ * Copyright (C) 2001-2004 Stony Brook University
+ * Copyright (C) 2004-2006 International Business Machines Corp.
+ *   Author(s): Michael A. Halcrow <mahalcro@xxxxxxxxxx>
+ *   		Michael C. Thompson <mcthomps@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/pagemap.h>
+#include <linux/random.h>
+#include <linux/compiler.h>
+#include <linux/key.h>
+#include <linux/namei.h>
+#include <linux/crypto.h>
+#include <linux/file.h>
+#include <linux/scatterlist.h>
+#include <asm/scatterlist.h>
+#include "ecryptfs_kernel.h"
+
+/**
+ * ecryptfs_to_hex
+ * @dst: Buffer to take hex character representation of contents of
+ *       src; must be at least of size (src_size * 2)
+ * @src: Buffer to be converted to a hex string respresentation
+ * @src_size: number of bytes to convert
+ */
+inline void ecryptfs_to_hex(char *dst, char *src, int src_size)
+{
+	int x;
+
+	for (x = 0; x < src_size; x++)
+		sprintf(&dst[x * 2], "%.2x", (unsigned char)src[x]);
+}
+
+/**
+ * ecryptfs_from_hex
+ * @dst: Buffer to take the bytes from src hex; must be at least of
+ *       size (src_size / 2)
+ * @src: Buffer to be converted from a hex string respresentation to raw value
+ * @dst_size: size of dst buffer, or number of hex characters pairs to convert
+ */
+inline void ecryptfs_from_hex(char *dst, char *src, int dst_size)
+{
+	int x;
+	char tmp[3] = { 0, };
+
+	for (x = 0; x < dst_size; x++) {
+		tmp[0] = src[x * 2];
+		tmp[1] = src[x * 2 + 1];
+		dst[x] = (unsigned char)simple_strtol(tmp, NULL, 16);
+	}
+}
+
+/**
+ * ecryptfs_calculate_md5 - calculates the md5 of @src
+ * @dst: Pointer to 16 bytes of allocated memory
+ * @crypt_stat: Pointer to crypt_stat struct for the current inode
+ * @src: Data to be md5'd
+ * @len: Length of @src
+ * 
+ * Uses the allocated crypto context that crypt_stat references to
+ * generate the MD5 sum of the contents of src.
+ */
+int ecryptfs_calculate_md5(char *dst, struct ecryptfs_crypt_stat *crypt_stat,
+			   char *src, int len)
+{
+	int rc = 0;
+	struct scatterlist sg;
+
+	sg_init_one(&sg, (u8 *)src, len);
+	if (!crypt_stat->md5_tfm) {
+		crypt_stat->md5_tfm =
+			crypto_alloc_tfm("md5", CRYPTO_TFM_REQ_MAY_SLEEP);
+		if (!crypt_stat->md5_tfm) {
+			rc = -ENOMEM;
+			ecryptfs_printk(KERN_ERR, "Error attempting to "
+					"allocate crypto context\n");
+			goto out;
+		}
+	}
+	crypto_digest_init(crypt_stat->md5_tfm);
+	crypto_digest_update(crypt_stat->md5_tfm, &sg, 1);
+	crypto_digest_final(crypt_stat->md5_tfm, dst);
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_derive_iv
+ * @iv: destination for the derived iv vale
+ * @crypt_stat: Pointer to crypt_stat struct for the current inode
+ * @offset: Offset of the page whose's iv we are to derive
+ * 
+ * Generate the initialization vector from the given root IV and page
+ * offset.
+ * 
+ * Returns zero on success; non-zero on error.
+ */
+int ecryptfs_derive_iv(char *iv, struct ecryptfs_crypt_stat *crypt_stat,
+		       pgoff_t offset)
+{
+	int rc = 0;
+	char dst[MD5_DIGEST_SIZE];
+	char src[ECRYPTFS_MAX_IV_BYTES + 16];
+
+	if (unlikely(ecryptfs_verbosity > 0)) {
+		ecryptfs_printk(KERN_DEBUG, "root iv:\n");
+		ecryptfs_dump_hex(crypt_stat->root_iv, crypt_stat->iv_bytes);
+	}
+	/* TODO: It is probably secure to just cast the least
+	 * significant bits of the root IV into an unsigned long and
+	 * add the offset to that rather than go through all this
+	 * hashing business. -Halcrow */
+	memcpy(src, crypt_stat->root_iv, crypt_stat->iv_bytes);
+	memset((src + crypt_stat->iv_bytes), 0, 16);
+	snprintf((src + crypt_stat->iv_bytes), 16, "%ld", offset);
+	if (unlikely(ecryptfs_verbosity > 0)) {
+		ecryptfs_printk(KERN_DEBUG, "source:\n");
+		ecryptfs_dump_hex(src, (crypt_stat->iv_bytes + 16));
+	}
+	rc = ecryptfs_calculate_md5(dst, crypt_stat, src,
+				    (crypt_stat->iv_bytes + 16));
+	if (rc) {
+		ecryptfs_printk(KERN_WARNING, "Error attempting to compute "
+				"MD5 while generating IV for a page\n");
+		goto out;
+	}
+	memcpy(iv, dst, crypt_stat->iv_bytes);
+	if (unlikely(ecryptfs_verbosity > 0)) {
+		ecryptfs_printk(KERN_DEBUG, "derived iv:\n");
+		ecryptfs_dump_hex(iv, crypt_stat->iv_bytes);
+	}
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_init_crypt_stat
+ * @crypt_stat: Pointer to the crypt_stat struct to initialize.
+ *
+ * Initialize the crypt_stat structure.
+ */
+void ecryptfs_init_crypt_stat(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	memset((void *)crypt_stat, 0, sizeof(struct ecryptfs_crypt_stat));
+	mutex_init(&crypt_stat->cs_mutex);
+	ECRYPTFS_SET_FLAG(crypt_stat->flags, ECRYPTFS_STRUCT_INITIALIZED);
+}
+
+/**
+ * ecryptfs_destruct_crypt_stat
+ * @crypt_stat: Pointer to the crypt_stat struct to initialize.
+ *
+ * Releases all memory associated with a crypt_stat struct.
+ */
+void ecryptfs_destruct_crypt_stat(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	if (crypt_stat->tfm)
+		crypto_free_tfm(crypt_stat->tfm);
+	if (crypt_stat->md5_tfm)
+		crypto_free_tfm(crypt_stat->md5_tfm);
+	memset(crypt_stat, 0, sizeof(struct ecryptfs_crypt_stat));
+}
+
+/**
+ * virt_to_scatterlist
+ * @addr: Virtual address
+ * @size: Size of data; should be an even multiple of the block size
+ * @sg: Pointer to scatterlist array; set to NULL to obtain only
+ *      the number of scatterlist structs required in array
+ * @sg_size: Max array size
+ *
+ * Fills in a scatterlist array with page references for a passed
+ * virtual address.
+ *
+ * Returns the number of scatterlist structs in array used
+ */
+int virt_to_scatterlist(const void *addr, int size, struct scatterlist *sg,
+			int sg_size)
+{
+	int i = 0;
+	struct page *pg;
+	int offset;
+	int remainder_of_page;
+
+	while (size > 0 && i < sg_size) {
+		pg = virt_to_page(addr);
+		offset = offset_in_page(addr);
+		if (sg) {
+			sg[i].page = pg;
+			sg[i].offset = offset;
+		}
+		remainder_of_page = PAGE_CACHE_SIZE - offset;
+		if (size >= remainder_of_page) {
+			if (sg)
+				sg[i].length = remainder_of_page;
+			addr += remainder_of_page;
+			size -= remainder_of_page;
+		} else {
+			if (sg)
+				sg[i].length = size;
+			addr += size;
+			size = 0;
+		}
+		i++;
+	}
+	if (size > 0)
+		return -ENOMEM;
+	return i;
+}
+
+/**
+ * encrypt_scatterlist
+ * @crypt_stat: Pointer to the crypt_stat struct to initialize.
+ * @dest_sg: Destination of encrypted data
+ * @src_sg: Data to be encrypted
+ * @size: Length of data to be encrypted
+ * @iv: iv to use during encryption
+ * 
+ * Returns the number of bytes encrypted; negative value on error
+ */
+static int encrypt_scatterlist(struct ecryptfs_crypt_stat *crypt_stat,
+			       struct scatterlist *dest_sg,
+			       struct scatterlist *src_sg, int size,
+			       unsigned char *iv)
+{
+	int rc = 0;
+
+	ASSERT(crypt_stat && crypt_stat->tfm
+	       && ECRYPTFS_CHECK_FLAG(crypt_stat->flags,
+				      ECRYPTFS_STRUCT_INITIALIZED));
+	if (unlikely(ecryptfs_verbosity > 0)) {
+		ecryptfs_printk(KERN_DEBUG, "Key size [%d]; key:\n",
+				crypt_stat->key_size_bits / 8);
+		ecryptfs_dump_hex(crypt_stat->key,
+				  crypt_stat->key_size_bits / 8);
+	}
+	/* Consider doing this once, when the file is opened */
+	rc = crypto_cipher_setkey(crypt_stat->tfm, crypt_stat->key,
+				  crypt_stat->key_size_bits / 8);
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error setting key; rc = [%d]\n",
+				rc);
+		rc = -EINVAL;
+		goto out;
+	}
+	ecryptfs_printk(KERN_DEBUG, "Encrypting [%d] bytes.\n", size);
+	crypto_cipher_encrypt_iv(crypt_stat->tfm, dest_sg, src_sg, size, iv);
+out:
+	return rc;
+}
+
+void
+ecryptfs_extent_to_lwr_pg_idx_and_offset(unsigned long *lower_page_idx,
+					 int *byte_offset,
+					 struct ecryptfs_crypt_stat *crypt_stat,
+					 unsigned long extent_num)
+{
+	unsigned long lower_extent_num;
+	int extents_occupied_by_headers_at_front;
+	int bytes_occupied_by_headers_at_front;
+	int extent_offset;
+	int extents_per_page;
+
+	bytes_occupied_by_headers_at_front =
+		( crypt_stat->header_extent_size
+		  * crypt_stat->num_header_extents_at_front );
+	extents_occupied_by_headers_at_front =
+		( bytes_occupied_by_headers_at_front
+		  / crypt_stat->extent_size );
+	lower_extent_num = extents_occupied_by_headers_at_front + extent_num;
+	extents_per_page = PAGE_CACHE_SIZE / crypt_stat->extent_size;
+	(*lower_page_idx) = lower_extent_num / extents_per_page;
+	extent_offset = lower_extent_num % extents_per_page;
+	(*byte_offset) = extent_offset * crypt_stat->extent_size;
+	ecryptfs_printk(KERN_DEBUG, " * crypt_stat->header_extent_size = "
+			"[%d]\n", crypt_stat->header_extent_size);
+	ecryptfs_printk(KERN_DEBUG, " * crypt_stat->"
+			"num_header_extents_at_front = [%d]\n",
+			crypt_stat->num_header_extents_at_front);	
+	ecryptfs_printk(KERN_DEBUG, " * extents_occupied_by_headers_at_"
+			"front = [%d]\n", extents_occupied_by_headers_at_front);
+	ecryptfs_printk(KERN_DEBUG, " * lower_extent_num = [0x%.16x]\n",
+			lower_extent_num);
+	ecryptfs_printk(KERN_DEBUG, " * extents_per_page = [%d]\n",
+			extents_per_page);
+	ecryptfs_printk(KERN_DEBUG, " * (*lower_page_idx) = [0x%.16x]\n",
+			(*lower_page_idx));
+	ecryptfs_printk(KERN_DEBUG, " * extent_offset = [%d]\n",
+			extent_offset);
+	ecryptfs_printk(KERN_DEBUG, " * (*byte_offset) = [%d]\n",
+			(*byte_offset));
+}
+
+int ecryptfs_write_out_page(struct ecryptfs_page_crypt_context *ctx,
+			    struct page *lower_page, struct inode *lower_inode,
+			    int byte_offset_in_page, int bytes_to_write)
+{
+	int rc = 0;
+
+	if (ctx->mode == ECRYPTFS_PREPARE_COMMIT_MODE) {
+		rc = ecryptfs_commit_lower_page(lower_page, lower_inode,
+						ctx->param.lower_file,
+						byte_offset_in_page,
+						bytes_to_write);
+		if (rc) {
+			ecryptfs_printk(KERN_ERR, "Error calling lower "
+					"commit; rc = [%d]\n", rc);
+			goto out;
+		}
+	} else {
+		rc = ecryptfs_writepage_and_release_lower_page(lower_page,
+							       lower_inode,
+							       ctx->param.wbc);
+		if (rc) {
+			ecryptfs_printk(KERN_ERR, "Error calling lower "
+					"writepage(); rc = [%d]\n", rc);
+			goto out;
+		}
+	}
+out:
+	return rc;
+}
+
+int ecryptfs_read_in_page(struct ecryptfs_page_crypt_context *ctx,
+			  struct page **lower_page, struct inode *lower_inode,
+			  unsigned long lower_page_idx, int byte_offset_in_page)
+{
+	int rc = 0;
+
+	if (ctx->mode == ECRYPTFS_PREPARE_COMMIT_MODE) {
+		/* TODO: Limit this to only the data extents that are
+		 * needed */
+		rc = ecryptfs_get_lower_page(lower_page, lower_inode,
+					     ctx->param.lower_file,
+					     lower_page_idx,
+					     byte_offset_in_page,
+					     (PAGE_CACHE_SIZE
+					      - byte_offset_in_page));
+		if (rc) {
+			ecryptfs_printk(
+				KERN_ERR, "Error attempting to grab, map, "
+				"and prepare_write lower page with index "
+				"[0x%.16x]; rc = [%d]\n", lower_page_idx, rc);
+			goto out;
+		}
+	} else {
+		rc = ecryptfs_grab_and_map_lower_page(lower_page, NULL,
+						      lower_inode,
+						      lower_page_idx);
+		if (rc) {
+			ecryptfs_printk(
+				KERN_ERR, "Error attempting to grab and map "
+				"lower page with index [0x%.16x]; rc = [%d]\n",
+				lower_page_idx, rc);
+			goto out;
+		}
+	}
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_encrypt_page
+ * @ctx: The context of the page
+ * 
+ * Encrypt an eCryptfs page. This is done on a per-extent basis. Note
+ * that eCryptfs pages may straddle the lower pages -- for instance,
+ * if the file was created on a machine with an 8K page size
+ * (resulting in an 8K header), and then the file is copied onto a
+ * host with a 32K page size, then when reading page 0 of the eCryptfs
+ * file, 24K of page 0 of the lower file will be read and decrypted,
+ * and then 8K of page 1 of the lower file will be read and decrypted.
+ *
+ * The actual operations performed on each page depends on the
+ * contents of the ecryptfs_page_crypt_context struct.
+ *
+ * Returns zero on success; negative on error
+ */
+int ecryptfs_encrypt_page(struct ecryptfs_page_crypt_context *ctx)
+{
+	char extent_iv[ECRYPTFS_MAX_IV_BYTES];
+	unsigned long base_extent;
+	unsigned long extent_offset = 0;
+	unsigned long lower_page_idx = 0;
+	unsigned long prior_lower_page_idx = 0;
+	struct page *lower_page;
+	struct inode *lower_inode;
+	struct ecryptfs_inode_info *inode_info;
+	struct ecryptfs_crypt_stat *crypt_stat;
+	int rc = 0;
+	int lower_byte_offset = 0;
+	int orig_byte_offset = 0;
+	int num_extents_per_page;
+#define ECRYPTFS_PAGE_STATE_UNREAD    0
+#define ECRYPTFS_PAGE_STATE_READ      1
+#define ECRYPTFS_PAGE_STATE_MODIFIED  2
+#define ECRYPTFS_PAGE_STATE_WRITTEN   3
+	int page_state;
+
+	lower_inode = ecryptfs_inode_to_lower(ctx->page->mapping->host);
+	inode_info = ecryptfs_inode_to_private(ctx->page->mapping->host);
+	crypt_stat = &inode_info->crypt_stat;
+	if (!ECRYPTFS_CHECK_FLAG(crypt_stat->flags, ECRYPTFS_ENCRYPTED)) {
+		rc = ecryptfs_copy_page_to_lower(ctx->page, lower_inode,
+						 ctx->param.lower_file);
+		if (rc)
+			ecryptfs_printk(KERN_ERR, "Error attempting to copy "
+					"page at index [0x%.16x]\n",
+					ctx->page->index);
+		goto out;
+	}
+	num_extents_per_page = PAGE_CACHE_SIZE / crypt_stat->extent_size;
+	base_extent = (ctx->page->index * num_extents_per_page);
+	page_state = ECRYPTFS_PAGE_STATE_UNREAD;
+	while (extent_offset < num_extents_per_page) {
+		ecryptfs_extent_to_lwr_pg_idx_and_offset(
+			&lower_page_idx, &lower_byte_offset, crypt_stat,
+			(base_extent + extent_offset));
+		if (prior_lower_page_idx != lower_page_idx
+		    && page_state == ECRYPTFS_PAGE_STATE_MODIFIED) {
+			rc = ecryptfs_write_out_page(ctx, lower_page,
+						     lower_inode,
+						     orig_byte_offset,
+						     (PAGE_CACHE_SIZE
+						      - orig_byte_offset));
+			if (rc) {
+				ecryptfs_printk(KERN_ERR, "Error attempting "
+						"to write out page; rc = [%d]"
+						"\n", rc);
+				goto out;
+			}
+			page_state = ECRYPTFS_PAGE_STATE_WRITTEN;
+		}
+		if (page_state == ECRYPTFS_PAGE_STATE_UNREAD
+		    || page_state == ECRYPTFS_PAGE_STATE_WRITTEN) {
+			rc = ecryptfs_read_in_page(ctx, &lower_page,
+						   lower_inode, lower_page_idx,
+						   lower_byte_offset);
+			if (rc) {
+				ecryptfs_printk(KERN_ERR, "Error attempting "
+						"to read in lower page with "
+						"index [0x%.16x]; rc = [%d]\n",
+						lower_page_idx, rc);
+				goto out;
+			}
+			orig_byte_offset = lower_byte_offset;
+			prior_lower_page_idx = lower_page_idx;
+			page_state = ECRYPTFS_PAGE_STATE_READ;
+		}
+		ASSERT(page_state == ECRYPTFS_PAGE_STATE_MODIFIED
+		       || page_state == ECRYPTFS_PAGE_STATE_READ);
+		rc = ecryptfs_derive_iv(extent_iv, crypt_stat,
+					(base_extent + extent_offset));
+		if (rc) {
+			ecryptfs_printk(KERN_ERR, "Error attempting to "
+					"derive IV for extent [0x%.16x]; "
+					"rc = [%d]\n",
+					(base_extent + extent_offset), rc);
+			goto out;
+		}
+		if (unlikely(ecryptfs_verbosity > 0)) {
+			ecryptfs_printk(KERN_DEBUG, "Encrypting extent "
+					"with iv:\n");
+			ecryptfs_dump_hex(extent_iv, crypt_stat->iv_bytes);
+			ecryptfs_printk(KERN_DEBUG, "First 8 bytes before "
+					"encryption:\n");
+			ecryptfs_dump_hex((char *)
+					  (page_address(ctx->page)
+					   + (extent_offset
+					      * crypt_stat->extent_size)), 8);
+		}
+		rc = ecryptfs_encrypt_page_offset(
+			crypt_stat, lower_page, lower_byte_offset, ctx->page,
+			(extent_offset * crypt_stat->extent_size),
+			crypt_stat->extent_size, extent_iv);
+		ecryptfs_printk(KERN_DEBUG, "Encrypt extent [0x%.16x]; "
+				"rc = [%d]\n",
+				(base_extent + extent_offset), rc);
+		if (unlikely(ecryptfs_verbosity > 0)) {
+			ecryptfs_printk(KERN_DEBUG, "First 8 bytes after "
+					"encryption:\n");
+			ecryptfs_dump_hex((char *)(page_address(lower_page)
+						   + lower_byte_offset), 8);
+		}
+		page_state = ECRYPTFS_PAGE_STATE_MODIFIED;
+		extent_offset++;
+	}
+	ASSERT(orig_byte_offset == 0);
+	rc = ecryptfs_write_out_page(ctx, lower_page, lower_inode, 0,
+				     (lower_byte_offset
+				      + crypt_stat->extent_size));
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error attempting to write out "
+				"page; rc = [%d]\n", rc);
+				goto out;
+	}
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_decrypt_page
+ * @file: The ecryptfs file
+ * @page: The page in ecryptfs to decrypt
+ * 
+ * Decrypt an eCryptfs page. This is done on a per-extent basis. Note
+ * that eCryptfs pages may straddle the lower pages -- for instance,
+ * if the file was created on a machine with an 8K page size
+ * (resulting in an 8K header), and then the file is copied onto a
+ * host with a 32K page size, then when reading page 0 of the eCryptfs
+ * file, 24K of page 0 of the lower file will be read and decrypted,
+ * and then 8K of page 1 of the lower file will be read and decrypted.
+ *
+ * Returns zero on success; negative on error
+ */
+int ecryptfs_decrypt_page(struct file *file, struct page *page)
+{
+	char extent_iv[ECRYPTFS_MAX_IV_BYTES];
+	unsigned long base_extent;
+	unsigned long extent_offset = 0;
+	unsigned long lower_page_idx = 0;
+	unsigned long prior_lower_page_idx = 0;
+	struct page *lower_page;
+	char *lower_page_virt = NULL;
+	struct inode *lower_inode;
+	struct ecryptfs_crypt_stat *crypt_stat;
+	int rc = 0;
+	int byte_offset;
+	int num_extents_per_page;
+	int page_state;
+
+	crypt_stat = &(ecryptfs_inode_to_private(
+			       page->mapping->host)->crypt_stat);
+	lower_inode = ecryptfs_inode_to_lower(page->mapping->host);
+	if (!ECRYPTFS_CHECK_FLAG(crypt_stat->flags, ECRYPTFS_ENCRYPTED)) {
+		rc = ecryptfs_do_readpage(file, page, page->index);
+		if (rc)
+			ecryptfs_printk(KERN_ERR, "Error attempting to copy "
+					"page at index [0x%.16x]\n",
+					page->index);
+		goto out;
+	}
+	num_extents_per_page = PAGE_CACHE_SIZE / crypt_stat->extent_size;
+	base_extent = (page->index * num_extents_per_page);
+	lower_page_virt = kmem_cache_alloc(ecryptfs_lower_page_cache,
+					   SLAB_KERNEL);
+	if (!lower_page_virt) {
+		rc = -ENOMEM;
+		ecryptfs_printk(KERN_ERR, "Error getting page for encrypted "
+				"lower page(s)\n");
+		goto out;
+	}
+	lower_page = virt_to_page(lower_page_virt);
+	page_state = ECRYPTFS_PAGE_STATE_UNREAD;
+	while (extent_offset < num_extents_per_page) {
+		ecryptfs_extent_to_lwr_pg_idx_and_offset(
+			&lower_page_idx, &byte_offset, crypt_stat,
+			(base_extent + extent_offset));
+		if (prior_lower_page_idx != lower_page_idx
+		    || page_state == ECRYPTFS_PAGE_STATE_UNREAD) {
+			rc = ecryptfs_do_readpage(file, lower_page,
+						  lower_page_idx);
+			if (rc) {
+				ecryptfs_printk(KERN_ERR, "Error reading "
+						"lower encrypted page; rc = "
+						"[%d]\n", rc);
+				goto out;
+			}
+			prior_lower_page_idx = lower_page_idx;
+			page_state = ECRYPTFS_PAGE_STATE_READ;
+		}
+		rc = ecryptfs_derive_iv(extent_iv, crypt_stat,
+					(base_extent + extent_offset));
+		if (rc) {
+			ecryptfs_printk(KERN_ERR, "Error attempting to "
+					"derive IV for extent [0x%.16x]; rc = "
+					"[%d]\n",
+					(base_extent + extent_offset), rc);
+			goto out;
+		}
+		if (unlikely(ecryptfs_verbosity > 0)) {
+			ecryptfs_printk(KERN_DEBUG, "Decrypting extent "
+					"with iv:\n");
+			ecryptfs_dump_hex(extent_iv, crypt_stat->iv_bytes);
+			ecryptfs_printk(KERN_DEBUG, "First 8 bytes before "
+					"decryption:\n");
+			ecryptfs_dump_hex((lower_page_virt + byte_offset), 8);
+		}
+		rc = ecryptfs_decrypt_page_offset(crypt_stat, page,
+						  (extent_offset
+						   * crypt_stat->extent_size),
+						  lower_page, byte_offset,
+						  crypt_stat->extent_size,
+						  extent_iv);
+		if (rc != crypt_stat->extent_size) {
+			ecryptfs_printk(KERN_ERR, "Error attempting to "
+					"decrypt extent [0x%.16x]\n",
+					(base_extent + extent_offset));
+			goto out;
+		}
+		rc = 0;
+		if (unlikely(ecryptfs_verbosity > 0)) {
+			ecryptfs_printk(KERN_DEBUG, "First 8 bytes after "
+					"decryption:\n");
+			ecryptfs_dump_hex((char *)(page_address(page)
+						   + byte_offset), 8);
+		}
+		extent_offset++;
+	}
+out:
+	if (lower_page_virt)
+		kmem_cache_free(ecryptfs_lower_page_cache, lower_page_virt);
+	return rc;
+}
+
+/**
+ * decrypt_scatterlist
+ * 
+ * Returns the number of bytes decrypted; negative value on error
+ */
+static int decrypt_scatterlist(struct ecryptfs_crypt_stat *crypt_stat,
+			       struct scatterlist *dest_sg,
+			       struct scatterlist *src_sg, int size,
+			       unsigned char *iv)
+{
+	int rc = 0;
+
+	/* Consider doing this once, when the file is opened */
+	rc = crypto_cipher_setkey(crypt_stat->tfm, crypt_stat->key,
+				  crypt_stat->key_size_bits / 8);
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error setting key; rc = [%d]\n",
+				rc);
+		rc = -EINVAL;
+		goto out;
+	}	
+	ecryptfs_printk(KERN_DEBUG, "Decrypting [%d] bytes.\n", size);
+	rc = crypto_cipher_decrypt_iv(crypt_stat->tfm, dest_sg, src_sg, size,
+				      iv);
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error decrypting; rc = [%d]\n",
+				rc);
+		goto out;
+	}
+	rc = size;
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_encrypt_page_offset
+ * 
+ * Returns the number of bytes encrypted
+ */
+int
+ecryptfs_encrypt_page_offset(struct ecryptfs_crypt_stat *crypt_stat,
+			     struct page *dst_page, int dst_offset,
+			     struct page *src_page, int src_offset, int size,
+			     unsigned char *iv)
+{
+	struct scatterlist src_sg, dst_sg;
+
+	src_sg.page = src_page;
+	src_sg.offset = src_offset;
+	src_sg.length = size;
+	dst_sg.page = dst_page;
+	dst_sg.offset = dst_offset;
+	dst_sg.length = size;
+	return encrypt_scatterlist(crypt_stat, &dst_sg, &src_sg, size, iv);
+}
+
+/**
+ * ecryptfs_decrypt_page_offset
+ * 
+ * Returns the number of bytes decrypted
+ */
+int
+ecryptfs_decrypt_page_offset(struct ecryptfs_crypt_stat *crypt_stat,
+			     struct page *dst_page, int dst_offset,
+			     struct page *src_page, int src_offset, int size,
+			     unsigned char *iv)
+{
+	struct scatterlist src_sg, dst_sg;
+
+	src_sg.page = src_page;
+	src_sg.offset = src_offset;
+	src_sg.length = size;
+	dst_sg.page = dst_page;
+	dst_sg.offset = dst_offset;
+	dst_sg.length = size;
+	return decrypt_scatterlist(crypt_stat, &dst_sg, &src_sg, size, iv);
+}
+
+#define ECRYPTFS_MAX_SCATTERLIST_LEN 4
+
+/**
+ * ecryptfs_init_crypt_ctx
+ * @crypt_stat: Uninitilized crypt stats structure
+ * 
+ * Initialize the crypto context.
+ *
+ * TODO: Performance: Keep a cache of initialized cipher contexts;
+ * only init if needed
+ */
+int ecryptfs_init_crypt_ctx(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	int rc = -EINVAL;
+
+	if (crypt_stat->cipher == NULL) {
+		ecryptfs_printk(KERN_ERR, "No cipher specified\n");
+		goto out;
+	}
+	ecryptfs_printk(KERN_DEBUG,
+			"Initializing cipher [%s]; strlen = [%d]\n",
+			crypt_stat->cipher, (int)strlen(crypt_stat->cipher));
+	if (crypt_stat->tfm) {
+		rc = 0;
+		goto out;
+	}
+	crypt_stat->tfm = crypto_alloc_tfm(crypt_stat->cipher,
+					   ECRYPTFS_DEFAULT_CHAINING_MODE);
+	if (crypt_stat->tfm == NULL) {
+		ecryptfs_printk(KERN_ERR, "cryptfs: init_crypt_ctx(): Error "
+				"initializing cipher [%s]\n",
+				crypt_stat->cipher);
+		goto out;
+	}
+	rc = 0;
+out:
+	return rc;
+}
+
+static void set_extent_mask_and_shift(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	int extent_size_tmp;
+
+	crypt_stat->extent_mask = 0xFFFFFFFF;
+	crypt_stat->extent_shift = 0;
+	if (crypt_stat->extent_size == 0)
+		return;
+	extent_size_tmp = crypt_stat->extent_size;
+	while ((extent_size_tmp & 0x01) == 0) {
+		extent_size_tmp >>= 1;
+		crypt_stat->extent_mask <<= 1;
+		crypt_stat->extent_shift++;
+	}
+}
+
+void ecryptfs_set_default_sizes(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	/* Default values; may be overwritten as we are parsing the
+	 * packets. */
+	crypt_stat->extent_size = ECRYPTFS_DEFAULT_EXTENT_SIZE;
+	set_extent_mask_and_shift(crypt_stat);
+	crypt_stat->iv_bytes = ECRYPTFS_DEFAULT_IV_BYTES;
+	if (PAGE_CACHE_SIZE <= ECRYPTFS_MINIMUM_HEADER_EXTENT_SIZE) {
+		crypt_stat->header_extent_size =
+			ECRYPTFS_MINIMUM_HEADER_EXTENT_SIZE;
+	} else
+		crypt_stat->header_extent_size = PAGE_CACHE_SIZE;
+	crypt_stat->num_header_extents_at_front = 1;
+}
+
+/**
+ * ecryptfs_compute_root_iv
+ * @crypt_stats
+ *
+ * On error, sets the root IV to all 0's.
+ */
+int ecryptfs_compute_root_iv(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	int rc = 0;
+	char dst[MD5_DIGEST_SIZE];
+
+	ASSERT(crypt_stat->iv_bytes <= MD5_DIGEST_SIZE);
+	ASSERT(crypt_stat->iv_bytes > 0);
+	if (!ECRYPTFS_CHECK_FLAG(crypt_stat->flags, ECRYPTFS_KEY_VALID)) {
+		rc = -EINVAL;
+		ecryptfs_printk(KERN_WARNING, "Session key not valid; "
+				"cannot generate root IV\n");
+		goto out;
+	}
+	rc = ecryptfs_calculate_md5(dst, crypt_stat, crypt_stat->key,
+				    (crypt_stat->key_size_bits / 8));
+	if (rc) {
+		ecryptfs_printk(KERN_WARNING, "Error attempting to compute "
+				"MD5 while generating root IV\n");
+		goto out;
+	}
+	memcpy(crypt_stat->root_iv, dst, crypt_stat->iv_bytes);
+out:
+	if (rc) {
+		memset(crypt_stat->root_iv, 0, crypt_stat->iv_bytes);
+		ECRYPTFS_SET_FLAG(crypt_stat->flags,
+				  ECRYPTFS_SECURITY_WARNING);
+	}
+	return rc;
+}
+
+/**
+ * ecryptfs_set_default_crypt_stat_vals
+ * @crypt_stat
+ *
+ * Default values in the event that policy does not override them.
+ */
+static void
+ecryptfs_set_default_crypt_stat_vals(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	int key_size_bits = ECRYPTFS_DEFAULT_KEY_BYTES * 8;
+
+	ecryptfs_set_default_sizes(crypt_stat);
+	strcpy(crypt_stat->cipher, ECRYPTFS_DEFAULT_CIPHER);
+	crypt_stat->key_size_bits = key_size_bits;
+	get_random_bytes(crypt_stat->key, key_size_bits / 8);
+	ECRYPTFS_SET_FLAG(crypt_stat->flags, ECRYPTFS_KEY_VALID);
+	ecryptfs_compute_root_iv(crypt_stat);
+	if (unlikely(ecryptfs_verbosity > 0)) {
+		ecryptfs_printk(KERN_DEBUG, "Generated new session key:\n");
+		ecryptfs_dump_hex(crypt_stat->key,
+				  crypt_stat->key_size_bits / 8);
+	}
+	crypt_stat->file_version = ECRYPTFS_FILE_VERSION;
+}
+
+/**
+ * ecryptfs_new_file_context
+ * @ecryptfs_dentry
+ * 
+ * If the crypto context for the file has not yet been established,
+ * this is where we do that.  Establishing a new crypto context
+ * involves the following decisions:
+ *  - What cipher to use?
+ *  - What set of authentication tokens to use?
+ * Here we just worry about getting enough information into the
+ * authentication tokens so that we know that they are available.
+ * We associate the available authentication tokens with the new file
+ * via the set of signatures in the crypt_stat struct.  Later, when
+ * the headers are actually written out, we may again defer to
+ * userspace to perform the encryption of the session key; for the
+ * foreseeable future, this will be the case with public key packets.
+ *
+ * Returns zero on success; non-zero otherwise
+ */
+/* Associate an authentication token(s) with the file */
+int ecryptfs_new_file_context(struct dentry *ecryptfs_dentry)
+{
+	int rc = 0;
+	struct ecryptfs_crypt_stat *crypt_stat =
+	    &ecryptfs_inode_to_private(ecryptfs_dentry->d_inode)->crypt_stat;
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
+	    &ecryptfs_superblock_to_private(
+		    ecryptfs_dentry->d_sb)->mount_crypt_stat;
+	int cipher_name_len;
+
+	ecryptfs_set_default_crypt_stat_vals(crypt_stat);
+	/* See if there are mount crypt options */
+	if (mount_crypt_stat->global_auth_tok) {
+		ecryptfs_printk(KERN_DEBUG, "Initializing context for new "
+				"file using mount_crypt_stat\n");
+		ECRYPTFS_SET_FLAG(crypt_stat->flags, ECRYPTFS_ENCRYPTED);
+		ECRYPTFS_SET_FLAG(crypt_stat->flags, ECRYPTFS_KEY_VALID);
+		memcpy(crypt_stat->keysigs[crypt_stat->num_keysigs++],
+		       mount_crypt_stat->global_auth_tok_sig,
+		       ECRYPTFS_SIG_SIZE_HEX);
+		cipher_name_len =
+		    strlen(mount_crypt_stat->global_default_cipher_name);
+		memcpy(crypt_stat->cipher,
+		       mount_crypt_stat->global_default_cipher_name,
+		       cipher_name_len);
+		crypt_stat->cipher[cipher_name_len] = '\0';
+	} else
+		/* We should not encounter this scenario since we
+		 * should detect lack of global_auth_tok at mount time
+		 * TODO: Applies to 0.1 release only; remove in future
+		 * release */
+		BUG();
+	rc = ecryptfs_init_crypt_ctx(crypt_stat);
+	if (rc)
+		ecryptfs_printk(KERN_ERR, "Error initializing cryptographic "
+				"context for cipher [%s]: rc = [%d]\n",
+				crypt_stat->cipher, rc);
+	return rc;
+}
+
+/**
+ * contains_ecryptfs_marker - check for the ecryptfs marker
+ * @data: The data block in which to check
+ * 
+ * Returns one if marker found; zero if not found
+ */
+int contains_ecryptfs_marker(char *data)
+{
+	u32 m_1, m_2;
+	
+	memcpy(&m_1, data, 4);
+	m_1 = be32_to_cpu(m_1);
+	memcpy(&m_2, (data + 4), 4);
+	m_2 = be32_to_cpu(m_2);
+	if ((m_1 ^ MAGIC_ECRYPTFS_MARKER) == m_2)
+		return 1;
+	ecryptfs_printk(KERN_DEBUG, "m_1 = [0x%.8x]; m_2 = [0x%.8x]; "
+			"MAGIC_ECRYPTFS_MARKER = [0x%.8x]\n", m_1, m_2,
+			MAGIC_ECRYPTFS_MARKER);
+	ecryptfs_printk(KERN_DEBUG, "(m_1 ^ MAGIC_ECRYPTFS_MARKER) = "
+			"[0x%.8x]\n", (m_1 ^ MAGIC_ECRYPTFS_MARKER));
+	return 0;
+}
+
+struct ecryptfs_flag_map_elem {
+	u32 file_flag;
+	u32 local_flag;
+};
+
+/* Add support for additional flags by adding elements here. */
+static struct ecryptfs_flag_map_elem ecryptfs_flag_map[] = {
+	{0x00000001, ECRYPTFS_ENABLE_HMAC},
+	{0x00000002, ECRYPTFS_ENCRYPTED}
+};
+
+/**
+ * ecryptfs_process_flags
+ * @crypt_stat
+ * @page_virt: Source data to be parsed
+ * @bytes_read: Updated with the number of bytes read
+ *
+ * Returns zero on success; non-zero if the flag set is invalid
+ */
+static int ecryptfs_process_flags(struct ecryptfs_crypt_stat *crypt_stat,
+				  char *page_virt, int *bytes_read)
+{
+	int rc = 0;
+	int i;
+	u32 flags;
+
+	memcpy(&flags, page_virt, 4);
+	flags = be32_to_cpu(flags);
+	for (i = 0; i < ((sizeof(ecryptfs_flag_map)
+			  / sizeof(struct ecryptfs_flag_map_elem))); i++)
+		if (flags & ecryptfs_flag_map[i].file_flag) {
+			ECRYPTFS_SET_FLAG(crypt_stat->flags,
+					  ecryptfs_flag_map[i].local_flag);
+		} else
+			ECRYPTFS_CLEAR_FLAG(crypt_stat->flags,
+					    ecryptfs_flag_map[i].local_flag);
+	/* Version is in top 8 bits of the 32-bit flag vector */
+	crypt_stat->file_version = ((flags >> 24) & 0xFF);
+	(*bytes_read) = 4;
+	return rc;
+}
+
+/**
+ * write_ecryptfs_marker
+ * @page_virt: The pointer to in a page to begin writing the marker
+ * @written: Number of bytes written
+ *
+ * Marker = 0x3c81b7f5
+ */
+static void write_ecryptfs_marker(char *page_virt, int *written)
+{
+	u32 m_1, m_2;
+
+	get_random_bytes(&m_1, (MAGIC_ECRYPTFS_MARKER_SIZE_BYTES / 2));
+	m_2 = (m_1 ^ MAGIC_ECRYPTFS_MARKER);
+	m_1 = cpu_to_be32(m_1);
+	memcpy(page_virt, &m_1, (MAGIC_ECRYPTFS_MARKER_SIZE_BYTES / 2));
+	m_2 = cpu_to_be32(m_2);
+	memcpy(page_virt + (MAGIC_ECRYPTFS_MARKER_SIZE_BYTES / 2), &m_2,
+	       (MAGIC_ECRYPTFS_MARKER_SIZE_BYTES / 2));
+	(*written) = MAGIC_ECRYPTFS_MARKER_SIZE_BYTES;
+}
+
+static void
+write_ecryptfs_flags(char *page_virt, struct ecryptfs_crypt_stat *crypt_stat,
+		     int *written)
+{
+	u32 flags = 0;
+	int i;
+
+	for (i = 0; i < ((sizeof(ecryptfs_flag_map)
+			  / sizeof(struct ecryptfs_flag_map_elem))); i++)
+		if (ECRYPTFS_CHECK_FLAG(crypt_stat->flags,
+					ecryptfs_flag_map[i].local_flag))
+			flags |= ecryptfs_flag_map[i].file_flag;
+	/* Version is in top 8 bits of the 32-bit flag vector */
+	flags |= ((((u8)crypt_stat->file_version) << 24) & 0xFF000000);
+	flags = cpu_to_be32(flags);
+	memcpy(page_virt, &flags, 4);
+	(*written) = 4;
+}
+
+struct ecryptfs_cipher_code_str_map_elem {
+	char cipher_str[16];
+	u16 cipher_code;
+};
+
+/* Add support for additional ciphers by adding elements here. The
+ * cipher_code is whatever OpenPGP applicatoins use to identify the
+ * ciphers. */
+/* List in order of probability. */
+static struct ecryptfs_cipher_code_str_map_elem
+ecryptfs_cipher_code_str_map[] = {
+	{"aes", 0x07},
+	{"blowfish", 0x04},
+	{"des3_ede", 0x02},
+	{"cast5", 0x03}
+};
+
+/**
+ * ecryptfs_code_for_cipher_string
+ * @str: The string representing the cipher name
+ * 
+ * Returns zero on no match, or the cipher code on match
+ */
+u16 ecryptfs_code_for_cipher_string(char *str)
+{
+	int i;
+	
+	for (i = 0; i < (sizeof(ecryptfs_cipher_code_str_map)
+			 / sizeof(struct ecryptfs_cipher_code_str_map_elem));
+	     i++)
+		if (strcmp(str, ecryptfs_cipher_code_str_map[i].cipher_str)==0)
+			return ecryptfs_cipher_code_str_map[i].cipher_code;
+	return 0;
+}
+
+/**
+ * ecryptfs_cipher_code_to_string
+ * @str: Destination to write out the cipher name
+ * @cipher_code: The code to convert to cipher name string
+ * 
+ * Returns zero on success
+ */
+int ecryptfs_cipher_code_to_string(char *str, u16 cipher_code)
+{
+	int rc = 0;
+	int i;
+
+	str[0] = '\0';
+	for (i = 0; i < (sizeof(ecryptfs_cipher_code_str_map)
+			 / sizeof(struct ecryptfs_cipher_code_str_map_elem));
+	     i++)
+		if (cipher_code == ecryptfs_cipher_code_str_map[i].cipher_code)
+			strcpy(str, ecryptfs_cipher_code_str_map[i].cipher_str);
+	if (str[0] == '\0') {
+		ecryptfs_printk(KERN_WARNING, "Cipher code not recognized: "
+				"[%d]\n", cipher_code);		
+		rc = -EINVAL;
+	}
+	return rc;
+}
+
+/**
+ * ecryptfs_read_header_region
+ * @data
+ * @dentry
+ * @nd
+ * 
+ * Returns zero on success; non-zero otherwise
+ */
+int ecryptfs_read_header_region(char *data, struct dentry *dentry,
+				struct nameidata *nd)
+{
+	int rc = 0;
+	struct vfsmount *mnt = NULL;
+	struct file *file = NULL;
+	mm_segment_t oldfs;
+
+	mnt = mntget(nd->mnt);
+	file = dentry_open(dentry, mnt, O_RDONLY);
+	if (IS_ERR(file)) {
+		ecryptfs_printk(KERN_DEBUG, "Error opening file to "
+				"read header region\n");
+		mntput(mnt);
+		rc = PTR_ERR(file);
+		goto out;
+	}
+	file->f_pos = 0;
+	oldfs = get_fs();
+	set_fs(get_ds());
+	/* For releases 0.1 and 0.2, all of the header information
+	 * fits in the first data extent-sized region. */
+	rc = file->f_op->read(file, (char __user *)data,
+			      ECRYPTFS_DEFAULT_EXTENT_SIZE, &file->f_pos);
+	set_fs(oldfs);
+	fput(file);
+	rc = 0;
+out:
+	return rc;
+}
+
+static void
+write_header_metadata(char *virt, struct ecryptfs_crypt_stat *crypt_stat,
+		      int *written)
+{
+	u32 header_extent_size;
+	u16 num_header_extents_at_front;
+
+	header_extent_size = (u32)crypt_stat->header_extent_size;
+	num_header_extents_at_front =
+		(u16)crypt_stat->num_header_extents_at_front;
+	header_extent_size = cpu_to_be32(header_extent_size);
+	memcpy(virt, &header_extent_size, 4);
+	virt += 4;
+	num_header_extents_at_front = cpu_to_be16(num_header_extents_at_front);
+	memcpy(virt, &num_header_extents_at_front, 2);
+	(*written) = 6;
+}
+
+struct kmem_cache *ecryptfs_header_cache_0;
+struct kmem_cache *ecryptfs_header_cache_1;
+struct kmem_cache *ecryptfs_header_cache_2;
+
+/**
+ * ecryptfs_write_headers_virt
+ * @page_virt
+ * @crypt_stat
+ * @ecryptfs_dentry
+ *
+ * Format version: 1
+ * 
+ *   Header Extent:
+ *     Octets 0-7:        Unencrypted file size (big-endian)
+ *     Octets 8-15:       eCryptfs special marker
+ *     Octets 16-19:      Flags
+ *      Octet 16:         File format version number (between 0 and 255)
+ *      Octets 17-18:     Reserved
+ *      Octet 19:         Bit 1 (lsb): Reserved 
+ *                        Bit 2: Encrypted?
+ *                        Bits 3-8: Reserved
+ *     Octets 20-23:      Header extent size (big-endian)
+ *     Octets 24-25:      Number of header extents at front of file
+ *                        (big-endian) 
+ *     Octet  26:         Begin RFC 2440 authentication token packet set
+ *   Data Extent 0:
+ *     Lower data (CBC encrypted)
+ *   Data Extent 1:
+ *     Lower data (CBC encrypted)
+ *   ...
+ *
+ * Returns zero on success
+ */
+int ecryptfs_write_headers_virt(char *page_virt,
+				struct ecryptfs_crypt_stat *crypt_stat,
+				struct dentry *ecryptfs_dentry)
+{
+	int rc;
+	int written;
+	int offset;
+
+	offset = ECRYPTFS_FILE_SIZE_BYTES;
+	write_ecryptfs_marker((page_virt + offset), &written);
+	offset += written;
+	write_ecryptfs_flags((page_virt + offset), crypt_stat, &written);
+	offset += written;
+	write_header_metadata((page_virt + offset), crypt_stat, &written);
+	offset += written;
+	rc = ecryptfs_generate_key_packet_set((page_virt + offset), crypt_stat,
+					      ecryptfs_dentry, &written);
+	if (rc)
+		ecryptfs_printk(KERN_WARNING, "Error generating key packet "
+				"set; rc = [%d]\n", rc);
+	return rc;
+}
+
+/**
+ * ecryptfs_write_headers
+ * @lower_file: The lower file struct, which was returned from dentry_open
+ * 
+ * Write the file headers out.  This will likely involve a userspace
+ * callout, in which the session key is encrypted with one or more
+ * public keys and/or the passphrase necessary to do the encryption is
+ * retrieved via a prompt.  Exactly what happens at this point should
+ * be policy-dependent.
+ *
+ * Returns zero on success; non-zero on error
+ */
+int ecryptfs_write_headers(struct dentry *ecryptfs_dentry,
+			   struct file *lower_file)
+{
+	mm_segment_t oldfs;
+	struct ecryptfs_crypt_stat *crypt_stat;
+	char *page_virt;
+	int current_header_page;
+	int header_pages;
+	int rc = 0;
+
+	crypt_stat = &ecryptfs_inode_to_private(
+		ecryptfs_dentry->d_inode)->crypt_stat;
+	if (likely(ECRYPTFS_CHECK_FLAG(crypt_stat->flags,
+				       ECRYPTFS_ENCRYPTED))) {
+		if (!ECRYPTFS_CHECK_FLAG(crypt_stat->flags,
+					 ECRYPTFS_KEY_VALID)) {
+			ecryptfs_printk(KERN_DEBUG, "Key is "
+					"invalid; bailing out\n");
+			rc = -EINVAL;
+			goto out;
+		}
+	} else {
+		rc = -EINVAL;
+		ecryptfs_printk(KERN_WARNING,
+				"Called with crypt_stat->encrypted == 0\n");
+		goto out;
+	}
+	/* Released in this function */
+	page_virt = kmem_cache_alloc(ecryptfs_header_cache_0, SLAB_USER);
+	if (!page_virt) {
+		ecryptfs_printk(KERN_ERR, "Out of memory\n");
+		rc = -ENOMEM;
+		goto out;
+	}
+	memset(page_virt, 0, PAGE_CACHE_SIZE);
+	rc = ecryptfs_write_headers_virt(page_virt, crypt_stat,
+					 ecryptfs_dentry);
+	if (unlikely(rc)) {
+		ecryptfs_printk(KERN_ERR, "Error whilst writing headers\n");
+		memset(page_virt, 0, PAGE_CACHE_SIZE);
+		goto out_free;
+	}
+	ecryptfs_printk(KERN_DEBUG,
+			"Writing key packet set to underlying file\n");
+	lower_file->f_pos = 0;
+	oldfs = get_fs();
+	set_fs(get_ds());
+	ecryptfs_printk(KERN_DEBUG, "Calling lower_file->f_op->"
+			"write() w/ header page; lower_file->f_pos = "
+			"[0x%.16x]\n", lower_file->f_pos);
+	lower_file->f_op->write(lower_file, (char __user *)page_virt,
+				PAGE_CACHE_SIZE, &lower_file->f_pos);
+	header_pages = ((crypt_stat->header_extent_size
+			 * crypt_stat->num_header_extents_at_front)
+			/ PAGE_CACHE_SIZE);
+	memset(page_virt, 0, PAGE_CACHE_SIZE);
+	current_header_page = 1;
+	while (current_header_page < header_pages) {
+		ecryptfs_printk(KERN_DEBUG, "Calling lower_file->f_op->"
+				"write() w/ zero'd page; lower_file->f_pos = "
+				"[0x%.16x]\n", lower_file->f_pos);
+		lower_file->f_op->write(lower_file, (char __user *)page_virt,
+					PAGE_CACHE_SIZE, &lower_file->f_pos);
+		current_header_page++;
+	}
+	set_fs(oldfs);
+	ecryptfs_printk(KERN_DEBUG,
+			"Done writing key packet set to underlying file.\n");
+out_free:
+	kmem_cache_free(ecryptfs_header_cache_0, page_virt);
+out:
+	return rc;
+}
+
+static int parse_header_metadata(struct ecryptfs_crypt_stat *crypt_stat,
+				 char *virt, int *bytes_read)
+{
+	int rc = 0;
+	u32 header_extent_size;
+	u16 num_header_extents_at_front;
+
+	memcpy(&header_extent_size, virt, 4);
+	header_extent_size = be32_to_cpu(header_extent_size);
+	virt += 4;
+	memcpy(&num_header_extents_at_front, virt, 2);
+	num_header_extents_at_front = be16_to_cpu(num_header_extents_at_front);
+	crypt_stat->header_extent_size = (int)header_extent_size;
+	crypt_stat->num_header_extents_at_front =
+		(int)num_header_extents_at_front;
+	(*bytes_read) = 6;
+	if (crypt_stat->header_extent_size
+	    < ECRYPTFS_MINIMUM_HEADER_EXTENT_SIZE) {
+		rc = -EINVAL;
+		ecryptfs_printk(KERN_WARNING, "Invalid header extent size: "
+				"[%d]\n", crypt_stat->header_extent_size);
+	}
+	return rc;
+}
+
+/**
+ * set_default_header_data
+ *
+ * For version 0 file format; this function is only for backwards
+ * compatibility for files created with the prior versions of
+ * eCryptfs.
+ */
+inline void set_default_header_data(struct ecryptfs_crypt_stat *crypt_stat)
+{
+	crypt_stat->header_extent_size = 4096;
+	crypt_stat->num_header_extents_at_front = 1;
+}
+
+/**
+ * ecryptfs_read_headers_virt
+ *
+ * Read/parse the header data. The header format is detailed in the
+ * comment block for the ecryptfs_write_headers_virt() function.
+ *
+ * Returns zero on success
+ */
+int ecryptfs_read_headers_virt(char *page_virt,
+			       struct ecryptfs_crypt_stat *crypt_stat,
+			       struct dentry *ecryptfs_dentry)
+{
+	int rc = 0;
+	int offset;
+	int bytes_read;
+
+	ecryptfs_set_default_sizes(crypt_stat);
+	offset = ECRYPTFS_FILE_SIZE_BYTES;
+	rc = contains_ecryptfs_marker(page_virt + offset);
+	if (rc == 0) {
+		ecryptfs_printk(KERN_WARNING, "Valid eCryptfs marker not "
+				"found\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	offset += MAGIC_ECRYPTFS_MARKER_SIZE_BYTES;
+	rc = ecryptfs_process_flags(crypt_stat, (page_virt + offset),
+				    &bytes_read);
+	if (rc) {
+		ecryptfs_printk(KERN_WARNING, "Error processing flags\n");
+		goto out;
+	}
+	if (crypt_stat->file_version > ECRYPTFS_SUPPORTED_FILE_VERSION) {
+		ecryptfs_printk(KERN_WARNING, "File version is [%d]; only "
+				"file version [%d] is supported by this "
+				"version of eCryptfs\n",
+				crypt_stat->file_version,
+				ECRYPTFS_SUPPORTED_FILE_VERSION);
+		rc = -EINVAL;
+		goto out;
+	}
+	offset += bytes_read;
+	if (crypt_stat->file_version >= 1) {
+		rc = parse_header_metadata(crypt_stat, (page_virt + offset),
+					   &bytes_read);
+		if (rc) {
+			ecryptfs_printk(KERN_WARNING, "Error reading header "
+					"metadata; rc = [%d]\n", rc);
+		}
+		offset += bytes_read;
+	} else
+		set_default_header_data(crypt_stat);
+	rc = ecryptfs_parse_packet_set(crypt_stat, (page_virt + offset),
+				       ecryptfs_dentry);
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_read_headers
+ * 
+ * Returns zero if valid headers found and parsed; non-zero otherwise
+ */
+int ecryptfs_read_headers(struct dentry *ecryptfs_dentry,
+			  struct file *lower_file)
+{
+	int rc = 0;
+	char *page_virt = NULL;
+	mm_segment_t oldfs;
+	ssize_t bytes_read;
+	struct ecryptfs_crypt_stat *crypt_stat =
+	    &ecryptfs_inode_to_private(ecryptfs_dentry->d_inode)->crypt_stat;
+
+	/* Read the first page from the underlying file */
+	page_virt = kmem_cache_alloc(ecryptfs_header_cache_1, SLAB_USER);
+	if (!page_virt) {
+		rc = -ENOMEM;
+		ecryptfs_printk(KERN_ERR, "Unable to allocate page_virt\n");
+		goto out;
+	}
+	lower_file->f_pos = 0;
+	oldfs = get_fs();
+	set_fs(get_ds());
+	bytes_read = lower_file->f_op->read(lower_file,
+					    (char __user *)page_virt,
+					    ECRYPTFS_DEFAULT_EXTENT_SIZE,
+					    &lower_file->f_pos);
+	set_fs(oldfs);
+	if (bytes_read != ECRYPTFS_DEFAULT_EXTENT_SIZE) {
+		ecryptfs_printk(KERN_ERR, "Expected size of header not read."
+				"Instead [%d] bytes were read\n", bytes_read);
+		rc = -EINVAL;
+		goto out;
+	}
+	rc = ecryptfs_read_headers_virt(page_virt, crypt_stat,
+					ecryptfs_dentry);
+	if (rc) {
+		ecryptfs_printk(KERN_DEBUG, "Valid eCryptfs headers not "
+				"found\n");
+		rc = -EINVAL;
+	}
+out:
+	if (page_virt) {
+		memset(page_virt, 0, PAGE_CACHE_SIZE);
+		kmem_cache_free(ecryptfs_header_cache_1, page_virt);
+	}
+	return rc;
+}
+
+/**
+ * ecryptfs_encode_filename - converts a plaintext file name to cipher text
+ * @crypt_stat: The crypt_stat struct associated with the file anem to encode
+ * @name: The plaintext name
+ * @length: The length of the plaintext
+ * @encoded_name: The encypted name
+ * 
+ * Encrypts and encodes a filename into something that constitutes a
+ * valid filename for a filesystem, with printable characters.
+ *
+ * We assume that we have a properly initialized crypto context,
+ * pointed to by crypt_stat->tfm.
+ *
+ * TODO: Implement filename decoding and decryption here, in place of
+ * memcpy. We are keeping the framework around for now to (1)
+ * facilitate testing of the components needed to implement filename
+ * encryption and (2) to provide a code base from which other
+ * developers in the community can easily implement this feature.
+ *
+ * Returns the length of encoded filename; negative if error
+ */
+int
+ecryptfs_encode_filename(struct ecryptfs_crypt_stat *crypt_stat,
+			 const char *name, int length, char **encoded_name)
+{
+	int error = 0;
+
+	(*encoded_name) = kmalloc(length + 2, GFP_KERNEL);
+	if (!(*encoded_name)) {
+		error = -ENOMEM;
+		goto out;
+	}
+	/* TODO: Filename encryption is a scheduled feature for a
+	 * future version of eCryptfs. This function is here only for
+	 * the purpose of providing a framework for other developers
+	 * to easily implement filename encryption. Hint: Replace this
+	 * memcpy() with a call to encrypt and encode the
+	 * filename, the set the length accordingly. */
+	memcpy((void *)(*encoded_name), (void *)name, length);
+	(*encoded_name)[length] = '\0';
+	error = length + 1;
+out:
+	return error;
+}
+
+/**
+ * ecryptfs_decode_filename - converts the cipher text name to plaintext
+ * @crypt_stat: The crypt_stat struct associated with the file
+ * @name: The filename in cipher text
+ * @length: The length of the cipher text name
+ * @decrypted_name: The plaintext name
+ * 
+ * Decodes and decrypts the filename.
+ *
+ * We assume that we have a properly initialized crypto context,
+ * pointed to by crypt_stat->tfm.
+ *
+ * TODO: Implement filename decoding and decryption here, in place of
+ * memcpy. We are keeping the framework around for now to (1)
+ * facilitate testing of the components needed to implement filename
+ * encryption and (2) to provide a code base from which other
+ * developers in the community can easily implement this feature.
+ *
+ * Returns the length of decoded filename; negative if error
+ */
+int
+ecryptfs_decode_filename(struct ecryptfs_crypt_stat *crypt_stat,
+			 const char *name, int length, char **decrypted_name)
+{
+	int error = 0;
+
+	(*decrypted_name) = kmalloc(length + 2, GFP_KERNEL);
+	if (!(*decrypted_name)) {
+		error = -ENOMEM;
+		goto out;
+	}
+	/* TODO: Filename encryption is a scheduled feature for a
+	 * future version of eCryptfs. This function is here only for
+	 * the purpose of providing a framework for other developers
+	 * to easily implement filename encryption. Hint: Replace this
+	 * memcpy() with a call to decode and decrypt the
+	 * filename, the set the length accordingly. */
+	memcpy((void *)(*decrypted_name), (void *)name, length);
+	(*decrypted_name)[length + 1] = '\0';	/* Only for convenience
+						 * in printing out the
+						 * string in debug
+						 * messages */
+	error = length;
+out:
+	return error;
+}
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