crypto.c

				"context for cipher [%s]: rc = [%d]\n",
				crypt_stat->cipher, rc);
out:
	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
 */
static 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},
	{0x00000004, ECRYPTFS_METADATA_IN_XATTR}
};

/**
 * ecryptfs_process_flags
 * @crypt_stat: The cryptographic context
 * @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) {
			crypt_stat->flags |= ecryptfs_flag_map[i].local_flag;
		} else
			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, size_t *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,
		     size_t *written)
{
	u32 flags = 0;
	int i;

	for (i = 0; i < ((sizeof(ecryptfs_flag_map)
			  / sizeof(struct ecryptfs_flag_map_elem))); i++)
		if (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",RFC2440_CIPHER_AES_128 },
	{"blowfish", RFC2440_CIPHER_BLOWFISH},
	{"des3_ede", RFC2440_CIPHER_DES3_EDE},
	{"cast5", RFC2440_CIPHER_CAST_5},
	{"twofish", RFC2440_CIPHER_TWOFISH},
	{"cast6", RFC2440_CIPHER_CAST_6},
	{"aes", RFC2440_CIPHER_AES_192},
	{"aes", RFC2440_CIPHER_AES_256}
};

/**
 * ecryptfs_code_for_cipher_string
 * @crypt_stat: The cryptographic context
 *
 * Returns zero on no match, or the cipher code on match
 */
u16 ecryptfs_code_for_cipher_string(struct ecryptfs_crypt_stat *crypt_stat)
{
	int i;
	u16 code = 0;
	struct ecryptfs_cipher_code_str_map_elem *map =
		ecryptfs_cipher_code_str_map;

	if (strcmp(crypt_stat->cipher, "aes") == 0) {
		switch (crypt_stat->key_size) {
		case 16:
			code = RFC2440_CIPHER_AES_128;
			break;
		case 24:
			code = RFC2440_CIPHER_AES_192;
			break;
		case 32:
			code = RFC2440_CIPHER_AES_256;
		}
	} else {
		for (i = 0; i < ARRAY_SIZE(ecryptfs_cipher_code_str_map); i++)
			if (strcmp(crypt_stat->cipher, map[i].cipher_str) == 0){
				code = map[i].cipher_code;
				break;
			}
	}
	return code;
}

/**
 * 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 < ARRAY_SIZE(ecryptfs_cipher_code_str_map); 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;
}

int ecryptfs_read_and_validate_header_region(char *data,
					     struct inode *ecryptfs_inode)
{
	struct ecryptfs_crypt_stat *crypt_stat =
		&(ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat);
	int rc;

	rc = ecryptfs_read_lower(data, 0, crypt_stat->extent_size,
				 ecryptfs_inode);
	if (rc) {
		printk(KERN_ERR "%s: Error reading header region; rc = [%d]\n",
		       __FUNCTION__, rc);
		goto out;
	}
	if (!contains_ecryptfs_marker(data + ECRYPTFS_FILE_SIZE_BYTES)) {
		rc = -EINVAL;
		ecryptfs_printk(KERN_DEBUG, "Valid marker not found\n");
	}
out:
	return rc;
}

void
ecryptfs_write_header_metadata(char *virt,
			       struct ecryptfs_crypt_stat *crypt_stat,
			       size_t *written)
{
	u32 header_extent_size;
	u16 num_header_extents_at_front;

	header_extent_size = (u32)crypt_stat->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: The virtual address to write the headers to
 * @size: Set to the number of bytes written by this function
 * @crypt_stat: The cryptographic context
 * @ecryptfs_dentry: The 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
 */
static int ecryptfs_write_headers_virt(char *page_virt, size_t *size,
				       struct ecryptfs_crypt_stat *crypt_stat,
				       struct dentry *ecryptfs_dentry)
{
	int rc;
	size_t written;
	size_t 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;
	ecryptfs_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,
					      PAGE_CACHE_SIZE - offset);
	if (rc)
		ecryptfs_printk(KERN_WARNING, "Error generating key packet "
				"set; rc = [%d]\n", rc);
	if (size) {
		offset += written;
		*size = offset;
	}
	return rc;
}

static int
ecryptfs_write_metadata_to_contents(struct ecryptfs_crypt_stat *crypt_stat,
				    struct dentry *ecryptfs_dentry,
				    char *page_virt)
{
	int current_header_page;
	int header_pages;
	int rc;

	rc = ecryptfs_write_lower(ecryptfs_dentry->d_inode, page_virt,
				  0, PAGE_CACHE_SIZE);
	if (rc) {
		printk(KERN_ERR "%s: Error attempting to write header "
		       "information to lower file; rc = [%d]\n", __FUNCTION__,
		       rc);
		goto out;
	}
	header_pages = ((crypt_stat->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) {
		loff_t offset;

		offset = (((loff_t)current_header_page) << PAGE_CACHE_SHIFT);
		if ((rc = ecryptfs_write_lower(ecryptfs_dentry->d_inode,
					       page_virt, offset,
					       PAGE_CACHE_SIZE))) {
			printk(KERN_ERR "%s: Error attempting to write header "
			       "information to lower file; rc = [%d]\n",
			       __FUNCTION__, rc);
			goto out;
		}
		current_header_page++;
	}
out:
	return rc;
}

static int
ecryptfs_write_metadata_to_xattr(struct dentry *ecryptfs_dentry,
				 struct ecryptfs_crypt_stat *crypt_stat,
				 char *page_virt, size_t size)
{
	int rc;

	rc = ecryptfs_setxattr(ecryptfs_dentry, ECRYPTFS_XATTR_NAME, page_virt,
			       size, 0);
	return rc;
}

/**
 * ecryptfs_write_metadata
 * @ecryptfs_dentry: The eCryptfs dentry
 *
 * 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.
 *
 * TODO: Support header information spanning multiple pages
 *
 * Returns zero on success; non-zero on error
 */
int ecryptfs_write_metadata(struct dentry *ecryptfs_dentry)
{
	struct ecryptfs_crypt_stat *crypt_stat =
		&ecryptfs_inode_to_private(ecryptfs_dentry->d_inode)->crypt_stat;
	char *page_virt;
	size_t size = 0;
	int rc = 0;

	if (likely(crypt_stat->flags & ECRYPTFS_ENCRYPTED)) {
		if (!(crypt_stat->flags & ECRYPTFS_KEY_VALID)) {
			printk(KERN_ERR "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_zalloc(ecryptfs_header_cache_0, GFP_USER);
	if (!page_virt) {
		ecryptfs_printk(KERN_ERR, "Out of memory\n");
		rc = -ENOMEM;
		goto out;
	}
	rc = ecryptfs_write_headers_virt(page_virt, &size, 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;
	}
	if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR)
		rc = ecryptfs_write_metadata_to_xattr(ecryptfs_dentry,
						      crypt_stat, page_virt,
						      size);
	else
		rc = ecryptfs_write_metadata_to_contents(crypt_stat,
							 ecryptfs_dentry,
							 page_virt);
	if (rc) {
		printk(KERN_ERR "Error writing metadata out to lower file; "
		       "rc = [%d]\n", rc);
		goto out_free;
	}
out_free:
	kmem_cache_free(ecryptfs_header_cache_0, page_virt);
out:
	return rc;
}

#define ECRYPTFS_DONT_VALIDATE_HEADER_SIZE 0
#define ECRYPTFS_VALIDATE_HEADER_SIZE 1
static int parse_header_metadata(struct ecryptfs_crypt_stat *crypt_stat,
				 char *virt, int *bytes_read,
				 int validate_header_size)
{
	int rc = 0;
	u32 header_extent_size;
	u16 num_header_extents_at_front;

	memcpy(&header_extent_size, virt, sizeof(u32));
	header_extent_size = be32_to_cpu(header_extent_size);
	virt += sizeof(u32);
	memcpy(&num_header_extents_at_front, virt, sizeof(u16));
	num_header_extents_at_front = be16_to_cpu(num_header_extents_at_front);
	crypt_stat->num_header_extents_at_front =
		(int)num_header_extents_at_front;
	(*bytes_read) = (sizeof(u32) + sizeof(u16));
	if ((validate_header_size == ECRYPTFS_VALIDATE_HEADER_SIZE)
	    && ((crypt_stat->extent_size
		 * crypt_stat->num_header_extents_at_front)
		< ECRYPTFS_MINIMUM_HEADER_EXTENT_SIZE)) {
		rc = -EINVAL;
		printk(KERN_WARNING "Invalid number of header extents: [%zd]\n",
		       crypt_stat->num_header_extents_at_front);
	}
	return rc;
}

/**
 * set_default_header_data
 * @crypt_stat: The cryptographic context
 *
 * For version 0 file format; this function is only for backwards
 * compatibility for files created with the prior versions of
 * eCryptfs.
 */
static void set_default_header_data(struct ecryptfs_crypt_stat *crypt_stat)
{
	crypt_stat->num_header_extents_at_front = 2;
}

/**
 * ecryptfs_read_headers_virt
 * @page_virt: The virtual address into which to read the headers
 * @crypt_stat: The cryptographic context
 * @ecryptfs_dentry: The eCryptfs dentry
 * @validate_header_size: Whether to validate the header size while reading
 *
 * 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
 */
static int ecryptfs_read_headers_virt(char *page_virt,
				      struct ecryptfs_crypt_stat *crypt_stat,
				      struct dentry *ecryptfs_dentry,
				      int validate_header_size)
{
	int rc = 0;
	int offset;
	int bytes_read;

	ecryptfs_set_default_sizes(crypt_stat);
	crypt_stat->mount_crypt_stat = &ecryptfs_superblock_to_private(
		ecryptfs_dentry->d_sb)->mount_crypt_stat;
	offset = ECRYPTFS_FILE_SIZE_BYTES;
	rc = contains_ecryptfs_marker(page_virt + offset);
	if (rc == 0) {
		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, validate_header_size);
		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_xattr_region
 * @page_virt: The vitual address into which to read the xattr data
 * @ecryptfs_inode: The eCryptfs inode
 *
 * Attempts to read the crypto metadata from the extended attribute
 * region of the lower file.
 *
 * Returns zero on success; non-zero on error
 */
int ecryptfs_read_xattr_region(char *page_virt, struct inode *ecryptfs_inode)
{
	struct dentry *lower_dentry =
		ecryptfs_inode_to_private(ecryptfs_inode)->lower_file->f_dentry;
	ssize_t size;
	int rc = 0;

	size = ecryptfs_getxattr_lower(lower_dentry, ECRYPTFS_XATTR_NAME,
				       page_virt, ECRYPTFS_DEFAULT_EXTENT_SIZE);
	if (size < 0) {
		printk(KERN_ERR "Error attempting to read the [%s] "
		       "xattr from the lower file; return value = [%zd]\n",
		       ECRYPTFS_XATTR_NAME, size);
		rc = -EINVAL;
		goto out;
	}
out:
	return rc;
}

int ecryptfs_read_and_validate_xattr_region(char *page_virt,
					    struct dentry *ecryptfs_dentry)
{
	int rc;

	rc = ecryptfs_read_xattr_region(page_virt, ecryptfs_dentry->d_inode);
	if (rc)
		goto out;
	if (!contains_ecryptfs_marker(page_virt	+ ECRYPTFS_FILE_SIZE_BYTES)) {
		printk(KERN_WARNING "Valid data found in [%s] xattr, but "
			"the marker is invalid\n", ECRYPTFS_XATTR_NAME);
		rc = -EINVAL;
	}
out:
	return rc;
}

/**
 * ecryptfs_read_metadata
 *
 * Common entry point for reading file metadata. From here, we could
 * retrieve the header information from the header region of the file,
 * the xattr region of the file, or some other repostory that is
 * stored separately from the file itself. The current implementation
 * supports retrieving the metadata information from the file contents
 * and from the xattr region.
 *
 * Returns zero if valid headers found and parsed; non-zero otherwise
 */
int ecryptfs_read_metadata(struct dentry *ecryptfs_dentry)
{
	int rc = 0;
	char *page_virt = NULL;
	struct inode *ecryptfs_inode = ecryptfs_dentry->d_inode;
	struct ecryptfs_crypt_stat *crypt_stat =
	    &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
	struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
		&ecryptfs_superblock_to_private(
			ecryptfs_dentry->d_sb)->mount_crypt_stat;

	ecryptfs_copy_mount_wide_flags_to_inode_flags(crypt_stat,
						      mount_crypt_stat);
	/* Read the first page from the underlying file */
	page_virt = kmem_cache_alloc(ecryptfs_header_cache_1, GFP_USER);
	if (!page_virt) {
		rc = -ENOMEM;
		printk(KERN_ERR "%s: Unable to allocate page_virt\n",
		       __FUNCTION__);
		goto out;
	}
	rc = ecryptfs_read_lower(page_virt, 0, crypt_stat->extent_size,
				 ecryptfs_inode);
	if (!rc)
		rc = ecryptfs_read_headers_virt(page_virt, crypt_stat,
						ecryptfs_dentry,
						ECRYPTFS_VALIDATE_HEADER_SIZE);
	if (rc) {
		rc = ecryptfs_read_xattr_region(page_virt, ecryptfs_inode);
		if (rc) {
			printk(KERN_DEBUG "Valid eCryptfs headers not found in "
			       "file header region or xattr region\n");
			rc = -EINVAL;
			goto out;
		}
		rc = ecryptfs_read_headers_virt(page_virt, crypt_stat,
						ecryptfs_dentry,
						ECRYPTFS_DONT_VALIDATE_HEADER_SIZE);
		if (rc) {
			printk(KERN_DEBUG "Valid eCryptfs headers not found in "
			       "file xattr region either\n");
			rc = -EINVAL;
		}
		if (crypt_stat->mount_crypt_stat->flags
		    & ECRYPTFS_XATTR_METADATA_ENABLED) {
			crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
		} else {
			printk(KERN_WARNING "Attempt to access file with "
			       "crypto metadata only in the extended attribute "
			       "region, but eCryptfs was mounted without "
			       "xattr support enabled. eCryptfs will not treat "
			       "this like an encrypted file.\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;
}

/**
 * ecryptfs_process_key_cipher - Perform key cipher initialization.
 * @key_tfm: Crypto context for key material, set by this function
 * @cipher_name: Name of the cipher
 * @key_size: Size of the key in bytes
 *
 * Returns zero on success. Any crypto_tfm structs allocated here
 * should be released by other functions, such as on a superblock put
 * event, regardless of whether this function succeeds for fails.
 */
static int
ecryptfs_process_key_cipher(struct crypto_blkcipher **key_tfm,
			    char *cipher_name, size_t *key_size)
{
	char dummy_key[ECRYPTFS_MAX_KEY_BYTES];
	char *full_alg_name;
	int rc;

	*key_tfm = NULL;
	if (*key_size > ECRYPTFS_MAX_KEY_BYTES) {
		rc = -EINVAL;
		printk(KERN_ERR "Requested key size is [%Zd] bytes; maximum "
		      "allowable is [%d]\n", *key_size, ECRYPTFS_MAX_KEY_BYTES);
		goto out;
	}
	rc = ecryptfs_crypto_api_algify_cipher_name(&full_alg_name, cipher_name,
						    "ecb");
	if (rc)
		goto out;
	*key_tfm = crypto_alloc_blkcipher(full_alg_name, 0, CRYPTO_ALG_ASYNC);
	kfree(full_alg_name);
	if (IS_ERR(*key_tfm)) {
		rc = PTR_ERR(*key_tfm);
		printk(KERN_ERR "Unable to allocate crypto cipher with name "
		       "[%s]; rc = [%d]\n", cipher_name, rc);
		goto out;
	}
	crypto_blkcipher_set_flags(*key_tfm, CRYPTO_TFM_REQ_WEAK_KEY);
	if (*key_size == 0) {
		struct blkcipher_alg *alg = crypto_blkcipher_alg(*key_tfm);

		*key_size = alg->max_keysize;
	}
	get_random_bytes(dummy_key, *key_size);
	rc = crypto_blkcipher_setkey(*key_tfm, dummy_key, *key_size);
	if (rc) {
		printk(KERN_ERR "Error attempting to set key of size [%Zd] for "
		       "cipher [%s]; rc = [%d]\n", *key_size, cipher_name, rc);
		rc = -EINVAL;
		goto out;
	}
out:
	return rc;
}

struct kmem_cache *ecryptfs_key_tfm_cache;
struct list_head key_tfm_list;
struct mutex key_tfm_list_mutex;

int ecryptfs_init_crypto(void)
{
	mutex_init(&key_tfm_list_mutex);
	INIT_LIST_HEAD(&key_tfm_list);
	return 0;
}

int ecryptfs_destroy_crypto(void)
{
	struct ecryptfs_key_tfm *key_tfm, *key_tfm_tmp;

	mutex_lock(&key_tfm_list_mutex);
	list_for_each_entry_safe(key_tfm, key_tfm_tmp, &key_tfm_list,
				 key_tfm_list) {
		list_del(&key_tfm->key_tfm_list);
		if (key_tfm->key_tfm)
			crypto_free_blkcipher(key_tfm->key_tfm);
		kmem_cache_free(ecryptfs_key_tfm_cache, key_tfm);
	}
	mutex_unlock(&key_tfm_list_mutex);
	return 0;
}

int
ecryptfs_add_new_key_tfm(struct ecryptfs_key_tfm **key_tfm, char *cipher_name,
			 size_t key_size)
{
	struct ecryptfs_key_tfm *tmp_tfm;
	int rc = 0;

	tmp_tfm = kmem_cache_alloc(ecryptfs_key_tfm_cache, GFP_KERNEL);
	if (key_tfm != NULL)
		(*key_tfm) = tmp_tfm;
	if (!tmp_tfm) {
		rc = -ENOMEM;
		printk(KERN_ERR "Error attempting to allocate from "
		       "ecryptfs_key_tfm_cache\n");
		goto out;
	}
	mutex_init(&tmp_tfm->key_tfm_mutex);
	strncpy(tmp_tfm->cipher_name, cipher_name,
		ECRYPTFS_MAX_CIPHER_NAME_SIZE);
	tmp_tfm->key_size = key_size;
	rc = ecryptfs_process_key_cipher(&tmp_tfm->key_tfm,
					 tmp_tfm->cipher_name,
					 &tmp_tfm->key_size);
	if (rc) {
		printk(KERN_ERR "Error attempting to initialize key TFM "
		       "cipher with name = [%s]; rc = [%d]\n",
		       tmp_tfm->cipher_name, rc);
		kmem_cache_free(ecryptfs_key_tfm_cache, tmp_tfm);
		if (key_tfm != NULL)
			(*key_tfm) = NULL;
		goto out;
	}
	mutex_lock(&key_tfm_list_mutex);
	list_add(&tmp_tfm->key_tfm_list, &key_tfm_list);
	mutex_unlock(&key_tfm_list_mutex);
out:
	return rc;
}

int ecryptfs_get_tfm_and_mutex_for_cipher_name(struct crypto_blkcipher **tfm,
					       struct mutex **tfm_mutex,
					       char *cipher_name)
{
	struct ecryptfs_key_tfm *key_tfm;
	int rc = 0;

	(*tfm) = NULL;
	(*tfm_mutex) = NULL;
	mutex_lock(&key_tfm_list_mutex);
	list_for_each_entry(key_tfm, &key_tfm_list, key_tfm_list) {
		if (strcmp(key_tfm->cipher_name, cipher_name) == 0) {
			(*tfm) = key_tfm->key_tfm;
			(*tfm_mutex) = &key_tfm->key_tfm_mutex;
			mutex_unlock(&key_tfm_list_mutex);
			goto out;
		}
	}
	mutex_unlock(&key_tfm_list_mutex);
	rc = ecryptfs_add_new_key_tfm(&key_tfm, cipher_name, 0);
	if (rc) {
		printk(KERN_ERR "Error adding new key_tfm to list; rc = [%d]\n",
		       rc);
		goto out;
	}
	(*tfm) = key_tfm->key_tfm;
	(*tfm_mutex) = &key_tfm->key_tfm_mutex;
out:
	return rc;
}