crypto.c

 */
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, 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 (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",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
 * @str: The string representing the cipher name
 *
 * 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;
}

/**
 * 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 vfsmount *mnt)
{
	struct file *file;
	mm_segment_t oldfs;
	int rc;

	mnt = mntget(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,
		      size_t *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;
	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;
	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);
	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
	     * crypt_stat->num_header_extents_at_front)
	    < 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.
 */
static 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
 */
static 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);
	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);
		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) {
		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;
}

/**
 * ecryptfs_process_cipher - Perform 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.
 */
int
ecryptfs_process_cipher(struct crypto_tfm **key_tfm, char *cipher_name,
			size_t *key_size)
{
	char dummy_key[ECRYPTFS_MAX_KEY_BYTES];
	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;
	}
	*key_tfm = crypto_alloc_tfm(cipher_name, CRYPTO_TFM_REQ_WEAK_KEY);
	if (!(*key_tfm)) {
		rc = -EINVAL;
		printk(KERN_ERR "Unable to allocate crypto cipher with name "
		       "[%s]\n", cipher_name);
		goto out;
	}
	if (*key_size == 0)
		*key_size = crypto_tfm_alg_max_keysize(*key_tfm);
	get_random_bytes(dummy_key, *key_size);
	rc = crypto_cipher_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;
}