fs/crypto/fname.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * This contains functions for filename crypto management
  *
  * Copyright (C) 2015, Google, Inc.
  * Copyright (C) 2015, Motorola Mobility
  *
  * Written by Uday Savagaonkar, 2014.
  * Modified by Jaegeuk Kim, 2015.
  *
  * This has not yet undergone a rigorous security audit.
  */

 #include <linux/scatterlist.h>
 #include <linux/ratelimit.h>
 #include <crypto/skcipher.h>
 #include "fscrypt_private.h"

 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
 {
 	if (str->len == 1 && str->name[0] == '.')
 		return true;

 	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
 		return true;

 	return false;
 }

 /**
  * fname_encrypt() - encrypt a filename
  *
  * The output buffer must be at least as large as the input buffer.
  * Any extra space is filled with NUL padding before encryption.
  *
  * Return: 0 on success, -errno on failure
  */
 int fname_encrypt(struct inode *inode, const struct qstr *iname,
 		  u8 *out, unsigned int olen)
 {
 	struct skcipher_request *req = NULL;
 	DECLARE_CRYPTO_WAIT(wait);
 	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
 	int res = 0;
 	char iv[FS_CRYPTO_BLOCK_SIZE];
 	struct scatterlist sg;

 	/*
 	 * Copy the filename to the output buffer for encrypting in-place and
 	 * pad it with the needed number of NUL bytes.
 	 */
 	if (WARN_ON(olen < iname->len))
 		return -ENOBUFS;
 	memcpy(out, iname->name, iname->len);
 	memset(out + iname->len, 0, olen - iname->len);

 	/* Initialize the IV */
 	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);

 	/* Set up the encryption request */
 	req = skcipher_request_alloc(tfm, GFP_NOFS);
 	if (!req)
 		return -ENOMEM;
 	skcipher_request_set_callback(req,
 			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 			crypto_req_done, &wait);
 	sg_init_one(&sg, out, olen);
 	skcipher_request_set_crypt(req, &sg, &sg, olen, iv);

 	/* Do the encryption */
 	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
 	skcipher_request_free(req);
 	if (res < 0) {
 		fscrypt_err(inode->i_sb,
 			    "Filename encryption failed for inode %lu: %d",
 			    inode->i_ino, res);
 		return res;
 	}

 	return 0;
 }

 /**
  * fname_decrypt() - decrypt a filename
  *
  * The caller must have allocated sufficient memory for the @oname string.
  *
  * Return: 0 on success, -errno on failure
  */
 static int fname_decrypt(struct inode *inode,
 				const struct fscrypt_str *iname,
 				struct fscrypt_str *oname)
 {
 	struct skcipher_request *req = NULL;
 	DECLARE_CRYPTO_WAIT(wait);
 	struct scatterlist src_sg, dst_sg;
 	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
 	int res = 0;
 	char iv[FS_CRYPTO_BLOCK_SIZE];

 	/* Allocate request */
 	req = skcipher_request_alloc(tfm, GFP_NOFS);
 	if (!req)
 		return -ENOMEM;
 	skcipher_request_set_callback(req,
 		CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 		crypto_req_done, &wait);

 	/* Initialize IV */
 	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);

 	/* Create decryption request */
 	sg_init_one(&src_sg, iname->name, iname->len);
 	sg_init_one(&dst_sg, oname->name, oname->len);
 	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 	skcipher_request_free(req);
 	if (res < 0) {
 		fscrypt_err(inode->i_sb,
 			    "Filename decryption failed for inode %lu: %d",
 			    inode->i_ino, res);
 		return res;
 	}

 	oname->len = strnlen(oname->name, iname->len);
 	return 0;
 }

 static const char *lookup_table =
 	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";

 #define BASE64_CHARS(nbytes)	DIV_ROUND_UP((nbytes) * 4, 3)

 /**
  * digest_encode() -
  *
  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
  * The encoded string is roughly 4/3 times the size of the input string.
  */
 static int digest_encode(const char *src, int len, char *dst)
 {
 	int i = 0, bits = 0, ac = 0;
 	char *cp = dst;

 	while (i < len) {
 		ac += (((unsigned char) src[i]) << bits);
 		bits += 8;
 		do {
 			*cp++ = lookup_table[ac & 0x3f];
 			ac >>= 6;
 			bits -= 6;
 		} while (bits >= 6);
 		i++;
 	}
 	if (bits)
 		*cp++ = lookup_table[ac & 0x3f];
 	return cp - dst;
 }

 static int digest_decode(const char *src, int len, char *dst)
 {
 	int i = 0, bits = 0, ac = 0;
 	const char *p;
 	char *cp = dst;

 	while (i < len) {
 		p = strchr(lookup_table, src[i]);
 		if (p == NULL || src[i] == 0)
 			return -2;
 		ac += (p - lookup_table) << bits;
 		bits += 6;
 		if (bits >= 8) {
 			*cp++ = ac & 0xff;
 			ac >>= 8;
 			bits -= 8;
 		}
 		i++;
 	}
 	if (ac)
 		return -1;
 	return cp - dst;
 }

 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
 				  u32 max_len, u32 *encrypted_len_ret)
 {
 	int padding = 4 << (inode->i_crypt_info->ci_flags &
 			    FS_POLICY_FLAGS_PAD_MASK);
 	u32 encrypted_len;

 	if (orig_len > max_len)
 		return false;
 	encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
 	encrypted_len = round_up(encrypted_len, padding);
 	*encrypted_len_ret = min(encrypted_len, max_len);
 	return true;
 }

 /**
  * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
  *
  * Allocate a buffer that is large enough to hold any decrypted or encoded
  * filename (null-terminated), for the given maximum encrypted filename length.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_fname_alloc_buffer(const struct inode *inode,
 			       u32 max_encrypted_len,
 			       struct fscrypt_str *crypto_str)
 {
 	const u32 max_encoded_len =
 		max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
 		      1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
 	u32 max_presented_len;

 	max_presented_len = max(max_encoded_len, max_encrypted_len);

 	crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
 	if (!crypto_str->name)
 		return -ENOMEM;
 	crypto_str->len = max_presented_len;
 	return 0;
 }
 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);

 /**
  * fscrypt_fname_free_buffer - free the buffer for presented filenames
  *
  * Free the buffer allocated by fscrypt_fname_alloc_buffer().
  */
 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 {
 	if (!crypto_str)
 		return;
 	kfree(crypto_str->name);
 	crypto_str->name = NULL;
 }
 EXPORT_SYMBOL(fscrypt_fname_free_buffer);

 /**
  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
  * space
  *
  * The caller must have allocated sufficient memory for the @oname string.
  *
  * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
  * it for presentation.  Short names are directly base64-encoded, while long
  * names are encoded in fscrypt_digested_name format.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_fname_disk_to_usr(struct inode *inode,
 			u32 hash, u32 minor_hash,
 			const struct fscrypt_str *iname,
 			struct fscrypt_str *oname)
 {
 	const struct qstr qname = FSTR_TO_QSTR(iname);
 	struct fscrypt_digested_name digested_name;

 	if (fscrypt_is_dot_dotdot(&qname)) {
 		oname->name[0] = '.';
 		oname->name[iname->len - 1] = '.';
 		oname->len = iname->len;
 		return 0;
 	}

 	if (iname->len < FS_CRYPTO_BLOCK_SIZE)
 		return -EUCLEAN;

 	if (inode->i_crypt_info)
 		return fname_decrypt(inode, iname, oname);

 	if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
 		oname->len = digest_encode(iname->name, iname->len,
 					   oname->name);
 		return 0;
 	}
 	if (hash) {
 		digested_name.hash = hash;
 		digested_name.minor_hash = minor_hash;
 	} else {
 		digested_name.hash = 0;
 		digested_name.minor_hash = 0;
 	}
 	memcpy(digested_name.digest,
 	       FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
 	       FSCRYPT_FNAME_DIGEST_SIZE);
 	oname->name[0] = '_';
 	oname->len = 1 + digest_encode((const char *)&digested_name,
 				       sizeof(digested_name), oname->name + 1);
 	return 0;
 }
 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);

 /**
  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
  * @dir: the directory that will be searched
  * @iname: the user-provided filename being searched for
  * @lookup: 1 if we're allowed to proceed without the key because it's
  *	->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
  *	proceed without the key because we're going to create the dir_entry.
  * @fname: the filename information to be filled in
  *
  * Given a user-provided filename @iname, this function sets @fname->disk_name
  * to the name that would be stored in the on-disk directory entry, if possible.
  * If the directory is unencrypted this is simply @iname.  Else, if we have the
  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
  * get the disk_name.
  *
  * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
  * we decode it to get either the ciphertext disk_name (for short names) or the
  * fscrypt_digested_name (for long names).  Non-@lookup operations will be
  * impossible in this case, so we fail them with ENOKEY.
  *
  * If successful, fscrypt_free_filename() must be called later to clean up.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 			      int lookup, struct fscrypt_name *fname)
 {
 	int ret;
 	int digested;

 	memset(fname, 0, sizeof(struct fscrypt_name));
 	fname->usr_fname = iname;

 	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
 		fname->disk_name.name = (unsigned char *)iname->name;
 		fname->disk_name.len = iname->len;
 		return 0;
 	}
 	ret = fscrypt_get_encryption_info(dir);
 	if (ret)
 		return ret;

 	if (dir->i_crypt_info) {
 		if (!fscrypt_fname_encrypted_size(dir, iname->len,
 						  dir->i_sb->s_cop->max_namelen,
 						  &fname->crypto_buf.len))
 			return -ENAMETOOLONG;
 		fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
 						 GFP_NOFS);
 		if (!fname->crypto_buf.name)
 			return -ENOMEM;

 		ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
 				    fname->crypto_buf.len);
 		if (ret)
 			goto errout;
 		fname->disk_name.name = fname->crypto_buf.name;
 		fname->disk_name.len = fname->crypto_buf.len;
 		return 0;
 	}
 	if (!lookup)
 		return -ENOKEY;

 	/*
 	 * We don't have the key and we are doing a lookup; decode the
 	 * user-supplied name
 	 */
 	if (iname->name[0] == '_') {
 		if (iname->len !=
 		    1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
 			return -ENOENT;
 		digested = 1;
 	} else {
 		if (iname->len >
 		    BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
 			return -ENOENT;
 		digested = 0;
 	}

 	fname->crypto_buf.name =
 		kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
 			      sizeof(struct fscrypt_digested_name)),
 			GFP_KERNEL);
 	if (fname->crypto_buf.name == NULL)
 		return -ENOMEM;

 	ret = digest_decode(iname->name + digested, iname->len - digested,
 				fname->crypto_buf.name);
 	if (ret < 0) {
 		ret = -ENOENT;
 		goto errout;
 	}
 	fname->crypto_buf.len = ret;
 	if (digested) {
 		const struct fscrypt_digested_name *n =
 			(const void *)fname->crypto_buf.name;
 		fname->hash = n->hash;
 		fname->minor_hash = n->minor_hash;
 	} else {
 		fname->disk_name.name = fname->crypto_buf.name;
 		fname->disk_name.len = fname->crypto_buf.len;
 	}
 	return 0;

 errout:
 	kfree(fname->crypto_buf.name);
 	return ret;
 }
 EXPORT_SYMBOL(fscrypt_setup_filename);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* This contains functions for filename crypto management
	*
	* Copyright (C) 2015, Google, Inc.
	* Copyright (C) 2015, Motorola Mobility
	*
	* Written by Uday Savagaonkar, 2014.
	* Modified by Jaegeuk Kim, 2015.
	*
	* This has not yet undergone a rigorous security audit.
	*/

	#include <linux/scatterlist.h>
	#include <linux/ratelimit.h>
	#include <crypto/skcipher.h>
	#include "fscrypt_private.h"

	static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
	{
	if (str->len == 1 && str->name[0] == '.')
	return true;

	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
	return true;

	return false;
	}

	/**
	* fname_encrypt() - encrypt a filename
	*
	* The output buffer must be at least as large as the input buffer.
	* Any extra space is filled with NUL padding before encryption.
	*
	* Return: 0 on success, -errno on failure
	*/
	int fname_encrypt(struct inode inode, const struct qstr iname,
	u8 *out, unsigned int olen)
	{
	struct skcipher_request *req = NULL;
	DECLARE_CRYPTO_WAIT(wait);
	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
	int res = 0;
	char iv[FS_CRYPTO_BLOCK_SIZE];
	struct scatterlist sg;

	/*
	* Copy the filename to the output buffer for encrypting in-place and
	* pad it with the needed number of NUL bytes.
	*/
	if (WARN_ON(olen < iname->len))
	return -ENOBUFS;
	memcpy(out, iname->name, iname->len);
	memset(out + iname->len, 0, olen - iname->len);

	/* Initialize the IV */
	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);

	/* Set up the encryption request */
	req = skcipher_request_alloc(tfm, GFP_NOFS);
	if (!req)
	return -ENOMEM;
	skcipher_request_set_callback(req,
	CRYPTO_TFM_REQ_MAY_BACKLOG \| CRYPTO_TFM_REQ_MAY_SLEEP,
	crypto_req_done, &wait);
	sg_init_one(&sg, out, olen);
	skcipher_request_set_crypt(req, &sg, &sg, olen, iv);

	/* Do the encryption */
	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
	skcipher_request_free(req);
	if (res < 0) {
	fscrypt_err(inode->i_sb,
	"Filename encryption failed for inode %lu: %d",
	inode->i_ino, res);
	return res;
	}

	return 0;
	}

	/**
	* fname_decrypt() - decrypt a filename
	*
	* The caller must have allocated sufficient memory for the @oname string.
	*
	* Return: 0 on success, -errno on failure
	*/
	static int fname_decrypt(struct inode *inode,
	const struct fscrypt_str *iname,
	struct fscrypt_str *oname)
	{
	struct skcipher_request *req = NULL;
	DECLARE_CRYPTO_WAIT(wait);
	struct scatterlist src_sg, dst_sg;
	struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
	int res = 0;
	char iv[FS_CRYPTO_BLOCK_SIZE];

	/* Allocate request */
	req = skcipher_request_alloc(tfm, GFP_NOFS);
	if (!req)
	return -ENOMEM;
	skcipher_request_set_callback(req,
	CRYPTO_TFM_REQ_MAY_BACKLOG \| CRYPTO_TFM_REQ_MAY_SLEEP,
	crypto_req_done, &wait);

	/* Initialize IV */
	memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);

	/* Create decryption request */
	sg_init_one(&src_sg, iname->name, iname->len);
	sg_init_one(&dst_sg, oname->name, oname->len);
	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
	skcipher_request_free(req);
	if (res < 0) {
	fscrypt_err(inode->i_sb,
	"Filename decryption failed for inode %lu: %d",
	inode->i_ino, res);
	return res;
	}

	oname->len = strnlen(oname->name, iname->len);
	return 0;
	}

	static const char *lookup_table =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";

	#define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)

	/**
	* digest_encode() -
	*
	* Encodes the input digest using characters from the set [a-zA-Z0-9_+].
	* The encoded string is roughly 4/3 times the size of the input string.
	*/
	static int digest_encode(const char src, int len, char dst)
	{
	int i = 0, bits = 0, ac = 0;
	char *cp = dst;

	while (i < len) {
	ac += (((unsigned char) src[i]) << bits);
	bits += 8;
	do {
	*cp++ = lookup_table[ac & 0x3f];
	ac >>= 6;
	bits -= 6;
	} while (bits >= 6);
	i++;
	}
	if (bits)
	*cp++ = lookup_table[ac & 0x3f];
	return cp - dst;
	}

	static int digest_decode(const char src, int len, char dst)
	{
	int i = 0, bits = 0, ac = 0;
	const char *p;
	char *cp = dst;

	while (i < len) {
	p = strchr(lookup_table, src[i]);
	if (p == NULL \|\| src[i] == 0)
	return -2;
	ac += (p - lookup_table) << bits;
	bits += 6;
	if (bits >= 8) {
	*cp++ = ac & 0xff;
	ac >>= 8;
	bits -= 8;
	}
	i++;
	}
	if (ac)
	return -1;
	return cp - dst;
	}

	bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
	u32 max_len, u32 *encrypted_len_ret)
	{
	int padding = 4 << (inode->i_crypt_info->ci_flags &
	FS_POLICY_FLAGS_PAD_MASK);
	u32 encrypted_len;

	if (orig_len > max_len)
	return false;
	encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
	encrypted_len = round_up(encrypted_len, padding);
	*encrypted_len_ret = min(encrypted_len, max_len);
	return true;
	}

	/**
	* fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
	*
	* Allocate a buffer that is large enough to hold any decrypted or encoded
	* filename (null-terminated), for the given maximum encrypted filename length.
	*
	* Return: 0 on success, -errno on failure
	*/
	int fscrypt_fname_alloc_buffer(const struct inode *inode,
	u32 max_encrypted_len,
	struct fscrypt_str *crypto_str)
	{
	const u32 max_encoded_len =
	max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
	1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
	u32 max_presented_len;

	max_presented_len = max(max_encoded_len, max_encrypted_len);

	crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
	if (!crypto_str->name)
	return -ENOMEM;
	crypto_str->len = max_presented_len;
	return 0;
	}
	EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);

	/**
	* fscrypt_fname_free_buffer - free the buffer for presented filenames
	*
	* Free the buffer allocated by fscrypt_fname_alloc_buffer().
	*/
	void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
	{
	if (!crypto_str)
	return;
	kfree(crypto_str->name);
	crypto_str->name = NULL;
	}
	EXPORT_SYMBOL(fscrypt_fname_free_buffer);

	/**
	* fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
	* space
	*
	* The caller must have allocated sufficient memory for the @oname string.
	*
	* If the key is available, we'll decrypt the disk name; otherwise, we'll encode
	* it for presentation. Short names are directly base64-encoded, while long
	* names are encoded in fscrypt_digested_name format.
	*
	* Return: 0 on success, -errno on failure
	*/
	int fscrypt_fname_disk_to_usr(struct inode *inode,
	u32 hash, u32 minor_hash,
	const struct fscrypt_str *iname,
	struct fscrypt_str *oname)
	{
	const struct qstr qname = FSTR_TO_QSTR(iname);
	struct fscrypt_digested_name digested_name;

	if (fscrypt_is_dot_dotdot(&qname)) {
	oname->name[0] = '.';
	oname->name[iname->len - 1] = '.';
	oname->len = iname->len;
	return 0;
	}

	if (iname->len < FS_CRYPTO_BLOCK_SIZE)
	return -EUCLEAN;

	if (inode->i_crypt_info)
	return fname_decrypt(inode, iname, oname);

	if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
	oname->len = digest_encode(iname->name, iname->len,
	oname->name);
	return 0;
	}
	if (hash) {
	digested_name.hash = hash;
	digested_name.minor_hash = minor_hash;
	} else {
	digested_name.hash = 0;
	digested_name.minor_hash = 0;
	}
	memcpy(digested_name.digest,
	FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
	FSCRYPT_FNAME_DIGEST_SIZE);
	oname->name[0] = '_';
	oname->len = 1 + digest_encode((const char *)&digested_name,
	sizeof(digested_name), oname->name + 1);
	return 0;
	}
	EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);

	/**
	* fscrypt_setup_filename() - prepare to search a possibly encrypted directory
	* @dir: the directory that will be searched
	* @iname: the user-provided filename being searched for
	* @lookup: 1 if we're allowed to proceed without the key because it's
	* ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
	* proceed without the key because we're going to create the dir_entry.
	* @fname: the filename information to be filled in
	*
	* Given a user-provided filename @iname, this function sets @fname->disk_name
	* to the name that would be stored in the on-disk directory entry, if possible.
	* If the directory is unencrypted this is simply @iname. Else, if we have the
	* directory's encryption key, then @iname is the plaintext, so we encrypt it to
	* get the disk_name.
	*
	* Else, for keyless @lookup operations, @iname is the presented ciphertext, so
	* we decode it to get either the ciphertext disk_name (for short names) or the
	* fscrypt_digested_name (for long names). Non-@lookup operations will be
	* impossible in this case, so we fail them with ENOKEY.
	*
	* If successful, fscrypt_free_filename() must be called later to clean up.
	*
	* Return: 0 on success, -errno on failure
	*/
	int fscrypt_setup_filename(struct inode dir, const struct qstr iname,
	int lookup, struct fscrypt_name *fname)
	{
	int ret;
	int digested;

	memset(fname, 0, sizeof(struct fscrypt_name));
	fname->usr_fname = iname;

	if (!IS_ENCRYPTED(dir) \|\| fscrypt_is_dot_dotdot(iname)) {
	fname->disk_name.name = (unsigned char *)iname->name;
	fname->disk_name.len = iname->len;
	return 0;
	}
	ret = fscrypt_get_encryption_info(dir);
	if (ret)
	return ret;

	if (dir->i_crypt_info) {
	if (!fscrypt_fname_encrypted_size(dir, iname->len,
	dir->i_sb->s_cop->max_namelen,
	&fname->crypto_buf.len))
	return -ENAMETOOLONG;
	fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
	GFP_NOFS);
	if (!fname->crypto_buf.name)
	return -ENOMEM;

	ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
	fname->crypto_buf.len);
	if (ret)
	goto errout;
	fname->disk_name.name = fname->crypto_buf.name;
	fname->disk_name.len = fname->crypto_buf.len;
	return 0;
	}
	if (!lookup)
	return -ENOKEY;

	/*
	* We don't have the key and we are doing a lookup; decode the
	* user-supplied name
	*/
	if (iname->name[0] == '_') {
	if (iname->len !=
	1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
	return -ENOENT;
	digested = 1;
	} else {
	if (iname->len >
	BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
	return -ENOENT;
	digested = 0;
	}

	fname->crypto_buf.name =
	kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
	sizeof(struct fscrypt_digested_name)),
	GFP_KERNEL);
	if (fname->crypto_buf.name == NULL)
	return -ENOMEM;

	ret = digest_decode(iname->name + digested, iname->len - digested,
	fname->crypto_buf.name);
	if (ret < 0) {
	ret = -ENOENT;
	goto errout;
	}
	fname->crypto_buf.len = ret;
	if (digested) {
	const struct fscrypt_digested_name *n =
	(const void *)fname->crypto_buf.name;
	fname->hash = n->hash;
	fname->minor_hash = n->minor_hash;
	} else {
	fname->disk_name.name = fname->crypto_buf.name;
	fname->disk_name.len = fname->crypto_buf.len;
	}
	return 0;

	errout:
	kfree(fname->crypto_buf.name);
	return ret;
	}
	EXPORT_SYMBOL(fscrypt_setup_filename);