// 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/namei.h>
#include <linux/scatterlist.h>
#include <crypto/hash.h>
#include <crypto/sha2.h>
#include <crypto/skcipher.h>
#include "fscrypt_private.h"
/*
* The minimum message length (input and output length), in bytes, for all
* filenames encryption modes. Filenames shorter than this will be zero-padded
* before being encrypted.
*/
#define FSCRYPT_FNAME_MIN_MSG_LEN 16
/*
* struct fscrypt_nokey_name - identifier for directory entry when key is absent
*
* When userspace lists an encrypted directory without access to the key, the
* filesystem must present a unique "no-key name" for each filename that allows
* it to find the directory entry again if requested. Naively, that would just
* mean using the ciphertext filenames. However, since the ciphertext filenames
* can contain illegal characters ('\0' and '/'), they must be encoded in some
* way. We use base64url. But that can cause names to exceed NAME_MAX (255
* bytes), so we also need to use a strong hash to abbreviate long names.
*
* The filesystem may also need another kind of hash, the "dirhash", to quickly
* find the directory entry. Since filesystems normally compute the dirhash
* over the on-disk filename (i.e. the ciphertext), it's not computable from
* no-key names that abbreviate the ciphertext using the strong hash to fit in
* NAME_MAX. It's also not computable if it's a keyed hash taken over the
* plaintext (but it may still be available in the on-disk directory entry);
* casefolded directories use this type of dirhash. At least in these cases,
* each no-key name must include the name's dirhash too.
*
* To meet all these requirements, we base64url-encode the following
* variable-length structure. It contains the dirhash, or 0's if the filesystem
* didn't provide one; up to 149 bytes of the ciphertext name; and for
* ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
*
* This ensures that each no-key name contains everything needed to find the
* directory entry again, contains only legal characters, doesn't exceed
* NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
* take the performance hit of SHA-256 on very long filenames (which are rare).
*/
struct fscrypt_nokey_name {
u32 dirhash[2];
u8 bytes[149];
u8 sha256[SHA256_DIGEST_SIZE];
}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */
/*
* Decoded size of max-size no-key name, i.e. a name that was abbreviated using
* the strong hash and thus includes the 'sha256' field. This isn't simply
* sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.
*/
#define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256)
/* Encoded size of max-size no-key name */
#define FSCRYPT_NOKEY_NAME_MAX_ENCODED \
FSCRYPT_BASE64URL_CHARS(FSCRYPT_NOKEY_NAME_MAX)
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;
}
/**
* fscrypt_fname_encrypt() - encrypt a filename
* @inode: inode of the parent directory (for regular filenames)
* or of the symlink (for symlink targets). Key must already be
* set up.
* @iname: the filename to encrypt
* @out: (output) the encrypted filename
* @olen: size of the encrypted filename. It must be at least @iname->len.
* Any extra space is filled with NUL padding before encryption.
*
* Return: 0 on success, -errno on failure
*/
int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
u8 *out, unsigned int olen)
{
struct skcipher_request *req = NULL;
DECLARE_CRYPTO_WAIT(wait);
const struct fscrypt_info *ci = inode->i_crypt_info;
struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
union fscrypt_iv iv;
struct scatterlist sg;
int res;
/*
* Copy the filename to the output buffer for encrypting in-place and
* pad it with the needed number of NUL bytes.
*/
if (WARN_ON_ONCE(olen < iname->len))
return -ENOBUFS;
memcpy(out, iname->name, iname->len);
memset(out + iname->len, 0, olen - iname->len);
/* Initialize the IV */
fscrypt_generate_iv(&iv, 0, ci);
/* 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, "Filename encryption failed: %d", res);
return res;
}
return 0;
}
EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt);
/**
* fname_decrypt() - decrypt a filename
* @inode: inode of the parent directory (for regular filenames)
* or of the symlink (for symlink targets)
* @iname: the encrypted filename to decrypt
* @oname: (output) the decrypted filename. The caller must have allocated
* enough space for this, e.g. using fscrypt_fname_alloc_buffer().
*
* Return: 0 on success, -errno on failure
*/
static int fname_decrypt(const 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;
const struct fscrypt_info *ci = inode->i_crypt_info;
struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
union fscrypt_iv iv;
int res;
/* 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 */
fscrypt_generate_iv(&iv, 0, ci);
/* 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, "Filename decryption failed: %d", res);
return res;
}
oname->len = strnlen(oname->name, iname->len);
return 0;
}
static const char base64url_table[65] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
#define FSCRYPT_BASE64URL_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
/**
* fscrypt_base64url_encode() - base64url-encode some binary data
* @src: the binary data to encode
* @srclen: the length of @src in bytes
* @dst: (output) the base64url-encoded string. Not NUL-terminated.
*
* Encodes data using base64url encoding, i.e. the "Base 64 Encoding with URL
* and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't used,
* as it's unneeded and not required by the RFC. base64url is used instead of
* base64 to avoid the '/' character, which isn't allowed in filenames.
*
* Return: the length of the resulting base64url-encoded string in bytes.
* This will be equal to FSCRYPT_BASE64URL_CHARS(srclen).
*/
static int fscrypt_base64url_encode(const u8 *src, int srclen, char *dst)
{
u32 ac = 0;
int bits = 0;
int i;
char *cp = dst;
for (i = 0; i < srclen; i++) {
ac = (ac << 8) | src[i];
bits += 8;
do {
bits -= 6;
*cp++ = base64url_table[(ac >> bits) & 0x3f];
} while (bits >= 6);
}
if (bits)
*cp++ = base64url_table[(ac << (6 - bits)) & 0x3f];
return cp - dst;
}
/**
* fscrypt_base64url_decode() - base64url-decode a string
* @src: the string to decode. Doesn't need to be NUL-terminated.
* @srclen: the length of @src in bytes
* @dst: (output) the decoded binary data
*
* Decodes a string using base64url encoding, i.e. the "Base 64 Encoding with
* URL and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't
* accepted, nor are non-encoding characters such as whitespace.
*
* This implementation hasn't been optimized for performance.
*
* Return: the length of the resulting decoded binary data in bytes,
* or -1 if the string isn't a valid base64url string.
*/
static int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)
{
u32 ac = 0;
int bits = 0;
int i;
u8 *bp = dst;
for (i = 0; i < srclen; i++) {
const char *p = strchr(base64url_table, src[i]);
if (p == NULL || src[i] == 0)
return -1;
ac = (ac << 6) | (p - base64url_table);
bits += 6;
if (bits >= 8) {
bits -= 8;
*bp++ = (u8)(ac >> bits);
}
}
if (ac & ((1 << bits) - 1))
return -1;
return bp - dst;
}
bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
u32 orig_len, u32 max_len,
u32 *encrypted_len_ret)
{
int padding = 4 << (fscrypt_policy_flags(policy) &
FSCRYPT_POLICY_FLAGS_PAD_MASK);
u32 encrypted_len;
if (orig_len > max_len)
return false;
encrypted_len = max_t(u32, orig_len, FSCRYPT_FNAME_MIN_MSG_LEN);
encrypted_len = round_up(encrypted_len, padding);
*encrypted_len_ret = min(encrypted_len, max_len);
return true;
}
/**
* fscrypt_fname_encrypted_size() - calculate length of encrypted filename
* @inode: parent inode of dentry name being encrypted. Key must
* already be set up.
* @orig_len: length of the original filename
* @max_len: maximum length to return
* @encrypted_len_ret: where calculated length should be returned (on success)
*
* Filenames that are shorter than the maximum length may have their lengths
* increased slightly by encryption, due to padding that is applied.
*
* Return: false if the orig_len is greater than max_len. Otherwise, true and
* fill out encrypted_len_ret with the length (up to max_len).
*/
bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
u32 max_len, u32 *encrypted_len_ret)
{
return __fscrypt_fname_encrypted_size(&inode->i_crypt_info->ci_policy,
orig_len, max_len,
encrypted_len_ret);
}
EXPORT_SYMBOL_GPL(fscrypt_fname_encrypted_size);
/**
* fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
* @max_encrypted_len: maximum length of encrypted filenames the buffer will be
* used to present
* @crypto_str: (output) buffer to allocate
*
* 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(u32 max_encrypted_len,
struct fscrypt_str *crypto_str)
{
u32 max_presented_len = max_t(u32, FSCRYPT_NOKEY_NAME_MAX_ENCODED,
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 a buffer for presented filenames
* @crypto_str: the buffer to free
*
* Free a buffer that was 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() - convert an encrypted filename to
* user-presentable form
* @inode: inode of the parent directory (for regular filenames)
* or of the symlink (for symlink targets)
* @hash: first part of the name's dirhash, if applicable. This only needs to
* be provided if the filename is located in an indexed directory whose
* encryption key may be unavailable. Not needed for symlink targets.
* @minor_hash: second part of the name's dirhash, if applicable
* @iname: encrypted filename to convert. May also be "." or "..", which
* aren't actually encrypted.
* @oname: output buffer for the user-presentable filename. The caller must
* have allocated enough space for this, e.g. using
* fscrypt_fname_alloc_buffer().
*
* If the key is available, we'll decrypt the disk name. Otherwise, we'll
* encode it for presentation in fscrypt_nokey_name format.
* See struct fscrypt_nokey_name for details.
*
* Return: 0 on success, -errno on failure
*/
int fscrypt_fname_disk_to_usr(const 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_nokey_name nokey_name;
u32 size; /* size of the unencoded no-key name */
if (fscrypt_is_dot_dotdot(&qname)) {
oname->name[0] = '.';
oname->name[iname->len - 1] = '.';
oname->len = iname->len;
return 0;
}
if (iname->len < FSCRYPT_FNAME_MIN_MSG_LEN)
return -EUCLEAN;
if (fscrypt_has_encryption_key(inode))
return fname_decrypt(inode, iname, oname);
/*
* Sanity check that struct fscrypt_nokey_name doesn't have padding
* between fields and that its encoded size never exceeds NAME_MAX.
*/
BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
offsetof(struct fscrypt_nokey_name, bytes));
BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
offsetof(struct fscrypt_nokey_name, sha256));
BUILD_BUG_ON(FSCRYPT_NOKEY_NAME_MAX_ENCODED > NAME_MAX);
nokey_name.dirhash[0] = hash;
nokey_name.dirhash[1] = minor_hash;
if (iname->len <= sizeof(nokey_name.bytes)) {
memcpy(nokey_name.bytes, iname->name, iname->len);
size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
} else {
memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
/* Compute strong hash of remaining part of name. */
sha256(&iname->name[sizeof(nokey_name.bytes)],
iname->len - sizeof(nokey_name.bytes),
nokey_name.sha256);
size = FSCRYPT_NOKEY_NAME_MAX;
}
oname->len = fscrypt_base64url_encode((const u8 *)&nokey_name, size,
oname->name);
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 should be a no-key name, so we
* decode it to get the struct fscrypt_nokey_name. 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)
{
struct fscrypt_nokey_name *nokey_name;
int ret;
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, lookup);
if (ret)
return ret;
if (fscrypt_has_encryption_key(dir)) {
if (!fscrypt_fname_encrypted_size(dir, iname->len, NAME_MAX,
&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 = fscrypt_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;
fname->is_nokey_name = true;
/*
* We don't have the key and we are doing a lookup; decode the
* user-supplied name
*/
if (iname->len > FSCRYPT_NOKEY_NAME_MAX_ENCODED)
return -ENOENT;
fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);
if (fname->crypto_buf.name == NULL)
return -ENOMEM;
ret = fscrypt_base64url_decode(iname->name, iname->len,
fname->crypto_buf.name);
if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||
(ret > offsetof(struct fscrypt_nokey_name, sha256) &&
ret != FSCRYPT_NOKEY_NAME_MAX)) {
ret = -ENOENT;
goto errout;
}
fname->crypto_buf.len = ret;
nokey_name = (void *)fname->crypto_buf.name;
fname->hash = nokey_name->dirhash[0];
fname->minor_hash = nokey_name->dirhash[1];
if (ret != FSCRYPT_NOKEY_NAME_MAX) {
/* The full ciphertext filename is available. */
fname->disk_name.name = nokey_name->bytes;
fname->disk_name.len =
ret - offsetof(struct fscrypt_nokey_name, bytes);
}
return 0;
errout:
kfree(fname->crypto_buf.name);
return ret;
}
EXPORT_SYMBOL(fscrypt_setup_filename);
/**
* fscrypt_match_name() - test whether the given name matches a directory entry
* @fname: the name being searched for
* @de_name: the name from the directory entry
* @de_name_len: the length of @de_name in bytes
*
* Normally @fname->disk_name will be set, and in that case we simply compare
* that to the name stored in the directory entry. The only exception is that
* if we don't have the key for an encrypted directory and the name we're
* looking for is very long, then we won't have the full disk_name and instead
* we'll need to match against a fscrypt_nokey_name that includes a strong hash.
*
* Return: %true if the name matches, otherwise %false.
*/
bool fscrypt_match_name(const struct fscrypt_name *fname,
const u8 *de_name, u32 de_name_len)
{
const struct fscrypt_nokey_name *nokey_name =
(const void *)fname->crypto_buf.name;
u8 digest[SHA256_DIGEST_SIZE];
if (likely(fname->disk_name.name)) {
if (de_name_len != fname->disk_name.len)
return false;
return !memcmp(de_name, fname->disk_name.name, de_name_len);
}
if (de_name_len <= sizeof(nokey_name->bytes))
return false;
if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))
return false;
sha256(&de_name[sizeof(nokey_name->bytes)],
de_name_len - sizeof(nokey_name->bytes), digest);
return !memcmp(digest, nokey_name->sha256, sizeof(digest));
}
EXPORT_SYMBOL_GPL(fscrypt_match_name);
/**
* fscrypt_fname_siphash() - calculate the SipHash of a filename
* @dir: the parent directory
* @name: the filename to calculate the SipHash of
*
* Given a plaintext filename @name and a directory @dir which uses SipHash as
* its dirhash method and has had its fscrypt key set up, this function
* calculates the SipHash of that name using the directory's secret dirhash key.
*
* Return: the SipHash of @name using the hash key of @dir
*/
u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)
{
const struct fscrypt_info *ci = dir->i_crypt_info;
WARN_ON_ONCE(!ci->ci_dirhash_key_initialized);
return siphash(name->name, name->len, &ci->ci_dirhash_key);
}
EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
/*
* Validate dentries in encrypted directories to make sure we aren't potentially
* caching stale dentries after a key has been added.
*/
int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
{
struct dentry *dir;
int err;
int valid;
/*
* Plaintext names are always valid, since fscrypt doesn't support
* reverting to no-key names without evicting the directory's inode
* -- which implies eviction of the dentries in the directory.
*/
if (!(dentry->d_flags & DCACHE_NOKEY_NAME))
return 1;
/*
* No-key name; valid if the directory's key is still unavailable.
*
* Although fscrypt forbids rename() on no-key names, we still must use
* dget_parent() here rather than use ->d_parent directly. That's
* because a corrupted fs image may contain directory hard links, which
* the VFS handles by moving the directory's dentry tree in the dcache
* each time ->lookup() finds the directory and it already has a dentry
* elsewhere. Thus ->d_parent can be changing, and we must safely grab
* a reference to some ->d_parent to prevent it from being freed.
*/
if (flags & LOOKUP_RCU)
return -ECHILD;
dir = dget_parent(dentry);
/*
* Pass allow_unsupported=true, so that files with an unsupported
* encryption policy can be deleted.
*/
err = fscrypt_get_encryption_info(d_inode(dir), true);
valid = !fscrypt_has_encryption_key(d_inode(dir));
dput(dir);
if (err < 0)
return err;
return valid;
}
EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);
