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1// SPDX-License-Identifier: GPL-2.02/*3 * This contains functions for filename crypto management4 *5 * Copyright (C) 2015, Google, Inc.6 * Copyright (C) 2015, Motorola Mobility7 *8 * Written by Uday Savagaonkar, 2014.9 * Modified by Jaegeuk Kim, 2015.10 *11 * This has not yet undergone a rigorous security audit.12 */13 14#include <linux/namei.h>15#include <linux/scatterlist.h>16#include <crypto/hash.h>17#include <crypto/sha2.h>18#include <crypto/skcipher.h>19#include "fscrypt_private.h"20 21/*22 * The minimum message length (input and output length), in bytes, for all23 * filenames encryption modes. Filenames shorter than this will be zero-padded24 * before being encrypted.25 */26#define FSCRYPT_FNAME_MIN_MSG_LEN 1627 28/*29 * struct fscrypt_nokey_name - identifier for directory entry when key is absent30 *31 * When userspace lists an encrypted directory without access to the key, the32 * filesystem must present a unique "no-key name" for each filename that allows33 * it to find the directory entry again if requested. Naively, that would just34 * mean using the ciphertext filenames. However, since the ciphertext filenames35 * can contain illegal characters ('\0' and '/'), they must be encoded in some36 * way. We use base64url. But that can cause names to exceed NAME_MAX (25537 * bytes), so we also need to use a strong hash to abbreviate long names.38 *39 * The filesystem may also need another kind of hash, the "dirhash", to quickly40 * find the directory entry. Since filesystems normally compute the dirhash41 * over the on-disk filename (i.e. the ciphertext), it's not computable from42 * no-key names that abbreviate the ciphertext using the strong hash to fit in43 * NAME_MAX. It's also not computable if it's a keyed hash taken over the44 * plaintext (but it may still be available in the on-disk directory entry);45 * casefolded directories use this type of dirhash. At least in these cases,46 * each no-key name must include the name's dirhash too.47 *48 * To meet all these requirements, we base64url-encode the following49 * variable-length structure. It contains the dirhash, or 0's if the filesystem50 * didn't provide one; up to 149 bytes of the ciphertext name; and for51 * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.52 *53 * This ensures that each no-key name contains everything needed to find the54 * directory entry again, contains only legal characters, doesn't exceed55 * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only56 * take the performance hit of SHA-256 on very long filenames (which are rare).57 */58struct fscrypt_nokey_name {59 u32 dirhash[2];60 u8 bytes[149];61 u8 sha256[SHA256_DIGEST_SIZE];62}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */63 64/*65 * Decoded size of max-size no-key name, i.e. a name that was abbreviated using66 * the strong hash and thus includes the 'sha256' field. This isn't simply67 * sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.68 */69#define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256)70 71/* Encoded size of max-size no-key name */72#define FSCRYPT_NOKEY_NAME_MAX_ENCODED \73 FSCRYPT_BASE64URL_CHARS(FSCRYPT_NOKEY_NAME_MAX)74 75static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)76{77 return is_dot_dotdot(str->name, str->len);78}79 80/**81 * fscrypt_fname_encrypt() - encrypt a filename82 * @inode: inode of the parent directory (for regular filenames)83 * or of the symlink (for symlink targets). Key must already be84 * set up.85 * @iname: the filename to encrypt86 * @out: (output) the encrypted filename87 * @olen: size of the encrypted filename. It must be at least @iname->len.88 * Any extra space is filled with NUL padding before encryption.89 *90 * Return: 0 on success, -errno on failure91 */92int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,93 u8 *out, unsigned int olen)94{95 struct skcipher_request *req = NULL;96 DECLARE_CRYPTO_WAIT(wait);97 const struct fscrypt_inode_info *ci = inode->i_crypt_info;98 struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;99 union fscrypt_iv iv;100 struct scatterlist sg;101 int res;102 103 /*104 * Copy the filename to the output buffer for encrypting in-place and105 * pad it with the needed number of NUL bytes.106 */107 if (WARN_ON_ONCE(olen < iname->len))108 return -ENOBUFS;109 memcpy(out, iname->name, iname->len);110 memset(out + iname->len, 0, olen - iname->len);111 112 /* Initialize the IV */113 fscrypt_generate_iv(&iv, 0, ci);114 115 /* Set up the encryption request */116 req = skcipher_request_alloc(tfm, GFP_NOFS);117 if (!req)118 return -ENOMEM;119 skcipher_request_set_callback(req,120 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,121 crypto_req_done, &wait);122 sg_init_one(&sg, out, olen);123 skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);124 125 /* Do the encryption */126 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);127 skcipher_request_free(req);128 if (res < 0) {129 fscrypt_err(inode, "Filename encryption failed: %d", res);130 return res;131 }132 133 return 0;134}135EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt);136 137/**138 * fname_decrypt() - decrypt a filename139 * @inode: inode of the parent directory (for regular filenames)140 * or of the symlink (for symlink targets)141 * @iname: the encrypted filename to decrypt142 * @oname: (output) the decrypted filename. The caller must have allocated143 * enough space for this, e.g. using fscrypt_fname_alloc_buffer().144 *145 * Return: 0 on success, -errno on failure146 */147static int fname_decrypt(const struct inode *inode,148 const struct fscrypt_str *iname,149 struct fscrypt_str *oname)150{151 struct skcipher_request *req = NULL;152 DECLARE_CRYPTO_WAIT(wait);153 struct scatterlist src_sg, dst_sg;154 const struct fscrypt_inode_info *ci = inode->i_crypt_info;155 struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;156 union fscrypt_iv iv;157 int res;158 159 /* Allocate request */160 req = skcipher_request_alloc(tfm, GFP_NOFS);161 if (!req)162 return -ENOMEM;163 skcipher_request_set_callback(req,164 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,165 crypto_req_done, &wait);166 167 /* Initialize IV */168 fscrypt_generate_iv(&iv, 0, ci);169 170 /* Create decryption request */171 sg_init_one(&src_sg, iname->name, iname->len);172 sg_init_one(&dst_sg, oname->name, oname->len);173 skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);174 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);175 skcipher_request_free(req);176 if (res < 0) {177 fscrypt_err(inode, "Filename decryption failed: %d", res);178 return res;179 }180 181 oname->len = strnlen(oname->name, iname->len);182 return 0;183}184 185static const char base64url_table[65] =186 "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";187 188#define FSCRYPT_BASE64URL_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)189 190/**191 * fscrypt_base64url_encode() - base64url-encode some binary data192 * @src: the binary data to encode193 * @srclen: the length of @src in bytes194 * @dst: (output) the base64url-encoded string. Not NUL-terminated.195 *196 * Encodes data using base64url encoding, i.e. the "Base 64 Encoding with URL197 * and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't used,198 * as it's unneeded and not required by the RFC. base64url is used instead of199 * base64 to avoid the '/' character, which isn't allowed in filenames.200 *201 * Return: the length of the resulting base64url-encoded string in bytes.202 * This will be equal to FSCRYPT_BASE64URL_CHARS(srclen).203 */204static int fscrypt_base64url_encode(const u8 *src, int srclen, char *dst)205{206 u32 ac = 0;207 int bits = 0;208 int i;209 char *cp = dst;210 211 for (i = 0; i < srclen; i++) {212 ac = (ac << 8) | src[i];213 bits += 8;214 do {215 bits -= 6;216 *cp++ = base64url_table[(ac >> bits) & 0x3f];217 } while (bits >= 6);218 }219 if (bits)220 *cp++ = base64url_table[(ac << (6 - bits)) & 0x3f];221 return cp - dst;222}223 224/**225 * fscrypt_base64url_decode() - base64url-decode a string226 * @src: the string to decode. Doesn't need to be NUL-terminated.227 * @srclen: the length of @src in bytes228 * @dst: (output) the decoded binary data229 *230 * Decodes a string using base64url encoding, i.e. the "Base 64 Encoding with231 * URL and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't232 * accepted, nor are non-encoding characters such as whitespace.233 *234 * This implementation hasn't been optimized for performance.235 *236 * Return: the length of the resulting decoded binary data in bytes,237 * or -1 if the string isn't a valid base64url string.238 */239static int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)240{241 u32 ac = 0;242 int bits = 0;243 int i;244 u8 *bp = dst;245 246 for (i = 0; i < srclen; i++) {247 const char *p = strchr(base64url_table, src[i]);248 249 if (p == NULL || src[i] == 0)250 return -1;251 ac = (ac << 6) | (p - base64url_table);252 bits += 6;253 if (bits >= 8) {254 bits -= 8;255 *bp++ = (u8)(ac >> bits);256 }257 }258 if (ac & ((1 << bits) - 1))259 return -1;260 return bp - dst;261}262 263bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,264 u32 orig_len, u32 max_len,265 u32 *encrypted_len_ret)266{267 int padding = 4 << (fscrypt_policy_flags(policy) &268 FSCRYPT_POLICY_FLAGS_PAD_MASK);269 u32 encrypted_len;270 271 if (orig_len > max_len)272 return false;273 encrypted_len = max_t(u32, orig_len, FSCRYPT_FNAME_MIN_MSG_LEN);274 encrypted_len = round_up(encrypted_len, padding);275 *encrypted_len_ret = min(encrypted_len, max_len);276 return true;277}278 279/**280 * fscrypt_fname_encrypted_size() - calculate length of encrypted filename281 * @inode: parent inode of dentry name being encrypted. Key must282 * already be set up.283 * @orig_len: length of the original filename284 * @max_len: maximum length to return285 * @encrypted_len_ret: where calculated length should be returned (on success)286 *287 * Filenames that are shorter than the maximum length may have their lengths288 * increased slightly by encryption, due to padding that is applied.289 *290 * Return: false if the orig_len is greater than max_len. Otherwise, true and291 * fill out encrypted_len_ret with the length (up to max_len).292 */293bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,294 u32 max_len, u32 *encrypted_len_ret)295{296 return __fscrypt_fname_encrypted_size(&inode->i_crypt_info->ci_policy,297 orig_len, max_len,298 encrypted_len_ret);299}300EXPORT_SYMBOL_GPL(fscrypt_fname_encrypted_size);301 302/**303 * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames304 * @max_encrypted_len: maximum length of encrypted filenames the buffer will be305 * used to present306 * @crypto_str: (output) buffer to allocate307 *308 * Allocate a buffer that is large enough to hold any decrypted or encoded309 * filename (null-terminated), for the given maximum encrypted filename length.310 *311 * Return: 0 on success, -errno on failure312 */313int fscrypt_fname_alloc_buffer(u32 max_encrypted_len,314 struct fscrypt_str *crypto_str)315{316 u32 max_presented_len = max_t(u32, FSCRYPT_NOKEY_NAME_MAX_ENCODED,317 max_encrypted_len);318 319 crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);320 if (!crypto_str->name)321 return -ENOMEM;322 crypto_str->len = max_presented_len;323 return 0;324}325EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);326 327/**328 * fscrypt_fname_free_buffer() - free a buffer for presented filenames329 * @crypto_str: the buffer to free330 *331 * Free a buffer that was allocated by fscrypt_fname_alloc_buffer().332 */333void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)334{335 if (!crypto_str)336 return;337 kfree(crypto_str->name);338 crypto_str->name = NULL;339}340EXPORT_SYMBOL(fscrypt_fname_free_buffer);341 342/**343 * fscrypt_fname_disk_to_usr() - convert an encrypted filename to344 * user-presentable form345 * @inode: inode of the parent directory (for regular filenames)346 * or of the symlink (for symlink targets)347 * @hash: first part of the name's dirhash, if applicable. This only needs to348 * be provided if the filename is located in an indexed directory whose349 * encryption key may be unavailable. Not needed for symlink targets.350 * @minor_hash: second part of the name's dirhash, if applicable351 * @iname: encrypted filename to convert. May also be "." or "..", which352 * aren't actually encrypted.353 * @oname: output buffer for the user-presentable filename. The caller must354 * have allocated enough space for this, e.g. using355 * fscrypt_fname_alloc_buffer().356 *357 * If the key is available, we'll decrypt the disk name. Otherwise, we'll358 * encode it for presentation in fscrypt_nokey_name format.359 * See struct fscrypt_nokey_name for details.360 *361 * Return: 0 on success, -errno on failure362 */363int fscrypt_fname_disk_to_usr(const struct inode *inode,364 u32 hash, u32 minor_hash,365 const struct fscrypt_str *iname,366 struct fscrypt_str *oname)367{368 const struct qstr qname = FSTR_TO_QSTR(iname);369 struct fscrypt_nokey_name nokey_name;370 u32 size; /* size of the unencoded no-key name */371 372 if (fscrypt_is_dot_dotdot(&qname)) {373 oname->name[0] = '.';374 oname->name[iname->len - 1] = '.';375 oname->len = iname->len;376 return 0;377 }378 379 if (iname->len < FSCRYPT_FNAME_MIN_MSG_LEN)380 return -EUCLEAN;381 382 if (fscrypt_has_encryption_key(inode))383 return fname_decrypt(inode, iname, oname);384 385 /*386 * Sanity check that struct fscrypt_nokey_name doesn't have padding387 * between fields and that its encoded size never exceeds NAME_MAX.388 */389 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=390 offsetof(struct fscrypt_nokey_name, bytes));391 BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=392 offsetof(struct fscrypt_nokey_name, sha256));393 BUILD_BUG_ON(FSCRYPT_NOKEY_NAME_MAX_ENCODED > NAME_MAX);394 395 nokey_name.dirhash[0] = hash;396 nokey_name.dirhash[1] = minor_hash;397 398 if (iname->len <= sizeof(nokey_name.bytes)) {399 memcpy(nokey_name.bytes, iname->name, iname->len);400 size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);401 } else {402 memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));403 /* Compute strong hash of remaining part of name. */404 sha256(&iname->name[sizeof(nokey_name.bytes)],405 iname->len - sizeof(nokey_name.bytes),406 nokey_name.sha256);407 size = FSCRYPT_NOKEY_NAME_MAX;408 }409 oname->len = fscrypt_base64url_encode((const u8 *)&nokey_name, size,410 oname->name);411 return 0;412}413EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);414 415/**416 * fscrypt_setup_filename() - prepare to search a possibly encrypted directory417 * @dir: the directory that will be searched418 * @iname: the user-provided filename being searched for419 * @lookup: 1 if we're allowed to proceed without the key because it's420 * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot421 * proceed without the key because we're going to create the dir_entry.422 * @fname: the filename information to be filled in423 *424 * Given a user-provided filename @iname, this function sets @fname->disk_name425 * to the name that would be stored in the on-disk directory entry, if possible.426 * If the directory is unencrypted this is simply @iname. Else, if we have the427 * directory's encryption key, then @iname is the plaintext, so we encrypt it to428 * get the disk_name.429 *430 * Else, for keyless @lookup operations, @iname should be a no-key name, so we431 * decode it to get the struct fscrypt_nokey_name. Non-@lookup operations will432 * be impossible in this case, so we fail them with ENOKEY.433 *434 * If successful, fscrypt_free_filename() must be called later to clean up.435 *436 * Return: 0 on success, -errno on failure437 */438int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,439 int lookup, struct fscrypt_name *fname)440{441 struct fscrypt_nokey_name *nokey_name;442 int ret;443 444 memset(fname, 0, sizeof(struct fscrypt_name));445 fname->usr_fname = iname;446 447 if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {448 fname->disk_name.name = (unsigned char *)iname->name;449 fname->disk_name.len = iname->len;450 return 0;451 }452 ret = fscrypt_get_encryption_info(dir, lookup);453 if (ret)454 return ret;455 456 if (fscrypt_has_encryption_key(dir)) {457 if (!fscrypt_fname_encrypted_size(dir, iname->len, NAME_MAX,458 &fname->crypto_buf.len))459 return -ENAMETOOLONG;460 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,461 GFP_NOFS);462 if (!fname->crypto_buf.name)463 return -ENOMEM;464 465 ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,466 fname->crypto_buf.len);467 if (ret)468 goto errout;469 fname->disk_name.name = fname->crypto_buf.name;470 fname->disk_name.len = fname->crypto_buf.len;471 return 0;472 }473 if (!lookup)474 return -ENOKEY;475 fname->is_nokey_name = true;476 477 /*478 * We don't have the key and we are doing a lookup; decode the479 * user-supplied name480 */481 482 if (iname->len > FSCRYPT_NOKEY_NAME_MAX_ENCODED)483 return -ENOENT;484 485 fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL);486 if (fname->crypto_buf.name == NULL)487 return -ENOMEM;488 489 ret = fscrypt_base64url_decode(iname->name, iname->len,490 fname->crypto_buf.name);491 if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) ||492 (ret > offsetof(struct fscrypt_nokey_name, sha256) &&493 ret != FSCRYPT_NOKEY_NAME_MAX)) {494 ret = -ENOENT;495 goto errout;496 }497 fname->crypto_buf.len = ret;498 499 nokey_name = (void *)fname->crypto_buf.name;500 fname->hash = nokey_name->dirhash[0];501 fname->minor_hash = nokey_name->dirhash[1];502 if (ret != FSCRYPT_NOKEY_NAME_MAX) {503 /* The full ciphertext filename is available. */504 fname->disk_name.name = nokey_name->bytes;505 fname->disk_name.len =506 ret - offsetof(struct fscrypt_nokey_name, bytes);507 }508 return 0;509 510errout:511 kfree(fname->crypto_buf.name);512 return ret;513}514EXPORT_SYMBOL(fscrypt_setup_filename);515 516/**517 * fscrypt_match_name() - test whether the given name matches a directory entry518 * @fname: the name being searched for519 * @de_name: the name from the directory entry520 * @de_name_len: the length of @de_name in bytes521 *522 * Normally @fname->disk_name will be set, and in that case we simply compare523 * that to the name stored in the directory entry. The only exception is that524 * if we don't have the key for an encrypted directory and the name we're525 * looking for is very long, then we won't have the full disk_name and instead526 * we'll need to match against a fscrypt_nokey_name that includes a strong hash.527 *528 * Return: %true if the name matches, otherwise %false.529 */530bool fscrypt_match_name(const struct fscrypt_name *fname,531 const u8 *de_name, u32 de_name_len)532{533 const struct fscrypt_nokey_name *nokey_name =534 (const void *)fname->crypto_buf.name;535 u8 digest[SHA256_DIGEST_SIZE];536 537 if (likely(fname->disk_name.name)) {538 if (de_name_len != fname->disk_name.len)539 return false;540 return !memcmp(de_name, fname->disk_name.name, de_name_len);541 }542 if (de_name_len <= sizeof(nokey_name->bytes))543 return false;544 if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes)))545 return false;546 sha256(&de_name[sizeof(nokey_name->bytes)],547 de_name_len - sizeof(nokey_name->bytes), digest);548 return !memcmp(digest, nokey_name->sha256, sizeof(digest));549}550EXPORT_SYMBOL_GPL(fscrypt_match_name);551 552/**553 * fscrypt_fname_siphash() - calculate the SipHash of a filename554 * @dir: the parent directory555 * @name: the filename to calculate the SipHash of556 *557 * Given a plaintext filename @name and a directory @dir which uses SipHash as558 * its dirhash method and has had its fscrypt key set up, this function559 * calculates the SipHash of that name using the directory's secret dirhash key.560 *561 * Return: the SipHash of @name using the hash key of @dir562 */563u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name)564{565 const struct fscrypt_inode_info *ci = dir->i_crypt_info;566 567 WARN_ON_ONCE(!ci->ci_dirhash_key_initialized);568 569 return siphash(name->name, name->len, &ci->ci_dirhash_key);570}571EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);572 573/*574 * Validate dentries in encrypted directories to make sure we aren't potentially575 * caching stale dentries after a key has been added.576 */577int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)578{579 struct dentry *dir;580 int err;581 int valid;582 583 /*584 * Plaintext names are always valid, since fscrypt doesn't support585 * reverting to no-key names without evicting the directory's inode586 * -- which implies eviction of the dentries in the directory.587 */588 if (!(dentry->d_flags & DCACHE_NOKEY_NAME))589 return 1;590 591 /*592 * No-key name; valid if the directory's key is still unavailable.593 *594 * Although fscrypt forbids rename() on no-key names, we still must use595 * dget_parent() here rather than use ->d_parent directly. That's596 * because a corrupted fs image may contain directory hard links, which597 * the VFS handles by moving the directory's dentry tree in the dcache598 * each time ->lookup() finds the directory and it already has a dentry599 * elsewhere. Thus ->d_parent can be changing, and we must safely grab600 * a reference to some ->d_parent to prevent it from being freed.601 */602 603 if (flags & LOOKUP_RCU)604 return -ECHILD;605 606 dir = dget_parent(dentry);607 /*608 * Pass allow_unsupported=true, so that files with an unsupported609 * encryption policy can be deleted.610 */611 err = fscrypt_get_encryption_info(d_inode(dir), true);612 valid = !fscrypt_has_encryption_key(d_inode(dir));613 dput(dir);614 615 if (err < 0)616 return err;617 618 return valid;619}620EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);621