fs/crypto/fname.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This contains functions for filename crypto management
   4  *
   5  * Copyright (C) 2015, Google, Inc.
   6  * Copyright (C) 2015, Motorola Mobility
   7  *
   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/scatterlist.h>
  15 #include <linux/ratelimit.h>
  16 #include <crypto/skcipher.h>
  17 #include "fscrypt_private.h"
  18
  19 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
  20 {
  21         if (str->len == 1 && str->name[0] == '.')
  22                 return true;
  23
  24         if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
  25                 return true;
  26
  27         return false;
  28 }
  29
  30 /**
  31  * fname_encrypt() - encrypt a filename
  32  *
  33  * The output buffer must be at least as large as the input buffer.
  34  * Any extra space is filled with NUL padding before encryption.
  35  *
  36  * Return: 0 on success, -errno on failure
  37  */
  38 int fname_encrypt(struct inode *inode, const struct qstr *iname,
  39                   u8 *out, unsigned int olen)
  40 {
  41         struct skcipher_request *req = NULL;
  42         DECLARE_CRYPTO_WAIT(wait);
  43         struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
  44         int res = 0;
  45         char iv[FS_CRYPTO_BLOCK_SIZE];
  46         struct scatterlist sg;
  47
  48         /*
  49          * Copy the filename to the output buffer for encrypting in-place and
  50          * pad it with the needed number of NUL bytes.
  51          */
  52         if (WARN_ON(olen < iname->len))
  53                 return -ENOBUFS;
  54         memcpy(out, iname->name, iname->len);
  55         memset(out + iname->len, 0, olen - iname->len);
  56
  57         /* Initialize the IV */
  58         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
  59
  60         /* Set up the encryption request */
  61         req = skcipher_request_alloc(tfm, GFP_NOFS);
  62         if (!req)
  63                 return -ENOMEM;
  64         skcipher_request_set_callback(req,
  65                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  66                         crypto_req_done, &wait);
  67         sg_init_one(&sg, out, olen);
  68         skcipher_request_set_crypt(req, &sg, &sg, olen, iv);
  69
  70         /* Do the encryption */
  71         res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
  72         skcipher_request_free(req);
  73         if (res < 0) {
  74                 fscrypt_err(inode->i_sb,
  75                             "Filename encryption failed for inode %lu: %d",
  76                             inode->i_ino, res);
  77                 return res;
  78         }
  79
  80         return 0;
  81 }
  82
  83 /**
  84  * fname_decrypt() - decrypt a filename
  85  *
  86  * The caller must have allocated sufficient memory for the @oname string.
  87  *
  88  * Return: 0 on success, -errno on failure
  89  */
  90 static int fname_decrypt(struct inode *inode,
  91                                 const struct fscrypt_str *iname,
  92                                 struct fscrypt_str *oname)
  93 {
  94         struct skcipher_request *req = NULL;
  95         DECLARE_CRYPTO_WAIT(wait);
  96         struct scatterlist src_sg, dst_sg;
  97         struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
  98         int res = 0;
  99         char iv[FS_CRYPTO_BLOCK_SIZE];
 100
 101         /* Allocate request */
 102         req = skcipher_request_alloc(tfm, GFP_NOFS);
 103         if (!req)
 104                 return -ENOMEM;
 105         skcipher_request_set_callback(req,
 106                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 107                 crypto_req_done, &wait);
 108
 109         /* Initialize IV */
 110         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
 111
 112         /* Create decryption request */
 113         sg_init_one(&src_sg, iname->name, iname->len);
 114         sg_init_one(&dst_sg, oname->name, oname->len);
 115         skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 116         res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 117         skcipher_request_free(req);
 118         if (res < 0) {
 119                 fscrypt_err(inode->i_sb,
 120                             "Filename decryption failed for inode %lu: %d",
 121                             inode->i_ino, res);
 122                 return res;
 123         }
 124
 125         oname->len = strnlen(oname->name, iname->len);
 126         return 0;
 127 }
 128
 129 static const char *lookup_table =
 130         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 131
 132 #define BASE64_CHARS(nbytes)    DIV_ROUND_UP((nbytes) * 4, 3)
 133
 134 /**
 135  * digest_encode() -
 136  *
 137  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 138  * The encoded string is roughly 4/3 times the size of the input string.
 139  */
 140 static int digest_encode(const char *src, int len, char *dst)
 141 {
 142         int i = 0, bits = 0, ac = 0;
 143         char *cp = dst;
 144
 145         while (i < len) {
 146                 ac += (((unsigned char) src[i]) << bits);
 147                 bits += 8;
 148                 do {
 149                         *cp++ = lookup_table[ac & 0x3f];
 150                         ac >>= 6;
 151                         bits -= 6;
 152                 } while (bits >= 6);
 153                 i++;
 154         }
 155         if (bits)
 156                 *cp++ = lookup_table[ac & 0x3f];
 157         return cp - dst;
 158 }
 159
 160 static int digest_decode(const char *src, int len, char *dst)
 161 {
 162         int i = 0, bits = 0, ac = 0;
 163         const char *p;
 164         char *cp = dst;
 165
 166         while (i < len) {
 167                 p = strchr(lookup_table, src[i]);
 168                 if (p == NULL || src[i] == 0)
 169                         return -2;
 170                 ac += (p - lookup_table) << bits;
 171                 bits += 6;
 172                 if (bits >= 8) {
 173                         *cp++ = ac & 0xff;
 174                         ac >>= 8;
 175                         bits -= 8;
 176                 }
 177                 i++;
 178         }
 179         if (ac)
 180                 return -1;
 181         return cp - dst;
 182 }
 183
 184 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
 185                                   u32 max_len, u32 *encrypted_len_ret)
 186 {
 187         int padding = 4 << (inode->i_crypt_info->ci_flags &
 188                             FS_POLICY_FLAGS_PAD_MASK);
 189         u32 encrypted_len;
 190
 191         if (orig_len > max_len)
 192                 return false;
 193         encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
 194         encrypted_len = round_up(encrypted_len, padding);
 195         *encrypted_len_ret = min(encrypted_len, max_len);
 196         return true;
 197 }
 198
 199 /**
 200  * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
 201  *
 202  * Allocate a buffer that is large enough to hold any decrypted or encoded
 203  * filename (null-terminated), for the given maximum encrypted filename length.
 204  *
 205  * Return: 0 on success, -errno on failure
 206  */
 207 int fscrypt_fname_alloc_buffer(const struct inode *inode,
 208                                u32 max_encrypted_len,
 209                                struct fscrypt_str *crypto_str)
 210 {
 211         const u32 max_encoded_len =
 212                 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
 213                       1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
 214         u32 max_presented_len;
 215
 216         max_presented_len = max(max_encoded_len, max_encrypted_len);
 217
 218         crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
 219         if (!crypto_str->name)
 220                 return -ENOMEM;
 221         crypto_str->len = max_presented_len;
 222         return 0;
 223 }
 224 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
 225
 226 /**
 227  * fscrypt_fname_free_buffer - free the buffer for presented filenames
 228  *
 229  * Free the buffer allocated by fscrypt_fname_alloc_buffer().
 230  */
 231 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 232 {
 233         if (!crypto_str)
 234                 return;
 235         kfree(crypto_str->name);
 236         crypto_str->name = NULL;
 237 }
 238 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
 239
 240 /**
 241  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 242  * space
 243  *
 244  * The caller must have allocated sufficient memory for the @oname string.
 245  *
 246  * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
 247  * it for presentation.  Short names are directly base64-encoded, while long
 248  * names are encoded in fscrypt_digested_name format.
 249  *
 250  * Return: 0 on success, -errno on failure
 251  */
 252 int fscrypt_fname_disk_to_usr(struct inode *inode,
 253                         u32 hash, u32 minor_hash,
 254                         const struct fscrypt_str *iname,
 255                         struct fscrypt_str *oname)
 256 {
 257         const struct qstr qname = FSTR_TO_QSTR(iname);
 258         struct fscrypt_digested_name digested_name;
 259
 260         if (fscrypt_is_dot_dotdot(&qname)) {
 261                 oname->name[0] = '.';
 262                 oname->name[iname->len - 1] = '.';
 263                 oname->len = iname->len;
 264                 return 0;
 265         }
 266
 267         if (iname->len < FS_CRYPTO_BLOCK_SIZE)
 268                 return -EUCLEAN;
 269
 270         if (inode->i_crypt_info)
 271                 return fname_decrypt(inode, iname, oname);
 272
 273         if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
 274                 oname->len = digest_encode(iname->name, iname->len,
 275                                            oname->name);
 276                 return 0;
 277         }
 278         if (hash) {
 279                 digested_name.hash = hash;
 280                 digested_name.minor_hash = minor_hash;
 281         } else {
 282                 digested_name.hash = 0;
 283                 digested_name.minor_hash = 0;
 284         }
 285         memcpy(digested_name.digest,
 286                FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
 287                FSCRYPT_FNAME_DIGEST_SIZE);
 288         oname->name[0] = '_';
 289         oname->len = 1 + digest_encode((const char *)&digested_name,
 290                                        sizeof(digested_name), oname->name + 1);
 291         return 0;
 292 }
 293 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
 294
 295 /**
 296  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
 297  * @dir: the directory that will be searched
 298  * @iname: the user-provided filename being searched for
 299  * @lookup: 1 if we're allowed to proceed without the key because it's
 300  *      ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
 301  *      proceed without the key because we're going to create the dir_entry.
 302  * @fname: the filename information to be filled in
 303  *
 304  * Given a user-provided filename @iname, this function sets @fname->disk_name
 305  * to the name that would be stored in the on-disk directory entry, if possible.
 306  * If the directory is unencrypted this is simply @iname.  Else, if we have the
 307  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
 308  * get the disk_name.
 309  *
 310  * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
 311  * we decode it to get either the ciphertext disk_name (for short names) or the
 312  * fscrypt_digested_name (for long names).  Non-@lookup operations will be
 313  * impossible in this case, so we fail them with ENOKEY.
 314  *
 315  * If successful, fscrypt_free_filename() must be called later to clean up.
 316  *
 317  * Return: 0 on success, -errno on failure
 318  */
 319 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 320                               int lookup, struct fscrypt_name *fname)
 321 {
 322         int ret;
 323         int digested;
 324
 325         memset(fname, 0, sizeof(struct fscrypt_name));
 326         fname->usr_fname = iname;
 327
 328         if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
 329                 fname->disk_name.name = (unsigned char *)iname->name;
 330                 fname->disk_name.len = iname->len;
 331                 return 0;
 332         }
 333         ret = fscrypt_get_encryption_info(dir);
 334         if (ret)
 335                 return ret;
 336
 337         if (dir->i_crypt_info) {
 338                 if (!fscrypt_fname_encrypted_size(dir, iname->len,
 339                                                   dir->i_sb->s_cop->max_namelen,
 340                                                   &fname->crypto_buf.len))
 341                         return -ENAMETOOLONG;
 342                 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
 343                                                  GFP_NOFS);
 344                 if (!fname->crypto_buf.name)
 345                         return -ENOMEM;
 346
 347                 ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
 348                                     fname->crypto_buf.len);
 349                 if (ret)
 350                         goto errout;
 351                 fname->disk_name.name = fname->crypto_buf.name;
 352                 fname->disk_name.len = fname->crypto_buf.len;
 353                 return 0;
 354         }
 355         if (!lookup)
 356                 return -ENOKEY;
 357
 358         /*
 359          * We don't have the key and we are doing a lookup; decode the
 360          * user-supplied name
 361          */
 362         if (iname->name[0] == '_') {
 363                 if (iname->len !=
 364                     1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
 365                         return -ENOENT;
 366                 digested = 1;
 367         } else {
 368                 if (iname->len >
 369                     BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
 370                         return -ENOENT;
 371                 digested = 0;
 372         }
 373
 374         fname->crypto_buf.name =
 375                 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
 376                               sizeof(struct fscrypt_digested_name)),
 377                         GFP_KERNEL);
 378         if (fname->crypto_buf.name == NULL)
 379                 return -ENOMEM;
 380
 381         ret = digest_decode(iname->name + digested, iname->len - digested,
 382                                 fname->crypto_buf.name);
 383         if (ret < 0) {
 384                 ret = -ENOENT;
 385                 goto errout;
 386         }
 387         fname->crypto_buf.len = ret;
 388         if (digested) {
 389                 const struct fscrypt_digested_name *n =
 390                         (const void *)fname->crypto_buf.name;
 391                 fname->hash = n->hash;
 392                 fname->minor_hash = n->minor_hash;
 393         } else {
 394                 fname->disk_name.name = fname->crypto_buf.name;
 395                 fname->disk_name.len = fname->crypto_buf.len;
 396         }
 397         return 0;
 398
 399 errout:
 400         kfree(fname->crypto_buf.name);
 401         return ret;
 402 }
 403 EXPORT_SYMBOL(fscrypt_setup_filename);