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 <crypto/skcipher.h>
  16 #include "fscrypt_private.h"
  17
  18 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
  19 {
  20         if (str->len == 1 && str->name[0] == '.')
  21                 return true;
  22
  23         if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
  24                 return true;
  25
  26         return false;
  27 }
  28
  29 /**
  30  * fname_encrypt() - encrypt a filename
  31  *
  32  * The output buffer must be at least as large as the input buffer.
  33  * Any extra space is filled with NUL padding before encryption.
  34  *
  35  * Return: 0 on success, -errno on failure
  36  */
  37 int fname_encrypt(struct inode *inode, const struct qstr *iname,
  38                   u8 *out, unsigned int olen)
  39 {
  40         struct skcipher_request *req = NULL;
  41         DECLARE_CRYPTO_WAIT(wait);
  42         struct fscrypt_info *ci = inode->i_crypt_info;
  43         struct crypto_skcipher *tfm = ci->ci_ctfm;
  44         union fscrypt_iv iv;
  45         struct scatterlist sg;
  46         int res;
  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         fscrypt_generate_iv(&iv, 0, ci);
  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, "Filename encryption failed: %d", res);
  75                 return res;
  76         }
  77
  78         return 0;
  79 }
  80
  81 /**
  82  * fname_decrypt() - decrypt a filename
  83  *
  84  * The caller must have allocated sufficient memory for the @oname string.
  85  *
  86  * Return: 0 on success, -errno on failure
  87  */
  88 static int fname_decrypt(struct inode *inode,
  89                                 const struct fscrypt_str *iname,
  90                                 struct fscrypt_str *oname)
  91 {
  92         struct skcipher_request *req = NULL;
  93         DECLARE_CRYPTO_WAIT(wait);
  94         struct scatterlist src_sg, dst_sg;
  95         struct fscrypt_info *ci = inode->i_crypt_info;
  96         struct crypto_skcipher *tfm = ci->ci_ctfm;
  97         union fscrypt_iv iv;
  98         int res;
  99
 100         /* Allocate request */
 101         req = skcipher_request_alloc(tfm, GFP_NOFS);
 102         if (!req)
 103                 return -ENOMEM;
 104         skcipher_request_set_callback(req,
 105                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 106                 crypto_req_done, &wait);
 107
 108         /* Initialize IV */
 109         fscrypt_generate_iv(&iv, 0, ci);
 110
 111         /* Create decryption request */
 112         sg_init_one(&src_sg, iname->name, iname->len);
 113         sg_init_one(&dst_sg, oname->name, oname->len);
 114         skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
 115         res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 116         skcipher_request_free(req);
 117         if (res < 0) {
 118                 fscrypt_err(inode, "Filename decryption failed: %d", res);
 119                 return res;
 120         }
 121
 122         oname->len = strnlen(oname->name, iname->len);
 123         return 0;
 124 }
 125
 126 static const char lookup_table[65] =
 127         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 128
 129 #define BASE64_CHARS(nbytes)    DIV_ROUND_UP((nbytes) * 4, 3)
 130
 131 /**
 132  * base64_encode() -
 133  *
 134  * Encodes the input string using characters from the set [A-Za-z0-9+,].
 135  * The encoded string is roughly 4/3 times the size of the input string.
 136  *
 137  * Return: length of the encoded string
 138  */
 139 static int base64_encode(const u8 *src, int len, char *dst)
 140 {
 141         int i, bits = 0, ac = 0;
 142         char *cp = dst;
 143
 144         for (i = 0; i < len; i++) {
 145                 ac += src[i] << bits;
 146                 bits += 8;
 147                 do {
 148                         *cp++ = lookup_table[ac & 0x3f];
 149                         ac >>= 6;
 150                         bits -= 6;
 151                 } while (bits >= 6);
 152         }
 153         if (bits)
 154                 *cp++ = lookup_table[ac & 0x3f];
 155         return cp - dst;
 156 }
 157
 158 static int base64_decode(const char *src, int len, u8 *dst)
 159 {
 160         int i, bits = 0, ac = 0;
 161         const char *p;
 162         u8 *cp = dst;
 163
 164         for (i = 0; i < len; i++) {
 165                 p = strchr(lookup_table, src[i]);
 166                 if (p == NULL || src[i] == 0)
 167                         return -2;
 168                 ac += (p - lookup_table) << bits;
 169                 bits += 6;
 170                 if (bits >= 8) {
 171                         *cp++ = ac & 0xff;
 172                         ac >>= 8;
 173                         bits -= 8;
 174                 }
 175         }
 176         if (ac)
 177                 return -1;
 178         return cp - dst;
 179 }
 180
 181 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
 182                                   u32 max_len, u32 *encrypted_len_ret)
 183 {
 184         const struct fscrypt_info *ci = inode->i_crypt_info;
 185         int padding = 4 << (fscrypt_policy_flags(&ci->ci_policy) &
 186                             FSCRYPT_POLICY_FLAGS_PAD_MASK);
 187         u32 encrypted_len;
 188
 189         if (orig_len > max_len)
 190                 return false;
 191         encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
 192         encrypted_len = round_up(encrypted_len, padding);
 193         *encrypted_len_ret = min(encrypted_len, max_len);
 194         return true;
 195 }
 196
 197 /**
 198  * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
 199  *
 200  * Allocate a buffer that is large enough to hold any decrypted or encoded
 201  * filename (null-terminated), for the given maximum encrypted filename length.
 202  *
 203  * Return: 0 on success, -errno on failure
 204  */
 205 int fscrypt_fname_alloc_buffer(const struct inode *inode,
 206                                u32 max_encrypted_len,
 207                                struct fscrypt_str *crypto_str)
 208 {
 209         const u32 max_encoded_len =
 210                 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
 211                       1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
 212         u32 max_presented_len;
 213
 214         max_presented_len = max(max_encoded_len, max_encrypted_len);
 215
 216         crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
 217         if (!crypto_str->name)
 218                 return -ENOMEM;
 219         crypto_str->len = max_presented_len;
 220         return 0;
 221 }
 222 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
 223
 224 /**
 225  * fscrypt_fname_free_buffer - free the buffer for presented filenames
 226  *
 227  * Free the buffer allocated by fscrypt_fname_alloc_buffer().
 228  */
 229 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 230 {
 231         if (!crypto_str)
 232                 return;
 233         kfree(crypto_str->name);
 234         crypto_str->name = NULL;
 235 }
 236 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
 237
 238 /**
 239  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 240  * space
 241  *
 242  * The caller must have allocated sufficient memory for the @oname string.
 243  *
 244  * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
 245  * it for presentation.  Short names are directly base64-encoded, while long
 246  * names are encoded in fscrypt_digested_name format.
 247  *
 248  * Return: 0 on success, -errno on failure
 249  */
 250 int fscrypt_fname_disk_to_usr(struct inode *inode,
 251                         u32 hash, u32 minor_hash,
 252                         const struct fscrypt_str *iname,
 253                         struct fscrypt_str *oname)
 254 {
 255         const struct qstr qname = FSTR_TO_QSTR(iname);
 256         struct fscrypt_digested_name digested_name;
 257
 258         if (fscrypt_is_dot_dotdot(&qname)) {
 259                 oname->name[0] = '.';
 260                 oname->name[iname->len - 1] = '.';
 261                 oname->len = iname->len;
 262                 return 0;
 263         }
 264
 265         if (iname->len < FS_CRYPTO_BLOCK_SIZE)
 266                 return -EUCLEAN;
 267
 268         if (fscrypt_has_encryption_key(inode))
 269                 return fname_decrypt(inode, iname, oname);
 270
 271         if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
 272                 oname->len = base64_encode(iname->name, iname->len,
 273                                            oname->name);
 274                 return 0;
 275         }
 276         if (hash) {
 277                 digested_name.hash = hash;
 278                 digested_name.minor_hash = minor_hash;
 279         } else {
 280                 digested_name.hash = 0;
 281                 digested_name.minor_hash = 0;
 282         }
 283         memcpy(digested_name.digest,
 284                FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
 285                FSCRYPT_FNAME_DIGEST_SIZE);
 286         oname->name[0] = '_';
 287         oname->len = 1 + base64_encode((const u8 *)&digested_name,
 288                                        sizeof(digested_name), oname->name + 1);
 289         return 0;
 290 }
 291 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
 292
 293 /**
 294  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
 295  * @dir: the directory that will be searched
 296  * @iname: the user-provided filename being searched for
 297  * @lookup: 1 if we're allowed to proceed without the key because it's
 298  *      ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
 299  *      proceed without the key because we're going to create the dir_entry.
 300  * @fname: the filename information to be filled in
 301  *
 302  * Given a user-provided filename @iname, this function sets @fname->disk_name
 303  * to the name that would be stored in the on-disk directory entry, if possible.
 304  * If the directory is unencrypted this is simply @iname.  Else, if we have the
 305  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
 306  * get the disk_name.
 307  *
 308  * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
 309  * we decode it to get either the ciphertext disk_name (for short names) or the
 310  * fscrypt_digested_name (for long names).  Non-@lookup operations will be
 311  * impossible in this case, so we fail them with ENOKEY.
 312  *
 313  * If successful, fscrypt_free_filename() must be called later to clean up.
 314  *
 315  * Return: 0 on success, -errno on failure
 316  */
 317 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 318                               int lookup, struct fscrypt_name *fname)
 319 {
 320         int ret;
 321         int digested;
 322
 323         memset(fname, 0, sizeof(struct fscrypt_name));
 324         fname->usr_fname = iname;
 325
 326         if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
 327                 fname->disk_name.name = (unsigned char *)iname->name;
 328                 fname->disk_name.len = iname->len;
 329                 return 0;
 330         }
 331         ret = fscrypt_get_encryption_info(dir);
 332         if (ret)
 333                 return ret;
 334
 335         if (fscrypt_has_encryption_key(dir)) {
 336                 if (!fscrypt_fname_encrypted_size(dir, iname->len,
 337                                                   dir->i_sb->s_cop->max_namelen,
 338                                                   &fname->crypto_buf.len))
 339                         return -ENAMETOOLONG;
 340                 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
 341                                                  GFP_NOFS);
 342                 if (!fname->crypto_buf.name)
 343                         return -ENOMEM;
 344
 345                 ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
 346                                     fname->crypto_buf.len);
 347                 if (ret)
 348                         goto errout;
 349                 fname->disk_name.name = fname->crypto_buf.name;
 350                 fname->disk_name.len = fname->crypto_buf.len;
 351                 return 0;
 352         }
 353         if (!lookup)
 354                 return -ENOKEY;
 355         fname->is_ciphertext_name = true;
 356
 357         /*
 358          * We don't have the key and we are doing a lookup; decode the
 359          * user-supplied name
 360          */
 361         if (iname->name[0] == '_') {
 362                 if (iname->len !=
 363                     1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
 364                         return -ENOENT;
 365                 digested = 1;
 366         } else {
 367                 if (iname->len >
 368                     BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
 369                         return -ENOENT;
 370                 digested = 0;
 371         }
 372
 373         fname->crypto_buf.name =
 374                 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
 375                               sizeof(struct fscrypt_digested_name)),
 376                         GFP_KERNEL);
 377         if (fname->crypto_buf.name == NULL)
 378                 return -ENOMEM;
 379
 380         ret = base64_decode(iname->name + digested, iname->len - digested,
 381                             fname->crypto_buf.name);
 382         if (ret < 0) {
 383                 ret = -ENOENT;
 384                 goto errout;
 385         }
 386         fname->crypto_buf.len = ret;
 387         if (digested) {
 388                 const struct fscrypt_digested_name *n =
 389                         (const void *)fname->crypto_buf.name;
 390                 fname->hash = n->hash;
 391                 fname->minor_hash = n->minor_hash;
 392         } else {
 393                 fname->disk_name.name = fname->crypto_buf.name;
 394                 fname->disk_name.len = fname->crypto_buf.len;
 395         }
 396         return 0;
 397
 398 errout:
 399         kfree(fname->crypto_buf.name);
 400         return ret;
 401 }
 402 EXPORT_SYMBOL(fscrypt_setup_filename);