fs/crypto/fname.c

   1 /*
   2  * This contains functions for filename crypto management
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  * Copyright (C) 2015, Motorola Mobility
   6  *
   7  * Written by Uday Savagaonkar, 2014.
   8  * Modified by Jaegeuk Kim, 2015.
   9  *
  10  * This has not yet undergone a rigorous security audit.
  11  */
  12
  13 #include <linux/scatterlist.h>
  14 #include <linux/ratelimit.h>
  15 #include "fscrypt_private.h"
  16
  17 /**
  18  * fname_crypt_complete() - completion callback for filename crypto
  19  * @req: The asynchronous cipher request context
  20  * @res: The result of the cipher operation
  21  */
  22 static void fname_crypt_complete(struct crypto_async_request *req, int res)
  23 {
  24         struct fscrypt_completion_result *ecr = req->data;
  25
  26         if (res == -EINPROGRESS)
  27                 return;
  28         ecr->res = res;
  29         complete(&ecr->completion);
  30 }
  31
  32 /**
  33  * fname_encrypt() - encrypt a filename
  34  *
  35  * The caller must have allocated sufficient memory for the @oname string.
  36  *
  37  * Return: 0 on success, -errno on failure
  38  */
  39 static int fname_encrypt(struct inode *inode,
  40                         const struct qstr *iname, struct fscrypt_str *oname)
  41 {
  42         struct skcipher_request *req = NULL;
  43         DECLARE_FS_COMPLETION_RESULT(ecr);
  44         struct fscrypt_info *ci = inode->i_crypt_info;
  45         struct crypto_skcipher *tfm = ci->ci_ctfm;
  46         int res = 0;
  47         char iv[FS_CRYPTO_BLOCK_SIZE];
  48         struct scatterlist sg;
  49         int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
  50         unsigned int lim;
  51         unsigned int cryptlen;
  52
  53         lim = inode->i_sb->s_cop->max_namelen(inode);
  54         if (iname->len <= 0 || iname->len > lim)
  55                 return -EIO;
  56
  57         /*
  58          * Copy the filename to the output buffer for encrypting in-place and
  59          * pad it with the needed number of NUL bytes.
  60          */
  61         cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
  62         cryptlen = round_up(cryptlen, padding);
  63         cryptlen = min(cryptlen, lim);
  64         memcpy(oname->name, iname->name, iname->len);
  65         memset(oname->name + iname->len, 0, cryptlen - iname->len);
  66
  67         /* Initialize the IV */
  68         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
  69
  70         /* Set up the encryption request */
  71         req = skcipher_request_alloc(tfm, GFP_NOFS);
  72         if (!req) {
  73                 printk_ratelimited(KERN_ERR
  74                         "%s: skcipher_request_alloc() failed\n", __func__);
  75                 return -ENOMEM;
  76         }
  77         skcipher_request_set_callback(req,
  78                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  79                         fname_crypt_complete, &ecr);
  80         sg_init_one(&sg, oname->name, cryptlen);
  81         skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);
  82
  83         /* Do the encryption */
  84         res = crypto_skcipher_encrypt(req);
  85         if (res == -EINPROGRESS || res == -EBUSY) {
  86                 /* Request is being completed asynchronously; wait for it */
  87                 wait_for_completion(&ecr.completion);
  88                 res = ecr.res;
  89         }
  90         skcipher_request_free(req);
  91         if (res < 0) {
  92                 printk_ratelimited(KERN_ERR
  93                                 "%s: Error (error code %d)\n", __func__, res);
  94                 return res;
  95         }
  96
  97         oname->len = cryptlen;
  98         return 0;
  99 }
 100
 101 /**
 102  * fname_decrypt() - decrypt a filename
 103  *
 104  * The caller must have allocated sufficient memory for the @oname string.
 105  *
 106  * Return: 0 on success, -errno on failure
 107  */
 108 static int fname_decrypt(struct inode *inode,
 109                                 const struct fscrypt_str *iname,
 110                                 struct fscrypt_str *oname)
 111 {
 112         struct skcipher_request *req = NULL;
 113         DECLARE_FS_COMPLETION_RESULT(ecr);
 114         struct scatterlist src_sg, dst_sg;
 115         struct fscrypt_info *ci = inode->i_crypt_info;
 116         struct crypto_skcipher *tfm = ci->ci_ctfm;
 117         int res = 0;
 118         char iv[FS_CRYPTO_BLOCK_SIZE];
 119         unsigned lim;
 120
 121         lim = inode->i_sb->s_cop->max_namelen(inode);
 122         if (iname->len <= 0 || iname->len > lim)
 123                 return -EIO;
 124
 125         /* Allocate request */
 126         req = skcipher_request_alloc(tfm, GFP_NOFS);
 127         if (!req) {
 128                 printk_ratelimited(KERN_ERR
 129                         "%s: crypto_request_alloc() failed\n",  __func__);
 130                 return -ENOMEM;
 131         }
 132         skcipher_request_set_callback(req,
 133                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 134                 fname_crypt_complete, &ecr);
 135
 136         /* Initialize IV */
 137         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
 138
 139         /* Create decryption request */
 140         sg_init_one(&src_sg, iname->name, iname->len);
 141         sg_init_one(&dst_sg, oname->name, oname->len);
 142         skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 143         res = crypto_skcipher_decrypt(req);
 144         if (res == -EINPROGRESS || res == -EBUSY) {
 145                 wait_for_completion(&ecr.completion);
 146                 res = ecr.res;
 147         }
 148         skcipher_request_free(req);
 149         if (res < 0) {
 150                 printk_ratelimited(KERN_ERR
 151                                 "%s: Error (error code %d)\n", __func__, res);
 152                 return res;
 153         }
 154
 155         oname->len = strnlen(oname->name, iname->len);
 156         return 0;
 157 }
 158
 159 static const char *lookup_table =
 160         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 161
 162 #define BASE64_CHARS(nbytes)    DIV_ROUND_UP((nbytes) * 4, 3)
 163
 164 /**
 165  * digest_encode() -
 166  *
 167  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 168  * The encoded string is roughly 4/3 times the size of the input string.
 169  */
 170 static int digest_encode(const char *src, int len, char *dst)
 171 {
 172         int i = 0, bits = 0, ac = 0;
 173         char *cp = dst;
 174
 175         while (i < len) {
 176                 ac += (((unsigned char) src[i]) << bits);
 177                 bits += 8;
 178                 do {
 179                         *cp++ = lookup_table[ac & 0x3f];
 180                         ac >>= 6;
 181                         bits -= 6;
 182                 } while (bits >= 6);
 183                 i++;
 184         }
 185         if (bits)
 186                 *cp++ = lookup_table[ac & 0x3f];
 187         return cp - dst;
 188 }
 189
 190 static int digest_decode(const char *src, int len, char *dst)
 191 {
 192         int i = 0, bits = 0, ac = 0;
 193         const char *p;
 194         char *cp = dst;
 195
 196         while (i < len) {
 197                 p = strchr(lookup_table, src[i]);
 198                 if (p == NULL || src[i] == 0)
 199                         return -2;
 200                 ac += (p - lookup_table) << bits;
 201                 bits += 6;
 202                 if (bits >= 8) {
 203                         *cp++ = ac & 0xff;
 204                         ac >>= 8;
 205                         bits -= 8;
 206                 }
 207                 i++;
 208         }
 209         if (ac)
 210                 return -1;
 211         return cp - dst;
 212 }
 213
 214 u32 fscrypt_fname_encrypted_size(const struct inode *inode, u32 ilen)
 215 {
 216         int padding = 32;
 217         struct fscrypt_info *ci = inode->i_crypt_info;
 218
 219         if (ci)
 220                 padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
 221         ilen = max(ilen, (u32)FS_CRYPTO_BLOCK_SIZE);
 222         return round_up(ilen, padding);
 223 }
 224 EXPORT_SYMBOL(fscrypt_fname_encrypted_size);
 225
 226 /**
 227  * fscrypt_fname_crypto_alloc_obuff() -
 228  *
 229  * Allocates an output buffer that is sufficient for the crypto operation
 230  * specified by the context and the direction.
 231  */
 232 int fscrypt_fname_alloc_buffer(const struct inode *inode,
 233                                 u32 ilen, struct fscrypt_str *crypto_str)
 234 {
 235         u32 olen = fscrypt_fname_encrypted_size(inode, ilen);
 236         const u32 max_encoded_len =
 237                 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
 238                       1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
 239
 240         crypto_str->len = olen;
 241         olen = max(olen, max_encoded_len);
 242
 243         /*
 244          * Allocated buffer can hold one more character to null-terminate the
 245          * string
 246          */
 247         crypto_str->name = kmalloc(olen + 1, GFP_NOFS);
 248         if (!(crypto_str->name))
 249                 return -ENOMEM;
 250         return 0;
 251 }
 252 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
 253
 254 /**
 255  * fscrypt_fname_crypto_free_buffer() -
 256  *
 257  * Frees the buffer allocated for crypto operation.
 258  */
 259 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 260 {
 261         if (!crypto_str)
 262                 return;
 263         kfree(crypto_str->name);
 264         crypto_str->name = NULL;
 265 }
 266 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
 267
 268 /**
 269  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 270  * space
 271  *
 272  * The caller must have allocated sufficient memory for the @oname string.
 273  *
 274  * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
 275  * it for presentation.  Short names are directly base64-encoded, while long
 276  * names are encoded in fscrypt_digested_name format.
 277  *
 278  * Return: 0 on success, -errno on failure
 279  */
 280 int fscrypt_fname_disk_to_usr(struct inode *inode,
 281                         u32 hash, u32 minor_hash,
 282                         const struct fscrypt_str *iname,
 283                         struct fscrypt_str *oname)
 284 {
 285         const struct qstr qname = FSTR_TO_QSTR(iname);
 286         struct fscrypt_digested_name digested_name;
 287
 288         if (fscrypt_is_dot_dotdot(&qname)) {
 289                 oname->name[0] = '.';
 290                 oname->name[iname->len - 1] = '.';
 291                 oname->len = iname->len;
 292                 return 0;
 293         }
 294
 295         if (iname->len < FS_CRYPTO_BLOCK_SIZE)
 296                 return -EUCLEAN;
 297
 298         if (inode->i_crypt_info)
 299                 return fname_decrypt(inode, iname, oname);
 300
 301         if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
 302                 oname->len = digest_encode(iname->name, iname->len,
 303                                            oname->name);
 304                 return 0;
 305         }
 306         if (hash) {
 307                 digested_name.hash = hash;
 308                 digested_name.minor_hash = minor_hash;
 309         } else {
 310                 digested_name.hash = 0;
 311                 digested_name.minor_hash = 0;
 312         }
 313         memcpy(digested_name.digest,
 314                FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
 315                FSCRYPT_FNAME_DIGEST_SIZE);
 316         oname->name[0] = '_';
 317         oname->len = 1 + digest_encode((const char *)&digested_name,
 318                                        sizeof(digested_name), oname->name + 1);
 319         return 0;
 320 }
 321 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
 322
 323 /**
 324  * fscrypt_fname_usr_to_disk() - converts a filename from user space to disk
 325  * space
 326  *
 327  * The caller must have allocated sufficient memory for the @oname string.
 328  *
 329  * Return: 0 on success, -errno on failure
 330  */
 331 int fscrypt_fname_usr_to_disk(struct inode *inode,
 332                         const struct qstr *iname,
 333                         struct fscrypt_str *oname)
 334 {
 335         if (fscrypt_is_dot_dotdot(iname)) {
 336                 oname->name[0] = '.';
 337                 oname->name[iname->len - 1] = '.';
 338                 oname->len = iname->len;
 339                 return 0;
 340         }
 341         if (inode->i_crypt_info)
 342                 return fname_encrypt(inode, iname, oname);
 343         /*
 344          * Without a proper key, a user is not allowed to modify the filenames
 345          * in a directory. Consequently, a user space name cannot be mapped to
 346          * a disk-space name
 347          */
 348         return -ENOKEY;
 349 }
 350 EXPORT_SYMBOL(fscrypt_fname_usr_to_disk);
 351
 352 /**
 353  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
 354  * @dir: the directory that will be searched
 355  * @iname: the user-provided filename being searched for
 356  * @lookup: 1 if we're allowed to proceed without the key because it's
 357  *      ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
 358  *      proceed without the key because we're going to create the dir_entry.
 359  * @fname: the filename information to be filled in
 360  *
 361  * Given a user-provided filename @iname, this function sets @fname->disk_name
 362  * to the name that would be stored in the on-disk directory entry, if possible.
 363  * If the directory is unencrypted this is simply @iname.  Else, if we have the
 364  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
 365  * get the disk_name.
 366  *
 367  * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
 368  * we decode it to get either the ciphertext disk_name (for short names) or the
 369  * fscrypt_digested_name (for long names).  Non-@lookup operations will be
 370  * impossible in this case, so we fail them with ENOKEY.
 371  *
 372  * If successful, fscrypt_free_filename() must be called later to clean up.
 373  *
 374  * Return: 0 on success, -errno on failure
 375  */
 376 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 377                               int lookup, struct fscrypt_name *fname)
 378 {
 379         int ret;
 380         int digested;
 381
 382         memset(fname, 0, sizeof(struct fscrypt_name));
 383         fname->usr_fname = iname;
 384
 385         if (!dir->i_sb->s_cop->is_encrypted(dir) ||
 386                                 fscrypt_is_dot_dotdot(iname)) {
 387                 fname->disk_name.name = (unsigned char *)iname->name;
 388                 fname->disk_name.len = iname->len;
 389                 return 0;
 390         }
 391         ret = fscrypt_get_encryption_info(dir);
 392         if (ret && ret != -EOPNOTSUPP)
 393                 return ret;
 394
 395         if (dir->i_crypt_info) {
 396                 ret = fscrypt_fname_alloc_buffer(dir, iname->len,
 397                                                         &fname->crypto_buf);
 398                 if (ret)
 399                         return ret;
 400                 ret = fname_encrypt(dir, iname, &fname->crypto_buf);
 401                 if (ret)
 402                         goto errout;
 403                 fname->disk_name.name = fname->crypto_buf.name;
 404                 fname->disk_name.len = fname->crypto_buf.len;
 405                 return 0;
 406         }
 407         if (!lookup)
 408                 return -ENOKEY;
 409
 410         /*
 411          * We don't have the key and we are doing a lookup; decode the
 412          * user-supplied name
 413          */
 414         if (iname->name[0] == '_') {
 415                 if (iname->len !=
 416                     1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
 417                         return -ENOENT;
 418                 digested = 1;
 419         } else {
 420                 if (iname->len >
 421                     BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
 422                         return -ENOENT;
 423                 digested = 0;
 424         }
 425
 426         fname->crypto_buf.name =
 427                 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
 428                               sizeof(struct fscrypt_digested_name)),
 429                         GFP_KERNEL);
 430         if (fname->crypto_buf.name == NULL)
 431                 return -ENOMEM;
 432
 433         ret = digest_decode(iname->name + digested, iname->len - digested,
 434                                 fname->crypto_buf.name);
 435         if (ret < 0) {
 436                 ret = -ENOENT;
 437                 goto errout;
 438         }
 439         fname->crypto_buf.len = ret;
 440         if (digested) {
 441                 const struct fscrypt_digested_name *n =
 442                         (const void *)fname->crypto_buf.name;
 443                 fname->hash = n->hash;
 444                 fname->minor_hash = n->minor_hash;
 445         } else {
 446                 fname->disk_name.name = fname->crypto_buf.name;
 447                 fname->disk_name.len = fname->crypto_buf.len;
 448         }
 449         return 0;
 450
 451 errout:
 452         fscrypt_fname_free_buffer(&fname->crypto_buf);
 453         return ret;
 454 }
 455 EXPORT_SYMBOL(fscrypt_setup_filename);
 456
 457 void fscrypt_free_filename(struct fscrypt_name *fname)
 458 {
 459         kfree(fname->crypto_buf.name);
 460         fname->crypto_buf.name = NULL;
 461         fname->usr_fname = NULL;
 462         fname->disk_name.name = NULL;
 463 }
 464 EXPORT_SYMBOL(fscrypt_free_filename);