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