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