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 <keys/encrypted-type.h>
  14 #include <keys/user-type.h>
  15 #include <linux/scatterlist.h>
  16 #include <linux/ratelimit.h>
  17 #include <linux/fscrypto.h>
  18
  19 static u32 size_round_up(size_t size, size_t blksize)
  20 {
  21         return ((size + blksize - 1) / blksize) * blksize;
  22 }
  23
  24 /**
  25  * dir_crypt_complete() -
  26  */
  27 static void dir_crypt_complete(struct crypto_async_request *req, int res)
  28 {
  29         struct fscrypt_completion_result *ecr = req->data;
  30
  31         if (res == -EINPROGRESS)
  32                 return;
  33         ecr->res = res;
  34         complete(&ecr->completion);
  35 }
  36
  37 /**
  38  * fname_encrypt() -
  39  *
  40  * This function encrypts the input filename, and returns the length of the
  41  * ciphertext. Errors are returned as negative numbers.  We trust the caller to
  42  * allocate sufficient memory to oname string.
  43  */
  44 static int fname_encrypt(struct inode *inode,
  45                         const struct qstr *iname, struct fscrypt_str *oname)
  46 {
  47         u32 ciphertext_len;
  48         struct skcipher_request *req = NULL;
  49         DECLARE_FS_COMPLETION_RESULT(ecr);
  50         struct fscrypt_info *ci = inode->i_crypt_info;
  51         struct crypto_skcipher *tfm = ci->ci_ctfm;
  52         int res = 0;
  53         char iv[FS_CRYPTO_BLOCK_SIZE];
  54         struct scatterlist src_sg, dst_sg;
  55         int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
  56         char *workbuf, buf[32], *alloc_buf = NULL;
  57         unsigned lim;
  58
  59         lim = inode->i_sb->s_cop->max_namelen(inode);
  60         if (iname->len <= 0 || iname->len > lim)
  61                 return -EIO;
  62
  63         ciphertext_len = (iname->len < FS_CRYPTO_BLOCK_SIZE) ?
  64                                         FS_CRYPTO_BLOCK_SIZE : iname->len;
  65         ciphertext_len = size_round_up(ciphertext_len, padding);
  66         ciphertext_len = (ciphertext_len > lim) ? lim : ciphertext_len;
  67
  68         if (ciphertext_len <= sizeof(buf)) {
  69                 workbuf = buf;
  70         } else {
  71                 alloc_buf = kmalloc(ciphertext_len, GFP_NOFS);
  72                 if (!alloc_buf)
  73                         return -ENOMEM;
  74                 workbuf = alloc_buf;
  75         }
  76
  77         /* Allocate request */
  78         req = skcipher_request_alloc(tfm, GFP_NOFS);
  79         if (!req) {
  80                 printk_ratelimited(KERN_ERR
  81                         "%s: crypto_request_alloc() failed\n", __func__);
  82                 kfree(alloc_buf);
  83                 return -ENOMEM;
  84         }
  85         skcipher_request_set_callback(req,
  86                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  87                         dir_crypt_complete, &ecr);
  88
  89         /* Copy the input */
  90         memcpy(workbuf, iname->name, iname->len);
  91         if (iname->len < ciphertext_len)
  92                 memset(workbuf + iname->len, 0, ciphertext_len - iname->len);
  93
  94         /* Initialize IV */
  95         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
  96
  97         /* Create encryption request */
  98         sg_init_one(&src_sg, workbuf, ciphertext_len);
  99         sg_init_one(&dst_sg, oname->name, ciphertext_len);
 100         skcipher_request_set_crypt(req, &src_sg, &dst_sg, ciphertext_len, iv);
 101         res = crypto_skcipher_encrypt(req);
 102         if (res == -EINPROGRESS || res == -EBUSY) {
 103                 wait_for_completion(&ecr.completion);
 104                 res = ecr.res;
 105         }
 106         kfree(alloc_buf);
 107         skcipher_request_free(req);
 108         if (res < 0)
 109                 printk_ratelimited(KERN_ERR
 110                                 "%s: Error (error code %d)\n", __func__, res);
 111
 112         oname->len = ciphertext_len;
 113         return res;
 114 }
 115
 116 /*
 117  * fname_decrypt()
 118  *      This function decrypts the input filename, and returns
 119  *      the length of the plaintext.
 120  *      Errors are returned as negative numbers.
 121  *      We trust the caller to allocate sufficient memory to oname string.
 122  */
 123 static int fname_decrypt(struct inode *inode,
 124                                 const struct fscrypt_str *iname,
 125                                 struct fscrypt_str *oname)
 126 {
 127         struct skcipher_request *req = NULL;
 128         DECLARE_FS_COMPLETION_RESULT(ecr);
 129         struct scatterlist src_sg, dst_sg;
 130         struct fscrypt_info *ci = inode->i_crypt_info;
 131         struct crypto_skcipher *tfm = ci->ci_ctfm;
 132         int res = 0;
 133         char iv[FS_CRYPTO_BLOCK_SIZE];
 134         unsigned lim;
 135
 136         lim = inode->i_sb->s_cop->max_namelen(inode);
 137         if (iname->len <= 0 || iname->len > lim)
 138                 return -EIO;
 139
 140         /* Allocate request */
 141         req = skcipher_request_alloc(tfm, GFP_NOFS);
 142         if (!req) {
 143                 printk_ratelimited(KERN_ERR
 144                         "%s: crypto_request_alloc() failed\n",  __func__);
 145                 return -ENOMEM;
 146         }
 147         skcipher_request_set_callback(req,
 148                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 149                 dir_crypt_complete, &ecr);
 150
 151         /* Initialize IV */
 152         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
 153
 154         /* Create decryption request */
 155         sg_init_one(&src_sg, iname->name, iname->len);
 156         sg_init_one(&dst_sg, oname->name, oname->len);
 157         skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 158         res = crypto_skcipher_decrypt(req);
 159         if (res == -EINPROGRESS || res == -EBUSY) {
 160                 wait_for_completion(&ecr.completion);
 161                 res = ecr.res;
 162         }
 163         skcipher_request_free(req);
 164         if (res < 0) {
 165                 printk_ratelimited(KERN_ERR
 166                                 "%s: Error (error code %d)\n", __func__, res);
 167                 return res;
 168         }
 169
 170         oname->len = strnlen(oname->name, iname->len);
 171         return oname->len;
 172 }
 173
 174 static const char *lookup_table =
 175         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 176
 177 /**
 178  * digest_encode() -
 179  *
 180  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 181  * The encoded string is roughly 4/3 times the size of the input string.
 182  */
 183 static int digest_encode(const char *src, int len, char *dst)
 184 {
 185         int i = 0, bits = 0, ac = 0;
 186         char *cp = dst;
 187
 188         while (i < len) {
 189                 ac += (((unsigned char) src[i]) << bits);
 190                 bits += 8;
 191                 do {
 192                         *cp++ = lookup_table[ac & 0x3f];
 193                         ac >>= 6;
 194                         bits -= 6;
 195                 } while (bits >= 6);
 196                 i++;
 197         }
 198         if (bits)
 199                 *cp++ = lookup_table[ac & 0x3f];
 200         return cp - dst;
 201 }
 202
 203 static int digest_decode(const char *src, int len, char *dst)
 204 {
 205         int i = 0, bits = 0, ac = 0;
 206         const char *p;
 207         char *cp = dst;
 208
 209         while (i < len) {
 210                 p = strchr(lookup_table, src[i]);
 211                 if (p == NULL || src[i] == 0)
 212                         return -2;
 213                 ac += (p - lookup_table) << bits;
 214                 bits += 6;
 215                 if (bits >= 8) {
 216                         *cp++ = ac & 0xff;
 217                         ac >>= 8;
 218                         bits -= 8;
 219                 }
 220                 i++;
 221         }
 222         if (ac)
 223                 return -1;
 224         return cp - dst;
 225 }
 226
 227 u32 fscrypt_fname_encrypted_size(struct inode *inode, u32 ilen)
 228 {
 229         int padding = 32;
 230         struct fscrypt_info *ci = inode->i_crypt_info;
 231
 232         if (ci)
 233                 padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
 234         if (ilen < FS_CRYPTO_BLOCK_SIZE)
 235                 ilen = FS_CRYPTO_BLOCK_SIZE;
 236         return size_round_up(ilen, padding);
 237 }
 238 EXPORT_SYMBOL(fscrypt_fname_encrypted_size);
 239
 240 /**
 241  * fscrypt_fname_crypto_alloc_obuff() -
 242  *
 243  * Allocates an output buffer that is sufficient for the crypto operation
 244  * specified by the context and the direction.
 245  */
 246 int fscrypt_fname_alloc_buffer(struct inode *inode,
 247                                 u32 ilen, struct fscrypt_str *crypto_str)
 248 {
 249         unsigned int olen = fscrypt_fname_encrypted_size(inode, ilen);
 250
 251         crypto_str->len = olen;
 252         if (olen < FS_FNAME_CRYPTO_DIGEST_SIZE * 2)
 253                 olen = FS_FNAME_CRYPTO_DIGEST_SIZE * 2;
 254         /*
 255          * Allocated buffer can hold one more character to null-terminate the
 256          * string
 257          */
 258         crypto_str->name = kmalloc(olen + 1, GFP_NOFS);
 259         if (!(crypto_str->name))
 260                 return -ENOMEM;
 261         return 0;
 262 }
 263 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
 264
 265 /**
 266  * fscrypt_fname_crypto_free_buffer() -
 267  *
 268  * Frees the buffer allocated for crypto operation.
 269  */
 270 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 271 {
 272         if (!crypto_str)
 273                 return;
 274         kfree(crypto_str->name);
 275         crypto_str->name = NULL;
 276 }
 277 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
 278
 279 /**
 280  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 281  * space
 282  */
 283 int fscrypt_fname_disk_to_usr(struct inode *inode,
 284                         u32 hash, u32 minor_hash,
 285                         const struct fscrypt_str *iname,
 286                         struct fscrypt_str *oname)
 287 {
 288         const struct qstr qname = FSTR_TO_QSTR(iname);
 289         char buf[24];
 290         int ret;
 291
 292         if (fscrypt_is_dot_dotdot(&qname)) {
 293                 oname->name[0] = '.';
 294                 oname->name[iname->len - 1] = '.';
 295                 oname->len = iname->len;
 296                 return oname->len;
 297         }
 298
 299         if (iname->len < FS_CRYPTO_BLOCK_SIZE)
 300                 return -EUCLEAN;
 301
 302         if (inode->i_crypt_info)
 303                 return fname_decrypt(inode, iname, oname);
 304
 305         if (iname->len <= FS_FNAME_CRYPTO_DIGEST_SIZE) {
 306                 ret = digest_encode(iname->name, iname->len, oname->name);
 307                 oname->len = ret;
 308                 return ret;
 309         }
 310         if (hash) {
 311                 memcpy(buf, &hash, 4);
 312                 memcpy(buf + 4, &minor_hash, 4);
 313         } else {
 314                 memset(buf, 0, 8);
 315         }
 316         memcpy(buf + 8, iname->name + iname->len - 16, 16);
 317         oname->name[0] = '_';
 318         ret = digest_encode(buf, 24, oname->name + 1);
 319         oname->len = ret + 1;
 320         return ret + 1;
 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 int fscrypt_fname_usr_to_disk(struct inode *inode,
 329                         const struct qstr *iname,
 330                         struct fscrypt_str *oname)
 331 {
 332         if (fscrypt_is_dot_dotdot(iname)) {
 333                 oname->name[0] = '.';
 334                 oname->name[iname->len - 1] = '.';
 335                 oname->len = iname->len;
 336                 return oname->len;
 337         }
 338         if (inode->i_crypt_info)
 339                 return fname_encrypt(inode, iname, oname);
 340         /*
 341          * Without a proper key, a user is not allowed to modify the filenames
 342          * in a directory. Consequently, a user space name cannot be mapped to
 343          * a disk-space name
 344          */
 345         return -EACCES;
 346 }
 347 EXPORT_SYMBOL(fscrypt_fname_usr_to_disk);
 348
 349 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 350                               int lookup, struct fscrypt_name *fname)
 351 {
 352         int ret = 0, bigname = 0;
 353
 354         memset(fname, 0, sizeof(struct fscrypt_name));
 355         fname->usr_fname = iname;
 356
 357         if (!dir->i_sb->s_cop->is_encrypted(dir) ||
 358                                 fscrypt_is_dot_dotdot(iname)) {
 359                 fname->disk_name.name = (unsigned char *)iname->name;
 360                 fname->disk_name.len = iname->len;
 361                 return 0;
 362         }
 363         ret = get_crypt_info(dir);
 364         if (ret && ret != -EOPNOTSUPP)
 365                 return ret;
 366
 367         if (dir->i_crypt_info) {
 368                 ret = fscrypt_fname_alloc_buffer(dir, iname->len,
 369                                                         &fname->crypto_buf);
 370                 if (ret < 0)
 371                         return ret;
 372                 ret = fname_encrypt(dir, iname, &fname->crypto_buf);
 373                 if (ret < 0)
 374                         goto errout;
 375                 fname->disk_name.name = fname->crypto_buf.name;
 376                 fname->disk_name.len = fname->crypto_buf.len;
 377                 return 0;
 378         }
 379         if (!lookup)
 380                 return -EACCES;
 381
 382         /*
 383          * We don't have the key and we are doing a lookup; decode the
 384          * user-supplied name
 385          */
 386         if (iname->name[0] == '_')
 387                 bigname = 1;
 388         if ((bigname && (iname->len != 33)) || (!bigname && (iname->len > 43)))
 389                 return -ENOENT;
 390
 391         fname->crypto_buf.name = kmalloc(32, GFP_KERNEL);
 392         if (fname->crypto_buf.name == NULL)
 393                 return -ENOMEM;
 394
 395         ret = digest_decode(iname->name + bigname, iname->len - bigname,
 396                                 fname->crypto_buf.name);
 397         if (ret < 0) {
 398                 ret = -ENOENT;
 399                 goto errout;
 400         }
 401         fname->crypto_buf.len = ret;
 402         if (bigname) {
 403                 memcpy(&fname->hash, fname->crypto_buf.name, 4);
 404                 memcpy(&fname->minor_hash, fname->crypto_buf.name + 4, 4);
 405         } else {
 406                 fname->disk_name.name = fname->crypto_buf.name;
 407                 fname->disk_name.len = fname->crypto_buf.len;
 408         }
 409         return 0;
 410
 411 errout:
 412         fscrypt_fname_free_buffer(&fname->crypto_buf);
 413         return ret;
 414 }
 415 EXPORT_SYMBOL(fscrypt_setup_filename);
 416
 417 void fscrypt_free_filename(struct fscrypt_name *fname)
 418 {
 419         kfree(fname->crypto_buf.name);
 420         fname->crypto_buf.name = NULL;
 421         fname->usr_fname = NULL;
 422         fname->disk_name.name = NULL;
 423 }
 424 EXPORT_SYMBOL(fscrypt_free_filename);