fs/ext4/crypto_fname.c

   1 /*
   2  * linux/fs/ext4/crypto_fname.c
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  *
   6  * This contains functions for filename crypto management in ext4
   7  *
   8  * Written by Uday Savagaonkar, 2014.
   9  *
  10  * This has not yet undergone a rigorous security audit.
  11  *
  12  */
  13
  14 #include <crypto/hash.h>
  15 #include <crypto/sha.h>
  16 #include <keys/encrypted-type.h>
  17 #include <keys/user-type.h>
  18 #include <linux/crypto.h>
  19 #include <linux/gfp.h>
  20 #include <linux/kernel.h>
  21 #include <linux/key.h>
  22 #include <linux/list.h>
  23 #include <linux/mempool.h>
  24 #include <linux/random.h>
  25 #include <linux/scatterlist.h>
  26 #include <linux/spinlock_types.h>
  27
  28 #include "ext4.h"
  29 #include "ext4_crypto.h"
  30 #include "xattr.h"
  31
  32 /**
  33  * ext4_dir_crypt_complete() -
  34  */
  35 static void ext4_dir_crypt_complete(struct crypto_async_request *req, int res)
  36 {
  37         struct ext4_completion_result *ecr = req->data;
  38
  39         if (res == -EINPROGRESS)
  40                 return;
  41         ecr->res = res;
  42         complete(&ecr->completion);
  43 }
  44
  45 bool ext4_valid_filenames_enc_mode(uint32_t mode)
  46 {
  47         return (mode == EXT4_ENCRYPTION_MODE_AES_256_CTS);
  48 }
  49
  50 static unsigned max_name_len(struct inode *inode)
  51 {
  52         return S_ISLNK(inode->i_mode) ? inode->i_sb->s_blocksize :
  53                 EXT4_NAME_LEN;
  54 }
  55
  56 /**
  57  * ext4_fname_encrypt() -
  58  *
  59  * This function encrypts the input filename, and returns the length of the
  60  * ciphertext. Errors are returned as negative numbers.  We trust the caller to
  61  * allocate sufficient memory to oname string.
  62  */
  63 static int ext4_fname_encrypt(struct inode *inode,
  64                               const struct qstr *iname,
  65                               struct ext4_str *oname)
  66 {
  67         u32 ciphertext_len;
  68         struct ablkcipher_request *req = NULL;
  69         DECLARE_EXT4_COMPLETION_RESULT(ecr);
  70         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
  71         struct crypto_ablkcipher *tfm = ci->ci_ctfm;
  72         int res = 0;
  73         char iv[EXT4_CRYPTO_BLOCK_SIZE];
  74         struct scatterlist src_sg, dst_sg;
  75         int padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
  76         char *workbuf, buf[32], *alloc_buf = NULL;
  77         unsigned lim = max_name_len(inode);
  78
  79         if (iname->len <= 0 || iname->len > lim)
  80                 return -EIO;
  81
  82         ciphertext_len = (iname->len < EXT4_CRYPTO_BLOCK_SIZE) ?
  83                 EXT4_CRYPTO_BLOCK_SIZE : iname->len;
  84         ciphertext_len = ext4_fname_crypto_round_up(ciphertext_len, padding);
  85         ciphertext_len = (ciphertext_len > lim)
  86                         ? lim : ciphertext_len;
  87
  88         if (ciphertext_len <= sizeof(buf)) {
  89                 workbuf = buf;
  90         } else {
  91                 alloc_buf = kmalloc(ciphertext_len, GFP_NOFS);
  92                 if (!alloc_buf)
  93                         return -ENOMEM;
  94                 workbuf = alloc_buf;
  95         }
  96
  97         /* Allocate request */
  98         req = ablkcipher_request_alloc(tfm, GFP_NOFS);
  99         if (!req) {
 100                 printk_ratelimited(
 101                     KERN_ERR "%s: crypto_request_alloc() failed\n", __func__);
 102                 kfree(alloc_buf);
 103                 return -ENOMEM;
 104         }
 105         ablkcipher_request_set_callback(req,
 106                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 107                 ext4_dir_crypt_complete, &ecr);
 108
 109         /* Copy the input */
 110         memcpy(workbuf, iname->name, iname->len);
 111         if (iname->len < ciphertext_len)
 112                 memset(workbuf + iname->len, 0, ciphertext_len - iname->len);
 113
 114         /* Initialize IV */
 115         memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
 116
 117         /* Create encryption request */
 118         sg_init_one(&src_sg, workbuf, ciphertext_len);
 119         sg_init_one(&dst_sg, oname->name, ciphertext_len);
 120         ablkcipher_request_set_crypt(req, &src_sg, &dst_sg, ciphertext_len, iv);
 121         res = crypto_ablkcipher_encrypt(req);
 122         if (res == -EINPROGRESS || res == -EBUSY) {
 123                 BUG_ON(req->base.data != &ecr);
 124                 wait_for_completion(&ecr.completion);
 125                 res = ecr.res;
 126         }
 127         kfree(alloc_buf);
 128         ablkcipher_request_free(req);
 129         if (res < 0) {
 130                 printk_ratelimited(
 131                     KERN_ERR "%s: Error (error code %d)\n", __func__, res);
 132         }
 133         oname->len = ciphertext_len;
 134         return res;
 135 }
 136
 137 /*
 138  * ext4_fname_decrypt()
 139  *      This function decrypts the input filename, and returns
 140  *      the length of the plaintext.
 141  *      Errors are returned as negative numbers.
 142  *      We trust the caller to allocate sufficient memory to oname string.
 143  */
 144 static int ext4_fname_decrypt(struct inode *inode,
 145                               const struct ext4_str *iname,
 146                               struct ext4_str *oname)
 147 {
 148         struct ext4_str tmp_in[2], tmp_out[1];
 149         struct ablkcipher_request *req = NULL;
 150         DECLARE_EXT4_COMPLETION_RESULT(ecr);
 151         struct scatterlist src_sg, dst_sg;
 152         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 153         struct crypto_ablkcipher *tfm = ci->ci_ctfm;
 154         int res = 0;
 155         char iv[EXT4_CRYPTO_BLOCK_SIZE];
 156         unsigned lim = max_name_len(inode);
 157
 158         if (iname->len <= 0 || iname->len > lim)
 159                 return -EIO;
 160
 161         tmp_in[0].name = iname->name;
 162         tmp_in[0].len = iname->len;
 163         tmp_out[0].name = oname->name;
 164
 165         /* Allocate request */
 166         req = ablkcipher_request_alloc(tfm, GFP_NOFS);
 167         if (!req) {
 168                 printk_ratelimited(
 169                     KERN_ERR "%s: crypto_request_alloc() failed\n",  __func__);
 170                 return -ENOMEM;
 171         }
 172         ablkcipher_request_set_callback(req,
 173                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 174                 ext4_dir_crypt_complete, &ecr);
 175
 176         /* Initialize IV */
 177         memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
 178
 179         /* Create encryption request */
 180         sg_init_one(&src_sg, iname->name, iname->len);
 181         sg_init_one(&dst_sg, oname->name, oname->len);
 182         ablkcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 183         res = crypto_ablkcipher_decrypt(req);
 184         if (res == -EINPROGRESS || res == -EBUSY) {
 185                 BUG_ON(req->base.data != &ecr);
 186                 wait_for_completion(&ecr.completion);
 187                 res = ecr.res;
 188         }
 189         ablkcipher_request_free(req);
 190         if (res < 0) {
 191                 printk_ratelimited(
 192                     KERN_ERR "%s: Error in ext4_fname_encrypt (error code %d)\n",
 193                     __func__, res);
 194                 return res;
 195         }
 196
 197         oname->len = strnlen(oname->name, iname->len);
 198         return oname->len;
 199 }
 200
 201 static const char *lookup_table =
 202         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 203
 204 /**
 205  * ext4_fname_encode_digest() -
 206  *
 207  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 208  * The encoded string is roughly 4/3 times the size of the input string.
 209  */
 210 static int digest_encode(const char *src, int len, char *dst)
 211 {
 212         int i = 0, bits = 0, ac = 0;
 213         char *cp = dst;
 214
 215         while (i < len) {
 216                 ac += (((unsigned char) src[i]) << bits);
 217                 bits += 8;
 218                 do {
 219                         *cp++ = lookup_table[ac & 0x3f];
 220                         ac >>= 6;
 221                         bits -= 6;
 222                 } while (bits >= 6);
 223                 i++;
 224         }
 225         if (bits)
 226                 *cp++ = lookup_table[ac & 0x3f];
 227         return cp - dst;
 228 }
 229
 230 static int digest_decode(const char *src, int len, char *dst)
 231 {
 232         int i = 0, bits = 0, ac = 0;
 233         const char *p;
 234         char *cp = dst;
 235
 236         while (i < len) {
 237                 p = strchr(lookup_table, src[i]);
 238                 if (p == NULL || src[i] == 0)
 239                         return -2;
 240                 ac += (p - lookup_table) << bits;
 241                 bits += 6;
 242                 if (bits >= 8) {
 243                         *cp++ = ac & 0xff;
 244                         ac >>= 8;
 245                         bits -= 8;
 246                 }
 247                 i++;
 248         }
 249         if (ac)
 250                 return -1;
 251         return cp - dst;
 252 }
 253
 254 /**
 255  * ext4_fname_crypto_round_up() -
 256  *
 257  * Return: The next multiple of block size
 258  */
 259 u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
 260 {
 261         return ((size+blksize-1)/blksize)*blksize;
 262 }
 263
 264 unsigned ext4_fname_encrypted_size(struct inode *inode, u32 ilen)
 265 {
 266         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 267         int padding = 32;
 268
 269         if (ci)
 270                 padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
 271         if (ilen < EXT4_CRYPTO_BLOCK_SIZE)
 272                 ilen = EXT4_CRYPTO_BLOCK_SIZE;
 273         return ext4_fname_crypto_round_up(ilen, padding);
 274 }
 275
 276 /*
 277  * ext4_fname_crypto_alloc_buffer() -
 278  *
 279  * Allocates an output buffer that is sufficient for the crypto operation
 280  * specified by the context and the direction.
 281  */
 282 int ext4_fname_crypto_alloc_buffer(struct inode *inode,
 283                                    u32 ilen, struct ext4_str *crypto_str)
 284 {
 285         unsigned int olen = ext4_fname_encrypted_size(inode, ilen);
 286
 287         crypto_str->len = olen;
 288         if (olen < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2)
 289                 olen = EXT4_FNAME_CRYPTO_DIGEST_SIZE*2;
 290         /* Allocated buffer can hold one more character to null-terminate the
 291          * string */
 292         crypto_str->name = kmalloc(olen+1, GFP_NOFS);
 293         if (!(crypto_str->name))
 294                 return -ENOMEM;
 295         return 0;
 296 }
 297
 298 /**
 299  * ext4_fname_crypto_free_buffer() -
 300  *
 301  * Frees the buffer allocated for crypto operation.
 302  */
 303 void ext4_fname_crypto_free_buffer(struct ext4_str *crypto_str)
 304 {
 305         if (!crypto_str)
 306                 return;
 307         kfree(crypto_str->name);
 308         crypto_str->name = NULL;
 309 }
 310
 311 /**
 312  * ext4_fname_disk_to_usr() - converts a filename from disk space to user space
 313  */
 314 int _ext4_fname_disk_to_usr(struct inode *inode,
 315                             struct dx_hash_info *hinfo,
 316                             const struct ext4_str *iname,
 317                             struct ext4_str *oname)
 318 {
 319         char buf[24];
 320         int ret;
 321
 322         if (iname->len < 3) {
 323                 /*Check for . and .. */
 324                 if (iname->name[0] == '.' && iname->name[iname->len-1] == '.') {
 325                         oname->name[0] = '.';
 326                         oname->name[iname->len-1] = '.';
 327                         oname->len = iname->len;
 328                         return oname->len;
 329                 }
 330         }
 331         if (iname->len < EXT4_CRYPTO_BLOCK_SIZE) {
 332                 EXT4_ERROR_INODE(inode, "encrypted inode too small");
 333                 return -EUCLEAN;
 334         }
 335         if (EXT4_I(inode)->i_crypt_info)
 336                 return ext4_fname_decrypt(inode, iname, oname);
 337
 338         if (iname->len <= EXT4_FNAME_CRYPTO_DIGEST_SIZE) {
 339                 ret = digest_encode(iname->name, iname->len, oname->name);
 340                 oname->len = ret;
 341                 return ret;
 342         }
 343         if (hinfo) {
 344                 memcpy(buf, &hinfo->hash, 4);
 345                 memcpy(buf+4, &hinfo->minor_hash, 4);
 346         } else
 347                 memset(buf, 0, 8);
 348         memcpy(buf + 8, iname->name + iname->len - 16, 16);
 349         oname->name[0] = '_';
 350         ret = digest_encode(buf, 24, oname->name+1);
 351         oname->len = ret + 1;
 352         return ret + 1;
 353 }
 354
 355 int ext4_fname_disk_to_usr(struct inode *inode,
 356                            struct dx_hash_info *hinfo,
 357                            const struct ext4_dir_entry_2 *de,
 358                            struct ext4_str *oname)
 359 {
 360         struct ext4_str iname = {.name = (unsigned char *) de->name,
 361                                  .len = de->name_len };
 362
 363         return _ext4_fname_disk_to_usr(inode, hinfo, &iname, oname);
 364 }
 365
 366
 367 /**
 368  * ext4_fname_usr_to_disk() - converts a filename from user space to disk space
 369  */
 370 int ext4_fname_usr_to_disk(struct inode *inode,
 371                            const struct qstr *iname,
 372                            struct ext4_str *oname)
 373 {
 374         int res;
 375         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 376
 377         if (iname->len < 3) {
 378                 /*Check for . and .. */
 379                 if (iname->name[0] == '.' &&
 380                                 iname->name[iname->len-1] == '.') {
 381                         oname->name[0] = '.';
 382                         oname->name[iname->len-1] = '.';
 383                         oname->len = iname->len;
 384                         return oname->len;
 385                 }
 386         }
 387         if (ci) {
 388                 res = ext4_fname_encrypt(inode, iname, oname);
 389                 return res;
 390         }
 391         /* Without a proper key, a user is not allowed to modify the filenames
 392          * in a directory. Consequently, a user space name cannot be mapped to
 393          * a disk-space name */
 394         return -EACCES;
 395 }
 396
 397 int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
 398                               int lookup, struct ext4_filename *fname)
 399 {
 400         struct ext4_crypt_info *ci;
 401         int ret = 0, bigname = 0;
 402
 403         memset(fname, 0, sizeof(struct ext4_filename));
 404         fname->usr_fname = iname;
 405
 406         if (!ext4_encrypted_inode(dir) ||
 407             ((iname->name[0] == '.') &&
 408              ((iname->len == 1) ||
 409               ((iname->name[1] == '.') && (iname->len == 2))))) {
 410                 fname->disk_name.name = (unsigned char *) iname->name;
 411                 fname->disk_name.len = iname->len;
 412                 return 0;
 413         }
 414         ret = ext4_get_encryption_info(dir);
 415         if (ret)
 416                 return ret;
 417         ci = EXT4_I(dir)->i_crypt_info;
 418         if (ci) {
 419                 ret = ext4_fname_crypto_alloc_buffer(dir, iname->len,
 420                                                      &fname->crypto_buf);
 421                 if (ret < 0)
 422                         return ret;
 423                 ret = ext4_fname_encrypt(dir, iname, &fname->crypto_buf);
 424                 if (ret < 0)
 425                         goto errout;
 426                 fname->disk_name.name = fname->crypto_buf.name;
 427                 fname->disk_name.len = fname->crypto_buf.len;
 428                 return 0;
 429         }
 430         if (!lookup)
 431                 return -EACCES;
 432
 433         /* We don't have the key and we are doing a lookup; decode the
 434          * user-supplied name
 435          */
 436         if (iname->name[0] == '_')
 437                 bigname = 1;
 438         if ((bigname && (iname->len != 33)) ||
 439             (!bigname && (iname->len > 43)))
 440                 return -ENOENT;
 441
 442         fname->crypto_buf.name = kmalloc(32, GFP_KERNEL);
 443         if (fname->crypto_buf.name == NULL)
 444                 return -ENOMEM;
 445         ret = digest_decode(iname->name + bigname, iname->len - bigname,
 446                             fname->crypto_buf.name);
 447         if (ret < 0) {
 448                 ret = -ENOENT;
 449                 goto errout;
 450         }
 451         fname->crypto_buf.len = ret;
 452         if (bigname) {
 453                 memcpy(&fname->hinfo.hash, fname->crypto_buf.name, 4);
 454                 memcpy(&fname->hinfo.minor_hash, fname->crypto_buf.name + 4, 4);
 455         } else {
 456                 fname->disk_name.name = fname->crypto_buf.name;
 457                 fname->disk_name.len = fname->crypto_buf.len;
 458         }
 459         return 0;
 460 errout:
 461         kfree(fname->crypto_buf.name);
 462         fname->crypto_buf.name = NULL;
 463         return ret;
 464 }
 465
 466 void ext4_fname_free_filename(struct ext4_filename *fname)
 467 {
 468         kfree(fname->crypto_buf.name);
 469         fname->crypto_buf.name = NULL;
 470         fname->usr_fname = NULL;
 471         fname->disk_name.name = NULL;
 472 }