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                 wait_for_completion(&ecr.completion);
 124                 res = ecr.res;
 125         }
 126         kfree(alloc_buf);
 127         ablkcipher_request_free(req);
 128         if (res < 0) {
 129                 printk_ratelimited(
 130                     KERN_ERR "%s: Error (error code %d)\n", __func__, res);
 131         }
 132         oname->len = ciphertext_len;
 133         return res;
 134 }
 135
 136 /*
 137  * ext4_fname_decrypt()
 138  *      This function decrypts the input filename, and returns
 139  *      the length of the plaintext.
 140  *      Errors are returned as negative numbers.
 141  *      We trust the caller to allocate sufficient memory to oname string.
 142  */
 143 static int ext4_fname_decrypt(struct inode *inode,
 144                               const struct ext4_str *iname,
 145                               struct ext4_str *oname)
 146 {
 147         struct ext4_str tmp_in[2], tmp_out[1];
 148         struct ablkcipher_request *req = NULL;
 149         DECLARE_EXT4_COMPLETION_RESULT(ecr);
 150         struct scatterlist src_sg, dst_sg;
 151         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 152         struct crypto_ablkcipher *tfm = ci->ci_ctfm;
 153         int res = 0;
 154         char iv[EXT4_CRYPTO_BLOCK_SIZE];
 155         unsigned lim = max_name_len(inode);
 156
 157         if (iname->len <= 0 || iname->len > lim)
 158                 return -EIO;
 159
 160         tmp_in[0].name = iname->name;
 161         tmp_in[0].len = iname->len;
 162         tmp_out[0].name = oname->name;
 163
 164         /* Allocate request */
 165         req = ablkcipher_request_alloc(tfm, GFP_NOFS);
 166         if (!req) {
 167                 printk_ratelimited(
 168                     KERN_ERR "%s: crypto_request_alloc() failed\n",  __func__);
 169                 return -ENOMEM;
 170         }
 171         ablkcipher_request_set_callback(req,
 172                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 173                 ext4_dir_crypt_complete, &ecr);
 174
 175         /* Initialize IV */
 176         memset(iv, 0, EXT4_CRYPTO_BLOCK_SIZE);
 177
 178         /* Create encryption request */
 179         sg_init_one(&src_sg, iname->name, iname->len);
 180         sg_init_one(&dst_sg, oname->name, oname->len);
 181         ablkcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 182         res = crypto_ablkcipher_decrypt(req);
 183         if (res == -EINPROGRESS || res == -EBUSY) {
 184                 wait_for_completion(&ecr.completion);
 185                 res = ecr.res;
 186         }
 187         ablkcipher_request_free(req);
 188         if (res < 0) {
 189                 printk_ratelimited(
 190                     KERN_ERR "%s: Error in ext4_fname_encrypt (error code %d)\n",
 191                     __func__, res);
 192                 return res;
 193         }
 194
 195         oname->len = strnlen(oname->name, iname->len);
 196         return oname->len;
 197 }
 198
 199 static const char *lookup_table =
 200         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 201
 202 /**
 203  * ext4_fname_encode_digest() -
 204  *
 205  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 206  * The encoded string is roughly 4/3 times the size of the input string.
 207  */
 208 static int digest_encode(const char *src, int len, char *dst)
 209 {
 210         int i = 0, bits = 0, ac = 0;
 211         char *cp = dst;
 212
 213         while (i < len) {
 214                 ac += (((unsigned char) src[i]) << bits);
 215                 bits += 8;
 216                 do {
 217                         *cp++ = lookup_table[ac & 0x3f];
 218                         ac >>= 6;
 219                         bits -= 6;
 220                 } while (bits >= 6);
 221                 i++;
 222         }
 223         if (bits)
 224                 *cp++ = lookup_table[ac & 0x3f];
 225         return cp - dst;
 226 }
 227
 228 static int digest_decode(const char *src, int len, char *dst)
 229 {
 230         int i = 0, bits = 0, ac = 0;
 231         const char *p;
 232         char *cp = dst;
 233
 234         while (i < len) {
 235                 p = strchr(lookup_table, src[i]);
 236                 if (p == NULL || src[i] == 0)
 237                         return -2;
 238                 ac += (p - lookup_table) << bits;
 239                 bits += 6;
 240                 if (bits >= 8) {
 241                         *cp++ = ac & 0xff;
 242                         ac >>= 8;
 243                         bits -= 8;
 244                 }
 245                 i++;
 246         }
 247         if (ac)
 248                 return -1;
 249         return cp - dst;
 250 }
 251
 252 /**
 253  * ext4_fname_crypto_round_up() -
 254  *
 255  * Return: The next multiple of block size
 256  */
 257 u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
 258 {
 259         return ((size+blksize-1)/blksize)*blksize;
 260 }
 261
 262 unsigned ext4_fname_encrypted_size(struct inode *inode, u32 ilen)
 263 {
 264         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 265         int padding = 32;
 266
 267         if (ci)
 268                 padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
 269         if (ilen < EXT4_CRYPTO_BLOCK_SIZE)
 270                 ilen = EXT4_CRYPTO_BLOCK_SIZE;
 271         return ext4_fname_crypto_round_up(ilen, padding);
 272 }
 273
 274 /*
 275  * ext4_fname_crypto_alloc_buffer() -
 276  *
 277  * Allocates an output buffer that is sufficient for the crypto operation
 278  * specified by the context and the direction.
 279  */
 280 int ext4_fname_crypto_alloc_buffer(struct inode *inode,
 281                                    u32 ilen, struct ext4_str *crypto_str)
 282 {
 283         unsigned int olen = ext4_fname_encrypted_size(inode, ilen);
 284
 285         crypto_str->len = olen;
 286         if (olen < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2)
 287                 olen = EXT4_FNAME_CRYPTO_DIGEST_SIZE*2;
 288         /* Allocated buffer can hold one more character to null-terminate the
 289          * string */
 290         crypto_str->name = kmalloc(olen+1, GFP_NOFS);
 291         if (!(crypto_str->name))
 292                 return -ENOMEM;
 293         return 0;
 294 }
 295
 296 /**
 297  * ext4_fname_crypto_free_buffer() -
 298  *
 299  * Frees the buffer allocated for crypto operation.
 300  */
 301 void ext4_fname_crypto_free_buffer(struct ext4_str *crypto_str)
 302 {
 303         if (!crypto_str)
 304                 return;
 305         kfree(crypto_str->name);
 306         crypto_str->name = NULL;
 307 }
 308
 309 /**
 310  * ext4_fname_disk_to_usr() - converts a filename from disk space to user space
 311  */
 312 int _ext4_fname_disk_to_usr(struct inode *inode,
 313                             struct dx_hash_info *hinfo,
 314                             const struct ext4_str *iname,
 315                             struct ext4_str *oname)
 316 {
 317         char buf[24];
 318         int ret;
 319
 320         if (iname->len < 3) {
 321                 /*Check for . and .. */
 322                 if (iname->name[0] == '.' && iname->name[iname->len-1] == '.') {
 323                         oname->name[0] = '.';
 324                         oname->name[iname->len-1] = '.';
 325                         oname->len = iname->len;
 326                         return oname->len;
 327                 }
 328         }
 329         if (iname->len < EXT4_CRYPTO_BLOCK_SIZE) {
 330                 EXT4_ERROR_INODE(inode, "encrypted inode too small");
 331                 return -EUCLEAN;
 332         }
 333         if (EXT4_I(inode)->i_crypt_info)
 334                 return ext4_fname_decrypt(inode, iname, oname);
 335
 336         if (iname->len <= EXT4_FNAME_CRYPTO_DIGEST_SIZE) {
 337                 ret = digest_encode(iname->name, iname->len, oname->name);
 338                 oname->len = ret;
 339                 return ret;
 340         }
 341         if (hinfo) {
 342                 memcpy(buf, &hinfo->hash, 4);
 343                 memcpy(buf+4, &hinfo->minor_hash, 4);
 344         } else
 345                 memset(buf, 0, 8);
 346         memcpy(buf + 8, iname->name + iname->len - 16, 16);
 347         oname->name[0] = '_';
 348         ret = digest_encode(buf, 24, oname->name+1);
 349         oname->len = ret + 1;
 350         return ret + 1;
 351 }
 352
 353 int ext4_fname_disk_to_usr(struct inode *inode,
 354                            struct dx_hash_info *hinfo,
 355                            const struct ext4_dir_entry_2 *de,
 356                            struct ext4_str *oname)
 357 {
 358         struct ext4_str iname = {.name = (unsigned char *) de->name,
 359                                  .len = de->name_len };
 360
 361         return _ext4_fname_disk_to_usr(inode, hinfo, &iname, oname);
 362 }
 363
 364
 365 /**
 366  * ext4_fname_usr_to_disk() - converts a filename from user space to disk space
 367  */
 368 int ext4_fname_usr_to_disk(struct inode *inode,
 369                            const struct qstr *iname,
 370                            struct ext4_str *oname)
 371 {
 372         int res;
 373         struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 374
 375         if (iname->len < 3) {
 376                 /*Check for . and .. */
 377                 if (iname->name[0] == '.' &&
 378                                 iname->name[iname->len-1] == '.') {
 379                         oname->name[0] = '.';
 380                         oname->name[iname->len-1] = '.';
 381                         oname->len = iname->len;
 382                         return oname->len;
 383                 }
 384         }
 385         if (ci) {
 386                 res = ext4_fname_encrypt(inode, iname, oname);
 387                 return res;
 388         }
 389         /* Without a proper key, a user is not allowed to modify the filenames
 390          * in a directory. Consequently, a user space name cannot be mapped to
 391          * a disk-space name */
 392         return -EACCES;
 393 }
 394
 395 int ext4_fname_setup_filename(struct inode *dir, const struct qstr *iname,
 396                               int lookup, struct ext4_filename *fname)
 397 {
 398         struct ext4_crypt_info *ci;
 399         int ret = 0, bigname = 0;
 400
 401         memset(fname, 0, sizeof(struct ext4_filename));
 402         fname->usr_fname = iname;
 403
 404         if (!ext4_encrypted_inode(dir) ||
 405             ((iname->name[0] == '.') &&
 406              ((iname->len == 1) ||
 407               ((iname->name[1] == '.') && (iname->len == 2))))) {
 408                 fname->disk_name.name = (unsigned char *) iname->name;
 409                 fname->disk_name.len = iname->len;
 410                 return 0;
 411         }
 412         ret = ext4_get_encryption_info(dir);
 413         if (ret)
 414                 return ret;
 415         ci = EXT4_I(dir)->i_crypt_info;
 416         if (ci) {
 417                 ret = ext4_fname_crypto_alloc_buffer(dir, iname->len,
 418                                                      &fname->crypto_buf);
 419                 if (ret < 0)
 420                         return ret;
 421                 ret = ext4_fname_encrypt(dir, iname, &fname->crypto_buf);
 422                 if (ret < 0)
 423                         goto errout;
 424                 fname->disk_name.name = fname->crypto_buf.name;
 425                 fname->disk_name.len = fname->crypto_buf.len;
 426                 return 0;
 427         }
 428         if (!lookup)
 429                 return -EACCES;
 430
 431         /* We don't have the key and we are doing a lookup; decode the
 432          * user-supplied name
 433          */
 434         if (iname->name[0] == '_')
 435                 bigname = 1;
 436         if ((bigname && (iname->len != 33)) ||
 437             (!bigname && (iname->len > 43)))
 438                 return -ENOENT;
 439
 440         fname->crypto_buf.name = kmalloc(32, GFP_KERNEL);
 441         if (fname->crypto_buf.name == NULL)
 442                 return -ENOMEM;
 443         ret = digest_decode(iname->name + bigname, iname->len - bigname,
 444                             fname->crypto_buf.name);
 445         if (ret < 0) {
 446                 ret = -ENOENT;
 447                 goto errout;
 448         }
 449         fname->crypto_buf.len = ret;
 450         if (bigname) {
 451                 memcpy(&fname->hinfo.hash, fname->crypto_buf.name, 4);
 452                 memcpy(&fname->hinfo.minor_hash, fname->crypto_buf.name + 4, 4);
 453         } else {
 454                 fname->disk_name.name = fname->crypto_buf.name;
 455                 fname->disk_name.len = fname->crypto_buf.len;
 456         }
 457         return 0;
 458 errout:
 459         kfree(fname->crypto_buf.name);
 460         fname->crypto_buf.name = NULL;
 461         return ret;
 462 }
 463
 464 void ext4_fname_free_filename(struct ext4_filename *fname)
 465 {
 466         kfree(fname->crypto_buf.name);
 467         fname->crypto_buf.name = NULL;
 468         fname->usr_fname = NULL;
 469         fname->disk_name.name = NULL;
 470 }