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