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