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