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