fs/crypto/fname.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This contains functions for filename crypto management
   4  *
   5  * Copyright (C) 2015, Google, Inc.
   6  * Copyright (C) 2015, Motorola Mobility
   7  *
   8  * Written by Uday Savagaonkar, 2014.
   9  * Modified by Jaegeuk Kim, 2015.
  10  *
  11  * This has not yet undergone a rigorous security audit.
  12  */
  13
  14 #include <linux/scatterlist.h>
  15 #include <linux/ratelimit.h>
  16 #include <crypto/skcipher.h>
  17 #include "fscrypt_private.h"
  18
  19 static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
  20 {
  21         if (str->len == 1 && str->name[0] == '.')
  22                 return true;
  23
  24         if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
  25                 return true;
  26
  27         return false;
  28 }
  29
  30 /**
  31  * fname_encrypt() - encrypt a filename
  32  *
  33  * The output buffer must be at least as large as the input buffer.
  34  * Any extra space is filled with NUL padding before encryption.
  35  *
  36  * Return: 0 on success, -errno on failure
  37  */
  38 int fname_encrypt(struct inode *inode, const struct qstr *iname,
  39                   u8 *out, unsigned int olen)
  40 {
  41         struct skcipher_request *req = NULL;
  42         DECLARE_CRYPTO_WAIT(wait);
  43         struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
  44         int res = 0;
  45         char iv[FS_CRYPTO_BLOCK_SIZE];
  46         struct scatterlist sg;
  47
  48         /*
  49          * Copy the filename to the output buffer for encrypting in-place and
  50          * pad it with the needed number of NUL bytes.
  51          */
  52         if (WARN_ON(olen < iname->len))
  53                 return -ENOBUFS;
  54         memcpy(out, iname->name, iname->len);
  55         memset(out + iname->len, 0, olen - iname->len);
  56
  57         /* Initialize the IV */
  58         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
  59
  60         /* Set up the encryption request */
  61         req = skcipher_request_alloc(tfm, GFP_NOFS);
  62         if (!req) {
  63                 printk_ratelimited(KERN_ERR
  64                         "%s: skcipher_request_alloc() failed\n", __func__);
  65                 return -ENOMEM;
  66         }
  67         skcipher_request_set_callback(req,
  68                         CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
  69                         crypto_req_done, &wait);
  70         sg_init_one(&sg, out, olen);
  71         skcipher_request_set_crypt(req, &sg, &sg, olen, iv);
  72
  73         /* Do the encryption */
  74         res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
  75         skcipher_request_free(req);
  76         if (res < 0) {
  77                 printk_ratelimited(KERN_ERR
  78                                 "%s: Error (error code %d)\n", __func__, res);
  79                 return res;
  80         }
  81
  82         return 0;
  83 }
  84
  85 /**
  86  * fname_decrypt() - decrypt a filename
  87  *
  88  * The caller must have allocated sufficient memory for the @oname string.
  89  *
  90  * Return: 0 on success, -errno on failure
  91  */
  92 static int fname_decrypt(struct inode *inode,
  93                                 const struct fscrypt_str *iname,
  94                                 struct fscrypt_str *oname)
  95 {
  96         struct skcipher_request *req = NULL;
  97         DECLARE_CRYPTO_WAIT(wait);
  98         struct scatterlist src_sg, dst_sg;
  99         struct fscrypt_info *ci = inode->i_crypt_info;
 100         struct crypto_skcipher *tfm = ci->ci_ctfm;
 101         int res = 0;
 102         char iv[FS_CRYPTO_BLOCK_SIZE];
 103         unsigned lim;
 104
 105         lim = inode->i_sb->s_cop->max_namelen(inode);
 106         if (iname->len <= 0 || iname->len > lim)
 107                 return -EIO;
 108
 109         /* Allocate request */
 110         req = skcipher_request_alloc(tfm, GFP_NOFS);
 111         if (!req) {
 112                 printk_ratelimited(KERN_ERR
 113                         "%s: crypto_request_alloc() failed\n",  __func__);
 114                 return -ENOMEM;
 115         }
 116         skcipher_request_set_callback(req,
 117                 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 118                 crypto_req_done, &wait);
 119
 120         /* Initialize IV */
 121         memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
 122
 123         /* Create decryption request */
 124         sg_init_one(&src_sg, iname->name, iname->len);
 125         sg_init_one(&dst_sg, oname->name, oname->len);
 126         skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
 127         res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 128         skcipher_request_free(req);
 129         if (res < 0) {
 130                 printk_ratelimited(KERN_ERR
 131                                 "%s: Error (error code %d)\n", __func__, res);
 132                 return res;
 133         }
 134
 135         oname->len = strnlen(oname->name, iname->len);
 136         return 0;
 137 }
 138
 139 static const char *lookup_table =
 140         "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
 141
 142 #define BASE64_CHARS(nbytes)    DIV_ROUND_UP((nbytes) * 4, 3)
 143
 144 /**
 145  * digest_encode() -
 146  *
 147  * Encodes the input digest using characters from the set [a-zA-Z0-9_+].
 148  * The encoded string is roughly 4/3 times the size of the input string.
 149  */
 150 static int digest_encode(const char *src, int len, char *dst)
 151 {
 152         int i = 0, bits = 0, ac = 0;
 153         char *cp = dst;
 154
 155         while (i < len) {
 156                 ac += (((unsigned char) src[i]) << bits);
 157                 bits += 8;
 158                 do {
 159                         *cp++ = lookup_table[ac & 0x3f];
 160                         ac >>= 6;
 161                         bits -= 6;
 162                 } while (bits >= 6);
 163                 i++;
 164         }
 165         if (bits)
 166                 *cp++ = lookup_table[ac & 0x3f];
 167         return cp - dst;
 168 }
 169
 170 static int digest_decode(const char *src, int len, char *dst)
 171 {
 172         int i = 0, bits = 0, ac = 0;
 173         const char *p;
 174         char *cp = dst;
 175
 176         while (i < len) {
 177                 p = strchr(lookup_table, src[i]);
 178                 if (p == NULL || src[i] == 0)
 179                         return -2;
 180                 ac += (p - lookup_table) << bits;
 181                 bits += 6;
 182                 if (bits >= 8) {
 183                         *cp++ = ac & 0xff;
 184                         ac >>= 8;
 185                         bits -= 8;
 186                 }
 187                 i++;
 188         }
 189         if (ac)
 190                 return -1;
 191         return cp - dst;
 192 }
 193
 194 bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
 195                                   u32 max_len, u32 *encrypted_len_ret)
 196 {
 197         int padding = 4 << (inode->i_crypt_info->ci_flags &
 198                             FS_POLICY_FLAGS_PAD_MASK);
 199         u32 encrypted_len;
 200
 201         if (orig_len > max_len)
 202                 return false;
 203         encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
 204         encrypted_len = round_up(encrypted_len, padding);
 205         *encrypted_len_ret = min(encrypted_len, max_len);
 206         return true;
 207 }
 208
 209 /**
 210  * fscrypt_fname_alloc_buffer - allocate a buffer for presented filenames
 211  *
 212  * Allocate a buffer that is large enough to hold any decrypted or encoded
 213  * filename (null-terminated), for the given maximum encrypted filename length.
 214  *
 215  * Return: 0 on success, -errno on failure
 216  */
 217 int fscrypt_fname_alloc_buffer(const struct inode *inode,
 218                                u32 max_encrypted_len,
 219                                struct fscrypt_str *crypto_str)
 220 {
 221         const u32 max_encoded_len =
 222                 max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE),
 223                       1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)));
 224         u32 max_presented_len;
 225
 226         max_presented_len = max(max_encoded_len, max_encrypted_len);
 227
 228         crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
 229         if (!crypto_str->name)
 230                 return -ENOMEM;
 231         crypto_str->len = max_presented_len;
 232         return 0;
 233 }
 234 EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
 235
 236 /**
 237  * fscrypt_fname_free_buffer - free the buffer for presented filenames
 238  *
 239  * Free the buffer allocated by fscrypt_fname_alloc_buffer().
 240  */
 241 void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
 242 {
 243         if (!crypto_str)
 244                 return;
 245         kfree(crypto_str->name);
 246         crypto_str->name = NULL;
 247 }
 248 EXPORT_SYMBOL(fscrypt_fname_free_buffer);
 249
 250 /**
 251  * fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
 252  * space
 253  *
 254  * The caller must have allocated sufficient memory for the @oname string.
 255  *
 256  * If the key is available, we'll decrypt the disk name; otherwise, we'll encode
 257  * it for presentation.  Short names are directly base64-encoded, while long
 258  * names are encoded in fscrypt_digested_name format.
 259  *
 260  * Return: 0 on success, -errno on failure
 261  */
 262 int fscrypt_fname_disk_to_usr(struct inode *inode,
 263                         u32 hash, u32 minor_hash,
 264                         const struct fscrypt_str *iname,
 265                         struct fscrypt_str *oname)
 266 {
 267         const struct qstr qname = FSTR_TO_QSTR(iname);
 268         struct fscrypt_digested_name digested_name;
 269
 270         if (fscrypt_is_dot_dotdot(&qname)) {
 271                 oname->name[0] = '.';
 272                 oname->name[iname->len - 1] = '.';
 273                 oname->len = iname->len;
 274                 return 0;
 275         }
 276
 277         if (iname->len < FS_CRYPTO_BLOCK_SIZE)
 278                 return -EUCLEAN;
 279
 280         if (inode->i_crypt_info)
 281                 return fname_decrypt(inode, iname, oname);
 282
 283         if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
 284                 oname->len = digest_encode(iname->name, iname->len,
 285                                            oname->name);
 286                 return 0;
 287         }
 288         if (hash) {
 289                 digested_name.hash = hash;
 290                 digested_name.minor_hash = minor_hash;
 291         } else {
 292                 digested_name.hash = 0;
 293                 digested_name.minor_hash = 0;
 294         }
 295         memcpy(digested_name.digest,
 296                FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
 297                FSCRYPT_FNAME_DIGEST_SIZE);
 298         oname->name[0] = '_';
 299         oname->len = 1 + digest_encode((const char *)&digested_name,
 300                                        sizeof(digested_name), oname->name + 1);
 301         return 0;
 302 }
 303 EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
 304
 305 /**
 306  * fscrypt_setup_filename() - prepare to search a possibly encrypted directory
 307  * @dir: the directory that will be searched
 308  * @iname: the user-provided filename being searched for
 309  * @lookup: 1 if we're allowed to proceed without the key because it's
 310  *      ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
 311  *      proceed without the key because we're going to create the dir_entry.
 312  * @fname: the filename information to be filled in
 313  *
 314  * Given a user-provided filename @iname, this function sets @fname->disk_name
 315  * to the name that would be stored in the on-disk directory entry, if possible.
 316  * If the directory is unencrypted this is simply @iname.  Else, if we have the
 317  * directory's encryption key, then @iname is the plaintext, so we encrypt it to
 318  * get the disk_name.
 319  *
 320  * Else, for keyless @lookup operations, @iname is the presented ciphertext, so
 321  * we decode it to get either the ciphertext disk_name (for short names) or the
 322  * fscrypt_digested_name (for long names).  Non-@lookup operations will be
 323  * impossible in this case, so we fail them with ENOKEY.
 324  *
 325  * If successful, fscrypt_free_filename() must be called later to clean up.
 326  *
 327  * Return: 0 on success, -errno on failure
 328  */
 329 int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 330                               int lookup, struct fscrypt_name *fname)
 331 {
 332         int ret;
 333         int digested;
 334
 335         memset(fname, 0, sizeof(struct fscrypt_name));
 336         fname->usr_fname = iname;
 337
 338         if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
 339                 fname->disk_name.name = (unsigned char *)iname->name;
 340                 fname->disk_name.len = iname->len;
 341                 return 0;
 342         }
 343         ret = fscrypt_get_encryption_info(dir);
 344         if (ret && ret != -EOPNOTSUPP)
 345                 return ret;
 346
 347         if (dir->i_crypt_info) {
 348                 if (!fscrypt_fname_encrypted_size(dir, iname->len,
 349                                                   dir->i_sb->s_cop->max_namelen(dir),
 350                                                   &fname->crypto_buf.len))
 351                         return -ENAMETOOLONG;
 352                 fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
 353                                                  GFP_NOFS);
 354                 if (!fname->crypto_buf.name)
 355                         return -ENOMEM;
 356
 357                 ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
 358                                     fname->crypto_buf.len);
 359                 if (ret)
 360                         goto errout;
 361                 fname->disk_name.name = fname->crypto_buf.name;
 362                 fname->disk_name.len = fname->crypto_buf.len;
 363                 return 0;
 364         }
 365         if (!lookup)
 366                 return -ENOKEY;
 367
 368         /*
 369          * We don't have the key and we are doing a lookup; decode the
 370          * user-supplied name
 371          */
 372         if (iname->name[0] == '_') {
 373                 if (iname->len !=
 374                     1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name)))
 375                         return -ENOENT;
 376                 digested = 1;
 377         } else {
 378                 if (iname->len >
 379                     BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE))
 380                         return -ENOENT;
 381                 digested = 0;
 382         }
 383
 384         fname->crypto_buf.name =
 385                 kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE,
 386                               sizeof(struct fscrypt_digested_name)),
 387                         GFP_KERNEL);
 388         if (fname->crypto_buf.name == NULL)
 389                 return -ENOMEM;
 390
 391         ret = digest_decode(iname->name + digested, iname->len - digested,
 392                                 fname->crypto_buf.name);
 393         if (ret < 0) {
 394                 ret = -ENOENT;
 395                 goto errout;
 396         }
 397         fname->crypto_buf.len = ret;
 398         if (digested) {
 399                 const struct fscrypt_digested_name *n =
 400                         (const void *)fname->crypto_buf.name;
 401                 fname->hash = n->hash;
 402                 fname->minor_hash = n->minor_hash;
 403         } else {
 404                 fname->disk_name.name = fname->crypto_buf.name;
 405                 fname->disk_name.len = fname->crypto_buf.len;
 406         }
 407         return 0;
 408
 409 errout:
 410         kfree(fname->crypto_buf.name);
 411         return ret;
 412 }
 413 EXPORT_SYMBOL(fscrypt_setup_filename);