fs/crypto/keyinfo.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Key setup facility for FS encryption support.
   4  *
   5  * Copyright (C) 2015, Google, Inc.
   6  *
   7  * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
   8  * Heavily modified since then.
   9  */
  10
  11 #include <crypto/aes.h>
  12 #include <crypto/sha.h>
  13 #include <crypto/skcipher.h>
  14 #include <linux/key.h>
  15
  16 #include "fscrypt_private.h"
  17
  18 static struct crypto_shash *essiv_hash_tfm;
  19
  20 static struct fscrypt_mode available_modes[] = {
  21         [FSCRYPT_MODE_AES_256_XTS] = {
  22                 .friendly_name = "AES-256-XTS",
  23                 .cipher_str = "xts(aes)",
  24                 .keysize = 64,
  25                 .ivsize = 16,
  26         },
  27         [FSCRYPT_MODE_AES_256_CTS] = {
  28                 .friendly_name = "AES-256-CTS-CBC",
  29                 .cipher_str = "cts(cbc(aes))",
  30                 .keysize = 32,
  31                 .ivsize = 16,
  32         },
  33         [FSCRYPT_MODE_AES_128_CBC] = {
  34                 .friendly_name = "AES-128-CBC",
  35                 .cipher_str = "cbc(aes)",
  36                 .keysize = 16,
  37                 .ivsize = 16,
  38                 .needs_essiv = true,
  39         },
  40         [FSCRYPT_MODE_AES_128_CTS] = {
  41                 .friendly_name = "AES-128-CTS-CBC",
  42                 .cipher_str = "cts(cbc(aes))",
  43                 .keysize = 16,
  44                 .ivsize = 16,
  45         },
  46         [FSCRYPT_MODE_ADIANTUM] = {
  47                 .friendly_name = "Adiantum",
  48                 .cipher_str = "adiantum(xchacha12,aes)",
  49                 .keysize = 32,
  50                 .ivsize = 32,
  51         },
  52 };
  53
  54 static struct fscrypt_mode *
  55 select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
  56 {
  57         if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
  58                 fscrypt_warn(inode,
  59                              "Unsupported encryption modes (contents mode %d, filenames mode %d)",
  60                              ci->ci_data_mode, ci->ci_filename_mode);
  61                 return ERR_PTR(-EINVAL);
  62         }
  63
  64         if (S_ISREG(inode->i_mode))
  65                 return &available_modes[ci->ci_data_mode];
  66
  67         if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
  68                 return &available_modes[ci->ci_filename_mode];
  69
  70         WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
  71                   inode->i_ino, (inode->i_mode & S_IFMT));
  72         return ERR_PTR(-EINVAL);
  73 }
  74
  75 /* Create a symmetric cipher object for the given encryption mode and key */
  76 struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
  77                                                   const u8 *raw_key,
  78                                                   const struct inode *inode)
  79 {
  80         struct crypto_skcipher *tfm;
  81         int err;
  82
  83         tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
  84         if (IS_ERR(tfm)) {
  85                 if (PTR_ERR(tfm) == -ENOENT) {
  86                         fscrypt_warn(inode,
  87                                      "Missing crypto API support for %s (API name: \"%s\")",
  88                                      mode->friendly_name, mode->cipher_str);
  89                         return ERR_PTR(-ENOPKG);
  90                 }
  91                 fscrypt_err(inode, "Error allocating '%s' transform: %ld",
  92                             mode->cipher_str, PTR_ERR(tfm));
  93                 return tfm;
  94         }
  95         if (unlikely(!mode->logged_impl_name)) {
  96                 /*
  97                  * fscrypt performance can vary greatly depending on which
  98                  * crypto algorithm implementation is used.  Help people debug
  99                  * performance problems by logging the ->cra_driver_name the
 100                  * first time a mode is used.  Note that multiple threads can
 101                  * race here, but it doesn't really matter.
 102                  */
 103                 mode->logged_impl_name = true;
 104                 pr_info("fscrypt: %s using implementation \"%s\"\n",
 105                         mode->friendly_name,
 106                         crypto_skcipher_alg(tfm)->base.cra_driver_name);
 107         }
 108         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
 109         err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
 110         if (err)
 111                 goto err_free_tfm;
 112
 113         return tfm;
 114
 115 err_free_tfm:
 116         crypto_free_skcipher(tfm);
 117         return ERR_PTR(err);
 118 }
 119
 120 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
 121 {
 122         struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
 123
 124         /* init hash transform on demand */
 125         if (unlikely(!tfm)) {
 126                 struct crypto_shash *prev_tfm;
 127
 128                 tfm = crypto_alloc_shash("sha256", 0, 0);
 129                 if (IS_ERR(tfm)) {
 130                         if (PTR_ERR(tfm) == -ENOENT) {
 131                                 fscrypt_warn(NULL,
 132                                              "Missing crypto API support for SHA-256");
 133                                 return -ENOPKG;
 134                         }
 135                         fscrypt_err(NULL,
 136                                     "Error allocating SHA-256 transform: %ld",
 137                                     PTR_ERR(tfm));
 138                         return PTR_ERR(tfm);
 139                 }
 140                 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
 141                 if (prev_tfm) {
 142                         crypto_free_shash(tfm);
 143                         tfm = prev_tfm;
 144                 }
 145         }
 146
 147         {
 148                 SHASH_DESC_ON_STACK(desc, tfm);
 149                 desc->tfm = tfm;
 150
 151                 return crypto_shash_digest(desc, key, keysize, salt);
 152         }
 153 }
 154
 155 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
 156                                 int keysize)
 157 {
 158         int err;
 159         struct crypto_cipher *essiv_tfm;
 160         u8 salt[SHA256_DIGEST_SIZE];
 161
 162         if (WARN_ON(ci->ci_mode->ivsize != AES_BLOCK_SIZE))
 163                 return -EINVAL;
 164
 165         essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
 166         if (IS_ERR(essiv_tfm))
 167                 return PTR_ERR(essiv_tfm);
 168
 169         ci->ci_essiv_tfm = essiv_tfm;
 170
 171         err = derive_essiv_salt(raw_key, keysize, salt);
 172         if (err)
 173                 goto out;
 174
 175         /*
 176          * Using SHA256 to derive the salt/key will result in AES-256 being
 177          * used for IV generation. File contents encryption will still use the
 178          * configured keysize (AES-128) nevertheless.
 179          */
 180         err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
 181         if (err)
 182                 goto out;
 183
 184 out:
 185         memzero_explicit(salt, sizeof(salt));
 186         return err;
 187 }
 188
 189 /* Given the per-file key, set up the file's crypto transform object(s) */
 190 int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
 191 {
 192         struct fscrypt_mode *mode = ci->ci_mode;
 193         struct crypto_skcipher *ctfm;
 194         int err;
 195
 196         ctfm = fscrypt_allocate_skcipher(mode, derived_key, ci->ci_inode);
 197         if (IS_ERR(ctfm))
 198                 return PTR_ERR(ctfm);
 199
 200         ci->ci_ctfm = ctfm;
 201
 202         if (mode->needs_essiv) {
 203                 err = init_essiv_generator(ci, derived_key, mode->keysize);
 204                 if (err) {
 205                         fscrypt_warn(ci->ci_inode,
 206                                      "Error initializing ESSIV generator: %d",
 207                                      err);
 208                         return err;
 209                 }
 210         }
 211         return 0;
 212 }
 213
 214 /*
 215  * Find the master key, then set up the inode's actual encryption key.
 216  */
 217 static int setup_file_encryption_key(struct fscrypt_info *ci)
 218 {
 219         return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
 220 }
 221
 222 static void put_crypt_info(struct fscrypt_info *ci)
 223 {
 224         if (!ci)
 225                 return;
 226
 227         if (ci->ci_direct_key) {
 228                 fscrypt_put_direct_key(ci->ci_direct_key);
 229         } else {
 230                 crypto_free_skcipher(ci->ci_ctfm);
 231                 crypto_free_cipher(ci->ci_essiv_tfm);
 232         }
 233         kmem_cache_free(fscrypt_info_cachep, ci);
 234 }
 235
 236 int fscrypt_get_encryption_info(struct inode *inode)
 237 {
 238         struct fscrypt_info *crypt_info;
 239         struct fscrypt_context ctx;
 240         struct fscrypt_mode *mode;
 241         int res;
 242
 243         if (fscrypt_has_encryption_key(inode))
 244                 return 0;
 245
 246         res = fscrypt_initialize(inode->i_sb->s_cop->flags);
 247         if (res)
 248                 return res;
 249
 250         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 251         if (res < 0) {
 252                 if (!fscrypt_dummy_context_enabled(inode) ||
 253                     IS_ENCRYPTED(inode)) {
 254                         fscrypt_warn(inode,
 255                                      "Error %d getting encryption context",
 256                                      res);
 257                         return res;
 258                 }
 259                 /* Fake up a context for an unencrypted directory */
 260                 memset(&ctx, 0, sizeof(ctx));
 261                 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 262                 ctx.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
 263                 ctx.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
 264                 memset(ctx.master_key_descriptor, 0x42,
 265                        FSCRYPT_KEY_DESCRIPTOR_SIZE);
 266         } else if (res != sizeof(ctx)) {
 267                 fscrypt_warn(inode,
 268                              "Unknown encryption context size (%d bytes)", res);
 269                 return -EINVAL;
 270         }
 271
 272         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1) {
 273                 fscrypt_warn(inode, "Unknown encryption context version (%d)",
 274                              ctx.format);
 275                 return -EINVAL;
 276         }
 277
 278         if (ctx.flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
 279                 fscrypt_warn(inode, "Unknown encryption context flags (0x%02x)",
 280                              ctx.flags);
 281                 return -EINVAL;
 282         }
 283
 284         crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
 285         if (!crypt_info)
 286                 return -ENOMEM;
 287
 288         crypt_info->ci_inode = inode;
 289
 290         crypt_info->ci_flags = ctx.flags;
 291         crypt_info->ci_data_mode = ctx.contents_encryption_mode;
 292         crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
 293         memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
 294                FSCRYPT_KEY_DESCRIPTOR_SIZE);
 295         memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 296
 297         mode = select_encryption_mode(crypt_info, inode);
 298         if (IS_ERR(mode)) {
 299                 res = PTR_ERR(mode);
 300                 goto out;
 301         }
 302         WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
 303         crypt_info->ci_mode = mode;
 304
 305         res = setup_file_encryption_key(crypt_info);
 306         if (res)
 307                 goto out;
 308
 309         if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL)
 310                 crypt_info = NULL;
 311 out:
 312         if (res == -ENOKEY)
 313                 res = 0;
 314         put_crypt_info(crypt_info);
 315         return res;
 316 }
 317 EXPORT_SYMBOL(fscrypt_get_encryption_info);
 318
 319 /**
 320  * fscrypt_put_encryption_info - free most of an inode's fscrypt data
 321  *
 322  * Free the inode's fscrypt_info.  Filesystems must call this when the inode is
 323  * being evicted.  An RCU grace period need not have elapsed yet.
 324  */
 325 void fscrypt_put_encryption_info(struct inode *inode)
 326 {
 327         put_crypt_info(inode->i_crypt_info);
 328         inode->i_crypt_info = NULL;
 329 }
 330 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 331
 332 /**
 333  * fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
 334  *
 335  * Free the inode's cached decrypted symlink target, if any.  Filesystems must
 336  * call this after an RCU grace period, just before they free the inode.
 337  */
 338 void fscrypt_free_inode(struct inode *inode)
 339 {
 340         if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
 341                 kfree(inode->i_link);
 342                 inode->i_link = NULL;
 343         }
 344 }
 345 EXPORT_SYMBOL(fscrypt_free_inode);