security/keys/big_key.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Large capacity key type
   3  *
   4  * Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
   5  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
   6  * Written by David Howells (dhowells@redhat.com)
   7  */
   8
   9 #define pr_fmt(fmt) "big_key: "fmt
  10 #include <linux/init.h>
  11 #include <linux/seq_file.h>
  12 #include <linux/file.h>
  13 #include <linux/shmem_fs.h>
  14 #include <linux/err.h>
  15 #include <linux/scatterlist.h>
  16 #include <linux/random.h>
  17 #include <linux/vmalloc.h>
  18 #include <keys/user-type.h>
  19 #include <keys/big_key-type.h>
  20 #include <crypto/aead.h>
  21 #include <crypto/gcm.h>
  22
  23 struct big_key_buf {
  24         unsigned int            nr_pages;
  25         void                    *virt;
  26         struct scatterlist      *sg;
  27         struct page             *pages[];
  28 };
  29
  30 /*
  31  * Layout of key payload words.
  32  */
  33 enum {
  34         big_key_data,
  35         big_key_path,
  36         big_key_path_2nd_part,
  37         big_key_len,
  38 };
  39
  40 /*
  41  * Crypto operation with big_key data
  42  */
  43 enum big_key_op {
  44         BIG_KEY_ENC,
  45         BIG_KEY_DEC,
  46 };
  47
  48 /*
  49  * If the data is under this limit, there's no point creating a shm file to
  50  * hold it as the permanently resident metadata for the shmem fs will be at
  51  * least as large as the data.
  52  */
  53 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
  54
  55 /*
  56  * Key size for big_key data encryption
  57  */
  58 #define ENC_KEY_SIZE 32
  59
  60 /*
  61  * Authentication tag length
  62  */
  63 #define ENC_AUTHTAG_SIZE 16
  64
  65 /*
  66  * big_key defined keys take an arbitrary string as the description and an
  67  * arbitrary blob of data as the payload
  68  */
  69 struct key_type key_type_big_key = {
  70         .name                   = "big_key",
  71         .preparse               = big_key_preparse,
  72         .free_preparse          = big_key_free_preparse,
  73         .instantiate            = generic_key_instantiate,
  74         .revoke                 = big_key_revoke,
  75         .destroy                = big_key_destroy,
  76         .describe               = big_key_describe,
  77         .read                   = big_key_read,
  78         /* no ->update(); don't add it without changing big_key_crypt() nonce */
  79 };
  80
  81 /*
  82  * Crypto names for big_key data authenticated encryption
  83  */
  84 static const char big_key_alg_name[] = "gcm(aes)";
  85 #define BIG_KEY_IV_SIZE         GCM_AES_IV_SIZE
  86
  87 /*
  88  * Crypto algorithms for big_key data authenticated encryption
  89  */
  90 static struct crypto_aead *big_key_aead;
  91
  92 /*
  93  * Since changing the key affects the entire object, we need a mutex.
  94  */
  95 static DEFINE_MUTEX(big_key_aead_lock);
  96
  97 /*
  98  * Encrypt/decrypt big_key data
  99  */
 100 static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)
 101 {
 102         int ret;
 103         struct aead_request *aead_req;
 104         /* We always use a zero nonce. The reason we can get away with this is
 105          * because we're using a different randomly generated key for every
 106          * different encryption. Notably, too, key_type_big_key doesn't define
 107          * an .update function, so there's no chance we'll wind up reusing the
 108          * key to encrypt updated data. Simply put: one key, one encryption.
 109          */
 110         u8 zero_nonce[BIG_KEY_IV_SIZE];
 111
 112         aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
 113         if (!aead_req)
 114                 return -ENOMEM;
 115
 116         memset(zero_nonce, 0, sizeof(zero_nonce));
 117         aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce);
 118         aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
 119         aead_request_set_ad(aead_req, 0);
 120
 121         mutex_lock(&big_key_aead_lock);
 122         if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
 123                 ret = -EAGAIN;
 124                 goto error;
 125         }
 126         if (op == BIG_KEY_ENC)
 127                 ret = crypto_aead_encrypt(aead_req);
 128         else
 129                 ret = crypto_aead_decrypt(aead_req);
 130 error:
 131         mutex_unlock(&big_key_aead_lock);
 132         aead_request_free(aead_req);
 133         return ret;
 134 }
 135
 136 /*
 137  * Free up the buffer.
 138  */
 139 static void big_key_free_buffer(struct big_key_buf *buf)
 140 {
 141         unsigned int i;
 142
 143         if (buf->virt) {
 144                 memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
 145                 vunmap(buf->virt);
 146         }
 147
 148         for (i = 0; i < buf->nr_pages; i++)
 149                 if (buf->pages[i])
 150                         __free_page(buf->pages[i]);
 151
 152         kfree(buf);
 153 }
 154
 155 /*
 156  * Allocate a buffer consisting of a set of pages with a virtual mapping
 157  * applied over them.
 158  */
 159 static void *big_key_alloc_buffer(size_t len)
 160 {
 161         struct big_key_buf *buf;
 162         unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 163         unsigned int i, l;
 164
 165         buf = kzalloc(sizeof(struct big_key_buf) +
 166                       sizeof(struct page) * npg +
 167                       sizeof(struct scatterlist) * npg,
 168                       GFP_KERNEL);
 169         if (!buf)
 170                 return NULL;
 171
 172         buf->nr_pages = npg;
 173         buf->sg = (void *)(buf->pages + npg);
 174         sg_init_table(buf->sg, npg);
 175
 176         for (i = 0; i < buf->nr_pages; i++) {
 177                 buf->pages[i] = alloc_page(GFP_KERNEL);
 178                 if (!buf->pages[i])
 179                         goto nomem;
 180
 181                 l = min_t(size_t, len, PAGE_SIZE);
 182                 sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
 183                 len -= l;
 184         }
 185
 186         buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
 187         if (!buf->virt)
 188                 goto nomem;
 189
 190         return buf;
 191
 192 nomem:
 193         big_key_free_buffer(buf);
 194         return NULL;
 195 }
 196
 197 /*
 198  * Preparse a big key
 199  */
 200 int big_key_preparse(struct key_preparsed_payload *prep)
 201 {
 202         struct big_key_buf *buf;
 203         struct path *path = (struct path *)&prep->payload.data[big_key_path];
 204         struct file *file;
 205         u8 *enckey;
 206         ssize_t written;
 207         size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE;
 208         int ret;
 209
 210         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
 211                 return -EINVAL;
 212
 213         /* Set an arbitrary quota */
 214         prep->quotalen = 16;
 215
 216         prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
 217
 218         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 219                 /* Create a shmem file to store the data in.  This will permit the data
 220                  * to be swapped out if needed.
 221                  *
 222                  * File content is stored encrypted with randomly generated key.
 223                  */
 224                 loff_t pos = 0;
 225
 226                 buf = big_key_alloc_buffer(enclen);
 227                 if (!buf)
 228                         return -ENOMEM;
 229                 memcpy(buf->virt, prep->data, datalen);
 230
 231                 /* generate random key */
 232                 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
 233                 if (!enckey) {
 234                         ret = -ENOMEM;
 235                         goto error;
 236                 }
 237                 ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
 238                 if (unlikely(ret))
 239                         goto err_enckey;
 240
 241                 /* encrypt aligned data */
 242                 ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);
 243                 if (ret)
 244                         goto err_enckey;
 245
 246                 /* save aligned data to file */
 247                 file = shmem_kernel_file_setup("", enclen, 0);
 248                 if (IS_ERR(file)) {
 249                         ret = PTR_ERR(file);
 250                         goto err_enckey;
 251                 }
 252
 253                 written = kernel_write(file, buf->virt, enclen, &pos);
 254                 if (written != enclen) {
 255                         ret = written;
 256                         if (written >= 0)
 257                                 ret = -ENOMEM;
 258                         goto err_fput;
 259                 }
 260
 261                 /* Pin the mount and dentry to the key so that we can open it again
 262                  * later
 263                  */
 264                 prep->payload.data[big_key_data] = enckey;
 265                 *path = file->f_path;
 266                 path_get(path);
 267                 fput(file);
 268                 big_key_free_buffer(buf);
 269         } else {
 270                 /* Just store the data in a buffer */
 271                 void *data = kmalloc(datalen, GFP_KERNEL);
 272
 273                 if (!data)
 274                         return -ENOMEM;
 275
 276                 prep->payload.data[big_key_data] = data;
 277                 memcpy(data, prep->data, prep->datalen);
 278         }
 279         return 0;
 280
 281 err_fput:
 282         fput(file);
 283 err_enckey:
 284         kzfree(enckey);
 285 error:
 286         big_key_free_buffer(buf);
 287         return ret;
 288 }
 289
 290 /*
 291  * Clear preparsement.
 292  */
 293 void big_key_free_preparse(struct key_preparsed_payload *prep)
 294 {
 295         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
 296                 struct path *path = (struct path *)&prep->payload.data[big_key_path];
 297
 298                 path_put(path);
 299         }
 300         kzfree(prep->payload.data[big_key_data]);
 301 }
 302
 303 /*
 304  * dispose of the links from a revoked keyring
 305  * - called with the key sem write-locked
 306  */
 307 void big_key_revoke(struct key *key)
 308 {
 309         struct path *path = (struct path *)&key->payload.data[big_key_path];
 310
 311         /* clear the quota */
 312         key_payload_reserve(key, 0);
 313         if (key_is_positive(key) &&
 314             (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
 315                 vfs_truncate(path, 0);
 316 }
 317
 318 /*
 319  * dispose of the data dangling from the corpse of a big_key key
 320  */
 321 void big_key_destroy(struct key *key)
 322 {
 323         size_t datalen = (size_t)key->payload.data[big_key_len];
 324
 325         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 326                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 327
 328                 path_put(path);
 329                 path->mnt = NULL;
 330                 path->dentry = NULL;
 331         }
 332         kzfree(key->payload.data[big_key_data]);
 333         key->payload.data[big_key_data] = NULL;
 334 }
 335
 336 /*
 337  * describe the big_key key
 338  */
 339 void big_key_describe(const struct key *key, struct seq_file *m)
 340 {
 341         size_t datalen = (size_t)key->payload.data[big_key_len];
 342
 343         seq_puts(m, key->description);
 344
 345         if (key_is_positive(key))
 346                 seq_printf(m, ": %zu [%s]",
 347                            datalen,
 348                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 349 }
 350
 351 /*
 352  * read the key data
 353  * - the key's semaphore is read-locked
 354  */
 355 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 356 {
 357         size_t datalen = (size_t)key->payload.data[big_key_len];
 358         long ret;
 359
 360         if (!buffer || buflen < datalen)
 361                 return datalen;
 362
 363         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 364                 struct big_key_buf *buf;
 365                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 366                 struct file *file;
 367                 u8 *enckey = (u8 *)key->payload.data[big_key_data];
 368                 size_t enclen = datalen + ENC_AUTHTAG_SIZE;
 369                 loff_t pos = 0;
 370
 371                 buf = big_key_alloc_buffer(enclen);
 372                 if (!buf)
 373                         return -ENOMEM;
 374
 375                 file = dentry_open(path, O_RDONLY, current_cred());
 376                 if (IS_ERR(file)) {
 377                         ret = PTR_ERR(file);
 378                         goto error;
 379                 }
 380
 381                 /* read file to kernel and decrypt */
 382                 ret = kernel_read(file, buf->virt, enclen, &pos);
 383                 if (ret >= 0 && ret != enclen) {
 384                         ret = -EIO;
 385                         goto err_fput;
 386                 }
 387
 388                 ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
 389                 if (ret)
 390                         goto err_fput;
 391
 392                 ret = datalen;
 393
 394                 /* copy decrypted data to user */
 395                 if (copy_to_user(buffer, buf->virt, datalen) != 0)
 396                         ret = -EFAULT;
 397
 398 err_fput:
 399                 fput(file);
 400 error:
 401                 big_key_free_buffer(buf);
 402         } else {
 403                 ret = datalen;
 404                 if (copy_to_user(buffer, key->payload.data[big_key_data],
 405                                  datalen) != 0)
 406                         ret = -EFAULT;
 407         }
 408
 409         return ret;
 410 }
 411
 412 /*
 413  * Register key type
 414  */
 415 static int __init big_key_init(void)
 416 {
 417         int ret;
 418
 419         /* init block cipher */
 420         big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
 421         if (IS_ERR(big_key_aead)) {
 422                 ret = PTR_ERR(big_key_aead);
 423                 pr_err("Can't alloc crypto: %d\n", ret);
 424                 return ret;
 425         }
 426
 427         if (unlikely(crypto_aead_ivsize(big_key_aead) != BIG_KEY_IV_SIZE)) {
 428                 WARN(1, "big key algorithm changed?");
 429                 ret = -EINVAL;
 430                 goto free_aead;
 431         }
 432
 433         ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
 434         if (ret < 0) {
 435                 pr_err("Can't set crypto auth tag len: %d\n", ret);
 436                 goto free_aead;
 437         }
 438
 439         ret = register_key_type(&key_type_big_key);
 440         if (ret < 0) {
 441                 pr_err("Can't register type: %d\n", ret);
 442                 goto free_aead;
 443         }
 444
 445         return 0;
 446
 447 free_aead:
 448         crypto_free_aead(big_key_aead);
 449         return ret;
 450 }
 451
 452 late_initcall(big_key_init);