security/keys/big_key.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Large capacity key type
   3  *
   4  * Copyright (C) 2017-2020 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/random.h>
  16 #include <keys/user-type.h>
  17 #include <keys/big_key-type.h>
  18 #include <crypto/chacha20poly1305.h>
  19
  20 /*
  21  * Layout of key payload words.
  22  */
  23 struct big_key_payload {
  24         u8 *data;
  25         struct path path;
  26         size_t length;
  27 };
  28 #define to_big_key_payload(payload)                     \
  29         (struct big_key_payload *)((payload).data)
  30
  31 /*
  32  * If the data is under this limit, there's no point creating a shm file to
  33  * hold it as the permanently resident metadata for the shmem fs will be at
  34  * least as large as the data.
  35  */
  36 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
  37
  38 /*
  39  * big_key defined keys take an arbitrary string as the description and an
  40  * arbitrary blob of data as the payload
  41  */
  42 struct key_type key_type_big_key = {
  43         .name                   = "big_key",
  44         .preparse               = big_key_preparse,
  45         .free_preparse          = big_key_free_preparse,
  46         .instantiate            = generic_key_instantiate,
  47         .revoke                 = big_key_revoke,
  48         .destroy                = big_key_destroy,
  49         .describe               = big_key_describe,
  50         .read                   = big_key_read,
  51         .update                 = big_key_update,
  52 };
  53
  54 /*
  55  * Preparse a big key
  56  */
  57 int big_key_preparse(struct key_preparsed_payload *prep)
  58 {
  59         struct big_key_payload *payload = to_big_key_payload(prep->payload);
  60         struct file *file;
  61         u8 *buf, *enckey;
  62         ssize_t written;
  63         size_t datalen = prep->datalen;
  64         size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
  65         int ret;
  66
  67         BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data));
  68
  69         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
  70                 return -EINVAL;
  71
  72         /* Set an arbitrary quota */
  73         prep->quotalen = 16;
  74
  75         payload->length = datalen;
  76
  77         if (datalen > BIG_KEY_FILE_THRESHOLD) {
  78                 /* Create a shmem file to store the data in.  This will permit the data
  79                  * to be swapped out if needed.
  80                  *
  81                  * File content is stored encrypted with randomly generated key.
  82                  * Since the key is random for each file, we can set the nonce
  83                  * to zero, provided we never define a ->update() call.
  84                  */
  85                 loff_t pos = 0;
  86
  87                 buf = kvmalloc(enclen, GFP_KERNEL);
  88                 if (!buf)
  89                         return -ENOMEM;
  90
  91                 /* generate random key */
  92                 enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
  93                 if (!enckey) {
  94                         ret = -ENOMEM;
  95                         goto error;
  96                 }
  97                 ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
  98                 if (unlikely(ret))
  99                         goto err_enckey;
 100
 101                 /* encrypt data */
 102                 chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
 103                                          0, enckey);
 104
 105                 /* save aligned data to file */
 106                 file = shmem_kernel_file_setup("", enclen, 0);
 107                 if (IS_ERR(file)) {
 108                         ret = PTR_ERR(file);
 109                         goto err_enckey;
 110                 }
 111
 112                 written = kernel_write(file, buf, enclen, &pos);
 113                 if (written != enclen) {
 114                         ret = written;
 115                         if (written >= 0)
 116                                 ret = -EIO;
 117                         goto err_fput;
 118                 }
 119
 120                 /* Pin the mount and dentry to the key so that we can open it again
 121                  * later
 122                  */
 123                 payload->data = enckey;
 124                 payload->path = file->f_path;
 125                 path_get(&payload->path);
 126                 fput(file);
 127                 kvfree_sensitive(buf, enclen);
 128         } else {
 129                 /* Just store the data in a buffer */
 130                 void *data = kmalloc(datalen, GFP_KERNEL);
 131
 132                 if (!data)
 133                         return -ENOMEM;
 134
 135                 payload->data = data;
 136                 memcpy(data, prep->data, prep->datalen);
 137         }
 138         return 0;
 139
 140 err_fput:
 141         fput(file);
 142 err_enckey:
 143         kfree_sensitive(enckey);
 144 error:
 145         kvfree_sensitive(buf, enclen);
 146         return ret;
 147 }
 148
 149 /*
 150  * Clear preparsement.
 151  */
 152 void big_key_free_preparse(struct key_preparsed_payload *prep)
 153 {
 154         struct big_key_payload *payload = to_big_key_payload(prep->payload);
 155
 156         if (prep->datalen > BIG_KEY_FILE_THRESHOLD)
 157                 path_put(&payload->path);
 158         kfree_sensitive(payload->data);
 159 }
 160
 161 /*
 162  * dispose of the links from a revoked keyring
 163  * - called with the key sem write-locked
 164  */
 165 void big_key_revoke(struct key *key)
 166 {
 167         struct big_key_payload *payload = to_big_key_payload(key->payload);
 168
 169         /* clear the quota */
 170         key_payload_reserve(key, 0);
 171         if (key_is_positive(key) && payload->length > BIG_KEY_FILE_THRESHOLD)
 172                 vfs_truncate(&payload->path, 0);
 173 }
 174
 175 /*
 176  * dispose of the data dangling from the corpse of a big_key key
 177  */
 178 void big_key_destroy(struct key *key)
 179 {
 180         struct big_key_payload *payload = to_big_key_payload(key->payload);
 181
 182         if (payload->length > BIG_KEY_FILE_THRESHOLD) {
 183                 path_put(&payload->path);
 184                 payload->path.mnt = NULL;
 185                 payload->path.dentry = NULL;
 186         }
 187         kfree_sensitive(payload->data);
 188         payload->data = NULL;
 189 }
 190
 191 /*
 192  * Update a big key
 193  */
 194 int big_key_update(struct key *key, struct key_preparsed_payload *prep)
 195 {
 196         int ret;
 197
 198         ret = key_payload_reserve(key, prep->datalen);
 199         if (ret < 0)
 200                 return ret;
 201
 202         if (key_is_positive(key))
 203                 big_key_destroy(key);
 204
 205         return generic_key_instantiate(key, prep);
 206 }
 207
 208 /*
 209  * describe the big_key key
 210  */
 211 void big_key_describe(const struct key *key, struct seq_file *m)
 212 {
 213         struct big_key_payload *payload = to_big_key_payload(key->payload);
 214
 215         seq_puts(m, key->description);
 216
 217         if (key_is_positive(key))
 218                 seq_printf(m, ": %zu [%s]",
 219                            payload->length,
 220                            payload->length > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 221 }
 222
 223 /*
 224  * read the key data
 225  * - the key's semaphore is read-locked
 226  */
 227 long big_key_read(const struct key *key, char *buffer, size_t buflen)
 228 {
 229         struct big_key_payload *payload = to_big_key_payload(key->payload);
 230         size_t datalen = payload->length;
 231         long ret;
 232
 233         if (!buffer || buflen < datalen)
 234                 return datalen;
 235
 236         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 237                 struct file *file;
 238                 u8 *buf, *enckey = payload->data;
 239                 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
 240                 loff_t pos = 0;
 241
 242                 buf = kvmalloc(enclen, GFP_KERNEL);
 243                 if (!buf)
 244                         return -ENOMEM;
 245
 246                 file = dentry_open(&payload->path, O_RDONLY, current_cred());
 247                 if (IS_ERR(file)) {
 248                         ret = PTR_ERR(file);
 249                         goto error;
 250                 }
 251
 252                 /* read file to kernel and decrypt */
 253                 ret = kernel_read(file, buf, enclen, &pos);
 254                 if (ret != enclen) {
 255                         if (ret >= 0)
 256                                 ret = -EIO;
 257                         goto err_fput;
 258                 }
 259
 260                 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
 261                                                enckey) ? 0 : -EBADMSG;
 262                 if (unlikely(ret))
 263                         goto err_fput;
 264
 265                 ret = datalen;
 266
 267                 /* copy out decrypted data */
 268                 memcpy(buffer, buf, datalen);
 269
 270 err_fput:
 271                 fput(file);
 272 error:
 273                 kvfree_sensitive(buf, enclen);
 274         } else {
 275                 ret = datalen;
 276                 memcpy(buffer, payload->data, datalen);
 277         }
 278
 279         return ret;
 280 }
 281
 282 /*
 283  * Register key type
 284  */
 285 static int __init big_key_init(void)
 286 {
 287         return register_key_type(&key_type_big_key);
 288 }
 289
 290 late_initcall(big_key_init);