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 enum {
  24         big_key_data,
  25         big_key_path,
  26         big_key_path_2nd_part,
  27         big_key_len,
  28 };
  29
  30 /*
  31  * If the data is under this limit, there's no point creating a shm file to
  32  * hold it as the permanently resident metadata for the shmem fs will be at
  33  * least as large as the data.
  34  */
  35 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
  36
  37 /*
  38  * big_key defined keys take an arbitrary string as the description and an
  39  * arbitrary blob of data as the payload
  40  */
  41 struct key_type key_type_big_key = {
  42         .name                   = "big_key",
  43         .preparse               = big_key_preparse,
  44         .free_preparse          = big_key_free_preparse,
  45         .instantiate            = generic_key_instantiate,
  46         .revoke                 = big_key_revoke,
  47         .destroy                = big_key_destroy,
  48         .describe               = big_key_describe,
  49         .read                   = big_key_read,
  50         .update                 = big_key_update,
  51 };
  52
  53 /*
  54  * Preparse a big key
  55  */
  56 int big_key_preparse(struct key_preparsed_payload *prep)
  57 {
  58         struct path *path = (struct path *)&prep->payload.data[big_key_path];
  59         struct file *file;
  60         u8 *buf, *enckey;
  61         ssize_t written;
  62         size_t datalen = prep->datalen;
  63         size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
  64         int ret;
  65
  66         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
  67                 return -EINVAL;
  68
  69         /* Set an arbitrary quota */
  70         prep->quotalen = 16;
  71
  72         prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
  73
  74         if (datalen > BIG_KEY_FILE_THRESHOLD) {
  75                 /* Create a shmem file to store the data in.  This will permit the data
  76                  * to be swapped out if needed.
  77                  *
  78                  * File content is stored encrypted with randomly generated key.
  79                  * Since the key is random for each file, we can set the nonce
  80                  * to zero, provided we never define a ->update() call.
  81                  */
  82                 loff_t pos = 0;
  83
  84                 buf = kvmalloc(enclen, GFP_KERNEL);
  85                 if (!buf)
  86                         return -ENOMEM;
  87
  88                 /* generate random key */
  89                 enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
  90                 if (!enckey) {
  91                         ret = -ENOMEM;
  92                         goto error;
  93                 }
  94                 ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
  95                 if (unlikely(ret))
  96                         goto err_enckey;
  97
  98                 /* encrypt data */
  99                 chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
 100                                          0, enckey);
 101
 102                 /* save aligned data to file */
 103                 file = shmem_kernel_file_setup("", enclen, 0);
 104                 if (IS_ERR(file)) {
 105                         ret = PTR_ERR(file);
 106                         goto err_enckey;
 107                 }
 108
 109                 written = kernel_write(file, buf, enclen, &pos);
 110                 if (written != enclen) {
 111                         ret = written;
 112                         if (written >= 0)
 113                                 ret = -EIO;
 114                         goto err_fput;
 115                 }
 116
 117                 /* Pin the mount and dentry to the key so that we can open it again
 118                  * later
 119                  */
 120                 prep->payload.data[big_key_data] = enckey;
 121                 *path = file->f_path;
 122                 path_get(path);
 123                 fput(file);
 124                 memzero_explicit(buf, enclen);
 125                 kvfree(buf);
 126         } else {
 127                 /* Just store the data in a buffer */
 128                 void *data = kmalloc(datalen, GFP_KERNEL);
 129
 130                 if (!data)
 131                         return -ENOMEM;
 132
 133                 prep->payload.data[big_key_data] = data;
 134                 memcpy(data, prep->data, prep->datalen);
 135         }
 136         return 0;
 137
 138 err_fput:
 139         fput(file);
 140 err_enckey:
 141         kfree_sensitive(enckey);
 142 error:
 143         memzero_explicit(buf, enclen);
 144         kvfree(buf);
 145         return ret;
 146 }
 147
 148 /*
 149  * Clear preparsement.
 150  */
 151 void big_key_free_preparse(struct key_preparsed_payload *prep)
 152 {
 153         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
 154                 struct path *path = (struct path *)&prep->payload.data[big_key_path];
 155
 156                 path_put(path);
 157         }
 158         kfree_sensitive(prep->payload.data[big_key_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 path *path = (struct path *)&key->payload.data[big_key_path];
 168
 169         /* clear the quota */
 170         key_payload_reserve(key, 0);
 171         if (key_is_positive(key) &&
 172             (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
 173                 vfs_truncate(path, 0);
 174 }
 175
 176 /*
 177  * dispose of the data dangling from the corpse of a big_key key
 178  */
 179 void big_key_destroy(struct key *key)
 180 {
 181         size_t datalen = (size_t)key->payload.data[big_key_len];
 182
 183         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 184                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 185
 186                 path_put(path);
 187                 path->mnt = NULL;
 188                 path->dentry = NULL;
 189         }
 190         kfree_sensitive(key->payload.data[big_key_data]);
 191         key->payload.data[big_key_data] = NULL;
 192 }
 193
 194 /*
 195  * Update a big key
 196  */
 197 int big_key_update(struct key *key, struct key_preparsed_payload *prep)
 198 {
 199         int ret;
 200
 201         ret = key_payload_reserve(key, prep->datalen);
 202         if (ret < 0)
 203                 return ret;
 204
 205         if (key_is_positive(key))
 206                 big_key_destroy(key);
 207
 208         return generic_key_instantiate(key, prep);
 209 }
 210
 211 /*
 212  * describe the big_key key
 213  */
 214 void big_key_describe(const struct key *key, struct seq_file *m)
 215 {
 216         size_t datalen = (size_t)key->payload.data[big_key_len];
 217
 218         seq_puts(m, key->description);
 219
 220         if (key_is_positive(key))
 221                 seq_printf(m, ": %zu [%s]",
 222                            datalen,
 223                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 224 }
 225
 226 /*
 227  * read the key data
 228  * - the key's semaphore is read-locked
 229  */
 230 long big_key_read(const struct key *key, char *buffer, size_t buflen)
 231 {
 232         size_t datalen = (size_t)key->payload.data[big_key_len];
 233         long ret;
 234
 235         if (!buffer || buflen < datalen)
 236                 return datalen;
 237
 238         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 239                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 240                 struct file *file;
 241                 u8 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
 242                 size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
 243                 loff_t pos = 0;
 244
 245                 buf = kvmalloc(enclen, GFP_KERNEL);
 246                 if (!buf)
 247                         return -ENOMEM;
 248
 249                 file = dentry_open(path, O_RDONLY, current_cred());
 250                 if (IS_ERR(file)) {
 251                         ret = PTR_ERR(file);
 252                         goto error;
 253                 }
 254
 255                 /* read file to kernel and decrypt */
 256                 ret = kernel_read(file, buf, enclen, &pos);
 257                 if (ret != enclen) {
 258                         if (ret >= 0)
 259                                 ret = -EIO;
 260                         goto err_fput;
 261                 }
 262
 263                 ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
 264                                                enckey) ? 0 : -EBADMSG;
 265                 if (unlikely(ret))
 266                         goto err_fput;
 267
 268                 ret = datalen;
 269
 270                 /* copy out decrypted data */
 271                 memcpy(buffer, buf, datalen);
 272
 273 err_fput:
 274                 fput(file);
 275 error:
 276                 memzero_explicit(buf, enclen);
 277                 kvfree(buf);
 278         } else {
 279                 ret = datalen;
 280                 memcpy(buffer, key->payload.data[big_key_data], datalen);
 281         }
 282
 283         return ret;
 284 }
 285
 286 /*
 287  * Register key type
 288  */
 289 static int __init big_key_init(void)
 290 {
 291         return register_key_type(&key_type_big_key);
 292 }
 293
 294 late_initcall(big_key_init);