security/keys/big_key.c

   1 /* Large capacity key type
   2  *
   3  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/seq_file.h>
  15 #include <linux/file.h>
  16 #include <linux/shmem_fs.h>
  17 #include <linux/err.h>
  18 #include <keys/user-type.h>
  19 #include <keys/big_key-type.h>
  20
  21 MODULE_LICENSE("GPL");
  22
  23 /*
  24  * Layout of key payload words.
  25  */
  26 enum {
  27         big_key_data,
  28         big_key_path,
  29         big_key_path_2nd_part,
  30         big_key_len,
  31 };
  32
  33 /*
  34  * If the data is under this limit, there's no point creating a shm file to
  35  * hold it as the permanently resident metadata for the shmem fs will be at
  36  * least as large as the data.
  37  */
  38 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
  39
  40 /*
  41  * big_key defined keys take an arbitrary string as the description and an
  42  * arbitrary blob of data as the payload
  43  */
  44 struct key_type key_type_big_key = {
  45         .name                   = "big_key",
  46         .preparse               = big_key_preparse,
  47         .free_preparse          = big_key_free_preparse,
  48         .instantiate            = generic_key_instantiate,
  49         .revoke                 = big_key_revoke,
  50         .destroy                = big_key_destroy,
  51         .describe               = big_key_describe,
  52         .read                   = big_key_read,
  53 };
  54
  55 /*
  56  * Preparse a big key
  57  */
  58 int big_key_preparse(struct key_preparsed_payload *prep)
  59 {
  60         struct path *path = (struct path *)&prep->payload.data[big_key_path];
  61         struct file *file;
  62         ssize_t written;
  63         size_t datalen = prep->datalen;
  64         int ret;
  65
  66         ret = -EINVAL;
  67         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
  68                 goto error;
  69
  70         /* Set an arbitrary quota */
  71         prep->quotalen = 16;
  72
  73         prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
  74
  75         if (datalen > BIG_KEY_FILE_THRESHOLD) {
  76                 /* Create a shmem file to store the data in.  This will permit the data
  77                  * to be swapped out if needed.
  78                  *
  79                  * TODO: Encrypt the stored data with a temporary key.
  80                  */
  81                 file = shmem_kernel_file_setup("", datalen, 0);
  82                 if (IS_ERR(file)) {
  83                         ret = PTR_ERR(file);
  84                         goto error;
  85                 }
  86
  87                 written = kernel_write(file, prep->data, prep->datalen, 0);
  88                 if (written != datalen) {
  89                         ret = written;
  90                         if (written >= 0)
  91                                 ret = -ENOMEM;
  92                         goto err_fput;
  93                 }
  94
  95                 /* Pin the mount and dentry to the key so that we can open it again
  96                  * later
  97                  */
  98                 *path = file->f_path;
  99                 path_get(path);
 100                 fput(file);
 101         } else {
 102                 /* Just store the data in a buffer */
 103                 void *data = kmalloc(datalen, GFP_KERNEL);
 104                 if (!data)
 105                         return -ENOMEM;
 106
 107                 prep->payload.data[big_key_data] = data;
 108                 memcpy(data, prep->data, prep->datalen);
 109         }
 110         return 0;
 111
 112 err_fput:
 113         fput(file);
 114 error:
 115         return ret;
 116 }
 117
 118 /*
 119  * Clear preparsement.
 120  */
 121 void big_key_free_preparse(struct key_preparsed_payload *prep)
 122 {
 123         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
 124                 struct path *path = (struct path *)&prep->payload.data[big_key_path];
 125                 path_put(path);
 126         } else {
 127                 kfree(prep->payload.data[big_key_data]);
 128         }
 129 }
 130
 131 /*
 132  * dispose of the links from a revoked keyring
 133  * - called with the key sem write-locked
 134  */
 135 void big_key_revoke(struct key *key)
 136 {
 137         struct path *path = (struct path *)&key->payload.data[big_key_path];
 138
 139         /* clear the quota */
 140         key_payload_reserve(key, 0);
 141         if (key_is_instantiated(key) &&
 142             (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
 143                 vfs_truncate(path, 0);
 144 }
 145
 146 /*
 147  * dispose of the data dangling from the corpse of a big_key key
 148  */
 149 void big_key_destroy(struct key *key)
 150 {
 151         size_t datalen = (size_t)key->payload.data[big_key_len];
 152
 153         if (datalen) {
 154                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 155                 path_put(path);
 156                 path->mnt = NULL;
 157                 path->dentry = NULL;
 158         } else {
 159                 kfree(key->payload.data[big_key_data]);
 160                 key->payload.data[big_key_data] = NULL;
 161         }
 162 }
 163
 164 /*
 165  * describe the big_key key
 166  */
 167 void big_key_describe(const struct key *key, struct seq_file *m)
 168 {
 169         size_t datalen = (size_t)key->payload.data[big_key_len];
 170
 171         seq_puts(m, key->description);
 172
 173         if (key_is_instantiated(key))
 174                 seq_printf(m, ": %zu [%s]",
 175                            datalen,
 176                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 177 }
 178
 179 /*
 180  * read the key data
 181  * - the key's semaphore is read-locked
 182  */
 183 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 184 {
 185         size_t datalen = (size_t)key->payload.data[big_key_len];
 186         long ret;
 187
 188         if (!buffer || buflen < datalen)
 189                 return datalen;
 190
 191         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 192                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 193                 struct file *file;
 194                 loff_t pos;
 195
 196                 file = dentry_open(path, O_RDONLY, current_cred());
 197                 if (IS_ERR(file))
 198                         return PTR_ERR(file);
 199
 200                 pos = 0;
 201                 ret = vfs_read(file, buffer, datalen, &pos);
 202                 fput(file);
 203                 if (ret >= 0 && ret != datalen)
 204                         ret = -EIO;
 205         } else {
 206                 ret = datalen;
 207                 if (copy_to_user(buffer, key->payload.data[big_key_data],
 208                                  datalen) != 0)
 209                         ret = -EFAULT;
 210         }
 211
 212         return ret;
 213 }
 214
 215 /*
 216  * Module stuff
 217  */
 218 static int __init big_key_init(void)
 219 {
 220         return register_key_type(&key_type_big_key);
 221 }
 222
 223 static void __exit big_key_cleanup(void)
 224 {
 225         unregister_key_type(&key_type_big_key);
 226 }
 227
 228 module_init(big_key_init);
 229 module_exit(big_key_cleanup);