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  * If the data is under this limit, there's no point creating a shm file to
  25  * hold it as the permanently resident metadata for the shmem fs will be at
  26  * least as large as the data.
  27  */
  28 #define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
  29
  30 /*
  31  * big_key defined keys take an arbitrary string as the description and an
  32  * arbitrary blob of data as the payload
  33  */
  34 struct key_type key_type_big_key = {
  35         .name                   = "big_key",
  36         .preparse               = big_key_preparse,
  37         .free_preparse          = big_key_free_preparse,
  38         .instantiate            = generic_key_instantiate,
  39         .revoke                 = big_key_revoke,
  40         .destroy                = big_key_destroy,
  41         .describe               = big_key_describe,
  42         .read                   = big_key_read,
  43 };
  44
  45 /*
  46  * Preparse a big key
  47  */
  48 int big_key_preparse(struct key_preparsed_payload *prep)
  49 {
  50         struct path *path = (struct path *)&prep->payload;
  51         struct file *file;
  52         ssize_t written;
  53         size_t datalen = prep->datalen;
  54         int ret;
  55
  56         ret = -EINVAL;
  57         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
  58                 goto error;
  59
  60         /* Set an arbitrary quota */
  61         prep->quotalen = 16;
  62
  63         prep->type_data[1] = (void *)(unsigned long)datalen;
  64
  65         if (datalen > BIG_KEY_FILE_THRESHOLD) {
  66                 /* Create a shmem file to store the data in.  This will permit the data
  67                  * to be swapped out if needed.
  68                  *
  69                  * TODO: Encrypt the stored data with a temporary key.
  70                  */
  71                 file = shmem_kernel_file_setup("", datalen, 0);
  72                 if (IS_ERR(file)) {
  73                         ret = PTR_ERR(file);
  74                         goto error;
  75                 }
  76
  77                 written = kernel_write(file, prep->data, prep->datalen, 0);
  78                 if (written != datalen) {
  79                         ret = written;
  80                         if (written >= 0)
  81                                 ret = -ENOMEM;
  82                         goto err_fput;
  83                 }
  84
  85                 /* Pin the mount and dentry to the key so that we can open it again
  86                  * later
  87                  */
  88                 *path = file->f_path;
  89                 path_get(path);
  90                 fput(file);
  91         } else {
  92                 /* Just store the data in a buffer */
  93                 void *data = kmalloc(datalen, GFP_KERNEL);
  94                 if (!data)
  95                         return -ENOMEM;
  96
  97                 prep->payload[0] = memcpy(data, prep->data, prep->datalen);
  98         }
  99         return 0;
 100
 101 err_fput:
 102         fput(file);
 103 error:
 104         return ret;
 105 }
 106
 107 /*
 108  * Clear preparsement.
 109  */
 110 void big_key_free_preparse(struct key_preparsed_payload *prep)
 111 {
 112         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
 113                 struct path *path = (struct path *)&prep->payload;
 114                 path_put(path);
 115         } else {
 116                 kfree(prep->payload[0]);
 117         }
 118 }
 119
 120 /*
 121  * dispose of the links from a revoked keyring
 122  * - called with the key sem write-locked
 123  */
 124 void big_key_revoke(struct key *key)
 125 {
 126         struct path *path = (struct path *)&key->payload.data2;
 127
 128         /* clear the quota */
 129         key_payload_reserve(key, 0);
 130         if (key_is_instantiated(key) && key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD)
 131                 vfs_truncate(path, 0);
 132 }
 133
 134 /*
 135  * dispose of the data dangling from the corpse of a big_key key
 136  */
 137 void big_key_destroy(struct key *key)
 138 {
 139         if (key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD) {
 140                 struct path *path = (struct path *)&key->payload.data2;
 141                 path_put(path);
 142                 path->mnt = NULL;
 143                 path->dentry = NULL;
 144         } else {
 145                 kfree(key->payload.data);
 146                 key->payload.data = NULL;
 147         }
 148 }
 149
 150 /*
 151  * describe the big_key key
 152  */
 153 void big_key_describe(const struct key *key, struct seq_file *m)
 154 {
 155         unsigned long datalen = key->type_data.x[1];
 156
 157         seq_puts(m, key->description);
 158
 159         if (key_is_instantiated(key))
 160                 seq_printf(m, ": %lu [%s]",
 161                            datalen,
 162                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 163 }
 164
 165 /*
 166  * read the key data
 167  * - the key's semaphore is read-locked
 168  */
 169 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 170 {
 171         unsigned long datalen = key->type_data.x[1];
 172         long ret;
 173
 174         if (!buffer || buflen < datalen)
 175                 return datalen;
 176
 177         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 178                 struct path *path = (struct path *)&key->payload.data2;
 179                 struct file *file;
 180                 loff_t pos;
 181
 182                 file = dentry_open(path, O_RDONLY, current_cred());
 183                 if (IS_ERR(file))
 184                         return PTR_ERR(file);
 185
 186                 pos = 0;
 187                 ret = vfs_read(file, buffer, datalen, &pos);
 188                 fput(file);
 189                 if (ret >= 0 && ret != datalen)
 190                         ret = -EIO;
 191         } else {
 192                 ret = datalen;
 193                 if (copy_to_user(buffer, key->payload.data, datalen) != 0)
 194                         ret = -EFAULT;
 195         }
 196
 197         return ret;
 198 }
 199
 200 /*
 201  * Module stuff
 202  */
 203 static int __init big_key_init(void)
 204 {
 205         return register_key_type(&key_type_big_key);
 206 }
 207
 208 static void __exit big_key_cleanup(void)
 209 {
 210         unregister_key_type(&key_type_big_key);
 211 }
 212
 213 module_init(big_key_init);
 214 module_exit(big_key_cleanup);