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         .def_lookup_type        = KEYRING_SEARCH_LOOKUP_DIRECT,
  37         .instantiate            = big_key_instantiate,
  38         .match                  = user_match,
  39         .revoke                 = big_key_revoke,
  40         .destroy                = big_key_destroy,
  41         .describe               = big_key_describe,
  42         .read                   = big_key_read,
  43 };
  44
  45 /*
  46  * Instantiate a big key
  47  */
  48 int big_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
  49 {
  50         struct path *path = (struct path *)&key->payload.data2;
  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         ret = key_payload_reserve(key, 16);
  62         if (ret < 0)
  63                 goto error;
  64
  65         key->type_data.x[1] = datalen;
  66
  67         if (datalen > BIG_KEY_FILE_THRESHOLD) {
  68                 /* Create a shmem file to store the data in.  This will permit the data
  69                  * to be swapped out if needed.
  70                  *
  71                  * TODO: Encrypt the stored data with a temporary key.
  72                  */
  73                 file = shmem_kernel_file_setup("", datalen, 0);
  74                 if (IS_ERR(file)) {
  75                         ret = PTR_ERR(file);
  76                         goto err_quota;
  77                 }
  78
  79                 written = kernel_write(file, prep->data, prep->datalen, 0);
  80                 if (written != datalen) {
  81                         ret = written;
  82                         if (written >= 0)
  83                                 ret = -ENOMEM;
  84                         goto err_fput;
  85                 }
  86
  87                 /* Pin the mount and dentry to the key so that we can open it again
  88                  * later
  89                  */
  90                 *path = file->f_path;
  91                 path_get(path);
  92                 fput(file);
  93         } else {
  94                 /* Just store the data in a buffer */
  95                 void *data = kmalloc(datalen, GFP_KERNEL);
  96                 if (!data) {
  97                         ret = -ENOMEM;
  98                         goto err_quota;
  99                 }
 100
 101                 key->payload.data = memcpy(data, prep->data, prep->datalen);
 102         }
 103         return 0;
 104
 105 err_fput:
 106         fput(file);
 107 err_quota:
 108         key_payload_reserve(key, 0);
 109 error:
 110         return ret;
 111 }
 112
 113 /*
 114  * dispose of the links from a revoked keyring
 115  * - called with the key sem write-locked
 116  */
 117 void big_key_revoke(struct key *key)
 118 {
 119         struct path *path = (struct path *)&key->payload.data2;
 120
 121         /* clear the quota */
 122         key_payload_reserve(key, 0);
 123         if (key_is_instantiated(key) && key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD)
 124                 vfs_truncate(path, 0);
 125 }
 126
 127 /*
 128  * dispose of the data dangling from the corpse of a big_key key
 129  */
 130 void big_key_destroy(struct key *key)
 131 {
 132         if (key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD) {
 133                 struct path *path = (struct path *)&key->payload.data2;
 134                 path_put(path);
 135                 path->mnt = NULL;
 136                 path->dentry = NULL;
 137         } else {
 138                 kfree(key->payload.data);
 139                 key->payload.data = NULL;
 140         }
 141 }
 142
 143 /*
 144  * describe the big_key key
 145  */
 146 void big_key_describe(const struct key *key, struct seq_file *m)
 147 {
 148         unsigned long datalen = key->type_data.x[1];
 149
 150         seq_puts(m, key->description);
 151
 152         if (key_is_instantiated(key))
 153                 seq_printf(m, ": %lu [%s]",
 154                            datalen,
 155                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 156 }
 157
 158 /*
 159  * read the key data
 160  * - the key's semaphore is read-locked
 161  */
 162 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 163 {
 164         unsigned long datalen = key->type_data.x[1];
 165         long ret;
 166
 167         if (!buffer || buflen < datalen)
 168                 return datalen;
 169
 170         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 171                 struct path *path = (struct path *)&key->payload.data2;
 172                 struct file *file;
 173                 loff_t pos;
 174
 175                 file = dentry_open(path, O_RDONLY, current_cred());
 176                 if (IS_ERR(file))
 177                         return PTR_ERR(file);
 178
 179                 pos = 0;
 180                 ret = vfs_read(file, buffer, datalen, &pos);
 181                 fput(file);
 182                 if (ret >= 0 && ret != datalen)
 183                         ret = -EIO;
 184         } else {
 185                 ret = datalen;
 186                 if (copy_to_user(buffer, key->payload.data, datalen) != 0)
 187                         ret = -EFAULT;
 188         }
 189
 190         return ret;
 191 }
 192
 193 /*
 194  * Module stuff
 195  */
 196 static int __init big_key_init(void)
 197 {
 198         return register_key_type(&key_type_big_key);
 199 }
 200
 201 static void __exit big_key_cleanup(void)
 202 {
 203         unregister_key_type(&key_type_big_key);
 204 }
 205
 206 module_init(big_key_init);
 207 module_exit(big_key_cleanup);