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/init.h>
  13 #include <linux/seq_file.h>
  14 #include <linux/file.h>
  15 #include <linux/shmem_fs.h>
  16 #include <linux/err.h>
  17 #include <keys/user-type.h>
  18 #include <keys/big_key-type.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 };
  51
  52 /*
  53  * Preparse a big key
  54  */
  55 int big_key_preparse(struct key_preparsed_payload *prep)
  56 {
  57         struct path *path = (struct path *)&prep->payload.data[big_key_path];
  58         struct file *file;
  59         ssize_t written;
  60         size_t datalen = prep->datalen;
  61         int ret;
  62
  63         ret = -EINVAL;
  64         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
  65                 goto error;
  66
  67         /* Set an arbitrary quota */
  68         prep->quotalen = 16;
  69
  70         prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
  71
  72         if (datalen > BIG_KEY_FILE_THRESHOLD) {
  73                 /* Create a shmem file to store the data in.  This will permit the data
  74                  * to be swapped out if needed.
  75                  *
  76                  * TODO: Encrypt the stored data with a temporary key.
  77                  */
  78                 file = shmem_kernel_file_setup("", datalen, 0);
  79                 if (IS_ERR(file)) {
  80                         ret = PTR_ERR(file);
  81                         goto error;
  82                 }
  83
  84                 written = kernel_write(file, prep->data, prep->datalen, 0);
  85                 if (written != datalen) {
  86                         ret = written;
  87                         if (written >= 0)
  88                                 ret = -ENOMEM;
  89                         goto err_fput;
  90                 }
  91
  92                 /* Pin the mount and dentry to the key so that we can open it again
  93                  * later
  94                  */
  95                 *path = file->f_path;
  96                 path_get(path);
  97                 fput(file);
  98         } else {
  99                 /* Just store the data in a buffer */
 100                 void *data = kmalloc(datalen, GFP_KERNEL);
 101                 if (!data)
 102                         return -ENOMEM;
 103
 104                 prep->payload.data[big_key_data] = data;
 105                 memcpy(data, prep->data, prep->datalen);
 106         }
 107         return 0;
 108
 109 err_fput:
 110         fput(file);
 111 error:
 112         return ret;
 113 }
 114
 115 /*
 116  * Clear preparsement.
 117  */
 118 void big_key_free_preparse(struct key_preparsed_payload *prep)
 119 {
 120         if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
 121                 struct path *path = (struct path *)&prep->payload.data[big_key_path];
 122                 path_put(path);
 123         } else {
 124                 kfree(prep->payload.data[big_key_data]);
 125         }
 126 }
 127
 128 /*
 129  * dispose of the links from a revoked keyring
 130  * - called with the key sem write-locked
 131  */
 132 void big_key_revoke(struct key *key)
 133 {
 134         struct path *path = (struct path *)&key->payload.data[big_key_path];
 135
 136         /* clear the quota */
 137         key_payload_reserve(key, 0);
 138         if (key_is_instantiated(key) &&
 139             (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
 140                 vfs_truncate(path, 0);
 141 }
 142
 143 /*
 144  * dispose of the data dangling from the corpse of a big_key key
 145  */
 146 void big_key_destroy(struct key *key)
 147 {
 148         size_t datalen = (size_t)key->payload.data[big_key_len];
 149
 150         if (datalen) {
 151                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 152                 path_put(path);
 153                 path->mnt = NULL;
 154                 path->dentry = NULL;
 155         } else {
 156                 kfree(key->payload.data[big_key_data]);
 157                 key->payload.data[big_key_data] = NULL;
 158         }
 159 }
 160
 161 /*
 162  * describe the big_key key
 163  */
 164 void big_key_describe(const struct key *key, struct seq_file *m)
 165 {
 166         size_t datalen = (size_t)key->payload.data[big_key_len];
 167
 168         seq_puts(m, key->description);
 169
 170         if (key_is_instantiated(key))
 171                 seq_printf(m, ": %zu [%s]",
 172                            datalen,
 173                            datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
 174 }
 175
 176 /*
 177  * read the key data
 178  * - the key's semaphore is read-locked
 179  */
 180 long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
 181 {
 182         size_t datalen = (size_t)key->payload.data[big_key_len];
 183         long ret;
 184
 185         if (!buffer || buflen < datalen)
 186                 return datalen;
 187
 188         if (datalen > BIG_KEY_FILE_THRESHOLD) {
 189                 struct path *path = (struct path *)&key->payload.data[big_key_path];
 190                 struct file *file;
 191                 loff_t pos;
 192
 193                 file = dentry_open(path, O_RDONLY, current_cred());
 194                 if (IS_ERR(file))
 195                         return PTR_ERR(file);
 196
 197                 pos = 0;
 198                 ret = vfs_read(file, buffer, datalen, &pos);
 199                 fput(file);
 200                 if (ret >= 0 && ret != datalen)
 201                         ret = -EIO;
 202         } else {
 203                 ret = datalen;
 204                 if (copy_to_user(buffer, key->payload.data[big_key_data],
 205                                  datalen) != 0)
 206                         ret = -EFAULT;
 207         }
 208
 209         return ret;
 210 }
 211
 212 static int __init big_key_init(void)
 213 {
 214         return register_key_type(&key_type_big_key);
 215 }
 216 device_initcall(big_key_init);