fs/crypto/policy.c

   1 /*
   2  * Encryption policy functions for per-file encryption support.
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  * Copyright (C) 2015, Motorola Mobility.
   6  *
   7  * Written by Michael Halcrow, 2015.
   8  * Modified by Jaegeuk Kim, 2015.
   9  */
  10
  11 #include <linux/random.h>
  12 #include <linux/string.h>
  13 #include <linux/mount.h>
  14 #include "fscrypt_private.h"
  15
  16 static int inode_has_encryption_context(struct inode *inode)
  17 {
  18         if (!inode->i_sb->s_cop->get_context)
  19                 return 0;
  20         return (inode->i_sb->s_cop->get_context(inode, NULL, 0L) > 0);
  21 }
  22
  23 /*
  24  * check whether the policy is consistent with the encryption context
  25  * for the inode
  26  */
  27 static int is_encryption_context_consistent_with_policy(struct inode *inode,
  28                                 const struct fscrypt_policy *policy)
  29 {
  30         struct fscrypt_context ctx;
  31         int res;
  32
  33         if (!inode->i_sb->s_cop->get_context)
  34                 return 0;
  35
  36         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  37         if (res != sizeof(ctx))
  38                 return 0;
  39
  40         return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
  41                         FS_KEY_DESCRIPTOR_SIZE) == 0 &&
  42                         (ctx.flags == policy->flags) &&
  43                         (ctx.contents_encryption_mode ==
  44                          policy->contents_encryption_mode) &&
  45                         (ctx.filenames_encryption_mode ==
  46                          policy->filenames_encryption_mode));
  47 }
  48
  49 static int create_encryption_context_from_policy(struct inode *inode,
  50                                 const struct fscrypt_policy *policy)
  51 {
  52         struct fscrypt_context ctx;
  53         int res;
  54
  55         if (!inode->i_sb->s_cop->set_context)
  56                 return -EOPNOTSUPP;
  57
  58         if (inode->i_sb->s_cop->prepare_context) {
  59                 res = inode->i_sb->s_cop->prepare_context(inode);
  60                 if (res)
  61                         return res;
  62         }
  63
  64         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  65         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  66                                         FS_KEY_DESCRIPTOR_SIZE);
  67
  68         if (!fscrypt_valid_contents_enc_mode(
  69                                 policy->contents_encryption_mode)) {
  70                 printk(KERN_WARNING
  71                        "%s: Invalid contents encryption mode %d\n", __func__,
  72                         policy->contents_encryption_mode);
  73                 return -EINVAL;
  74         }
  75
  76         if (!fscrypt_valid_filenames_enc_mode(
  77                                 policy->filenames_encryption_mode)) {
  78                 printk(KERN_WARNING
  79                         "%s: Invalid filenames encryption mode %d\n", __func__,
  80                         policy->filenames_encryption_mode);
  81                 return -EINVAL;
  82         }
  83
  84         if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  85                 return -EINVAL;
  86
  87         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  88         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  89         ctx.flags = policy->flags;
  90         BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  91         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  92
  93         return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  94 }
  95
  96 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
  97 {
  98         struct fscrypt_policy policy;
  99         struct inode *inode = file_inode(filp);
 100         int ret;
 101
 102         if (copy_from_user(&policy, arg, sizeof(policy)))
 103                 return -EFAULT;
 104
 105         if (!inode_owner_or_capable(inode))
 106                 return -EACCES;
 107
 108         if (policy.version != 0)
 109                 return -EINVAL;
 110
 111         ret = mnt_want_write_file(filp);
 112         if (ret)
 113                 return ret;
 114
 115         inode_lock(inode);
 116
 117         if (!inode_has_encryption_context(inode)) {
 118                 if (!S_ISDIR(inode->i_mode))
 119                         ret = -EINVAL;
 120                 else if (!inode->i_sb->s_cop->empty_dir)
 121                         ret = -EOPNOTSUPP;
 122                 else if (!inode->i_sb->s_cop->empty_dir(inode))
 123                         ret = -ENOTEMPTY;
 124                 else
 125                         ret = create_encryption_context_from_policy(inode,
 126                                                                     &policy);
 127         } else if (!is_encryption_context_consistent_with_policy(inode,
 128                                                                  &policy)) {
 129                 printk(KERN_WARNING
 130                        "%s: Policy inconsistent with encryption context\n",
 131                        __func__);
 132                 ret = -EINVAL;
 133         }
 134
 135         inode_unlock(inode);
 136
 137         mnt_drop_write_file(filp);
 138         return ret;
 139 }
 140 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
 141
 142 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 143 {
 144         struct inode *inode = file_inode(filp);
 145         struct fscrypt_context ctx;
 146         struct fscrypt_policy policy;
 147         int res;
 148
 149         if (!inode->i_sb->s_cop->get_context ||
 150                         !inode->i_sb->s_cop->is_encrypted(inode))
 151                 return -ENODATA;
 152
 153         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 154         if (res != sizeof(ctx))
 155                 return -ENODATA;
 156         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 157                 return -EINVAL;
 158
 159         policy.version = 0;
 160         policy.contents_encryption_mode = ctx.contents_encryption_mode;
 161         policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
 162         policy.flags = ctx.flags;
 163         memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
 164                                 FS_KEY_DESCRIPTOR_SIZE);
 165
 166         if (copy_to_user(arg, &policy, sizeof(policy)))
 167                 return -EFAULT;
 168         return 0;
 169 }
 170 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
 171
 172 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 173 {
 174         struct fscrypt_info *parent_ci, *child_ci;
 175         int res;
 176
 177         if ((parent == NULL) || (child == NULL)) {
 178                 printk(KERN_ERR "parent %p child %p\n", parent, child);
 179                 BUG_ON(1);
 180         }
 181
 182         /* No restrictions on file types which are never encrypted */
 183         if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
 184             !S_ISLNK(child->i_mode))
 185                 return 1;
 186
 187         /* no restrictions if the parent directory is not encrypted */
 188         if (!parent->i_sb->s_cop->is_encrypted(parent))
 189                 return 1;
 190         /* if the child directory is not encrypted, this is always a problem */
 191         if (!parent->i_sb->s_cop->is_encrypted(child))
 192                 return 0;
 193         res = fscrypt_get_encryption_info(parent);
 194         if (res)
 195                 return 0;
 196         res = fscrypt_get_encryption_info(child);
 197         if (res)
 198                 return 0;
 199         parent_ci = parent->i_crypt_info;
 200         child_ci = child->i_crypt_info;
 201         if (!parent_ci && !child_ci)
 202                 return 1;
 203         if (!parent_ci || !child_ci)
 204                 return 0;
 205
 206         return (memcmp(parent_ci->ci_master_key,
 207                         child_ci->ci_master_key,
 208                         FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 209                 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 210                 (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
 211                 (parent_ci->ci_flags == child_ci->ci_flags));
 212 }
 213 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 214
 215 /**
 216  * fscrypt_inherit_context() - Sets a child context from its parent
 217  * @parent: Parent inode from which the context is inherited.
 218  * @child:  Child inode that inherits the context from @parent.
 219  * @fs_data:  private data given by FS.
 220  * @preload:  preload child i_crypt_info
 221  *
 222  * Return: Zero on success, non-zero otherwise
 223  */
 224 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 225                                                 void *fs_data, bool preload)
 226 {
 227         struct fscrypt_context ctx;
 228         struct fscrypt_info *ci;
 229         int res;
 230
 231         if (!parent->i_sb->s_cop->set_context)
 232                 return -EOPNOTSUPP;
 233
 234         res = fscrypt_get_encryption_info(parent);
 235         if (res < 0)
 236                 return res;
 237
 238         ci = parent->i_crypt_info;
 239         if (ci == NULL)
 240                 return -ENOKEY;
 241
 242         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 243         if (fscrypt_dummy_context_enabled(parent)) {
 244                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 245                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 246                 ctx.flags = 0;
 247                 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 248                 res = 0;
 249         } else {
 250                 ctx.contents_encryption_mode = ci->ci_data_mode;
 251                 ctx.filenames_encryption_mode = ci->ci_filename_mode;
 252                 ctx.flags = ci->ci_flags;
 253                 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 254                                 FS_KEY_DESCRIPTOR_SIZE);
 255         }
 256         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 257         res = parent->i_sb->s_cop->set_context(child, &ctx,
 258                                                 sizeof(ctx), fs_data);
 259         if (res)
 260                 return res;
 261         return preload ? fscrypt_get_encryption_info(child): 0;
 262 }
 263 EXPORT_SYMBOL(fscrypt_inherit_context);