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/fscrypto.h>
  14
  15 static int inode_has_encryption_context(struct inode *inode)
  16 {
  17         if (!inode->i_sb->s_cop->get_context)
  18                 return 0;
  19         return (inode->i_sb->s_cop->get_context(inode, NULL, 0L) > 0);
  20 }
  21
  22 /*
  23  * check whether the policy is consistent with the encryption context
  24  * for the inode
  25  */
  26 static int is_encryption_context_consistent_with_policy(struct inode *inode,
  27                                 const struct fscrypt_policy *policy)
  28 {
  29         struct fscrypt_context ctx;
  30         int res;
  31
  32         if (!inode->i_sb->s_cop->get_context)
  33                 return 0;
  34
  35         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  36         if (res != sizeof(ctx))
  37                 return 0;
  38
  39         return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
  40                         FS_KEY_DESCRIPTOR_SIZE) == 0 &&
  41                         (ctx.flags == policy->flags) &&
  42                         (ctx.contents_encryption_mode ==
  43                          policy->contents_encryption_mode) &&
  44                         (ctx.filenames_encryption_mode ==
  45                          policy->filenames_encryption_mode));
  46 }
  47
  48 static int create_encryption_context_from_policy(struct inode *inode,
  49                                 const struct fscrypt_policy *policy)
  50 {
  51         struct fscrypt_context ctx;
  52         int res;
  53
  54         if (!inode->i_sb->s_cop->set_context)
  55                 return -EOPNOTSUPP;
  56
  57         if (inode->i_sb->s_cop->prepare_context) {
  58                 res = inode->i_sb->s_cop->prepare_context(inode);
  59                 if (res)
  60                         return res;
  61         }
  62
  63         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  64         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  65                                         FS_KEY_DESCRIPTOR_SIZE);
  66
  67         if (!fscrypt_valid_contents_enc_mode(
  68                                 policy->contents_encryption_mode)) {
  69                 printk(KERN_WARNING
  70                        "%s: Invalid contents encryption mode %d\n", __func__,
  71                         policy->contents_encryption_mode);
  72                 return -EINVAL;
  73         }
  74
  75         if (!fscrypt_valid_filenames_enc_mode(
  76                                 policy->filenames_encryption_mode)) {
  77                 printk(KERN_WARNING
  78                         "%s: Invalid filenames encryption mode %d\n", __func__,
  79                         policy->filenames_encryption_mode);
  80                 return -EINVAL;
  81         }
  82
  83         if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  84                 return -EINVAL;
  85
  86         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  87         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  88         ctx.flags = policy->flags;
  89         BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  90         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  91
  92         return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  93 }
  94
  95 int fscrypt_process_policy(struct inode *inode,
  96                                 const struct fscrypt_policy *policy)
  97 {
  98         if (policy->version != 0)
  99                 return -EINVAL;
 100
 101         if (!inode_has_encryption_context(inode)) {
 102                 if (!inode->i_sb->s_cop->empty_dir)
 103                         return -EOPNOTSUPP;
 104                 if (!inode->i_sb->s_cop->empty_dir(inode))
 105                         return -ENOTEMPTY;
 106                 return create_encryption_context_from_policy(inode, policy);
 107         }
 108
 109         if (is_encryption_context_consistent_with_policy(inode, policy))
 110                 return 0;
 111
 112         printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
 113                __func__);
 114         return -EINVAL;
 115 }
 116 EXPORT_SYMBOL(fscrypt_process_policy);
 117
 118 int fscrypt_get_policy(struct inode *inode, struct fscrypt_policy *policy)
 119 {
 120         struct fscrypt_context ctx;
 121         int res;
 122
 123         if (!inode->i_sb->s_cop->get_context ||
 124                         !inode->i_sb->s_cop->is_encrypted(inode))
 125                 return -ENODATA;
 126
 127         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 128         if (res != sizeof(ctx))
 129                 return -ENODATA;
 130         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 131                 return -EINVAL;
 132
 133         policy->version = 0;
 134         policy->contents_encryption_mode = ctx.contents_encryption_mode;
 135         policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
 136         policy->flags = ctx.flags;
 137         memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
 138                                 FS_KEY_DESCRIPTOR_SIZE);
 139         return 0;
 140 }
 141 EXPORT_SYMBOL(fscrypt_get_policy);
 142
 143 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 144 {
 145         struct fscrypt_info *parent_ci, *child_ci;
 146         int res;
 147
 148         if ((parent == NULL) || (child == NULL)) {
 149                 printk(KERN_ERR "parent %p child %p\n", parent, child);
 150                 BUG_ON(1);
 151         }
 152
 153         /* no restrictions if the parent directory is not encrypted */
 154         if (!parent->i_sb->s_cop->is_encrypted(parent))
 155                 return 1;
 156         /* if the child directory is not encrypted, this is always a problem */
 157         if (!parent->i_sb->s_cop->is_encrypted(child))
 158                 return 0;
 159         res = fscrypt_get_encryption_info(parent);
 160         if (res)
 161                 return 0;
 162         res = fscrypt_get_encryption_info(child);
 163         if (res)
 164                 return 0;
 165         parent_ci = parent->i_crypt_info;
 166         child_ci = child->i_crypt_info;
 167         if (!parent_ci && !child_ci)
 168                 return 1;
 169         if (!parent_ci || !child_ci)
 170                 return 0;
 171
 172         return (memcmp(parent_ci->ci_master_key,
 173                         child_ci->ci_master_key,
 174                         FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 175                 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 176                 (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
 177                 (parent_ci->ci_flags == child_ci->ci_flags));
 178 }
 179 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 180
 181 /**
 182  * fscrypt_inherit_context() - Sets a child context from its parent
 183  * @parent: Parent inode from which the context is inherited.
 184  * @child:  Child inode that inherits the context from @parent.
 185  * @fs_data:  private data given by FS.
 186  * @preload:  preload child i_crypt_info
 187  *
 188  * Return: Zero on success, non-zero otherwise
 189  */
 190 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 191                                                 void *fs_data, bool preload)
 192 {
 193         struct fscrypt_context ctx;
 194         struct fscrypt_info *ci;
 195         int res;
 196
 197         if (!parent->i_sb->s_cop->set_context)
 198                 return -EOPNOTSUPP;
 199
 200         res = fscrypt_get_encryption_info(parent);
 201         if (res < 0)
 202                 return res;
 203
 204         ci = parent->i_crypt_info;
 205         if (ci == NULL)
 206                 return -ENOKEY;
 207
 208         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 209         if (fscrypt_dummy_context_enabled(parent)) {
 210                 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
 211                 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 212                 ctx.flags = 0;
 213                 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 214                 res = 0;
 215         } else {
 216                 ctx.contents_encryption_mode = ci->ci_data_mode;
 217                 ctx.filenames_encryption_mode = ci->ci_filename_mode;
 218                 ctx.flags = ci->ci_flags;
 219                 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 220                                 FS_KEY_DESCRIPTOR_SIZE);
 221         }
 222         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 223         res = parent->i_sb->s_cop->set_context(child, &ctx,
 224                                                 sizeof(ctx), fs_data);
 225         if (res)
 226                 return res;
 227         return preload ? fscrypt_get_encryption_info(child): 0;
 228 }
 229 EXPORT_SYMBOL(fscrypt_inherit_context);