fs/ext4/crypto_policy.c

   1 /*
   2  * linux/fs/ext4/crypto_policy.c
   3  *
   4  * Copyright (C) 2015, Google, Inc.
   5  *
   6  * This contains encryption policy functions for ext4
   7  *
   8  * Written by Michael Halcrow, 2015.
   9  */
  10
  11 #include <linux/random.h>
  12 #include <linux/string.h>
  13 #include <linux/types.h>
  14
  15 #include "ext4_jbd2.h"
  16 #include "ext4.h"
  17 #include "xattr.h"
  18
  19 static int ext4_inode_has_encryption_context(struct inode *inode)
  20 {
  21         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
  22                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
  23         return (res > 0);
  24 }
  25
  26 /*
  27  * check whether the policy is consistent with the encryption context
  28  * for the inode
  29  */
  30 static int ext4_is_encryption_context_consistent_with_policy(
  31         struct inode *inode, const struct ext4_encryption_policy *policy)
  32 {
  33         struct ext4_encryption_context ctx;
  34         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
  35                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
  36                                  sizeof(ctx));
  37         if (res != sizeof(ctx))
  38                 return 0;
  39         return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
  40                         EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
  41                 (ctx.flags ==
  42                  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 ext4_create_encryption_context_from_policy(
  50         struct inode *inode, const struct ext4_encryption_policy *policy)
  51 {
  52         struct ext4_encryption_context ctx;
  53         handle_t *handle;
  54         int res, res2;
  55
  56         res = ext4_convert_inline_data(inode);
  57         if (res)
  58                 return res;
  59
  60         ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
  61         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  62                EXT4_KEY_DESCRIPTOR_SIZE);
  63         if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
  64                 printk(KERN_WARNING
  65                        "%s: Invalid contents encryption mode %d\n", __func__,
  66                         policy->contents_encryption_mode);
  67                 return -EINVAL;
  68         }
  69         if (!ext4_valid_filenames_enc_mode(policy->filenames_encryption_mode)) {
  70                 printk(KERN_WARNING
  71                        "%s: Invalid filenames encryption mode %d\n", __func__,
  72                         policy->filenames_encryption_mode);
  73                 return -EINVAL;
  74         }
  75         if (policy->flags & ~EXT4_POLICY_FLAGS_VALID)
  76                 return -EINVAL;
  77         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  78         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  79         ctx.flags = policy->flags;
  80         BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
  81         get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
  82
  83         handle = ext4_journal_start(inode, EXT4_HT_MISC,
  84                                     ext4_jbd2_credits_xattr(inode));
  85         if (IS_ERR(handle))
  86                 return PTR_ERR(handle);
  87         res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
  88                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
  89                              sizeof(ctx), 0);
  90         if (!res) {
  91                 ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
  92                 res = ext4_mark_inode_dirty(handle, inode);
  93                 if (res)
  94                         EXT4_ERROR_INODE(inode, "Failed to mark inode dirty");
  95         }
  96         res2 = ext4_journal_stop(handle);
  97         if (!res)
  98                 res = res2;
  99         return res;
 100 }
 101
 102 int ext4_process_policy(const struct ext4_encryption_policy *policy,
 103                         struct inode *inode)
 104 {
 105         if (!inode_owner_or_capable(inode))
 106                 return -EACCES;
 107
 108         if (policy->version != 0)
 109                 return -EINVAL;
 110
 111         if (!ext4_inode_has_encryption_context(inode)) {
 112                 if (!S_ISDIR(inode->i_mode))
 113                         return -EINVAL;
 114                 if (!ext4_empty_dir(inode))
 115                         return -ENOTEMPTY;
 116                 return ext4_create_encryption_context_from_policy(inode,
 117                                                                   policy);
 118         }
 119
 120         if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
 121                 return 0;
 122
 123         printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
 124                __func__);
 125         return -EINVAL;
 126 }
 127
 128 int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
 129 {
 130         struct ext4_encryption_context ctx;
 131
 132         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 133                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 134                                  &ctx, sizeof(ctx));
 135         if (res != sizeof(ctx))
 136                 return -ENOENT;
 137         if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
 138                 return -EINVAL;
 139         policy->version = 0;
 140         policy->contents_encryption_mode = ctx.contents_encryption_mode;
 141         policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
 142         policy->flags = ctx.flags;
 143         memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
 144                EXT4_KEY_DESCRIPTOR_SIZE);
 145         return 0;
 146 }
 147
 148 int ext4_is_child_context_consistent_with_parent(struct inode *parent,
 149                                                  struct inode *child)
 150 {
 151         const struct ext4_crypt_info *parent_ci, *child_ci;
 152         struct ext4_encryption_context parent_ctx, child_ctx;
 153         int res;
 154
 155         /* No restrictions on file types which are never encrypted */
 156         if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
 157             !S_ISLNK(child->i_mode))
 158                 return 1;
 159
 160         /* No restrictions if the parent directory is unencrypted */
 161         if (!ext4_encrypted_inode(parent))
 162                 return 1;
 163
 164         /* Encrypted directories must not contain unencrypted files */
 165         if (!ext4_encrypted_inode(child))
 166                 return 0;
 167
 168         /*
 169          * Both parent and child are encrypted, so verify they use the same
 170          * encryption policy.  Compare the fscrypt_info structs if the keys are
 171          * available, otherwise retrieve and compare the fscrypt_contexts.
 172          *
 173          * Note that the fscrypt_context retrieval will be required frequently
 174          * when accessing an encrypted directory tree without the key.
 175          * Performance-wise this is not a big deal because we already don't
 176          * really optimize for file access without the key (to the extent that
 177          * such access is even possible), given that any attempted access
 178          * already causes a fscrypt_context retrieval and keyring search.
 179          *
 180          * In any case, if an unexpected error occurs, fall back to "forbidden".
 181          */
 182
 183         res = ext4_get_encryption_info(parent);
 184         if (res)
 185                 return 0;
 186         res = ext4_get_encryption_info(child);
 187         if (res)
 188                 return 0;
 189         parent_ci = EXT4_I(parent)->i_crypt_info;
 190         child_ci = EXT4_I(child)->i_crypt_info;
 191         if (parent_ci && child_ci) {
 192                 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
 193                               EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
 194                         (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 195                         (parent_ci->ci_filename_mode ==
 196                          child_ci->ci_filename_mode) &&
 197                         (parent_ci->ci_flags == child_ci->ci_flags);
 198         }
 199
 200         res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
 201                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 202                              &parent_ctx, sizeof(parent_ctx));
 203         if (res != sizeof(parent_ctx))
 204                 return 0;
 205
 206         res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
 207                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 208                              &child_ctx, sizeof(child_ctx));
 209         if (res != sizeof(child_ctx))
 210                 return 0;
 211
 212         return memcmp(parent_ctx.master_key_descriptor,
 213                       child_ctx.master_key_descriptor,
 214                       EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
 215                 (parent_ctx.contents_encryption_mode ==
 216                  child_ctx.contents_encryption_mode) &&
 217                 (parent_ctx.filenames_encryption_mode ==
 218                  child_ctx.filenames_encryption_mode) &&
 219                 (parent_ctx.flags == child_ctx.flags);
 220 }
 221
 222 /**
 223  * ext4_inherit_context() - Sets a child context from its parent
 224  * @parent: Parent inode from which the context is inherited.
 225  * @child:  Child inode that inherits the context from @parent.
 226  *
 227  * Return: Zero on success, non-zero otherwise
 228  */
 229 int ext4_inherit_context(struct inode *parent, struct inode *child)
 230 {
 231         struct ext4_encryption_context ctx;
 232         struct ext4_crypt_info *ci;
 233         int res;
 234
 235         res = ext4_get_encryption_info(parent);
 236         if (res < 0)
 237                 return res;
 238         ci = EXT4_I(parent)->i_crypt_info;
 239         if (ci == NULL)
 240                 return -ENOKEY;
 241
 242         ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
 243         if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
 244                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 245                 ctx.filenames_encryption_mode =
 246                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 247                 ctx.flags = 0;
 248                 memset(ctx.master_key_descriptor, 0x42,
 249                        EXT4_KEY_DESCRIPTOR_SIZE);
 250                 res = 0;
 251         } else {
 252                 ctx.contents_encryption_mode = ci->ci_data_mode;
 253                 ctx.filenames_encryption_mode = ci->ci_filename_mode;
 254                 ctx.flags = ci->ci_flags;
 255                 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 256                        EXT4_KEY_DESCRIPTOR_SIZE);
 257         }
 258         get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
 259         res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
 260                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 261                              sizeof(ctx), 0);
 262         if (!res) {
 263                 ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
 264                 ext4_clear_inode_state(child, EXT4_STATE_MAY_INLINE_DATA);
 265                 res = ext4_get_encryption_info(child);
 266         }
 267         return res;
 268 }