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 (IS_DEADDIR(inode))
 115                         return -ENOENT;
 116                 if (!ext4_empty_dir(inode))
 117                         return -ENOTEMPTY;
 118                 return ext4_create_encryption_context_from_policy(inode,
 119                                                                   policy);
 120         }
 121
 122         if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
 123                 return 0;
 124
 125         printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
 126                __func__);
 127         return -EINVAL;
 128 }
 129
 130 int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
 131 {
 132         struct ext4_encryption_context ctx;
 133
 134         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 135                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 136                                  &ctx, sizeof(ctx));
 137         if (res != sizeof(ctx))
 138                 return -ENOENT;
 139         if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
 140                 return -EINVAL;
 141         policy->version = 0;
 142         policy->contents_encryption_mode = ctx.contents_encryption_mode;
 143         policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
 144         policy->flags = ctx.flags;
 145         memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
 146                EXT4_KEY_DESCRIPTOR_SIZE);
 147         return 0;
 148 }
 149
 150 int ext4_is_child_context_consistent_with_parent(struct inode *parent,
 151                                                  struct inode *child)
 152 {
 153         const struct ext4_crypt_info *parent_ci, *child_ci;
 154         struct ext4_encryption_context parent_ctx, child_ctx;
 155         int res;
 156
 157         /* No restrictions on file types which are never encrypted */
 158         if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
 159             !S_ISLNK(child->i_mode))
 160                 return 1;
 161
 162         /* No restrictions if the parent directory is unencrypted */
 163         if (!ext4_encrypted_inode(parent))
 164                 return 1;
 165
 166         /* Encrypted directories must not contain unencrypted files */
 167         if (!ext4_encrypted_inode(child))
 168                 return 0;
 169
 170         /*
 171          * Both parent and child are encrypted, so verify they use the same
 172          * encryption policy.  Compare the fscrypt_info structs if the keys are
 173          * available, otherwise retrieve and compare the fscrypt_contexts.
 174          *
 175          * Note that the fscrypt_context retrieval will be required frequently
 176          * when accessing an encrypted directory tree without the key.
 177          * Performance-wise this is not a big deal because we already don't
 178          * really optimize for file access without the key (to the extent that
 179          * such access is even possible), given that any attempted access
 180          * already causes a fscrypt_context retrieval and keyring search.
 181          *
 182          * In any case, if an unexpected error occurs, fall back to "forbidden".
 183          */
 184
 185         res = ext4_get_encryption_info(parent);
 186         if (res)
 187                 return 0;
 188         res = ext4_get_encryption_info(child);
 189         if (res)
 190                 return 0;
 191         parent_ci = EXT4_I(parent)->i_crypt_info;
 192         child_ci = EXT4_I(child)->i_crypt_info;
 193         if (parent_ci && child_ci) {
 194                 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
 195                               EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
 196                         (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 197                         (parent_ci->ci_filename_mode ==
 198                          child_ci->ci_filename_mode) &&
 199                         (parent_ci->ci_flags == child_ci->ci_flags);
 200         }
 201
 202         res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
 203                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 204                              &parent_ctx, sizeof(parent_ctx));
 205         if (res != sizeof(parent_ctx))
 206                 return 0;
 207
 208         res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
 209                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 210                              &child_ctx, sizeof(child_ctx));
 211         if (res != sizeof(child_ctx))
 212                 return 0;
 213
 214         return memcmp(parent_ctx.master_key_descriptor,
 215                       child_ctx.master_key_descriptor,
 216                       EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
 217                 (parent_ctx.contents_encryption_mode ==
 218                  child_ctx.contents_encryption_mode) &&
 219                 (parent_ctx.filenames_encryption_mode ==
 220                  child_ctx.filenames_encryption_mode) &&
 221                 (parent_ctx.flags == child_ctx.flags);
 222 }
 223
 224 /**
 225  * ext4_inherit_context() - Sets a child context from its parent
 226  * @parent: Parent inode from which the context is inherited.
 227  * @child:  Child inode that inherits the context from @parent.
 228  *
 229  * Return: Zero on success, non-zero otherwise
 230  */
 231 int ext4_inherit_context(struct inode *parent, struct inode *child)
 232 {
 233         struct ext4_encryption_context ctx;
 234         struct ext4_crypt_info *ci;
 235         int res;
 236
 237         res = ext4_get_encryption_info(parent);
 238         if (res < 0)
 239                 return res;
 240         ci = EXT4_I(parent)->i_crypt_info;
 241         if (ci == NULL)
 242                 return -ENOKEY;
 243
 244         ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
 245         if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
 246                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 247                 ctx.filenames_encryption_mode =
 248                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 249                 ctx.flags = 0;
 250                 memset(ctx.master_key_descriptor, 0x42,
 251                        EXT4_KEY_DESCRIPTOR_SIZE);
 252                 res = 0;
 253         } else {
 254                 ctx.contents_encryption_mode = ci->ci_data_mode;
 255                 ctx.filenames_encryption_mode = ci->ci_filename_mode;
 256                 ctx.flags = ci->ci_flags;
 257                 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 258                        EXT4_KEY_DESCRIPTOR_SIZE);
 259         }
 260         get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
 261         res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
 262                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 263                              sizeof(ctx), 0);
 264         if (!res) {
 265                 ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
 266                 ext4_clear_inode_state(child, EXT4_STATE_MAY_INLINE_DATA);
 267                 res = ext4_get_encryption_info(child);
 268         }
 269         return res;
 270 }