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.h"
  16 #include "xattr.h"
  17
  18 static int ext4_inode_has_encryption_context(struct inode *inode)
  19 {
  20         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
  21                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, NULL, 0);
  22         return (res > 0);
  23 }
  24
  25 /*
  26  * check whether the policy is consistent with the encryption context
  27  * for the inode
  28  */
  29 static int ext4_is_encryption_context_consistent_with_policy(
  30         struct inode *inode, const struct ext4_encryption_policy *policy)
  31 {
  32         struct ext4_encryption_context ctx;
  33         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
  34                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
  35                                  sizeof(ctx));
  36         if (res != sizeof(ctx))
  37                 return 0;
  38         return (memcmp(ctx.master_key_descriptor, policy->master_key_descriptor,
  39                         EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
  40                 (ctx.flags ==
  41                  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 ext4_create_encryption_context_from_policy(
  49         struct inode *inode, const struct ext4_encryption_policy *policy)
  50 {
  51         struct ext4_encryption_context ctx;
  52         int res = 0;
  53
  54         res = ext4_convert_inline_data(inode);
  55         if (res)
  56                 return res;
  57
  58         ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
  59         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  60                EXT4_KEY_DESCRIPTOR_SIZE);
  61         if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
  62                 printk(KERN_WARNING
  63                        "%s: Invalid contents encryption mode %d\n", __func__,
  64                         policy->contents_encryption_mode);
  65                 return -EINVAL;
  66         }
  67         if (!ext4_valid_filenames_enc_mode(policy->filenames_encryption_mode)) {
  68                 printk(KERN_WARNING
  69                        "%s: Invalid filenames encryption mode %d\n", __func__,
  70                         policy->filenames_encryption_mode);
  71                 return -EINVAL;
  72         }
  73         if (policy->flags & ~EXT4_POLICY_FLAGS_VALID)
  74                 return -EINVAL;
  75         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  76         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  77         ctx.flags = policy->flags;
  78         BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
  79         get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
  80
  81         res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
  82                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
  83                              sizeof(ctx), 0);
  84         if (!res)
  85                 ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
  86         return res;
  87 }
  88
  89 int ext4_process_policy(const struct ext4_encryption_policy *policy,
  90                         struct inode *inode)
  91 {
  92         if (policy->version != 0)
  93                 return -EINVAL;
  94
  95         if (!ext4_inode_has_encryption_context(inode)) {
  96                 if (!S_ISDIR(inode->i_mode))
  97                         return -EINVAL;
  98                 if (!ext4_empty_dir(inode))
  99                         return -ENOTEMPTY;
 100                 return ext4_create_encryption_context_from_policy(inode,
 101                                                                   policy);
 102         }
 103
 104         if (ext4_is_encryption_context_consistent_with_policy(inode, policy))
 105                 return 0;
 106
 107         printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
 108                __func__);
 109         return -EINVAL;
 110 }
 111
 112 int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
 113 {
 114         struct ext4_encryption_context ctx;
 115
 116         int res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 117                                  EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
 118                                  &ctx, sizeof(ctx));
 119         if (res != sizeof(ctx))
 120                 return -ENOENT;
 121         if (ctx.format != EXT4_ENCRYPTION_CONTEXT_FORMAT_V1)
 122                 return -EINVAL;
 123         policy->version = 0;
 124         policy->contents_encryption_mode = ctx.contents_encryption_mode;
 125         policy->filenames_encryption_mode = ctx.filenames_encryption_mode;
 126         policy->flags = ctx.flags;
 127         memcpy(&policy->master_key_descriptor, ctx.master_key_descriptor,
 128                EXT4_KEY_DESCRIPTOR_SIZE);
 129         return 0;
 130 }
 131
 132 int ext4_is_child_context_consistent_with_parent(struct inode *parent,
 133                                                  struct inode *child)
 134 {
 135         struct ext4_crypt_info *parent_ci, *child_ci;
 136         int res;
 137
 138         if ((parent == NULL) || (child == NULL)) {
 139                 pr_err("parent %p child %p\n", parent, child);
 140                 BUG_ON(1);
 141         }
 142         /* no restrictions if the parent directory is not encrypted */
 143         if (!ext4_encrypted_inode(parent))
 144                 return 1;
 145         /* if the child directory is not encrypted, this is always a problem */
 146         if (!ext4_encrypted_inode(child))
 147                 return 0;
 148         res = ext4_get_encryption_info(parent);
 149         if (res)
 150                 return 0;
 151         res = ext4_get_encryption_info(child);
 152         if (res)
 153                 return 0;
 154         parent_ci = EXT4_I(parent)->i_crypt_info;
 155         child_ci = EXT4_I(child)->i_crypt_info;
 156         if (!parent_ci && !child_ci)
 157                 return 1;
 158         if (!parent_ci || !child_ci)
 159                 return 0;
 160
 161         return (memcmp(parent_ci->ci_master_key,
 162                        child_ci->ci_master_key,
 163                        EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
 164                 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 165                 (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
 166                 (parent_ci->ci_flags == child_ci->ci_flags));
 167 }
 168
 169 /**
 170  * ext4_inherit_context() - Sets a child context from its parent
 171  * @parent: Parent inode from which the context is inherited.
 172  * @child:  Child inode that inherits the context from @parent.
 173  *
 174  * Return: Zero on success, non-zero otherwise
 175  */
 176 int ext4_inherit_context(struct inode *parent, struct inode *child)
 177 {
 178         struct ext4_encryption_context ctx;
 179         struct ext4_crypt_info *ci;
 180         int res;
 181
 182         res = ext4_get_encryption_info(parent);
 183         if (res < 0)
 184                 return res;
 185         ci = EXT4_I(parent)->i_crypt_info;
 186         if (ci == NULL)
 187                 return -ENOKEY;
 188
 189         ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
 190         if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
 191                 ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
 192                 ctx.filenames_encryption_mode =
 193                         EXT4_ENCRYPTION_MODE_AES_256_CTS;
 194                 ctx.flags = 0;
 195                 memset(ctx.master_key_descriptor, 0x42,
 196                        EXT4_KEY_DESCRIPTOR_SIZE);
 197                 res = 0;
 198         } else {
 199                 ctx.contents_encryption_mode = ci->ci_data_mode;
 200                 ctx.filenames_encryption_mode = ci->ci_filename_mode;
 201                 ctx.flags = ci->ci_flags;
 202                 memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 203                        EXT4_KEY_DESCRIPTOR_SIZE);
 204         }
 205         get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
 206         res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
 207                              EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 208                              sizeof(ctx), 0);
 209         if (!res) {
 210                 ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
 211                 ext4_clear_inode_state(child, EXT4_STATE_MAY_INLINE_DATA);
 212                 res = ext4_get_encryption_info(child);
 213         }
 214         return res;
 215 }