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 /*
  17  * check whether an encryption policy is consistent with an encryption context
  18  */
  19 static bool is_encryption_context_consistent_with_policy(
  20                                 const struct fscrypt_context *ctx,
  21                                 const struct fscrypt_policy *policy)
  22 {
  23         return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
  24                       FS_KEY_DESCRIPTOR_SIZE) == 0 &&
  25                 (ctx->flags == policy->flags) &&
  26                 (ctx->contents_encryption_mode ==
  27                  policy->contents_encryption_mode) &&
  28                 (ctx->filenames_encryption_mode ==
  29                  policy->filenames_encryption_mode);
  30 }
  31
  32 static int create_encryption_context_from_policy(struct inode *inode,
  33                                 const struct fscrypt_policy *policy)
  34 {
  35         struct fscrypt_context ctx;
  36         int res;
  37
  38         if (!inode->i_sb->s_cop->set_context)
  39                 return -EOPNOTSUPP;
  40
  41         if (inode->i_sb->s_cop->prepare_context) {
  42                 res = inode->i_sb->s_cop->prepare_context(inode);
  43                 if (res)
  44                         return res;
  45         }
  46
  47         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  48         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  49                                         FS_KEY_DESCRIPTOR_SIZE);
  50
  51         if (!fscrypt_valid_contents_enc_mode(
  52                                 policy->contents_encryption_mode))
  53                 return -EINVAL;
  54
  55         if (!fscrypt_valid_filenames_enc_mode(
  56                                 policy->filenames_encryption_mode))
  57                 return -EINVAL;
  58
  59         if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  60                 return -EINVAL;
  61
  62         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  63         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  64         ctx.flags = policy->flags;
  65         BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  66         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  67
  68         return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  69 }
  70
  71 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
  72 {
  73         struct fscrypt_policy policy;
  74         struct inode *inode = file_inode(filp);
  75         int ret;
  76         struct fscrypt_context ctx;
  77
  78         if (copy_from_user(&policy, arg, sizeof(policy)))
  79                 return -EFAULT;
  80
  81         if (!inode_owner_or_capable(inode))
  82                 return -EACCES;
  83
  84         if (policy.version != 0)
  85                 return -EINVAL;
  86
  87         ret = mnt_want_write_file(filp);
  88         if (ret)
  89                 return ret;
  90
  91         inode_lock(inode);
  92
  93         ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  94         if (ret == -ENODATA) {
  95                 if (!S_ISDIR(inode->i_mode))
  96                         ret = -ENOTDIR;
  97                 else if (!inode->i_sb->s_cop->empty_dir)
  98                         ret = -EOPNOTSUPP;
  99                 else if (!inode->i_sb->s_cop->empty_dir(inode))
 100                         ret = -ENOTEMPTY;
 101                 else
 102                         ret = create_encryption_context_from_policy(inode,
 103                                                                     &policy);
 104         } else if (ret == sizeof(ctx) &&
 105                    is_encryption_context_consistent_with_policy(&ctx,
 106                                                                 &policy)) {
 107                 /* The file already uses the same encryption policy. */
 108                 ret = 0;
 109         } else if (ret >= 0 || ret == -ERANGE) {
 110                 /* The file already uses a different encryption policy. */
 111                 ret = -EEXIST;
 112         }
 113
 114         inode_unlock(inode);
 115
 116         mnt_drop_write_file(filp);
 117         return ret;
 118 }
 119 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
 120
 121 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 122 {
 123         struct inode *inode = file_inode(filp);
 124         struct fscrypt_context ctx;
 125         struct fscrypt_policy policy;
 126         int res;
 127
 128         if (!inode->i_sb->s_cop->get_context ||
 129                         !inode->i_sb->s_cop->is_encrypted(inode))
 130                 return -ENODATA;
 131
 132         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 133         if (res < 0 && res != -ERANGE)
 134                 return res;
 135         if (res != sizeof(ctx))
 136                 return -EINVAL;
 137         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 138                 return -EINVAL;
 139
 140         policy.version = 0;
 141         policy.contents_encryption_mode = ctx.contents_encryption_mode;
 142         policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
 143         policy.flags = ctx.flags;
 144         memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
 145                                 FS_KEY_DESCRIPTOR_SIZE);
 146
 147         if (copy_to_user(arg, &policy, sizeof(policy)))
 148                 return -EFAULT;
 149         return 0;
 150 }
 151 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
 152
 153 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 154 {
 155         struct fscrypt_info *parent_ci, *child_ci;
 156         int res;
 157
 158         if ((parent == NULL) || (child == NULL)) {
 159                 printk(KERN_ERR "parent %p child %p\n", parent, child);
 160                 BUG_ON(1);
 161         }
 162
 163         /* No restrictions on file types which are never encrypted */
 164         if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
 165             !S_ISLNK(child->i_mode))
 166                 return 1;
 167
 168         /* no restrictions if the parent directory is not encrypted */
 169         if (!parent->i_sb->s_cop->is_encrypted(parent))
 170                 return 1;
 171         /* if the child directory is not encrypted, this is always a problem */
 172         if (!parent->i_sb->s_cop->is_encrypted(child))
 173                 return 0;
 174         res = fscrypt_get_encryption_info(parent);
 175         if (res)
 176                 return 0;
 177         res = fscrypt_get_encryption_info(child);
 178         if (res)
 179                 return 0;
 180         parent_ci = parent->i_crypt_info;
 181         child_ci = child->i_crypt_info;
 182         if (!parent_ci && !child_ci)
 183                 return 1;
 184         if (!parent_ci || !child_ci)
 185                 return 0;
 186
 187         return (memcmp(parent_ci->ci_master_key,
 188                         child_ci->ci_master_key,
 189                         FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 190                 (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 191                 (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
 192                 (parent_ci->ci_flags == child_ci->ci_flags));
 193 }
 194 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 195
 196 /**
 197  * fscrypt_inherit_context() - Sets a child context from its parent
 198  * @parent: Parent inode from which the context is inherited.
 199  * @child:  Child inode that inherits the context from @parent.
 200  * @fs_data:  private data given by FS.
 201  * @preload:  preload child i_crypt_info if true
 202  *
 203  * Return: 0 on success, -errno on failure
 204  */
 205 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 206                                                 void *fs_data, bool preload)
 207 {
 208         struct fscrypt_context ctx;
 209         struct fscrypt_info *ci;
 210         int res;
 211
 212         if (!parent->i_sb->s_cop->set_context)
 213                 return -EOPNOTSUPP;
 214
 215         res = fscrypt_get_encryption_info(parent);
 216         if (res < 0)
 217                 return res;
 218
 219         ci = parent->i_crypt_info;
 220         if (ci == NULL)
 221                 return -ENOKEY;
 222
 223         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 224         ctx.contents_encryption_mode = ci->ci_data_mode;
 225         ctx.filenames_encryption_mode = ci->ci_filename_mode;
 226         ctx.flags = ci->ci_flags;
 227         memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 228                FS_KEY_DESCRIPTOR_SIZE);
 229         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 230         res = parent->i_sb->s_cop->set_context(child, &ctx,
 231                                                 sizeof(ctx), fs_data);
 232         if (res)
 233                 return res;
 234         return preload ? fscrypt_get_encryption_info(child): 0;
 235 }
 236 EXPORT_SYMBOL(fscrypt_inherit_context);