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