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         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  38         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  39                                         FS_KEY_DESCRIPTOR_SIZE);
  40
  41         if (!fscrypt_valid_contents_enc_mode(
  42                                 policy->contents_encryption_mode))
  43                 return -EINVAL;
  44
  45         if (!fscrypt_valid_filenames_enc_mode(
  46                                 policy->filenames_encryption_mode))
  47                 return -EINVAL;
  48
  49         if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  50                 return -EINVAL;
  51
  52         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  53         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  54         ctx.flags = policy->flags;
  55         BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  56         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  57
  58         return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  59 }
  60
  61 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
  62 {
  63         struct fscrypt_policy policy;
  64         struct inode *inode = file_inode(filp);
  65         int ret;
  66         struct fscrypt_context ctx;
  67
  68         if (copy_from_user(&policy, arg, sizeof(policy)))
  69                 return -EFAULT;
  70
  71         if (!inode_owner_or_capable(inode))
  72                 return -EACCES;
  73
  74         if (policy.version != 0)
  75                 return -EINVAL;
  76
  77         ret = mnt_want_write_file(filp);
  78         if (ret)
  79                 return ret;
  80
  81         inode_lock(inode);
  82
  83         ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  84         if (ret == -ENODATA) {
  85                 if (!S_ISDIR(inode->i_mode))
  86                         ret = -ENOTDIR;
  87                 else if (!inode->i_sb->s_cop->empty_dir(inode))
  88                         ret = -ENOTEMPTY;
  89                 else
  90                         ret = create_encryption_context_from_policy(inode,
  91                                                                     &policy);
  92         } else if (ret == sizeof(ctx) &&
  93                    is_encryption_context_consistent_with_policy(&ctx,
  94                                                                 &policy)) {
  95                 /* The file already uses the same encryption policy. */
  96                 ret = 0;
  97         } else if (ret >= 0 || ret == -ERANGE) {
  98                 /* The file already uses a different encryption policy. */
  99                 ret = -EEXIST;
 100         }
 101
 102         inode_unlock(inode);
 103
 104         mnt_drop_write_file(filp);
 105         return ret;
 106 }
 107 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
 108
 109 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 110 {
 111         struct inode *inode = file_inode(filp);
 112         struct fscrypt_context ctx;
 113         struct fscrypt_policy policy;
 114         int res;
 115
 116         if (!inode->i_sb->s_cop->is_encrypted(inode))
 117                 return -ENODATA;
 118
 119         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 120         if (res < 0 && res != -ERANGE)
 121                 return res;
 122         if (res != sizeof(ctx))
 123                 return -EINVAL;
 124         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 125                 return -EINVAL;
 126
 127         policy.version = 0;
 128         policy.contents_encryption_mode = ctx.contents_encryption_mode;
 129         policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
 130         policy.flags = ctx.flags;
 131         memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
 132                                 FS_KEY_DESCRIPTOR_SIZE);
 133
 134         if (copy_to_user(arg, &policy, sizeof(policy)))
 135                 return -EFAULT;
 136         return 0;
 137 }
 138 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
 139
 140 /**
 141  * fscrypt_has_permitted_context() - is a file's encryption policy permitted
 142  *                                   within its directory?
 143  *
 144  * @parent: inode for parent directory
 145  * @child: inode for file being looked up, opened, or linked into @parent
 146  *
 147  * Filesystems must call this before permitting access to an inode in a
 148  * situation where the parent directory is encrypted (either before allowing
 149  * ->lookup() to succeed, or for a regular file before allowing it to be opened)
 150  * and before any operation that involves linking an inode into an encrypted
 151  * directory, including link, rename, and cross rename.  It enforces the
 152  * constraint that within a given encrypted directory tree, all files use the
 153  * same encryption policy.  The pre-access check is needed to detect potentially
 154  * malicious offline violations of this constraint, while the link and rename
 155  * checks are needed to prevent online violations of this constraint.
 156  *
 157  * Return: 1 if permitted, 0 if forbidden.  If forbidden, the caller must fail
 158  * the filesystem operation with EPERM.
 159  */
 160 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 161 {
 162         const struct fscrypt_operations *cops = parent->i_sb->s_cop;
 163         const struct fscrypt_info *parent_ci, *child_ci;
 164         struct fscrypt_context parent_ctx, child_ctx;
 165         int res;
 166
 167         /* No restrictions on file types which are never encrypted */
 168         if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
 169             !S_ISLNK(child->i_mode))
 170                 return 1;
 171
 172         /* No restrictions if the parent directory is unencrypted */
 173         if (!cops->is_encrypted(parent))
 174                 return 1;
 175
 176         /* Encrypted directories must not contain unencrypted files */
 177         if (!cops->is_encrypted(child))
 178                 return 0;
 179
 180         /*
 181          * Both parent and child are encrypted, so verify they use the same
 182          * encryption policy.  Compare the fscrypt_info structs if the keys are
 183          * available, otherwise retrieve and compare the fscrypt_contexts.
 184          *
 185          * Note that the fscrypt_context retrieval will be required frequently
 186          * when accessing an encrypted directory tree without the key.
 187          * Performance-wise this is not a big deal because we already don't
 188          * really optimize for file access without the key (to the extent that
 189          * such access is even possible), given that any attempted access
 190          * already causes a fscrypt_context retrieval and keyring search.
 191          *
 192          * In any case, if an unexpected error occurs, fall back to "forbidden".
 193          */
 194
 195         res = fscrypt_get_encryption_info(parent);
 196         if (res)
 197                 return 0;
 198         res = fscrypt_get_encryption_info(child);
 199         if (res)
 200                 return 0;
 201         parent_ci = parent->i_crypt_info;
 202         child_ci = child->i_crypt_info;
 203
 204         if (parent_ci && child_ci) {
 205                 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
 206                               FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 207                         (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 208                         (parent_ci->ci_filename_mode ==
 209                          child_ci->ci_filename_mode) &&
 210                         (parent_ci->ci_flags == child_ci->ci_flags);
 211         }
 212
 213         res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
 214         if (res != sizeof(parent_ctx))
 215                 return 0;
 216
 217         res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
 218         if (res != sizeof(child_ctx))
 219                 return 0;
 220
 221         return memcmp(parent_ctx.master_key_descriptor,
 222                       child_ctx.master_key_descriptor,
 223                       FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 224                 (parent_ctx.contents_encryption_mode ==
 225                  child_ctx.contents_encryption_mode) &&
 226                 (parent_ctx.filenames_encryption_mode ==
 227                  child_ctx.filenames_encryption_mode) &&
 228                 (parent_ctx.flags == child_ctx.flags);
 229 }
 230 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 231
 232 /**
 233  * fscrypt_inherit_context() - Sets a child context from its parent
 234  * @parent: Parent inode from which the context is inherited.
 235  * @child:  Child inode that inherits the context from @parent.
 236  * @fs_data:  private data given by FS.
 237  * @preload:  preload child i_crypt_info if true
 238  *
 239  * Return: 0 on success, -errno on failure
 240  */
 241 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 242                                                 void *fs_data, bool preload)
 243 {
 244         struct fscrypt_context ctx;
 245         struct fscrypt_info *ci;
 246         int res;
 247
 248         res = fscrypt_get_encryption_info(parent);
 249         if (res < 0)
 250                 return res;
 251
 252         ci = parent->i_crypt_info;
 253         if (ci == NULL)
 254                 return -ENOKEY;
 255
 256         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 257         ctx.contents_encryption_mode = ci->ci_data_mode;
 258         ctx.filenames_encryption_mode = ci->ci_filename_mode;
 259         ctx.flags = ci->ci_flags;
 260         memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 261                FS_KEY_DESCRIPTOR_SIZE);
 262         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 263         res = parent->i_sb->s_cop->set_context(child, &ctx,
 264                                                 sizeof(ctx), fs_data);
 265         if (res)
 266                 return res;
 267         return preload ? fscrypt_get_encryption_info(child): 0;
 268 }
 269 EXPORT_SYMBOL(fscrypt_inherit_context);