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_enc_modes(policy->contents_encryption_mode,
  42                                      policy->filenames_encryption_mode))
  43                 return -EINVAL;
  44
  45         if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  46                 return -EINVAL;
  47
  48         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  49         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  50         ctx.flags = policy->flags;
  51         BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  52         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  53
  54         return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  55 }
  56
  57 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
  58 {
  59         struct fscrypt_policy policy;
  60         struct inode *inode = file_inode(filp);
  61         int ret;
  62         struct fscrypt_context ctx;
  63
  64         if (copy_from_user(&policy, arg, sizeof(policy)))
  65                 return -EFAULT;
  66
  67         if (!inode_owner_or_capable(inode))
  68                 return -EACCES;
  69
  70         if (policy.version != 0)
  71                 return -EINVAL;
  72
  73         ret = mnt_want_write_file(filp);
  74         if (ret)
  75                 return ret;
  76
  77         inode_lock(inode);
  78
  79         ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  80         if (ret == -ENODATA) {
  81                 if (!S_ISDIR(inode->i_mode))
  82                         ret = -ENOTDIR;
  83                 else if (!inode->i_sb->s_cop->empty_dir(inode))
  84                         ret = -ENOTEMPTY;
  85                 else
  86                         ret = create_encryption_context_from_policy(inode,
  87                                                                     &policy);
  88         } else if (ret == sizeof(ctx) &&
  89                    is_encryption_context_consistent_with_policy(&ctx,
  90                                                                 &policy)) {
  91                 /* The file already uses the same encryption policy. */
  92                 ret = 0;
  93         } else if (ret >= 0 || ret == -ERANGE) {
  94                 /* The file already uses a different encryption policy. */
  95                 ret = -EEXIST;
  96         }
  97
  98         inode_unlock(inode);
  99
 100         mnt_drop_write_file(filp);
 101         return ret;
 102 }
 103 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
 104
 105 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 106 {
 107         struct inode *inode = file_inode(filp);
 108         struct fscrypt_context ctx;
 109         struct fscrypt_policy policy;
 110         int res;
 111
 112         if (!inode->i_sb->s_cop->is_encrypted(inode))
 113                 return -ENODATA;
 114
 115         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 116         if (res < 0 && res != -ERANGE)
 117                 return res;
 118         if (res != sizeof(ctx))
 119                 return -EINVAL;
 120         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 121                 return -EINVAL;
 122
 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                                 FS_KEY_DESCRIPTOR_SIZE);
 129
 130         if (copy_to_user(arg, &policy, sizeof(policy)))
 131                 return -EFAULT;
 132         return 0;
 133 }
 134 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
 135
 136 /**
 137  * fscrypt_has_permitted_context() - is a file's encryption policy permitted
 138  *                                   within its directory?
 139  *
 140  * @parent: inode for parent directory
 141  * @child: inode for file being looked up, opened, or linked into @parent
 142  *
 143  * Filesystems must call this before permitting access to an inode in a
 144  * situation where the parent directory is encrypted (either before allowing
 145  * ->lookup() to succeed, or for a regular file before allowing it to be opened)
 146  * and before any operation that involves linking an inode into an encrypted
 147  * directory, including link, rename, and cross rename.  It enforces the
 148  * constraint that within a given encrypted directory tree, all files use the
 149  * same encryption policy.  The pre-access check is needed to detect potentially
 150  * malicious offline violations of this constraint, while the link and rename
 151  * checks are needed to prevent online violations of this constraint.
 152  *
 153  * Return: 1 if permitted, 0 if forbidden.  If forbidden, the caller must fail
 154  * the filesystem operation with EPERM.
 155  */
 156 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 157 {
 158         const struct fscrypt_operations *cops = parent->i_sb->s_cop;
 159         const struct fscrypt_info *parent_ci, *child_ci;
 160         struct fscrypt_context parent_ctx, child_ctx;
 161         int res;
 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 unencrypted */
 169         if (!cops->is_encrypted(parent))
 170                 return 1;
 171
 172         /* Encrypted directories must not contain unencrypted files */
 173         if (!cops->is_encrypted(child))
 174                 return 0;
 175
 176         /*
 177          * Both parent and child are encrypted, so verify they use the same
 178          * encryption policy.  Compare the fscrypt_info structs if the keys are
 179          * available, otherwise retrieve and compare the fscrypt_contexts.
 180          *
 181          * Note that the fscrypt_context retrieval will be required frequently
 182          * when accessing an encrypted directory tree without the key.
 183          * Performance-wise this is not a big deal because we already don't
 184          * really optimize for file access without the key (to the extent that
 185          * such access is even possible), given that any attempted access
 186          * already causes a fscrypt_context retrieval and keyring search.
 187          *
 188          * In any case, if an unexpected error occurs, fall back to "forbidden".
 189          */
 190
 191         res = fscrypt_get_encryption_info(parent);
 192         if (res)
 193                 return 0;
 194         res = fscrypt_get_encryption_info(child);
 195         if (res)
 196                 return 0;
 197         parent_ci = parent->i_crypt_info;
 198         child_ci = child->i_crypt_info;
 199
 200         if (parent_ci && child_ci) {
 201                 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
 202                               FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 203                         (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 204                         (parent_ci->ci_filename_mode ==
 205                          child_ci->ci_filename_mode) &&
 206                         (parent_ci->ci_flags == child_ci->ci_flags);
 207         }
 208
 209         res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
 210         if (res != sizeof(parent_ctx))
 211                 return 0;
 212
 213         res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
 214         if (res != sizeof(child_ctx))
 215                 return 0;
 216
 217         return memcmp(parent_ctx.master_key_descriptor,
 218                       child_ctx.master_key_descriptor,
 219                       FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 220                 (parent_ctx.contents_encryption_mode ==
 221                  child_ctx.contents_encryption_mode) &&
 222                 (parent_ctx.filenames_encryption_mode ==
 223                  child_ctx.filenames_encryption_mode) &&
 224                 (parent_ctx.flags == child_ctx.flags);
 225 }
 226 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 227
 228 /**
 229  * fscrypt_inherit_context() - Sets a child context from its parent
 230  * @parent: Parent inode from which the context is inherited.
 231  * @child:  Child inode that inherits the context from @parent.
 232  * @fs_data:  private data given by FS.
 233  * @preload:  preload child i_crypt_info if true
 234  *
 235  * Return: 0 on success, -errno on failure
 236  */
 237 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 238                                                 void *fs_data, bool preload)
 239 {
 240         struct fscrypt_context ctx;
 241         struct fscrypt_info *ci;
 242         int res;
 243
 244         res = fscrypt_get_encryption_info(parent);
 245         if (res < 0)
 246                 return res;
 247
 248         ci = parent->i_crypt_info;
 249         if (ci == NULL)
 250                 return -ENOKEY;
 251
 252         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 253         ctx.contents_encryption_mode = ci->ci_data_mode;
 254         ctx.filenames_encryption_mode = ci->ci_filename_mode;
 255         ctx.flags = ci->ci_flags;
 256         memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 257                FS_KEY_DESCRIPTOR_SIZE);
 258         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 259         BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
 260         res = parent->i_sb->s_cop->set_context(child, &ctx,
 261                                                 sizeof(ctx), fs_data);
 262         if (res)
 263                 return res;
 264         return preload ? fscrypt_get_encryption_info(child): 0;
 265 }
 266 EXPORT_SYMBOL(fscrypt_inherit_context);