fs/crypto/policy.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Encryption policy functions for per-file encryption support.
   4  *
   5  * Copyright (C) 2015, Google, Inc.
   6  * Copyright (C) 2015, Motorola Mobility.
   7  *
   8  * Written by Michael Halcrow, 2015.
   9  * Modified by Jaegeuk Kim, 2015.
  10  */
  11
  12 #include <linux/random.h>
  13 #include <linux/string.h>
  14 #include <linux/mount.h>
  15 #include "fscrypt_private.h"
  16
  17 /*
  18  * check whether an encryption policy is consistent with an encryption context
  19  */
  20 static bool is_encryption_context_consistent_with_policy(
  21                                 const struct fscrypt_context *ctx,
  22                                 const struct fscrypt_policy *policy)
  23 {
  24         return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor,
  25                       FS_KEY_DESCRIPTOR_SIZE) == 0 &&
  26                 (ctx->flags == policy->flags) &&
  27                 (ctx->contents_encryption_mode ==
  28                  policy->contents_encryption_mode) &&
  29                 (ctx->filenames_encryption_mode ==
  30                  policy->filenames_encryption_mode);
  31 }
  32
  33 static int create_encryption_context_from_policy(struct inode *inode,
  34                                 const struct fscrypt_policy *policy)
  35 {
  36         struct fscrypt_context ctx;
  37
  38         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
  39         memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
  40                                         FS_KEY_DESCRIPTOR_SIZE);
  41
  42         if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
  43                                      policy->filenames_encryption_mode))
  44                 return -EINVAL;
  45
  46         if (policy->flags & ~FS_POLICY_FLAGS_VALID)
  47                 return -EINVAL;
  48
  49         ctx.contents_encryption_mode = policy->contents_encryption_mode;
  50         ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
  51         ctx.flags = policy->flags;
  52         BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE);
  53         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
  54
  55         return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
  56 }
  57
  58 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
  59 {
  60         struct fscrypt_policy policy;
  61         struct inode *inode = file_inode(filp);
  62         int ret;
  63         struct fscrypt_context ctx;
  64
  65         if (copy_from_user(&policy, arg, sizeof(policy)))
  66                 return -EFAULT;
  67
  68         if (!inode_owner_or_capable(inode))
  69                 return -EACCES;
  70
  71         if (policy.version != 0)
  72                 return -EINVAL;
  73
  74         ret = mnt_want_write_file(filp);
  75         if (ret)
  76                 return ret;
  77
  78         inode_lock(inode);
  79
  80         ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  81         if (ret == -ENODATA) {
  82                 if (!S_ISDIR(inode->i_mode))
  83                         ret = -ENOTDIR;
  84                 else if (IS_DEADDIR(inode))
  85                         ret = -ENOENT;
  86                 else if (!inode->i_sb->s_cop->empty_dir(inode))
  87                         ret = -ENOTEMPTY;
  88                 else
  89                         ret = create_encryption_context_from_policy(inode,
  90                                                                     &policy);
  91         } else if (ret == sizeof(ctx) &&
  92                    is_encryption_context_consistent_with_policy(&ctx,
  93                                                                 &policy)) {
  94                 /* The file already uses the same encryption policy. */
  95                 ret = 0;
  96         } else if (ret >= 0 || ret == -ERANGE) {
  97                 /* The file already uses a different encryption policy. */
  98                 ret = -EEXIST;
  99         }
 100
 101         inode_unlock(inode);
 102
 103         mnt_drop_write_file(filp);
 104         return ret;
 105 }
 106 EXPORT_SYMBOL(fscrypt_ioctl_set_policy);
 107
 108 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
 109 {
 110         struct inode *inode = file_inode(filp);
 111         struct fscrypt_context ctx;
 112         struct fscrypt_policy policy;
 113         int res;
 114
 115         if (!IS_ENCRYPTED(inode))
 116                 return -ENODATA;
 117
 118         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 119         if (res < 0 && res != -ERANGE)
 120                 return res;
 121         if (res != sizeof(ctx))
 122                 return -EINVAL;
 123         if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
 124                 return -EINVAL;
 125
 126         policy.version = 0;
 127         policy.contents_encryption_mode = ctx.contents_encryption_mode;
 128         policy.filenames_encryption_mode = ctx.filenames_encryption_mode;
 129         policy.flags = ctx.flags;
 130         memcpy(policy.master_key_descriptor, ctx.master_key_descriptor,
 131                                 FS_KEY_DESCRIPTOR_SIZE);
 132
 133         if (copy_to_user(arg, &policy, sizeof(policy)))
 134                 return -EFAULT;
 135         return 0;
 136 }
 137 EXPORT_SYMBOL(fscrypt_ioctl_get_policy);
 138
 139 /**
 140  * fscrypt_has_permitted_context() - is a file's encryption policy permitted
 141  *                                   within its directory?
 142  *
 143  * @parent: inode for parent directory
 144  * @child: inode for file being looked up, opened, or linked into @parent
 145  *
 146  * Filesystems must call this before permitting access to an inode in a
 147  * situation where the parent directory is encrypted (either before allowing
 148  * ->lookup() to succeed, or for a regular file before allowing it to be opened)
 149  * and before any operation that involves linking an inode into an encrypted
 150  * directory, including link, rename, and cross rename.  It enforces the
 151  * constraint that within a given encrypted directory tree, all files use the
 152  * same encryption policy.  The pre-access check is needed to detect potentially
 153  * malicious offline violations of this constraint, while the link and rename
 154  * checks are needed to prevent online violations of this constraint.
 155  *
 156  * Return: 1 if permitted, 0 if forbidden.  If forbidden, the caller must fail
 157  * the filesystem operation with EPERM.
 158  */
 159 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
 160 {
 161         const struct fscrypt_operations *cops = parent->i_sb->s_cop;
 162         const struct fscrypt_info *parent_ci, *child_ci;
 163         struct fscrypt_context parent_ctx, child_ctx;
 164         int res;
 165
 166         /* No restrictions on file types which are never encrypted */
 167         if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
 168             !S_ISLNK(child->i_mode))
 169                 return 1;
 170
 171         /* No restrictions if the parent directory is unencrypted */
 172         if (!IS_ENCRYPTED(parent))
 173                 return 1;
 174
 175         /* Encrypted directories must not contain unencrypted files */
 176         if (!IS_ENCRYPTED(child))
 177                 return 0;
 178
 179         /*
 180          * Both parent and child are encrypted, so verify they use the same
 181          * encryption policy.  Compare the fscrypt_info structs if the keys are
 182          * available, otherwise retrieve and compare the fscrypt_contexts.
 183          *
 184          * Note that the fscrypt_context retrieval will be required frequently
 185          * when accessing an encrypted directory tree without the key.
 186          * Performance-wise this is not a big deal because we already don't
 187          * really optimize for file access without the key (to the extent that
 188          * such access is even possible), given that any attempted access
 189          * already causes a fscrypt_context retrieval and keyring search.
 190          *
 191          * In any case, if an unexpected error occurs, fall back to "forbidden".
 192          */
 193
 194         res = fscrypt_get_encryption_info(parent);
 195         if (res)
 196                 return 0;
 197         res = fscrypt_get_encryption_info(child);
 198         if (res)
 199                 return 0;
 200         parent_ci = parent->i_crypt_info;
 201         child_ci = child->i_crypt_info;
 202
 203         if (parent_ci && child_ci) {
 204                 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key,
 205                               FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 206                         (parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
 207                         (parent_ci->ci_filename_mode ==
 208                          child_ci->ci_filename_mode) &&
 209                         (parent_ci->ci_flags == child_ci->ci_flags);
 210         }
 211
 212         res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx));
 213         if (res != sizeof(parent_ctx))
 214                 return 0;
 215
 216         res = cops->get_context(child, &child_ctx, sizeof(child_ctx));
 217         if (res != sizeof(child_ctx))
 218                 return 0;
 219
 220         return memcmp(parent_ctx.master_key_descriptor,
 221                       child_ctx.master_key_descriptor,
 222                       FS_KEY_DESCRIPTOR_SIZE) == 0 &&
 223                 (parent_ctx.contents_encryption_mode ==
 224                  child_ctx.contents_encryption_mode) &&
 225                 (parent_ctx.filenames_encryption_mode ==
 226                  child_ctx.filenames_encryption_mode) &&
 227                 (parent_ctx.flags == child_ctx.flags);
 228 }
 229 EXPORT_SYMBOL(fscrypt_has_permitted_context);
 230
 231 /**
 232  * fscrypt_inherit_context() - Sets a child context from its parent
 233  * @parent: Parent inode from which the context is inherited.
 234  * @child:  Child inode that inherits the context from @parent.
 235  * @fs_data:  private data given by FS.
 236  * @preload:  preload child i_crypt_info if true
 237  *
 238  * Return: 0 on success, -errno on failure
 239  */
 240 int fscrypt_inherit_context(struct inode *parent, struct inode *child,
 241                                                 void *fs_data, bool preload)
 242 {
 243         struct fscrypt_context ctx;
 244         struct fscrypt_info *ci;
 245         int res;
 246
 247         res = fscrypt_get_encryption_info(parent);
 248         if (res < 0)
 249                 return res;
 250
 251         ci = parent->i_crypt_info;
 252         if (ci == NULL)
 253                 return -ENOKEY;
 254
 255         ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
 256         ctx.contents_encryption_mode = ci->ci_data_mode;
 257         ctx.filenames_encryption_mode = ci->ci_filename_mode;
 258         ctx.flags = ci->ci_flags;
 259         memcpy(ctx.master_key_descriptor, ci->ci_master_key,
 260                FS_KEY_DESCRIPTOR_SIZE);
 261         get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
 262         BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_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);