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