fs/crypto/hooks.c

   1 /*
   2  * fs/crypto/hooks.c
   3  *
   4  * Encryption hooks for higher-level filesystem operations.
   5  */
   6
   7 #include <linux/ratelimit.h>
   8 #include "fscrypt_private.h"
   9
  10 /**
  11  * fscrypt_file_open - prepare to open a possibly-encrypted regular file
  12  * @inode: the inode being opened
  13  * @filp: the struct file being set up
  14  *
  15  * Currently, an encrypted regular file can only be opened if its encryption key
  16  * is available; access to the raw encrypted contents is not supported.
  17  * Therefore, we first set up the inode's encryption key (if not already done)
  18  * and return an error if it's unavailable.
  19  *
  20  * We also verify that if the parent directory (from the path via which the file
  21  * is being opened) is encrypted, then the inode being opened uses the same
  22  * encryption policy.  This is needed as part of the enforcement that all files
  23  * in an encrypted directory tree use the same encryption policy, as a
  24  * protection against certain types of offline attacks.  Note that this check is
  25  * needed even when opening an *unencrypted* file, since it's forbidden to have
  26  * an unencrypted file in an encrypted directory.
  27  *
  28  * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
  29  */
  30 int fscrypt_file_open(struct inode *inode, struct file *filp)
  31 {
  32         int err;
  33         struct dentry *dir;
  34
  35         err = fscrypt_require_key(inode);
  36         if (err)
  37                 return err;
  38
  39         dir = dget_parent(file_dentry(filp));
  40         if (IS_ENCRYPTED(d_inode(dir)) &&
  41             !fscrypt_has_permitted_context(d_inode(dir), inode)) {
  42                 fscrypt_warn(inode->i_sb,
  43                              "inconsistent encryption contexts: %lu/%lu",
  44                              d_inode(dir)->i_ino, inode->i_ino);
  45                 err = -EPERM;
  46         }
  47         dput(dir);
  48         return err;
  49 }
  50 EXPORT_SYMBOL_GPL(fscrypt_file_open);
  51
  52 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
  53 {
  54         int err;
  55
  56         err = fscrypt_require_key(dir);
  57         if (err)
  58                 return err;
  59
  60         if (!fscrypt_has_permitted_context(dir, inode))
  61                 return -EPERM;
  62
  63         return 0;
  64 }
  65 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
  66
  67 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
  68                              struct inode *new_dir, struct dentry *new_dentry,
  69                              unsigned int flags)
  70 {
  71         int err;
  72
  73         err = fscrypt_require_key(old_dir);
  74         if (err)
  75                 return err;
  76
  77         err = fscrypt_require_key(new_dir);
  78         if (err)
  79                 return err;
  80
  81         if (old_dir != new_dir) {
  82                 if (IS_ENCRYPTED(new_dir) &&
  83                     !fscrypt_has_permitted_context(new_dir,
  84                                                    d_inode(old_dentry)))
  85                         return -EPERM;
  86
  87                 if ((flags & RENAME_EXCHANGE) &&
  88                     IS_ENCRYPTED(old_dir) &&
  89                     !fscrypt_has_permitted_context(old_dir,
  90                                                    d_inode(new_dentry)))
  91                         return -EPERM;
  92         }
  93         return 0;
  94 }
  95 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
  96
  97 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry)
  98 {
  99         int err = fscrypt_get_encryption_info(dir);
 100
 101         if (err)
 102                 return err;
 103
 104         if (fscrypt_has_encryption_key(dir)) {
 105                 spin_lock(&dentry->d_lock);
 106                 dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
 107                 spin_unlock(&dentry->d_lock);
 108         }
 109
 110         d_set_d_op(dentry, &fscrypt_d_ops);
 111         return 0;
 112 }
 113 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
 114
 115 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
 116                               unsigned int max_len,
 117                               struct fscrypt_str *disk_link)
 118 {
 119         int err;
 120
 121         /*
 122          * To calculate the size of the encrypted symlink target we need to know
 123          * the amount of NUL padding, which is determined by the flags set in
 124          * the encryption policy which will be inherited from the directory.
 125          * The easiest way to get access to this is to just load the directory's
 126          * fscrypt_info, since we'll need it to create the dir_entry anyway.
 127          *
 128          * Note: in test_dummy_encryption mode, @dir may be unencrypted.
 129          */
 130         err = fscrypt_get_encryption_info(dir);
 131         if (err)
 132                 return err;
 133         if (!fscrypt_has_encryption_key(dir))
 134                 return -ENOKEY;
 135
 136         /*
 137          * Calculate the size of the encrypted symlink and verify it won't
 138          * exceed max_len.  Note that for historical reasons, encrypted symlink
 139          * targets are prefixed with the ciphertext length, despite this
 140          * actually being redundant with i_size.  This decreases by 2 bytes the
 141          * longest symlink target we can accept.
 142          *
 143          * We could recover 1 byte by not counting a null terminator, but
 144          * counting it (even though it is meaningless for ciphertext) is simpler
 145          * for now since filesystems will assume it is there and subtract it.
 146          */
 147         if (!fscrypt_fname_encrypted_size(dir, len,
 148                                           max_len - sizeof(struct fscrypt_symlink_data),
 149                                           &disk_link->len))
 150                 return -ENAMETOOLONG;
 151         disk_link->len += sizeof(struct fscrypt_symlink_data);
 152
 153         disk_link->name = NULL;
 154         return 0;
 155 }
 156 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
 157
 158 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
 159                               unsigned int len, struct fscrypt_str *disk_link)
 160 {
 161         int err;
 162         struct qstr iname = QSTR_INIT(target, len);
 163         struct fscrypt_symlink_data *sd;
 164         unsigned int ciphertext_len;
 165
 166         err = fscrypt_require_key(inode);
 167         if (err)
 168                 return err;
 169
 170         if (disk_link->name) {
 171                 /* filesystem-provided buffer */
 172                 sd = (struct fscrypt_symlink_data *)disk_link->name;
 173         } else {
 174                 sd = kmalloc(disk_link->len, GFP_NOFS);
 175                 if (!sd)
 176                         return -ENOMEM;
 177         }
 178         ciphertext_len = disk_link->len - sizeof(*sd);
 179         sd->len = cpu_to_le16(ciphertext_len);
 180
 181         err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
 182         if (err) {
 183                 if (!disk_link->name)
 184                         kfree(sd);
 185                 return err;
 186         }
 187         /*
 188          * Null-terminating the ciphertext doesn't make sense, but we still
 189          * count the null terminator in the length, so we might as well
 190          * initialize it just in case the filesystem writes it out.
 191          */
 192         sd->encrypted_path[ciphertext_len] = '\0';
 193
 194         if (!disk_link->name)
 195                 disk_link->name = (unsigned char *)sd;
 196         return 0;
 197 }
 198 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
 199
 200 /**
 201  * fscrypt_get_symlink - get the target of an encrypted symlink
 202  * @inode: the symlink inode
 203  * @caddr: the on-disk contents of the symlink
 204  * @max_size: size of @caddr buffer
 205  * @done: if successful, will be set up to free the returned target
 206  *
 207  * If the symlink's encryption key is available, we decrypt its target.
 208  * Otherwise, we encode its target for presentation.
 209  *
 210  * This may sleep, so the filesystem must have dropped out of RCU mode already.
 211  *
 212  * Return: the presentable symlink target or an ERR_PTR()
 213  */
 214 const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
 215                                 unsigned int max_size,
 216                                 struct delayed_call *done)
 217 {
 218         const struct fscrypt_symlink_data *sd;
 219         struct fscrypt_str cstr, pstr;
 220         int err;
 221
 222         /* This is for encrypted symlinks only */
 223         if (WARN_ON(!IS_ENCRYPTED(inode)))
 224                 return ERR_PTR(-EINVAL);
 225
 226         /*
 227          * Try to set up the symlink's encryption key, but we can continue
 228          * regardless of whether the key is available or not.
 229          */
 230         err = fscrypt_get_encryption_info(inode);
 231         if (err)
 232                 return ERR_PTR(err);
 233
 234         /*
 235          * For historical reasons, encrypted symlink targets are prefixed with
 236          * the ciphertext length, even though this is redundant with i_size.
 237          */
 238
 239         if (max_size < sizeof(*sd))
 240                 return ERR_PTR(-EUCLEAN);
 241         sd = caddr;
 242         cstr.name = (unsigned char *)sd->encrypted_path;
 243         cstr.len = le16_to_cpu(sd->len);
 244
 245         if (cstr.len == 0)
 246                 return ERR_PTR(-EUCLEAN);
 247
 248         if (cstr.len + sizeof(*sd) - 1 > max_size)
 249                 return ERR_PTR(-EUCLEAN);
 250
 251         err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
 252         if (err)
 253                 return ERR_PTR(err);
 254
 255         err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
 256         if (err)
 257                 goto err_kfree;
 258
 259         err = -EUCLEAN;
 260         if (pstr.name[0] == '\0')
 261                 goto err_kfree;
 262
 263         pstr.name[pstr.len] = '\0';
 264         set_delayed_call(done, kfree_link, pstr.name);
 265         return pstr.name;
 266
 267 err_kfree:
 268         kfree(pstr.name);
 269         return ERR_PTR(err);
 270 }
 271 EXPORT_SYMBOL_GPL(fscrypt_get_symlink);