1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * fs/crypto/hooks.c
  4 *
  5 * Encryption hooks for higher-level filesystem operations.
  6 */
  7
  8#include <linux/key.h>
  9
 10#include "fscrypt_private.h"
 11
 12/**
 13 * fscrypt_file_open() - prepare to open a possibly-encrypted regular file
 14 * @inode: the inode being opened
 15 * @filp: the struct file being set up
 16 *
 17 * Currently, an encrypted regular file can only be opened if its encryption key
 18 * is available; access to the raw encrypted contents is not supported.
 19 * Therefore, we first set up the inode's encryption key (if not already done)
 20 * and return an error if it's unavailable.
 21 *
 22 * We also verify that if the parent directory (from the path via which the file
 23 * is being opened) is encrypted, then the inode being opened uses the same
 24 * encryption policy.  This is needed as part of the enforcement that all files
 25 * in an encrypted directory tree use the same encryption policy, as a
 26 * protection against certain types of offline attacks.  Note that this check is
 27 * needed even when opening an *unencrypted* file, since it's forbidden to have
 28 * an unencrypted file in an encrypted directory.
 29 *
 30 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
 31 */
 32int fscrypt_file_open(struct inode *inode, struct file *filp)
 33{
 34	int err;
 35	struct dentry *dir;
 36
 37	err = fscrypt_require_key(inode);
 38	if (err)
 39		return err;
 40
 41	dir = dget_parent(file_dentry(filp));
 42	if (IS_ENCRYPTED(d_inode(dir)) &&
 43	    !fscrypt_has_permitted_context(d_inode(dir), inode)) {
 44		fscrypt_warn(inode,
 45			     "Inconsistent encryption context (parent directory: %lu)",
 46			     d_inode(dir)->i_ino);
 47		err = -EPERM;
 48	}
 49	dput(dir);
 50	return err;
 51}
 52EXPORT_SYMBOL_GPL(fscrypt_file_open);
 53
 54int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
 55			   struct dentry *dentry)
 56{
 57	int err;
 58
 59	err = fscrypt_require_key(dir);
 60	if (err)
 61		return err;
 62
 63	/* ... in case we looked up ciphertext name before key was added */
 64	if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
 65		return -ENOKEY;
 66
 67	if (!fscrypt_has_permitted_context(dir, inode))
 68		return -EXDEV;
 69
 70	return 0;
 71}
 72EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
 73
 74int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
 75			     struct inode *new_dir, struct dentry *new_dentry,
 76			     unsigned int flags)
 77{
 78	int err;
 79
 80	err = fscrypt_require_key(old_dir);
 81	if (err)
 82		return err;
 83
 84	err = fscrypt_require_key(new_dir);
 85	if (err)
 86		return err;
 87
 88	/* ... in case we looked up ciphertext name(s) before key was added */
 89	if ((old_dentry->d_flags | new_dentry->d_flags) &
 90	    DCACHE_ENCRYPTED_NAME)
 91		return -ENOKEY;
 92
 93	if (old_dir != new_dir) {
 94		if (IS_ENCRYPTED(new_dir) &&
 95		    !fscrypt_has_permitted_context(new_dir,
 96						   d_inode(old_dentry)))
 97			return -EXDEV;
 98
 99		if ((flags & RENAME_EXCHANGE) &&
100		    IS_ENCRYPTED(old_dir) &&
101		    !fscrypt_has_permitted_context(old_dir,
102						   d_inode(new_dentry)))
103			return -EXDEV;
104	}
105	return 0;
106}
107EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
108
109int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
110			     struct fscrypt_name *fname)
111{
112	int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
113
114	if (err && err != -ENOENT)
115		return err;
116
117	if (fname->is_ciphertext_name) {
118		spin_lock(&dentry->d_lock);
119		dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
120		spin_unlock(&dentry->d_lock);
121		d_set_d_op(dentry, &fscrypt_d_ops);
122	}
123	return err;
124}
125EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
126
127/**
128 * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
129 * @inode: the inode on which flags are being changed
130 * @oldflags: the old flags
131 * @flags: the new flags
132 *
133 * The caller should be holding i_rwsem for write.
134 *
135 * Return: 0 on success; -errno if the flags change isn't allowed or if
136 *	   another error occurs.
137 */
138int fscrypt_prepare_setflags(struct inode *inode,
139			     unsigned int oldflags, unsigned int flags)
140{
141	struct fscrypt_info *ci;
142	struct fscrypt_master_key *mk;
143	int err;
144
145	/*
146	 * When the CASEFOLD flag is set on an encrypted directory, we must
147	 * derive the secret key needed for the dirhash.  This is only possible
148	 * if the directory uses a v2 encryption policy.
149	 */
150	if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {
151		err = fscrypt_require_key(inode);
152		if (err)
153			return err;
154		ci = inode->i_crypt_info;
155		if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
156			return -EINVAL;
157		mk = ci->ci_master_key->payload.data[0];
158		down_read(&mk->mk_secret_sem);
159		if (is_master_key_secret_present(&mk->mk_secret))
160			err = fscrypt_derive_dirhash_key(ci, mk);
161		else
162			err = -ENOKEY;
163		up_read(&mk->mk_secret_sem);
164		return err;
165	}
166	return 0;
167}
168
169int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
170			      unsigned int max_len,
171			      struct fscrypt_str *disk_link)
172{
173	int err;
174
175	/*
176	 * To calculate the size of the encrypted symlink target we need to know
177	 * the amount of NUL padding, which is determined by the flags set in
178	 * the encryption policy which will be inherited from the directory.
179	 * The easiest way to get access to this is to just load the directory's
180	 * fscrypt_info, since we'll need it to create the dir_entry anyway.
181	 *
182	 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
183	 */
184	err = fscrypt_get_encryption_info(dir);
185	if (err)
186		return err;
187	if (!fscrypt_has_encryption_key(dir))
188		return -ENOKEY;
189
190	/*
191	 * Calculate the size of the encrypted symlink and verify it won't
192	 * exceed max_len.  Note that for historical reasons, encrypted symlink
193	 * targets are prefixed with the ciphertext length, despite this
194	 * actually being redundant with i_size.  This decreases by 2 bytes the
195	 * longest symlink target we can accept.
196	 *
197	 * We could recover 1 byte by not counting a null terminator, but
198	 * counting it (even though it is meaningless for ciphertext) is simpler
199	 * for now since filesystems will assume it is there and subtract it.
200	 */
201	if (!fscrypt_fname_encrypted_size(dir, len,
202					  max_len - sizeof(struct fscrypt_symlink_data),
203					  &disk_link->len))
204		return -ENAMETOOLONG;
205	disk_link->len += sizeof(struct fscrypt_symlink_data);
206
207	disk_link->name = NULL;
208	return 0;
209}
210EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
211
212int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
213			      unsigned int len, struct fscrypt_str *disk_link)
214{
215	int err;
216	struct qstr iname = QSTR_INIT(target, len);
217	struct fscrypt_symlink_data *sd;
218	unsigned int ciphertext_len;
219
220	err = fscrypt_require_key(inode);
221	if (err)
222		return err;
223
224	if (disk_link->name) {
225		/* filesystem-provided buffer */
226		sd = (struct fscrypt_symlink_data *)disk_link->name;
227	} else {
228		sd = kmalloc(disk_link->len, GFP_NOFS);
229		if (!sd)
230			return -ENOMEM;
231	}
232	ciphertext_len = disk_link->len - sizeof(*sd);
233	sd->len = cpu_to_le16(ciphertext_len);
234
235	err = fscrypt_fname_encrypt(inode, &iname, sd->encrypted_path,
236				    ciphertext_len);
237	if (err)
238		goto err_free_sd;
239
240	/*
241	 * Null-terminating the ciphertext doesn't make sense, but we still
242	 * count the null terminator in the length, so we might as well
243	 * initialize it just in case the filesystem writes it out.
244	 */
245	sd->encrypted_path[ciphertext_len] = '\0';
246
247	/* Cache the plaintext symlink target for later use by get_link() */
248	err = -ENOMEM;
249	inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
250	if (!inode->i_link)
251		goto err_free_sd;
252
253	if (!disk_link->name)
254		disk_link->name = (unsigned char *)sd;
255	return 0;
256
257err_free_sd:
258	if (!disk_link->name)
259		kfree(sd);
260	return err;
261}
262EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
263
264/**
265 * fscrypt_get_symlink() - get the target of an encrypted symlink
266 * @inode: the symlink inode
267 * @caddr: the on-disk contents of the symlink
268 * @max_size: size of @caddr buffer
269 * @done: if successful, will be set up to free the returned target if needed
270 *
271 * If the symlink's encryption key is available, we decrypt its target.
272 * Otherwise, we encode its target for presentation.
273 *
274 * This may sleep, so the filesystem must have dropped out of RCU mode already.
275 *
276 * Return: the presentable symlink target or an ERR_PTR()
277 */
278const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
279				unsigned int max_size,
280				struct delayed_call *done)
281{
282	const struct fscrypt_symlink_data *sd;
283	struct fscrypt_str cstr, pstr;
284	bool has_key;
285	int err;
286
287	/* This is for encrypted symlinks only */
288	if (WARN_ON(!IS_ENCRYPTED(inode)))
289		return ERR_PTR(-EINVAL);
290
291	/* If the decrypted target is already cached, just return it. */
292	pstr.name = READ_ONCE(inode->i_link);
293	if (pstr.name)
294		return pstr.name;
295
296	/*
297	 * Try to set up the symlink's encryption key, but we can continue
298	 * regardless of whether the key is available or not.
299	 */
300	err = fscrypt_get_encryption_info(inode);
301	if (err)
302		return ERR_PTR(err);
303	has_key = fscrypt_has_encryption_key(inode);
304
305	/*
306	 * For historical reasons, encrypted symlink targets are prefixed with
307	 * the ciphertext length, even though this is redundant with i_size.
308	 */
309
310	if (max_size < sizeof(*sd))
311		return ERR_PTR(-EUCLEAN);
312	sd = caddr;
313	cstr.name = (unsigned char *)sd->encrypted_path;
314	cstr.len = le16_to_cpu(sd->len);
315
316	if (cstr.len == 0)
317		return ERR_PTR(-EUCLEAN);
318
319	if (cstr.len + sizeof(*sd) - 1 > max_size)
320		return ERR_PTR(-EUCLEAN);
321
322	err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
323	if (err)
324		return ERR_PTR(err);
325
326	err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
327	if (err)
328		goto err_kfree;
329
330	err = -EUCLEAN;
331	if (pstr.name[0] == '\0')
332		goto err_kfree;
333
334	pstr.name[pstr.len] = '\0';
335
336	/*
337	 * Cache decrypted symlink targets in i_link for later use.  Don't cache
338	 * symlink targets encoded without the key, since those become outdated
339	 * once the key is added.  This pairs with the READ_ONCE() above and in
340	 * the VFS path lookup code.
341	 */
342	if (!has_key ||
343	    cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
344		set_delayed_call(done, kfree_link, pstr.name);
345
346	return pstr.name;
347
348err_kfree:
349	kfree(pstr.name);
350	return ERR_PTR(err);
351}
352EXPORT_SYMBOL_GPL(fscrypt_get_symlink);