[linux-2.6-block.git] / fs / crypto / hooks.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * fs/crypto/hooks.c
 *
 * Encryption hooks for higher-level filesystem operations.
 */

#include "fscrypt_private.h"

/**
 * fscrypt_file_open - prepare to open a possibly-encrypted regular file
 * @inode: the inode being opened
 * @filp: the struct file being set up
 *
 * Currently, an encrypted regular file can only be opened if its encryption key
 * is available; access to the raw encrypted contents is not supported.
 * Therefore, we first set up the inode's encryption key (if not already done)
 * and return an error if it's unavailable.
 *
 * We also verify that if the parent directory (from the path via which the file
 * is being opened) is encrypted, then the inode being opened uses the same
 * encryption policy.  This is needed as part of the enforcement that all files
 * in an encrypted directory tree use the same encryption policy, as a
 * protection against certain types of offline attacks.  Note that this check is
 * needed even when opening an *unencrypted* file, since it's forbidden to have
 * an unencrypted file in an encrypted directory.
 *
 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
 */
int fscrypt_file_open(struct inode *inode, struct file *filp)
{
	int err;
	struct dentry *dir;

	err = fscrypt_require_key(inode);
	if (err)
		return err;

	dir = dget_parent(file_dentry(filp));
	if (IS_ENCRYPTED(d_inode(dir)) &&
	    !fscrypt_has_permitted_context(d_inode(dir), inode)) {
		fscrypt_warn(inode,
			     "Inconsistent encryption context (parent directory: %lu)",
			     d_inode(dir)->i_ino);
		err = -EPERM;
	}
	dput(dir);
	return err;
}
EXPORT_SYMBOL_GPL(fscrypt_file_open);

int __fscrypt_prepare_link(struct inode *inode, struct inode *dir,
			   struct dentry *dentry)
{
	int err;

	err = fscrypt_require_key(dir);
	if (err)
		return err;

	/* ... in case we looked up ciphertext name before key was added */
	if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
		return -ENOKEY;

	if (!fscrypt_has_permitted_context(dir, inode))
		return -EXDEV;

	return 0;
}
EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);

int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
			     struct inode *new_dir, struct dentry *new_dentry,
			     unsigned int flags)
{
	int err;

	err = fscrypt_require_key(old_dir);
	if (err)
		return err;

	err = fscrypt_require_key(new_dir);
	if (err)
		return err;

	/* ... in case we looked up ciphertext name(s) before key was added */
	if ((old_dentry->d_flags | new_dentry->d_flags) &
	    DCACHE_ENCRYPTED_NAME)
		return -ENOKEY;

	if (old_dir != new_dir) {
		if (IS_ENCRYPTED(new_dir) &&
		    !fscrypt_has_permitted_context(new_dir,
						   d_inode(old_dentry)))
			return -EXDEV;

		if ((flags & RENAME_EXCHANGE) &&
		    IS_ENCRYPTED(old_dir) &&
		    !fscrypt_has_permitted_context(old_dir,
						   d_inode(new_dentry)))
			return -EXDEV;
	}
	return 0;
}
EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);

int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
			     struct fscrypt_name *fname)
{
	int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);

	if (err && err != -ENOENT)
		return err;

	if (fname->is_ciphertext_name) {
		spin_lock(&dentry->d_lock);
		dentry->d_flags |= DCACHE_ENCRYPTED_NAME;
		spin_unlock(&dentry->d_lock);
		d_set_d_op(dentry, &fscrypt_d_ops);
	}
	return err;
}
EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);

int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
			      unsigned int max_len,
			      struct fscrypt_str *disk_link)
{
	int err;

	/*
	 * To calculate the size of the encrypted symlink target we need to know
	 * the amount of NUL padding, which is determined by the flags set in
	 * the encryption policy which will be inherited from the directory.
	 * The easiest way to get access to this is to just load the directory's
	 * fscrypt_info, since we'll need it to create the dir_entry anyway.
	 *
	 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
	 */
	err = fscrypt_get_encryption_info(dir);
	if (err)
		return err;
	if (!fscrypt_has_encryption_key(dir))
		return -ENOKEY;

	/*
	 * Calculate the size of the encrypted symlink and verify it won't
	 * exceed max_len.  Note that for historical reasons, encrypted symlink
	 * targets are prefixed with the ciphertext length, despite this
	 * actually being redundant with i_size.  This decreases by 2 bytes the
	 * longest symlink target we can accept.
	 *
	 * We could recover 1 byte by not counting a null terminator, but
	 * counting it (even though it is meaningless for ciphertext) is simpler
	 * for now since filesystems will assume it is there and subtract it.
	 */
	if (!fscrypt_fname_encrypted_size(dir, len,
					  max_len - sizeof(struct fscrypt_symlink_data),
					  &disk_link->len))
		return -ENAMETOOLONG;
	disk_link->len += sizeof(struct fscrypt_symlink_data);

	disk_link->name = NULL;
	return 0;
}
EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);

int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
			      unsigned int len, struct fscrypt_str *disk_link)
{
	int err;
	struct qstr iname = QSTR_INIT(target, len);
	struct fscrypt_symlink_data *sd;
	unsigned int ciphertext_len;

	err = fscrypt_require_key(inode);
	if (err)
		return err;

	if (disk_link->name) {
		/* filesystem-provided buffer */
		sd = (struct fscrypt_symlink_data *)disk_link->name;
	} else {
		sd = kmalloc(disk_link->len, GFP_NOFS);
		if (!sd)
			return -ENOMEM;
	}
	ciphertext_len = disk_link->len - sizeof(*sd);
	sd->len = cpu_to_le16(ciphertext_len);

	err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
	if (err)
		goto err_free_sd;

	/*
	 * Null-terminating the ciphertext doesn't make sense, but we still
	 * count the null terminator in the length, so we might as well
	 * initialize it just in case the filesystem writes it out.
	 */
	sd->encrypted_path[ciphertext_len] = '\0';

	/* Cache the plaintext symlink target for later use by get_link() */
	err = -ENOMEM;
	inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
	if (!inode->i_link)
		goto err_free_sd;

	if (!disk_link->name)
		disk_link->name = (unsigned char *)sd;
	return 0;

err_free_sd:
	if (!disk_link->name)
		kfree(sd);
	return err;
}
EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);

/**
 * fscrypt_get_symlink - get the target of an encrypted symlink
 * @inode: the symlink inode
 * @caddr: the on-disk contents of the symlink
 * @max_size: size of @caddr buffer
 * @done: if successful, will be set up to free the returned target if needed
 *
 * If the symlink's encryption key is available, we decrypt its target.
 * Otherwise, we encode its target for presentation.
 *
 * This may sleep, so the filesystem must have dropped out of RCU mode already.
 *
 * Return: the presentable symlink target or an ERR_PTR()
 */
const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
				unsigned int max_size,
				struct delayed_call *done)
{
	const struct fscrypt_symlink_data *sd;
	struct fscrypt_str cstr, pstr;
	bool has_key;
	int err;

	/* This is for encrypted symlinks only */
	if (WARN_ON(!IS_ENCRYPTED(inode)))
		return ERR_PTR(-EINVAL);

	/* If the decrypted target is already cached, just return it. */
	pstr.name = READ_ONCE(inode->i_link);
	if (pstr.name)
		return pstr.name;

	/*
	 * Try to set up the symlink's encryption key, but we can continue
	 * regardless of whether the key is available or not.
	 */
	err = fscrypt_get_encryption_info(inode);
	if (err)
		return ERR_PTR(err);
	has_key = fscrypt_has_encryption_key(inode);

	/*
	 * For historical reasons, encrypted symlink targets are prefixed with
	 * the ciphertext length, even though this is redundant with i_size.
	 */

	if (max_size < sizeof(*sd))
		return ERR_PTR(-EUCLEAN);
	sd = caddr;
	cstr.name = (unsigned char *)sd->encrypted_path;
	cstr.len = le16_to_cpu(sd->len);

	if (cstr.len == 0)
		return ERR_PTR(-EUCLEAN);

	if (cstr.len + sizeof(*sd) - 1 > max_size)
		return ERR_PTR(-EUCLEAN);

	err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
	if (err)
		return ERR_PTR(err);

	err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
	if (err)
		goto err_kfree;

	err = -EUCLEAN;
	if (pstr.name[0] == '\0')
		goto err_kfree;

	pstr.name[pstr.len] = '\0';

	/*
	 * Cache decrypted symlink targets in i_link for later use.  Don't cache
	 * symlink targets encoded without the key, since those become outdated
	 * once the key is added.  This pairs with the READ_ONCE() above and in
	 * the VFS path lookup code.
	 */
	if (!has_key ||
	    cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
		set_delayed_call(done, kfree_link, pstr.name);

	return pstr.name;

err_kfree:
	kfree(pstr.name);
	return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(fscrypt_get_symlink);
Commit	Line	Data
457c8996	1	// SPDX-License-Identifier: GPL-2.0-only
efcc7ae2 EB	2	/*
	3	* fs/crypto/hooks.c
	4	*
	5	* Encryption hooks for higher-level filesystem operations.
	6	*/
	7
efcc7ae2 EB	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)) {
886da8b3 EB	42	fscrypt_warn(inode,
	43	"Inconsistent encryption context (parent directory: %lu)",
	44	d_inode(dir)->i_ino);
efcc7ae2 EB	45	err = -EPERM;
	46	}
	47	dput(dir);
	48	return err;
	49	}
	50	EXPORT_SYMBOL_GPL(fscrypt_file_open);
0ea87a96	51
968dd6d0 EB	52	int __fscrypt_prepare_link(struct inode inode, struct inode dir,
968dd6d0 EB	53	struct dentry *dentry)
0ea87a96 EB	54	{
	55	int err;
	56
	57	err = fscrypt_require_key(dir);
	58	if (err)
	59	return err;
	60
968dd6d0 EB	61	/* ... in case we looked up ciphertext name before key was added */
	62	if (dentry->d_flags & DCACHE_ENCRYPTED_NAME)
	63	return -ENOKEY;
	64
0ea87a96	65	if (!fscrypt_has_permitted_context(dir, inode))
f5e55e77	66	return -EXDEV;
0ea87a96 EB	67
	68	return 0;
	69	}
	70	EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);
94b26f36 EB	71
	72	int __fscrypt_prepare_rename(struct inode old_dir, struct dentry old_dentry,
	73	struct inode new_dir, struct dentry new_dentry,
	74	unsigned int flags)
	75	{
	76	int err;
	77
	78	err = fscrypt_require_key(old_dir);
	79	if (err)
	80	return err;
	81
	82	err = fscrypt_require_key(new_dir);
	83	if (err)
	84	return err;
	85
968dd6d0 EB	86	/* ... in case we looked up ciphertext name(s) before key was added */
	87	if ((old_dentry->d_flags \| new_dentry->d_flags) &
	88	DCACHE_ENCRYPTED_NAME)
	89	return -ENOKEY;
	90
94b26f36 EB	91	if (old_dir != new_dir) {
	92	if (IS_ENCRYPTED(new_dir) &&
	93	!fscrypt_has_permitted_context(new_dir,
	94	d_inode(old_dentry)))
f5e55e77	95	return -EXDEV;
94b26f36 EB	96
	97	if ((flags & RENAME_EXCHANGE) &&
	98	IS_ENCRYPTED(old_dir) &&
	99	!fscrypt_has_permitted_context(old_dir,
	100	d_inode(new_dentry)))
f5e55e77	101	return -EXDEV;
94b26f36 EB	102	}
	103	return 0;
	104	}
	105	EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename);
32c3cf02	106
b01531db EB	107	int __fscrypt_prepare_lookup(struct inode dir, struct dentry dentry,
b01531db EB	108	struct fscrypt_name *fname)
32c3cf02	109	{
b01531db	110	int err = fscrypt_setup_filename(dir, &dentry->d_name, 1, fname);
32c3cf02	111
b01531db	112	if (err && err != -ENOENT)
32c3cf02 EB	113	return err;
32c3cf02 EB	114
b01531db	115	if (fname->is_ciphertext_name) {
32c3cf02	116	spin_lock(&dentry->d_lock);
6cc24868	117	dentry->d_flags \|= DCACHE_ENCRYPTED_NAME;
32c3cf02	118	spin_unlock(&dentry->d_lock);
d456a33f	119	d_set_d_op(dentry, &fscrypt_d_ops);
32c3cf02	120	}
b01531db	121	return err;
32c3cf02 EB	122	}
32c3cf02 EB	123	EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
76e81d6d EB	124
	125	int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
	126	unsigned int max_len,
	127	struct fscrypt_str *disk_link)
	128	{
	129	int err;
	130
	131	/*
	132	* To calculate the size of the encrypted symlink target we need to know
	133	* the amount of NUL padding, which is determined by the flags set in
	134	* the encryption policy which will be inherited from the directory.
	135	* The easiest way to get access to this is to just load the directory's
	136	* fscrypt_info, since we'll need it to create the dir_entry anyway.
	137	*
	138	* Note: in test_dummy_encryption mode, @dir may be unencrypted.
	139	*/
	140	err = fscrypt_get_encryption_info(dir);
	141	if (err)
	142	return err;
	143	if (!fscrypt_has_encryption_key(dir))
	144	return -ENOKEY;
	145
	146	/*
	147	* Calculate the size of the encrypted symlink and verify it won't
	148	* exceed max_len. Note that for historical reasons, encrypted symlink
	149	* targets are prefixed with the ciphertext length, despite this
	150	* actually being redundant with i_size. This decreases by 2 bytes the
	151	* longest symlink target we can accept.
	152	*
	153	* We could recover 1 byte by not counting a null terminator, but
	154	* counting it (even though it is meaningless for ciphertext) is simpler
	155	* for now since filesystems will assume it is there and subtract it.
	156	*/
b9db0b4a EB	157	if (!fscrypt_fname_encrypted_size(dir, len,
	158	max_len - sizeof(struct fscrypt_symlink_data),
	159	&disk_link->len))
76e81d6d	160	return -ENAMETOOLONG;
b9db0b4a EB	161	disk_link->len += sizeof(struct fscrypt_symlink_data);
b9db0b4a EB	162
76e81d6d EB	163	disk_link->name = NULL;
	164	return 0;
	165	}
	166	EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
	167
	168	int __fscrypt_encrypt_symlink(struct inode inode, const char target,
	169	unsigned int len, struct fscrypt_str *disk_link)
	170	{
	171	int err;
0b1dfa4c	172	struct qstr iname = QSTR_INIT(target, len);
76e81d6d EB	173	struct fscrypt_symlink_data *sd;
76e81d6d EB	174	unsigned int ciphertext_len;
76e81d6d EB	175
	176	err = fscrypt_require_key(inode);
	177	if (err)
	178	return err;
	179
	180	if (disk_link->name) {
	181	/* filesystem-provided buffer */
	182	sd = (struct fscrypt_symlink_data *)disk_link->name;
	183	} else {
	184	sd = kmalloc(disk_link->len, GFP_NOFS);
	185	if (!sd)
	186	return -ENOMEM;
	187	}
	188	ciphertext_len = disk_link->len - sizeof(*sd);
	189	sd->len = cpu_to_le16(ciphertext_len);
	190
50c961de	191	err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
2c58d548 EB	192	if (err)
	193	goto err_free_sd;
	194
76e81d6d EB	195	/*
	196	* Null-terminating the ciphertext doesn't make sense, but we still
	197	* count the null terminator in the length, so we might as well
	198	* initialize it just in case the filesystem writes it out.
	199	*/
	200	sd->encrypted_path[ciphertext_len] = '\0';
	201
2c58d548 EB	202	/* Cache the plaintext symlink target for later use by get_link() */
	203	err = -ENOMEM;
	204	inode->i_link = kmemdup(target, len + 1, GFP_NOFS);
	205	if (!inode->i_link)
	206	goto err_free_sd;
	207
76e81d6d EB	208	if (!disk_link->name)
	209	disk_link->name = (unsigned char *)sd;
	210	return 0;
2c58d548 EB	211
	212	err_free_sd:
	213	if (!disk_link->name)
	214	kfree(sd);
	215	return err;
76e81d6d EB	216	}
76e81d6d EB	217	EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
3b0d8837 EB	218
	219	/**
	220	* fscrypt_get_symlink - get the target of an encrypted symlink
	221	* @inode: the symlink inode
	222	* @caddr: the on-disk contents of the symlink
	223	* @max_size: size of @caddr buffer
2c58d548	224	* @done: if successful, will be set up to free the returned target if needed
3b0d8837 EB	225	*
	226	* If the symlink's encryption key is available, we decrypt its target.
	227	* Otherwise, we encode its target for presentation.
	228	*
	229	* This may sleep, so the filesystem must have dropped out of RCU mode already.
	230	*
	231	* Return: the presentable symlink target or an ERR_PTR()
	232	*/
	233	const char fscrypt_get_symlink(struct inode inode, const void *caddr,
	234	unsigned int max_size,
	235	struct delayed_call *done)
	236	{
	237	const struct fscrypt_symlink_data *sd;
	238	struct fscrypt_str cstr, pstr;
2c58d548	239	bool has_key;
3b0d8837 EB	240	int err;
	241
	242	/* This is for encrypted symlinks only */
	243	if (WARN_ON(!IS_ENCRYPTED(inode)))
	244	return ERR_PTR(-EINVAL);
	245
2c58d548 EB	246	/* If the decrypted target is already cached, just return it. */
	247	pstr.name = READ_ONCE(inode->i_link);
	248	if (pstr.name)
	249	return pstr.name;
	250
3b0d8837 EB	251	/*
	252	* Try to set up the symlink's encryption key, but we can continue
	253	* regardless of whether the key is available or not.
	254	*/
	255	err = fscrypt_get_encryption_info(inode);
	256	if (err)
	257	return ERR_PTR(err);
2c58d548	258	has_key = fscrypt_has_encryption_key(inode);
3b0d8837 EB	259
	260	/*
	261	* For historical reasons, encrypted symlink targets are prefixed with
	262	* the ciphertext length, even though this is redundant with i_size.
	263	*/
	264
	265	if (max_size < sizeof(*sd))
	266	return ERR_PTR(-EUCLEAN);
	267	sd = caddr;
	268	cstr.name = (unsigned char *)sd->encrypted_path;
	269	cstr.len = le16_to_cpu(sd->len);
	270
	271	if (cstr.len == 0)
	272	return ERR_PTR(-EUCLEAN);
	273
	274	if (cstr.len + sizeof(*sd) - 1 > max_size)
	275	return ERR_PTR(-EUCLEAN);
	276
	277	err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
	278	if (err)
	279	return ERR_PTR(err);
	280
	281	err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
	282	if (err)
	283	goto err_kfree;
	284
	285	err = -EUCLEAN;
	286	if (pstr.name[0] == '\0')
	287	goto err_kfree;
	288
	289	pstr.name[pstr.len] = '\0';
2c58d548 EB	290
	291	/*
	292	* Cache decrypted symlink targets in i_link for later use. Don't cache
	293	* symlink targets encoded without the key, since those become outdated
	294	* once the key is added. This pairs with the READ_ONCE() above and in
	295	* the VFS path lookup code.
	296	*/
	297	if (!has_key \|\|
	298	cmpxchg_release(&inode->i_link, NULL, pstr.name) != NULL)
	299	set_delayed_call(done, kfree_link, pstr.name);
	300
3b0d8837 EB	301	return pstr.name;
	302
	303	err_kfree:
	304	kfree(pstr.name);
	305	return ERR_PTR(err);
	306	}
	307	EXPORT_SYMBOL_GPL(fscrypt_get_symlink);