fs/crypto/hooks.c - linux - Git at Google

 // 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->i_sb,
 			     "inconsistent encryption contexts: %lu/%lu",
 			     d_inode(dir)->i_ino, inode->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);
	// 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->i_sb,
	"inconsistent encryption contexts: %lu/%lu",
	d_inode(dir)->i_ino, inode->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);