include/linux/fscrypt_supp.h

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * fscrypt_supp.h
 *
 * This is included by filesystems configured with encryption support.
 */

#ifndef _LINUX_FSCRYPT_SUPP_H
#define _LINUX_FSCRYPT_SUPP_H

#include <linux/fscrypt_common.h>

/* crypto.c */
extern struct kmem_cache *fscrypt_info_cachep;
extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
extern void fscrypt_release_ctx(struct fscrypt_ctx *);
extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *,
						unsigned int, unsigned int,
						u64, gfp_t);
extern int fscrypt_decrypt_page(const struct inode *, struct page *, unsigned int,
				unsigned int, u64);
extern void fscrypt_restore_control_page(struct page *);

extern const struct dentry_operations fscrypt_d_ops;

static inline void fscrypt_set_d_op(struct dentry *dentry)
{
	d_set_d_op(dentry, &fscrypt_d_ops);
}

static inline void fscrypt_set_encrypted_dentry(struct dentry *dentry)
{
	spin_lock(&dentry->d_lock);
	dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
	spin_unlock(&dentry->d_lock);
}

/* policy.c */
extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
extern int fscrypt_inherit_context(struct inode *, struct inode *,
					void *, bool);
/* keyinfo.c */
extern int fscrypt_get_encryption_info(struct inode *);
extern void fscrypt_put_encryption_info(struct inode *, struct fscrypt_info *);

/* fname.c */
extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
				int lookup, struct fscrypt_name *);

static inline void fscrypt_free_filename(struct fscrypt_name *fname)
{
	kfree(fname->crypto_buf.name);
}

extern u32 fscrypt_fname_encrypted_size(const struct inode *, u32);
extern int fscrypt_fname_alloc_buffer(const struct inode *, u32,
				struct fscrypt_str *);
extern void fscrypt_fname_free_buffer(struct fscrypt_str *);
extern int fscrypt_fname_disk_to_usr(struct inode *, u32, u32,
			const struct fscrypt_str *, struct fscrypt_str *);
extern int fscrypt_fname_usr_to_disk(struct inode *, const struct qstr *,
			struct fscrypt_str *);

#define FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE	32

/* Extracts the second-to-last ciphertext block; see explanation below */
#define FSCRYPT_FNAME_DIGEST(name, len)	\
	((name) + round_down((len) - FS_CRYPTO_BLOCK_SIZE - 1, \
			     FS_CRYPTO_BLOCK_SIZE))

#define FSCRYPT_FNAME_DIGEST_SIZE	FS_CRYPTO_BLOCK_SIZE

/**
 * fscrypt_digested_name - alternate identifier for an on-disk filename
 *
 * When userspace lists an encrypted directory without access to the key,
 * filenames whose ciphertext is longer than FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE
 * bytes are shown in this abbreviated form (base64-encoded) rather than as the
 * full ciphertext (base64-encoded).  This is necessary to allow supporting
 * filenames up to NAME_MAX bytes, since base64 encoding expands the length.
 *
 * To make it possible for filesystems to still find the correct directory entry
 * despite not knowing the full on-disk name, we encode any filesystem-specific
 * 'hash' and/or 'minor_hash' which the filesystem may need for its lookups,
 * followed by the second-to-last ciphertext block of the filename.  Due to the
 * use of the CBC-CTS encryption mode, the second-to-last ciphertext block
 * depends on the full plaintext.  (Note that ciphertext stealing causes the
 * last two blocks to appear "flipped".)  This makes accidental collisions very
 * unlikely: just a 1 in 2^128 chance for two filenames to collide even if they
 * share the same filesystem-specific hashes.
 *
 * However, this scheme isn't immune to intentional collisions, which can be
 * created by anyone able to create arbitrary plaintext filenames and view them
 * without the key.  Making the "digest" be a real cryptographic hash like
 * SHA-256 over the full ciphertext would prevent this, although it would be
 * less efficient and harder to implement, especially since the filesystem would
 * need to calculate it for each directory entry examined during a search.
 */
struct fscrypt_digested_name {
	u32 hash;
	u32 minor_hash;
	u8 digest[FSCRYPT_FNAME_DIGEST_SIZE];
};

/**
 * fscrypt_match_name() - test whether the given name matches a directory entry
 * @fname: the name being searched for
 * @de_name: the name from the directory entry
 * @de_name_len: the length of @de_name in bytes
 *
 * Normally @fname->disk_name will be set, and in that case we simply compare
 * that to the name stored in the directory entry.  The only exception is that
 * if we don't have the key for an encrypted directory and a filename in it is
 * very long, then we won't have the full disk_name and we'll instead need to
 * match against the fscrypt_digested_name.
 *
 * Return: %true if the name matches, otherwise %false.
 */
static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
				      const u8 *de_name, u32 de_name_len)
{
	if (unlikely(!fname->disk_name.name)) {
		const struct fscrypt_digested_name *n =
			(const void *)fname->crypto_buf.name;
		if (WARN_ON_ONCE(fname->usr_fname->name[0] != '_'))
			return false;
		if (de_name_len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)
			return false;
		return !memcmp(FSCRYPT_FNAME_DIGEST(de_name, de_name_len),
			       n->digest, FSCRYPT_FNAME_DIGEST_SIZE);
	}

	if (de_name_len != fname->disk_name.len)
		return false;
	return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
}

/* bio.c */
extern void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *, struct bio *);
extern void fscrypt_pullback_bio_page(struct page **, bool);
extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
				 unsigned int);

#endif	/* _LINUX_FSCRYPT_SUPP_H */