// SPDX-License-Identifier: GPL-2.0 /* * This contains functions for filename crypto management * * Copyright (C) 2015, Google, Inc. * Copyright (C) 2015, Motorola Mobility * * Written by Uday Savagaonkar, 2014. * Modified by Jaegeuk Kim, 2015. * * This has not yet undergone a rigorous security audit. */ #include <crypto/sha2.h> #include <crypto/skcipher.h> #include <linux/export.h> #include <linux/namei.h> #include <linux/scatterlist.h> #include <linux/base64.h> #include "fscrypt_private.h" /* * The minimum message length (input and output length), in bytes, for all * filenames encryption modes. Filenames shorter than this will be zero-padded * before being encrypted. */ #define FSCRYPT_FNAME_MIN_MSG_LEN 16 /* * struct fscrypt_nokey_name - identifier for directory entry when key is absent * * When userspace lists an encrypted directory without access to the key, the * filesystem must present a unique "no-key name" for each filename that allows * it to find the directory entry again if requested. Naively, that would just * mean using the ciphertext filenames. However, since the ciphertext filenames * can contain illegal characters ('\0' and '/'), they must be encoded in some * way. We use base64url. But that can cause names to exceed NAME_MAX (255 * bytes), so we also need to use a strong hash to abbreviate long names. * * The filesystem may also need another kind of hash, the "dirhash", to quickly * find the directory entry. Since filesystems normally compute the dirhash * over the on-disk filename (i.e. the ciphertext), it's not computable from * no-key names that abbreviate the ciphertext using the strong hash to fit in * NAME_MAX. It's also not computable if it's a keyed hash taken over the * plaintext (but it may still be available in the on-disk directory entry); * casefolded directories use this type of dirhash. At least in these cases, * each no-key name must include the name's dirhash too. * * To meet all these requirements, we base64url-encode the following * variable-length structure. It contains the dirhash, or 0's if the filesystem * didn't provide one; up to 149 bytes of the ciphertext name; and for * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes. * * This ensures that each no-key name contains everything needed to find the * directory entry again, contains only legal characters, doesn't exceed * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only * take the performance hit of SHA-256 on very long filenames (which are rare). */ struct fscrypt_nokey_name { u32 dirhash[2]; u8 bytes[149]; u8 sha256[SHA256_DIGEST_SIZE]; }; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */ /* * Decoded size of max-size no-key name, i.e. a name that was abbreviated using * the strong hash and thus includes the 'sha256' field. This isn't simply * sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included. */ #define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256) /* Encoded size of max-size no-key name */ #define FSCRYPT_NOKEY_NAME_MAX_ENCODED \ BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX) static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) { return name_is_dot_dotdot(str->name, str->len); } /** * fscrypt_fname_encrypt() - encrypt a filename * @inode: inode of the parent directory (for regular filenames) * or of the symlink (for symlink targets). Key must already be * set up. * @iname: the filename to encrypt * @out: (output) the encrypted filename * @olen: size of the encrypted filename. It must be at least @iname->len. * Any extra space is filled with NUL padding before encryption. * * Return: 0 on success, -errno on failure */ int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname, u8 *out, unsigned int olen) { const struct fscrypt_inode_info *ci = fscrypt_get_inode_info_raw(inode); struct crypto_sync_skcipher *tfm = ci->ci_enc_key.tfm; SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm); union fscrypt_iv iv; struct scatterlist sg; int err; /* * Copy the filename to the output buffer for encrypting in-place and * pad it with the needed number of NUL bytes. */ if (WARN_ON_ONCE(olen < iname->len)) return -ENOBUFS; memcpy(out, iname->name, iname->len); memset(out + iname->len, 0, olen - iname->len); fscrypt_generate_iv(&iv, 0, ci); skcipher_request_set_callback( req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL); sg_init_one(&sg, out, olen); skcipher_request_set_crypt(req, &sg, &sg, olen, &iv); err = crypto_skcipher_encrypt(req); if (err) fscrypt_err(inode, "Filename encryption failed: %d", err); return err; } EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt); /** * fname_decrypt() - decrypt a filename * @inode: inode of the parent directory (for regular filenames) * or of the symlink (for symlink targets) * @iname: the encrypted filename to decrypt * @oname: (output) the decrypted filename. The caller must have allocated * enough space for this, e.g. using fscrypt_fname_alloc_buffer(). * * Return: 0 on success, -errno on failure */ static int fname_decrypt(const struct inode *inode, const struct fscrypt_str *iname, struct fscrypt_str *oname) { const struct fscrypt_inode_info *ci = fscrypt_get_inode_info_raw(inode); struct crypto_sync_skcipher *tfm = ci->ci_enc_key.tfm; SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm); union fscrypt_iv iv; struct scatterlist src_sg, dst_sg; int err; fscrypt_generate_iv(&iv, 0, ci); skcipher_request_set_callback( req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL); sg_init_one(&src_sg, iname->name, iname->len); sg_init_one(&dst_sg, oname->name, oname->len); skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv); err = crypto_skcipher_decrypt(req); if (err) { fscrypt_err(inode, "Filename decryption failed: %d", err); return err; } oname->len = strnlen(oname->name, iname->len); return 0; } bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy, u32 orig_len, u32 max_len, u32 *encrypted_len_ret) { int padding = 4 << (fscrypt_policy_flags(policy) & FSCRYPT_POLICY_FLAGS_PAD_MASK); u32 encrypted_len; if (orig_len > max_len) return false; encrypted_len = max_t(u32, orig_len, FSCRYPT_FNAME_MIN_MSG_LEN); encrypted_len = round_up(encrypted_len, padding); *encrypted_len_ret = min(encrypted_len, max_len); return true; } /** * fscrypt_fname_encrypted_size() - calculate length of encrypted filename * @inode: parent inode of dentry name being encrypted. Key must * already be set up. * @orig_len: length of the original filename * @max_len: maximum length to return * @encrypted_len_ret: where calculated length should be returned (on success) * * Filenames that are shorter than the maximum length may have their lengths * increased slightly by encryption, due to padding that is applied. * * Return: false if the orig_len is greater than max_len. Otherwise, true and * fill out encrypted_len_ret with the length (up to max_len). */ bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len, u32 max_len, u32 *encrypted_len_ret) { const struct fscrypt_inode_info *ci = fscrypt_get_inode_info_raw(inode); return __fscrypt_fname_encrypted_size(&ci->ci_policy, orig_len, max_len, encrypted_len_ret); } EXPORT_SYMBOL_GPL(fscrypt_fname_encrypted_size); /** * fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames * @max_encrypted_len: maximum length of encrypted filenames the buffer will be * used to present * @crypto_str: (output) buffer to allocate * * Allocate a buffer that is large enough to hold any decrypted or encoded * filename (null-terminated), for the given maximum encrypted filename length. * * Return: 0 on success, -errno on failure */ int fscrypt_fname_alloc_buffer(u32 max_encrypted_len, struct fscrypt_str *crypto_str) { u32 max_presented_len = max_t(u32, FSCRYPT_NOKEY_NAME_MAX_ENCODED, max_encrypted_len); crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS); if (!crypto_str->name) return -ENOMEM; crypto_str->len = max_presented_len; return 0; } EXPORT_SYMBOL(fscrypt_fname_alloc_buffer); /** * fscrypt_fname_free_buffer() - free a buffer for presented filenames * @crypto_str: the buffer to free * * Free a buffer that was allocated by fscrypt_fname_alloc_buffer(). */ void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str) { if (!crypto_str) return; kfree(crypto_str->name); crypto_str->name = NULL; } EXPORT_SYMBOL(fscrypt_fname_free_buffer); /** * fscrypt_fname_disk_to_usr() - convert an encrypted filename to * user-presentable form * @inode: inode of the parent directory (for regular filenames) * or of the symlink (for symlink targets) * @hash: first part of the name's dirhash, if applicable. This only needs to * be provided if the filename is located in an indexed directory whose * encryption key may be unavailable. Not needed for symlink targets. * @minor_hash: second part of the name's dirhash, if applicable * @iname: encrypted filename to convert. May also be "." or "..", which * aren't actually encrypted. * @oname: output buffer for the user-presentable filename. The caller must * have allocated enough space for this, e.g. using * fscrypt_fname_alloc_buffer(). * * If the key is available, we'll decrypt the disk name. Otherwise, we'll * encode it for presentation in fscrypt_nokey_name format. * See struct fscrypt_nokey_name for details. * * Return: 0 on success, -errno on failure */ int fscrypt_fname_disk_to_usr(const struct inode *inode, u32 hash, u32 minor_hash, const struct fscrypt_str *iname, struct fscrypt_str *oname) { const struct qstr qname = FSTR_TO_QSTR(iname); struct fscrypt_nokey_name nokey_name; u32 size; /* size of the unencoded no-key name */ if (fscrypt_is_dot_dotdot(&qname)) { oname->name[0] = '.'; oname->name[iname->len - 1] = '.'; oname->len = iname->len; return 0; } if (iname->len < FSCRYPT_FNAME_MIN_MSG_LEN) return -EUCLEAN; if (fscrypt_has_encryption_key(inode)) return fname_decrypt(inode, iname, oname); /* * Sanity check that struct fscrypt_nokey_name doesn't have padding * between fields and that its encoded size never exceeds NAME_MAX. */ BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) != offsetof(struct fscrypt_nokey_name, bytes)); BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) != offsetof(struct fscrypt_nokey_name, sha256)); BUILD_BUG_ON(FSCRYPT_NOKEY_NAME_MAX_ENCODED > NAME_MAX); nokey_name.dirhash[0] = hash; nokey_name.dirhash[1] = minor_hash; if (iname->len <= sizeof(nokey_name.bytes)) { memcpy(nokey_name.bytes, iname->name, iname->len); size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]); } else { memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes)); /* Compute strong hash of remaining part of name. */ sha256(&iname->name[sizeof(nokey_name.bytes)], iname->len - sizeof(nokey_name.bytes), nokey_name.sha256); size = FSCRYPT_NOKEY_NAME_MAX; } oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name, false, BASE64_URLSAFE); return 0; } EXPORT_SYMBOL(fscrypt_fname_disk_to_usr); /** * fscrypt_setup_filename() - prepare to search a possibly encrypted directory * @dir: the directory that will be searched * @iname: the user-provided filename being searched for * @lookup: 1 if we're allowed to proceed without the key because it's * ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot * proceed without the key because we're going to create the dir_entry. * @fname: the filename information to be filled in * * Given a user-provided filename @iname, this function sets @fname->disk_name * to the name that would be stored in the on-disk directory entry, if possible. * If the directory is unencrypted this is simply @iname. Else, if we have the * directory's encryption key, then @iname is the plaintext, so we encrypt it to * get the disk_name. * * Else, for keyless @lookup operations, @iname should be a no-key name, so we * decode it to get the struct fscrypt_nokey_name. Non-@lookup operations will * be impossible in this case, so we fail them with ENOKEY. * * If successful, fscrypt_free_filename() must be called later to clean up. * * Return: 0 on success, -errno on failure */ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname, int lookup, struct fscrypt_name *fname) { struct fscrypt_nokey_name *nokey_name; int ret; memset(fname, 0, sizeof(struct fscrypt_name)); fname->usr_fname = iname; if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) { fname->disk_name.name = (unsigned char *)iname->name; fname->disk_name.len = iname->len; return 0; } ret = fscrypt_get_encryption_info(dir, lookup); if (ret) return ret; if (fscrypt_has_encryption_key(dir)) { if (!fscrypt_fname_encrypted_size(dir, iname->len, NAME_MAX, &fname->crypto_buf.len)) return -ENAMETOOLONG; fname->crypto_buf.name = kmalloc(fname->crypto_buf.len, GFP_NOFS); if (!fname->crypto_buf.name) return -ENOMEM; ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name, fname->crypto_buf.len); if (ret) goto errout; fname->disk_name.name = fname->crypto_buf.name; fname->disk_name.len = fname->crypto_buf.len; return 0; } if (!lookup) return -ENOKEY; fname->is_nokey_name = true; /* * We don't have the key and we are doing a lookup; decode the * user-supplied name */ if (iname->len > FSCRYPT_NOKEY_NAME_MAX_ENCODED) return -ENOENT; fname->crypto_buf.name = kmalloc(FSCRYPT_NOKEY_NAME_MAX, GFP_KERNEL); if (fname->crypto_buf.name == NULL) return -ENOMEM; ret = base64_decode(iname->name, iname->len, fname->crypto_buf.name, false, BASE64_URLSAFE); if (ret < (int)offsetof(struct fscrypt_nokey_name, bytes[1]) || (ret > offsetof(struct fscrypt_nokey_name, sha256) && ret != FSCRYPT_NOKEY_NAME_MAX)) { ret = -ENOENT; goto errout; } fname->crypto_buf.len = ret; nokey_name = (void *)fname->crypto_buf.name; fname->hash = nokey_name->dirhash[0]; fname->minor_hash = nokey_name->dirhash[1]; if (ret != FSCRYPT_NOKEY_NAME_MAX) { /* The full ciphertext filename is available. */ fname->disk_name.name = nokey_name->bytes; fname->disk_name.len = ret - offsetof(struct fscrypt_nokey_name, bytes); } return 0; errout: kfree(fname->crypto_buf.name); return ret; } EXPORT_SYMBOL(fscrypt_setup_filename); /** * 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 the name we're * looking for is very long, then we won't have the full disk_name and instead * we'll need to match against a fscrypt_nokey_name that includes a strong hash. * * Return: %true if the name matches, otherwise %false. */ bool fscrypt_match_name(const struct fscrypt_name *fname, const u8 *de_name, u32 de_name_len) { const struct fscrypt_nokey_name *nokey_name = (const void *)fname->crypto_buf.name; u8 digest[SHA256_DIGEST_SIZE]; if (likely(fname->disk_name.name)) { if (de_name_len != fname->disk_name.len) return false; return !memcmp(de_name, fname->disk_name.name, de_name_len); } if (de_name_len <= sizeof(nokey_name->bytes)) return false; if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes))) return false; sha256(&de_name[sizeof(nokey_name->bytes)], de_name_len - sizeof(nokey_name->bytes), digest); return !memcmp(digest, nokey_name->sha256, sizeof(digest)); } EXPORT_SYMBOL_GPL(fscrypt_match_name); /** * fscrypt_fname_siphash() - calculate the SipHash of a filename * @dir: the parent directory * @name: the filename to calculate the SipHash of * * Given a plaintext filename @name and a directory @dir which uses SipHash as * its dirhash method and has had its fscrypt key set up, this function * calculates the SipHash of that name using the directory's secret dirhash key. * * Return: the SipHash of @name using the hash key of @dir */ u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name) { const struct fscrypt_inode_info *ci = fscrypt_get_inode_info_raw(dir); WARN_ON_ONCE(!ci->ci_dirhash_key_initialized); return siphash(name->name, name->len, &ci->ci_dirhash_key); } EXPORT_SYMBOL_GPL(fscrypt_fname_siphash); /* * Validate dentries in encrypted directories to make sure we aren't potentially * caching stale dentries after a key has been added. */ int fscrypt_d_revalidate(struct inode *dir, const struct qstr *name, struct dentry *dentry, unsigned int flags) { int err; /* * Plaintext names are always valid, since fscrypt doesn't support * reverting to no-key names without evicting the directory's inode * -- which implies eviction of the dentries in the directory. */ if (!(dentry->d_flags & DCACHE_NOKEY_NAME)) return 1; /* * No-key name; valid if the directory's key is still unavailable. * * Note in RCU mode we have to bail if we get here - * fscrypt_get_encryption_info() may block. */ if (flags & LOOKUP_RCU) return -ECHILD; /* * Pass allow_unsupported=true, so that files with an unsupported * encryption policy can be deleted. */ err = fscrypt_get_encryption_info(dir, true); if (err < 0) return err; return !fscrypt_has_encryption_key(dir); } EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);
