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![Eric Biggers](/assets/img/avatar_default.png)
The max_namelen field is unnecessary, as it is set to 255 (NAME_MAX) on all filesystems that support fscrypt (or plan to support fscrypt). For simplicity, just use NAME_MAX directly instead. Link: https://lore.kernel.org/r/20210909184513.139281-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
595 lines
20 KiB
C
595 lines
20 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This contains functions for filename crypto management
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*
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* Copyright (C) 2015, Google, Inc.
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* Copyright (C) 2015, Motorola Mobility
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*
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* Written by Uday Savagaonkar, 2014.
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* Modified by Jaegeuk Kim, 2015.
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*
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* This has not yet undergone a rigorous security audit.
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*/
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#include <linux/namei.h>
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#include <linux/scatterlist.h>
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#include <crypto/hash.h>
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#include <crypto/sha2.h>
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#include <crypto/skcipher.h>
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#include "fscrypt_private.h"
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/*
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* struct fscrypt_nokey_name - identifier for directory entry when key is absent
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*
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* When userspace lists an encrypted directory without access to the key, the
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* filesystem must present a unique "no-key name" for each filename that allows
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* it to find the directory entry again if requested. Naively, that would just
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* mean using the ciphertext filenames. However, since the ciphertext filenames
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* can contain illegal characters ('\0' and '/'), they must be encoded in some
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* way. We use base64url. But that can cause names to exceed NAME_MAX (255
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* bytes), so we also need to use a strong hash to abbreviate long names.
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*
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* The filesystem may also need another kind of hash, the "dirhash", to quickly
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* find the directory entry. Since filesystems normally compute the dirhash
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* over the on-disk filename (i.e. the ciphertext), it's not computable from
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* no-key names that abbreviate the ciphertext using the strong hash to fit in
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* NAME_MAX. It's also not computable if it's a keyed hash taken over the
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* plaintext (but it may still be available in the on-disk directory entry);
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* casefolded directories use this type of dirhash. At least in these cases,
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* each no-key name must include the name's dirhash too.
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*
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* To meet all these requirements, we base64url-encode the following
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* variable-length structure. It contains the dirhash, or 0's if the filesystem
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* didn't provide one; up to 149 bytes of the ciphertext name; and for
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* ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
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*
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* This ensures that each no-key name contains everything needed to find the
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* directory entry again, contains only legal characters, doesn't exceed
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* NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
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* take the performance hit of SHA-256 on very long filenames (which are rare).
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*/
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struct fscrypt_nokey_name {
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u32 dirhash[2];
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u8 bytes[149];
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u8 sha256[SHA256_DIGEST_SIZE];
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}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */
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/*
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* Decoded size of max-size no-key name, i.e. a name that was abbreviated using
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* the strong hash and thus includes the 'sha256' field. This isn't simply
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* sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.
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*/
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#define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256)
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/* Encoded size of max-size no-key name */
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#define FSCRYPT_NOKEY_NAME_MAX_ENCODED \
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FSCRYPT_BASE64URL_CHARS(FSCRYPT_NOKEY_NAME_MAX)
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static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
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{
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if (str->len == 1 && str->name[0] == '.')
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return true;
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if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
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return true;
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return false;
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}
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/**
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* fscrypt_fname_encrypt() - encrypt a filename
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* @inode: inode of the parent directory (for regular filenames)
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* or of the symlink (for symlink targets)
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* @iname: the filename to encrypt
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* @out: (output) the encrypted filename
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* @olen: size of the encrypted filename. It must be at least @iname->len.
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* Any extra space is filled with NUL padding before encryption.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
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u8 *out, unsigned int olen)
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{
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struct skcipher_request *req = NULL;
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DECLARE_CRYPTO_WAIT(wait);
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const struct fscrypt_info *ci = inode->i_crypt_info;
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struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
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union fscrypt_iv iv;
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struct scatterlist sg;
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int res;
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/*
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* Copy the filename to the output buffer for encrypting in-place and
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* pad it with the needed number of NUL bytes.
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*/
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if (WARN_ON(olen < iname->len))
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return -ENOBUFS;
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memcpy(out, iname->name, iname->len);
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memset(out + iname->len, 0, olen - iname->len);
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/* Initialize the IV */
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fscrypt_generate_iv(&iv, 0, ci);
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/* Set up the encryption request */
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req = skcipher_request_alloc(tfm, GFP_NOFS);
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if (!req)
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return -ENOMEM;
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skcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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crypto_req_done, &wait);
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sg_init_one(&sg, out, olen);
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skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
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/* Do the encryption */
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res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
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skcipher_request_free(req);
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if (res < 0) {
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fscrypt_err(inode, "Filename encryption failed: %d", res);
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return res;
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}
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return 0;
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}
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/**
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* fname_decrypt() - decrypt a filename
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* @inode: inode of the parent directory (for regular filenames)
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* or of the symlink (for symlink targets)
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* @iname: the encrypted filename to decrypt
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* @oname: (output) the decrypted filename. The caller must have allocated
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* enough space for this, e.g. using fscrypt_fname_alloc_buffer().
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*
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* Return: 0 on success, -errno on failure
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*/
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static int fname_decrypt(const struct inode *inode,
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const struct fscrypt_str *iname,
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struct fscrypt_str *oname)
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{
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struct skcipher_request *req = NULL;
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DECLARE_CRYPTO_WAIT(wait);
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struct scatterlist src_sg, dst_sg;
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const struct fscrypt_info *ci = inode->i_crypt_info;
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struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
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union fscrypt_iv iv;
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int res;
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/* Allocate request */
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req = skcipher_request_alloc(tfm, GFP_NOFS);
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if (!req)
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return -ENOMEM;
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skcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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crypto_req_done, &wait);
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/* Initialize IV */
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fscrypt_generate_iv(&iv, 0, ci);
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/* Create decryption request */
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sg_init_one(&src_sg, iname->name, iname->len);
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sg_init_one(&dst_sg, oname->name, oname->len);
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skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
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res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
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skcipher_request_free(req);
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if (res < 0) {
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fscrypt_err(inode, "Filename decryption failed: %d", res);
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return res;
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}
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oname->len = strnlen(oname->name, iname->len);
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return 0;
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}
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static const char base64url_table[65] =
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"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
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#define FSCRYPT_BASE64URL_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
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/**
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* fscrypt_base64url_encode() - base64url-encode some binary data
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* @src: the binary data to encode
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* @srclen: the length of @src in bytes
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* @dst: (output) the base64url-encoded string. Not NUL-terminated.
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*
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* Encodes data using base64url encoding, i.e. the "Base 64 Encoding with URL
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* and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't used,
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* as it's unneeded and not required by the RFC. base64url is used instead of
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* base64 to avoid the '/' character, which isn't allowed in filenames.
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*
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* Return: the length of the resulting base64url-encoded string in bytes.
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* This will be equal to FSCRYPT_BASE64URL_CHARS(srclen).
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*/
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static int fscrypt_base64url_encode(const u8 *src, int srclen, char *dst)
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{
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u32 ac = 0;
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int bits = 0;
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int i;
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char *cp = dst;
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for (i = 0; i < srclen; i++) {
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ac = (ac << 8) | src[i];
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bits += 8;
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do {
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bits -= 6;
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*cp++ = base64url_table[(ac >> bits) & 0x3f];
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} while (bits >= 6);
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}
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if (bits)
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*cp++ = base64url_table[(ac << (6 - bits)) & 0x3f];
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return cp - dst;
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}
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/**
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* fscrypt_base64url_decode() - base64url-decode a string
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* @src: the string to decode. Doesn't need to be NUL-terminated.
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* @srclen: the length of @src in bytes
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* @dst: (output) the decoded binary data
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*
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* Decodes a string using base64url encoding, i.e. the "Base 64 Encoding with
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* URL and Filename Safe Alphabet" specified by RFC 4648. '='-padding isn't
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* accepted, nor are non-encoding characters such as whitespace.
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*
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* This implementation hasn't been optimized for performance.
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*
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* Return: the length of the resulting decoded binary data in bytes,
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* or -1 if the string isn't a valid base64url string.
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*/
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static int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)
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{
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u32 ac = 0;
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int bits = 0;
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int i;
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u8 *bp = dst;
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for (i = 0; i < srclen; i++) {
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const char *p = strchr(base64url_table, src[i]);
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if (p == NULL || src[i] == 0)
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return -1;
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ac = (ac << 6) | (p - base64url_table);
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bits += 6;
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if (bits >= 8) {
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bits -= 8;
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*bp++ = (u8)(ac >> bits);
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}
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}
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if (ac & ((1 << bits) - 1))
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return -1;
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return bp - dst;
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}
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bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
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u32 orig_len, u32 max_len,
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u32 *encrypted_len_ret)
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{
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int padding = 4 << (fscrypt_policy_flags(policy) &
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FSCRYPT_POLICY_FLAGS_PAD_MASK);
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u32 encrypted_len;
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if (orig_len > max_len)
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return false;
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encrypted_len = max(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
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encrypted_len = round_up(encrypted_len, padding);
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*encrypted_len_ret = min(encrypted_len, max_len);
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return true;
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}
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/**
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* fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
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* @max_encrypted_len: maximum length of encrypted filenames the buffer will be
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* used to present
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* @crypto_str: (output) buffer to allocate
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*
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* Allocate a buffer that is large enough to hold any decrypted or encoded
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* filename (null-terminated), for the given maximum encrypted filename length.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_fname_alloc_buffer(u32 max_encrypted_len,
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struct fscrypt_str *crypto_str)
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{
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u32 max_presented_len = max_t(u32, FSCRYPT_NOKEY_NAME_MAX_ENCODED,
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max_encrypted_len);
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crypto_str->name = kmalloc(max_presented_len + 1, GFP_NOFS);
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if (!crypto_str->name)
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return -ENOMEM;
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crypto_str->len = max_presented_len;
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return 0;
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}
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EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
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/**
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* fscrypt_fname_free_buffer() - free a buffer for presented filenames
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* @crypto_str: the buffer to free
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*
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* Free a buffer that was allocated by fscrypt_fname_alloc_buffer().
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*/
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void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
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{
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if (!crypto_str)
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return;
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kfree(crypto_str->name);
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crypto_str->name = NULL;
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}
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EXPORT_SYMBOL(fscrypt_fname_free_buffer);
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/**
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* fscrypt_fname_disk_to_usr() - convert an encrypted filename to
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* user-presentable form
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* @inode: inode of the parent directory (for regular filenames)
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* or of the symlink (for symlink targets)
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* @hash: first part of the name's dirhash, if applicable. This only needs to
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* be provided if the filename is located in an indexed directory whose
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* encryption key may be unavailable. Not needed for symlink targets.
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* @minor_hash: second part of the name's dirhash, if applicable
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* @iname: encrypted filename to convert. May also be "." or "..", which
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* aren't actually encrypted.
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* @oname: output buffer for the user-presentable filename. The caller must
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* have allocated enough space for this, e.g. using
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* fscrypt_fname_alloc_buffer().
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*
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* If the key is available, we'll decrypt the disk name. Otherwise, we'll
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* encode it for presentation in fscrypt_nokey_name format.
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* See struct fscrypt_nokey_name for details.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_fname_disk_to_usr(const struct inode *inode,
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u32 hash, u32 minor_hash,
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const struct fscrypt_str *iname,
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struct fscrypt_str *oname)
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{
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const struct qstr qname = FSTR_TO_QSTR(iname);
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struct fscrypt_nokey_name nokey_name;
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u32 size; /* size of the unencoded no-key name */
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if (fscrypt_is_dot_dotdot(&qname)) {
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oname->name[0] = '.';
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oname->name[iname->len - 1] = '.';
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oname->len = iname->len;
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return 0;
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}
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if (iname->len < FS_CRYPTO_BLOCK_SIZE)
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return -EUCLEAN;
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if (fscrypt_has_encryption_key(inode))
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return fname_decrypt(inode, iname, oname);
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/*
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* Sanity check that struct fscrypt_nokey_name doesn't have padding
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* between fields and that its encoded size never exceeds NAME_MAX.
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*/
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BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, dirhash) !=
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offsetof(struct fscrypt_nokey_name, bytes));
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BUILD_BUG_ON(offsetofend(struct fscrypt_nokey_name, bytes) !=
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offsetof(struct fscrypt_nokey_name, sha256));
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BUILD_BUG_ON(FSCRYPT_NOKEY_NAME_MAX_ENCODED > NAME_MAX);
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nokey_name.dirhash[0] = hash;
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nokey_name.dirhash[1] = minor_hash;
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if (iname->len <= sizeof(nokey_name.bytes)) {
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memcpy(nokey_name.bytes, iname->name, iname->len);
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size = offsetof(struct fscrypt_nokey_name, bytes[iname->len]);
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} else {
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memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes));
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/* Compute strong hash of remaining part of name. */
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sha256(&iname->name[sizeof(nokey_name.bytes)],
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iname->len - sizeof(nokey_name.bytes),
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nokey_name.sha256);
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size = FSCRYPT_NOKEY_NAME_MAX;
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}
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oname->len = fscrypt_base64url_encode((const u8 *)&nokey_name, size,
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oname->name);
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return 0;
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}
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EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
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/**
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* fscrypt_setup_filename() - prepare to search a possibly encrypted directory
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* @dir: the directory that will be searched
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* @iname: the user-provided filename being searched for
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* @lookup: 1 if we're allowed to proceed without the key because it's
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* ->lookup() or we're finding the dir_entry for deletion; 0 if we cannot
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* proceed without the key because we're going to create the dir_entry.
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* @fname: the filename information to be filled in
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*
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* Given a user-provided filename @iname, this function sets @fname->disk_name
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* to the name that would be stored in the on-disk directory entry, if possible.
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* If the directory is unencrypted this is simply @iname. Else, if we have the
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* directory's encryption key, then @iname is the plaintext, so we encrypt it to
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* get the disk_name.
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*
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* Else, for keyless @lookup operations, @iname should be a no-key name, so we
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* decode it to get the struct fscrypt_nokey_name. Non-@lookup operations will
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* be impossible in this case, so we fail them with ENOKEY.
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*
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* If successful, fscrypt_free_filename() must be called later to clean up.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
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int lookup, struct fscrypt_name *fname)
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{
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struct fscrypt_nokey_name *nokey_name;
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int ret;
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memset(fname, 0, sizeof(struct fscrypt_name));
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fname->usr_fname = iname;
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if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
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fname->disk_name.name = (unsigned char *)iname->name;
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fname->disk_name.len = iname->len;
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return 0;
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}
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ret = fscrypt_get_encryption_info(dir, lookup);
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if (ret)
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return ret;
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if (fscrypt_has_encryption_key(dir)) {
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if (!fscrypt_fname_encrypted_size(&dir->i_crypt_info->ci_policy,
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iname->len, NAME_MAX,
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&fname->crypto_buf.len))
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return -ENAMETOOLONG;
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fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
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GFP_NOFS);
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if (!fname->crypto_buf.name)
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return -ENOMEM;
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ret = fscrypt_fname_encrypt(dir, iname, fname->crypto_buf.name,
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fname->crypto_buf.len);
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if (ret)
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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 = fscrypt_base64url_decode(iname->name, iname->len,
|
|
fname->crypto_buf.name);
|
|
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_info *ci = dir->i_crypt_info;
|
|
|
|
WARN_ON(!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 dentry *dentry, unsigned int flags)
|
|
{
|
|
struct dentry *dir;
|
|
int err;
|
|
int valid;
|
|
|
|
/*
|
|
* 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.
|
|
*
|
|
* Although fscrypt forbids rename() on no-key names, we still must use
|
|
* dget_parent() here rather than use ->d_parent directly. That's
|
|
* because a corrupted fs image may contain directory hard links, which
|
|
* the VFS handles by moving the directory's dentry tree in the dcache
|
|
* each time ->lookup() finds the directory and it already has a dentry
|
|
* elsewhere. Thus ->d_parent can be changing, and we must safely grab
|
|
* a reference to some ->d_parent to prevent it from being freed.
|
|
*/
|
|
|
|
if (flags & LOOKUP_RCU)
|
|
return -ECHILD;
|
|
|
|
dir = dget_parent(dentry);
|
|
/*
|
|
* Pass allow_unsupported=true, so that files with an unsupported
|
|
* encryption policy can be deleted.
|
|
*/
|
|
err = fscrypt_get_encryption_info(d_inode(dir), true);
|
|
valid = !fscrypt_has_encryption_key(d_inode(dir));
|
|
dput(dir);
|
|
|
|
if (err < 0)
|
|
return err;
|
|
|
|
return valid;
|
|
}
|
|
EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);
|