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- // 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 <linux/namei.h>
- #include <linux/scatterlist.h>
- #include <crypto/hash.h>
- #include <crypto/sha.h>
- #include <crypto/skcipher.h>
- #include "fscrypt_private.h"
- /*
- * 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 base64. 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 base64-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 base64-encoded, which is <= NAME_MAX (255) */
- /*
- * Decoded size of max-size nokey 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)
- static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
- {
- if (str->len == 1 && str->name[0] == '.')
- return true;
- if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
- return true;
- return false;
- }
- /**
- * fscrypt_fname_encrypt() - encrypt a filename
- * @inode: inode of the parent directory (for regular filenames)
- * or of the symlink (for symlink targets)
- * @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)
- {
- struct skcipher_request *req = NULL;
- DECLARE_CRYPTO_WAIT(wait);
- const struct fscrypt_info *ci = inode->i_crypt_info;
- struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
- union fscrypt_iv iv;
- struct scatterlist sg;
- int res;
- /*
- * Copy the filename to the output buffer for encrypting in-place and
- * pad it with the needed number of NUL bytes.
- */
- if (WARN_ON(olen < iname->len))
- return -ENOBUFS;
- memcpy(out, iname->name, iname->len);
- memset(out + iname->len, 0, olen - iname->len);
- /* Initialize the IV */
- fscrypt_generate_iv(&iv, 0, ci);
- /* Set up the encryption request */
- req = skcipher_request_alloc(tfm, GFP_NOFS);
- if (!req)
- return -ENOMEM;
- skcipher_request_set_callback(req,
- CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
- crypto_req_done, &wait);
- sg_init_one(&sg, out, olen);
- skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
- /* Do the encryption */
- res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
- skcipher_request_free(req);
- if (res < 0) {
- fscrypt_err(inode, "Filename encryption failed: %d", res);
- return res;
- }
- return 0;
- }
- /**
- * 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)
- {
- struct skcipher_request *req = NULL;
- DECLARE_CRYPTO_WAIT(wait);
- struct scatterlist src_sg, dst_sg;
- const struct fscrypt_info *ci = inode->i_crypt_info;
- struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
- union fscrypt_iv iv;
- int res;
- /* Allocate request */
- req = skcipher_request_alloc(tfm, GFP_NOFS);
- if (!req)
- return -ENOMEM;
- skcipher_request_set_callback(req,
- CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
- crypto_req_done, &wait);
- /* Initialize IV */
- fscrypt_generate_iv(&iv, 0, ci);
- /* Create decryption request */
- 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);
- res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
- skcipher_request_free(req);
- if (res < 0) {
- fscrypt_err(inode, "Filename decryption failed: %d", res);
- return res;
- }
- oname->len = strnlen(oname->name, iname->len);
- return 0;
- }
- static const char lookup_table[65] =
- "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
- #define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
- /**
- * base64_encode() - base64-encode some bytes
- * @src: the bytes to encode
- * @len: number of bytes to encode
- * @dst: (output) the base64-encoded string. Not NUL-terminated.
- *
- * Encodes the input string using characters from the set [A-Za-z0-9+,].
- * The encoded string is roughly 4/3 times the size of the input string.
- *
- * Return: length of the encoded string
- */
- static int base64_encode(const u8 *src, int len, char *dst)
- {
- int i, bits = 0, ac = 0;
- char *cp = dst;
- for (i = 0; i < len; i++) {
- ac += src[i] << bits;
- bits += 8;
- do {
- *cp++ = lookup_table[ac & 0x3f];
- ac >>= 6;
- bits -= 6;
- } while (bits >= 6);
- }
- if (bits)
- *cp++ = lookup_table[ac & 0x3f];
- return cp - dst;
- }
- static int base64_decode(const char *src, int len, u8 *dst)
- {
- int i, bits = 0, ac = 0;
- const char *p;
- u8 *cp = dst;
- for (i = 0; i < len; i++) {
- p = strchr(lookup_table, src[i]);
- if (p == NULL || src[i] == 0)
- return -2;
- ac += (p - lookup_table) << bits;
- bits += 6;
- if (bits >= 8) {
- *cp++ = ac & 0xff;
- ac >>= 8;
- bits -= 8;
- }
- }
- if (ac)
- return -1;
- return cp - dst;
- }
- 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(orig_len, (u32)FS_CRYPTO_BLOCK_SIZE);
- encrypted_len = round_up(encrypted_len, padding);
- *encrypted_len_ret = min(encrypted_len, max_len);
- return true;
- }
- /**
- * 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)
- {
- const u32 max_encoded_len = BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX);
- u32 max_presented_len;
- max_presented_len = max(max_encoded_len, 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 < FS_CRYPTO_BLOCK_SIZE)
- 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(BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX) > 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);
- 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->i_crypt_info->ci_policy,
- iname->len,
- dir->i_sb->s_cop->max_namelen,
- &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 > BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX))
- 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);
- 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);
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