diff options
Diffstat (limited to 'fs/crypto/fname.c')
| -rw-r--r-- | fs/crypto/fname.c | 514 |
1 files changed, 514 insertions, 0 deletions
diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c new file mode 100644 index 000000000..629eb0d72 --- /dev/null +++ b/fs/crypto/fname.c @@ -0,0 +1,514 @@ +// 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); |