diff options
Diffstat (limited to 'fs/crypto')
| -rw-r--r-- | fs/crypto/Kconfig | 1 | ||||
| -rw-r--r-- | fs/crypto/fname.c | 218 |
2 files changed, 168 insertions, 51 deletions
diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig index 02df95b44331..8046d7c7a3e9 100644 --- a/fs/crypto/Kconfig +++ b/fs/crypto/Kconfig @@ -21,5 +21,6 @@ config FS_ENCRYPTION_ALGS select CRYPTO_CTS select CRYPTO_ECB select CRYPTO_HMAC + select CRYPTO_SHA256 select CRYPTO_SHA512 select CRYPTO_XTS diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c index 851d2082ecfe..4c212442a8f7 100644 --- a/fs/crypto/fname.c +++ b/fs/crypto/fname.c @@ -13,9 +13,85 @@ #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 struct crypto_shash *sha256_hash_tfm; + +static int fscrypt_do_sha256(const u8 *data, unsigned int data_len, u8 *result) +{ + struct crypto_shash *tfm = READ_ONCE(sha256_hash_tfm); + + if (unlikely(!tfm)) { + struct crypto_shash *prev_tfm; + + tfm = crypto_alloc_shash("sha256", 0, 0); + if (IS_ERR(tfm)) { + fscrypt_err(NULL, + "Error allocating SHA-256 transform: %ld", + PTR_ERR(tfm)); + return PTR_ERR(tfm); + } + prev_tfm = cmpxchg(&sha256_hash_tfm, NULL, tfm); + if (prev_tfm) { + crypto_free_shash(tfm); + tfm = prev_tfm; + } + } + { + SHASH_DESC_ON_STACK(desc, tfm); + + desc->tfm = tfm; + + return crypto_shash_digest(desc, data, data_len, result); + } +} + static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) { if (str->len == 1 && str->name[0] == '.') @@ -207,9 +283,7 @@ int fscrypt_fname_alloc_buffer(const struct inode *inode, u32 max_encrypted_len, struct fscrypt_str *crypto_str) { - const u32 max_encoded_len = - max_t(u32, BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE), - 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name))); + 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); @@ -242,9 +316,9 @@ EXPORT_SYMBOL(fscrypt_fname_free_buffer); * * The caller must have allocated sufficient memory for the @oname string. * - * If the key is available, we'll decrypt the disk name; otherwise, we'll encode - * it for presentation. Short names are directly base64-encoded, while long - * names are encoded in fscrypt_digested_name format. + * 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 */ @@ -254,7 +328,9 @@ int fscrypt_fname_disk_to_usr(const struct inode *inode, struct fscrypt_str *oname) { const struct qstr qname = FSTR_TO_QSTR(iname); - struct fscrypt_digested_name digested_name; + struct fscrypt_nokey_name nokey_name; + u32 size; /* size of the unencoded no-key name */ + int err; if (fscrypt_is_dot_dotdot(&qname)) { oname->name[0] = '.'; @@ -269,24 +345,37 @@ int fscrypt_fname_disk_to_usr(const struct inode *inode, if (fscrypt_has_encryption_key(inode)) return fname_decrypt(inode, iname, oname); - if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) { - oname->len = base64_encode(iname->name, iname->len, - oname->name); - return 0; - } + /* + * 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); + if (hash) { - digested_name.hash = hash; - digested_name.minor_hash = minor_hash; + nokey_name.dirhash[0] = hash; + nokey_name.dirhash[1] = minor_hash; + } else { + nokey_name.dirhash[0] = 0; + nokey_name.dirhash[1] = 0; + } + 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 { - digested_name.hash = 0; - digested_name.minor_hash = 0; + memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes)); + /* Compute strong hash of remaining part of name. */ + err = fscrypt_do_sha256(&iname->name[sizeof(nokey_name.bytes)], + iname->len - sizeof(nokey_name.bytes), + nokey_name.sha256); + if (err) + return err; + size = FSCRYPT_NOKEY_NAME_MAX; } - memcpy(digested_name.digest, - FSCRYPT_FNAME_DIGEST(iname->name, iname->len), - FSCRYPT_FNAME_DIGEST_SIZE); - oname->name[0] = '_'; - oname->len = 1 + base64_encode((const u8 *)&digested_name, - sizeof(digested_name), oname->name + 1); + oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name); return 0; } EXPORT_SYMBOL(fscrypt_fname_disk_to_usr); @@ -307,8 +396,7 @@ EXPORT_SYMBOL(fscrypt_fname_disk_to_usr); * get the disk_name. * * Else, for keyless @lookup operations, @iname is the presented ciphertext, so - * we decode it to get either the ciphertext disk_name (for short names) or the - * fscrypt_digested_name (for long names). Non-@lookup operations will be + * we decode it to get the 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. @@ -318,8 +406,8 @@ EXPORT_SYMBOL(fscrypt_fname_disk_to_usr); 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; - int digested; memset(fname, 0, sizeof(struct fscrypt_name)); fname->usr_fname = iname; @@ -359,40 +447,31 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname, * We don't have the key and we are doing a lookup; decode the * user-supplied name */ - if (iname->name[0] == '_') { - if (iname->len != - 1 + BASE64_CHARS(sizeof(struct fscrypt_digested_name))) - return -ENOENT; - digested = 1; - } else { - if (iname->len > - BASE64_CHARS(FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)) - return -ENOENT; - digested = 0; - } - fname->crypto_buf.name = - kmalloc(max_t(size_t, FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE, - sizeof(struct fscrypt_digested_name)), - GFP_KERNEL); + 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 + digested, iname->len - digested, - fname->crypto_buf.name); - if (ret < 0) { + 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; - if (digested) { - const struct fscrypt_digested_name *n = - (const void *)fname->crypto_buf.name; - fname->hash = n->hash; - fname->minor_hash = n->minor_hash; - } else { - fname->disk_name.name = fname->crypto_buf.name; - fname->disk_name.len = fname->crypto_buf.len; + + 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; @@ -403,6 +482,43 @@ errout: 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 sha256[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; + if (fscrypt_do_sha256(&de_name[sizeof(nokey_name->bytes)], + de_name_len - sizeof(nokey_name->bytes), sha256)) + return false; + return !memcmp(sha256, nokey_name->sha256, sizeof(sha256)); +} +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 |