fscrypt updates for 5.14

A couple bug fixes for fs/crypto/:
 
 - Fix handling of major dirhash values that happen to be 0.
 
 - Fix cases where keys were derived differently on big endian systems
   than on little endian systems (affecting some newer features only).
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Merge tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt

Pull fscrypt updates from Eric Biggers:
 "A couple bug fixes for fs/crypto/:

   - Fix handling of major dirhash values that happen to be 0.

   - Fix cases where keys were derived differently on big endian systems
     than on little endian systems (affecting some newer features only)"

* tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt:
  fscrypt: fix derivation of SipHash keys on big endian CPUs
  fscrypt: don't ignore minor_hash when hash is 0

fs/crypto/fname.c

@@ -344,13 +344,9 @@ int fscrypt_fname_disk_to_usr(const struct inode *inode,
 		     offsetof(struct fscrypt_nokey_name, sha256));
 	BUILD_BUG_ON(BASE64_CHARS(FSCRYPT_NOKEY_NAME_MAX) > NAME_MAX);
 
-	if (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]);

fs/crypto/keysetup.c

@@ -210,15 +210,40 @@ out_unlock:
 	return err;
 }
 
+/*
+ * Derive a SipHash key from the given fscrypt master key and the given
+ * application-specific information string.
+ *
+ * Note that the KDF produces a byte array, but the SipHash APIs expect the key
+ * as a pair of 64-bit words.  Therefore, on big endian CPUs we have to do an
+ * endianness swap in order to get the same results as on little endian CPUs.
+ */
+static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
+				      u8 context, const u8 *info,
+				      unsigned int infolen, siphash_key_t *key)
+{
+	int err;
+
+	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
+				  (u8 *)key, sizeof(*key));
+	if (err)
+		return err;
+
+	BUILD_BUG_ON(sizeof(*key) != 16);
+	BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
+	le64_to_cpus(&key->key[0]);
+	le64_to_cpus(&key->key[1]);
+	return 0;
+}
+
 int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
 			       const struct fscrypt_master_key *mk)
 {
 	int err;
 
-	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, HKDF_CONTEXT_DIRHASH_KEY,
+	err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
 					 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
-				  (u8 *)&ci->ci_dirhash_key,
+					 &ci->ci_dirhash_key);
-				  sizeof(ci->ci_dirhash_key));
 	if (err)
 		return err;
 	ci->ci_dirhash_key_initialized = true;
@@ -253,10 +278,9 @@ static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_info *ci,
 		if (mk->mk_ino_hash_key_initialized)
 			goto unlock;
 
-		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
+		err = fscrypt_derive_siphash_key(mk,
-					  HKDF_CONTEXT_INODE_HASH_KEY, NULL, 0,
+						 HKDF_CONTEXT_INODE_HASH_KEY,
-					  (u8 *)&mk->mk_ino_hash_key,
+						 NULL, 0, &mk->mk_ino_hash_key);
-					  sizeof(mk->mk_ino_hash_key));
 		if (err)
 			goto unlock;
 		/* pairs with smp_load_acquire() above */