Fix of possible DoS attack related session_cipher_decrypt processing

src/session_builder.c

@@ -45,11 +45,13 @@ int session_builder_create(session_builder **builder,
 }
 
 int session_builder_process_pre_key_signal_message(session_builder *builder,
-        session_record *record, pre_key_signal_message *message, uint32_t *unsigned_pre_key_id)
+        session_record *record, pre_key_signal_message *message, uint32_t *unsigned_pre_key_id,
+        uint8_t *identity_key_changed)
 {
     int result = 0;
     int has_unsigned_pre_key_id_result = 0;
     uint32_t unsigned_pre_key_id_result = 0;
+    *identity_key_changed = 0;
     ec_public_key *their_identity_key = pre_key_signal_message_get_identity_key(message);
 
     result = signal_protocol_identity_is_trusted_identity(builder->store,
@@ -75,6 +77,9 @@ int session_builder_process_pre_key_signal_message(session_builder *builder,
     if(result < 0) {
         goto complete;
     }
+    else if(result == 0) {
+        *identity_key_changed = 1;
+    }
 
     result = has_unsigned_pre_key_id_result;
 

src/session_builder_internal.h

@@ -13,6 +13,8 @@
  * @param message The received pre_key_signal_message.
  * @param unsigned_pre_key_id set to the unsigned pre key ID, if available.
  *     Return value indicates whether or not this value is available.
+ * @param identity_key_changed set to 1 if identity key was changed during processing,
+ *     otherwise 0.
  * @retval 0 Success, no unsigned pre key value available
  * @retval 1 Success, an unsigned pre key is available
  * @retval SG_ERR_INVALID_KEY_ID when there is no local pre_key_record that
@@ -21,6 +23,7 @@
  * @retval SG_ERR_UNTRUSTED_IDENTITY when the identity key of the sender is untrusted.
  */
 int session_builder_process_pre_key_signal_message(session_builder *builder,
-        session_record *record, pre_key_signal_message *message, uint32_t *unsigned_pre_key_id);
+        session_record *record, pre_key_signal_message *message, uint32_t *unsigned_pre_key_id,
+        uint8_t *identity_key_changed);
 
 #endif /* SESSION_BUILDER_INTERNAL_H */

src/session_cipher.c

@@ -265,6 +265,7 @@ int session_cipher_decrypt_pre_key_signal_message(session_cipher *cipher,
     session_record *record = 0;
     int has_unsigned_pre_key_id = 0;
     uint32_t unsigned_pre_key_id = 0;
+    uint8_t identity_key_changed = 0;
 
     assert(cipher);
     signal_lock(cipher->global_context);
@@ -279,7 +280,7 @@ int session_cipher_decrypt_pre_key_signal_message(session_cipher *cipher,
         goto complete;
     }
 
-    result = session_builder_process_pre_key_signal_message(cipher->builder, record, ciphertext, &unsigned_pre_key_id);
+    result = session_builder_process_pre_key_signal_message(cipher->builder, record, ciphertext, &unsigned_pre_key_id, &identity_key_changed);
     if(result < 0) {
         goto complete;
     }
@@ -289,6 +290,10 @@ int session_cipher_decrypt_pre_key_signal_message(session_cipher *cipher,
             pre_key_signal_message_get_signal_message(ciphertext),
             &result_buf);
     if(result < 0) {
+        if(identity_key_changed) {
+            signal_protocol_identity_save_identity(cipher->store, cipher->remote_address, NULL);
+        }
+
         goto complete;
     }
 

src/signal_protocol.h

@@ -618,7 +618,7 @@ typedef struct signal_protocol_identity_key_store {
      * @param address the address of the remote client
      * @param key_data Pointer to the remote client's identity key, may be null
      * @param key_len Length of the remote client's identity key
-     * @return 0 on success, negative on failure
+     * @return 0 on success, 1 on the same identity key as already stored, negative on failure
      */
     int (*save_identity)(const signal_protocol_address *address, uint8_t *key_data, size_t key_len, void *user_data);
 

tests/test_common.c

@@ -646,7 +646,13 @@ int test_identity_key_store_save_identity(const signal_protocol_address *address
     HASH_FIND(hh, data->keys, &recipient_hash, sizeof(int64_t), s);
     if(s) {
         signal_buffer_free(s->identity_key);
-        s->identity_key = key_buf;
+        if (key_data == NULL) {
+            HASH_DEL(data->keys, s);
+            signal_buffer_free(key_buf);
+            return 0;
+        } else {
+            s->identity_key = key_buf;
+        }
     }
     else {
         s = malloc(sizeof(test_identity_store_key));