From b28f8b3ebd7f00eb69216e1a7ea4c6ae241ee519 Mon Sep 17 00:00:00 2001
From: SomberNight <SomberNight@users.noreply.github.com>
Date: Mon, 6 Nov 2017 12:27:47 +0100
Subject: [PATCH] make tx deserialization more robust to ill-formed tx

---
 gui/qt/main_window.py | 20 ++++++++++++++------
 lib/transaction.py    | 33 ++++++++++++++++++---------------
 2 files changed, 32 insertions(+), 21 deletions(-)

diff --git a/gui/qt/main_window.py b/gui/qt/main_window.py
index c2cfb06e..1cfd6e67 100644
--- a/gui/qt/main_window.py
+++ b/gui/qt/main_window.py
@@ -2119,17 +2119,25 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
         return self.tx_from_text(file_content)
 
     def do_process_from_text(self):
+        from electrum.transaction import SerializationError
         text = text_dialog(self, _('Input raw transaction'), _("Transaction:"), _("Load transaction"))
         if not text:
             return
-        tx = self.tx_from_text(text)
-        if tx:
-            self.show_transaction(tx)
+        try:
+            tx = self.tx_from_text(text)
+            if tx:
+                self.show_transaction(tx)
+        except SerializationError as e:
+            self.show_critical(_("Electrum was unable to deserialize the transaction:") + "\n" + str(e))
 
     def do_process_from_file(self):
-        tx = self.read_tx_from_file()
-        if tx:
-            self.show_transaction(tx)
+        from electrum.transaction import SerializationError
+        try:
+            tx = self.read_tx_from_file()
+            if tx:
+                self.show_transaction(tx)
+        except SerializationError as e:
+            self.show_critical(_("Electrum was unable to deserialize the transaction:") + "\n" + str(e))
 
     def do_process_from_txid(self):
         from electrum import transaction
diff --git a/lib/transaction.py b/lib/transaction.py
index b5094738..eec28744 100644
--- a/lib/transaction.py
+++ b/lib/transaction.py
@@ -77,10 +77,7 @@ class BCDataStream(object):
         if self.input is None:
             raise SerializationError("call write(bytes) before trying to deserialize")
 
-        try:
-            length = self.read_compact_size()
-        except IndexError:
-            raise SerializationError("attempt to read past end of buffer")
+        length = self.read_compact_size()
 
         return self.read_bytes(length).decode(encoding)
 
@@ -117,15 +114,18 @@ class BCDataStream(object):
     def write_uint64(self, val): return self._write_num('<Q', val)
 
     def read_compact_size(self):
-        size = self.input[self.read_cursor]
-        self.read_cursor += 1
-        if size == 253:
-            size = self._read_num('<H')
-        elif size == 254:
-            size = self._read_num('<I')
-        elif size == 255:
-            size = self._read_num('<Q')
-        return size
+        try:
+            size = self.input[self.read_cursor]
+            self.read_cursor += 1
+            if size == 253:
+                size = self._read_num('<H')
+            elif size == 254:
+                size = self._read_num('<I')
+            elif size == 255:
+                size = self._read_num('<Q')
+            return size
+        except IndexError:
+            raise SerializationError("attempt to read past end of buffer")
 
     def write_compact_size(self, size):
         if size < 0:
@@ -143,8 +143,11 @@ class BCDataStream(object):
             self._write_num('<Q', size)
 
     def _read_num(self, format):
-        (i,) = struct.unpack_from(format, self.input, self.read_cursor)
-        self.read_cursor += struct.calcsize(format)
+        try:
+            (i,) = struct.unpack_from(format, self.input, self.read_cursor)
+            self.read_cursor += struct.calcsize(format)
+        except Exception as e:
+            raise SerializationError(e)
         return i
 
     def _write_num(self, format, num):