From fdaa58a6fa5bd32190a81dade2e82337d2d34d2e Mon Sep 17 00:00:00 2001
From: Mark Qvist <mark@unsigned.io>
Date: Tue, 11 Jan 2022 03:06:16 +0100
Subject: [PATCH] Improved malformed packet detection

---
 RNS/Link.py      |  2 +-
 RNS/Packet.py    | 42 ++++++++++++++++++++++++------------------
 RNS/Transport.py |  4 +++-
 3 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/RNS/Link.py b/RNS/Link.py
index 9cc4019..1978389 100644
--- a/RNS/Link.py
+++ b/RNS/Link.py
@@ -765,7 +765,7 @@ class Link:
             return plaintext
         except Exception as e:
             RNS.log("Decryption failed on link "+str(self)+". The contained exception was: "+str(e), RNS.LOG_ERROR)
-            RNS.log(traceback.format_exc(), RNS.LOG_ERROR)
+            # RNS.log(traceback.format_exc(), RNS.LOG_ERROR)
             # TODO: Think long about implications here
             # self.teardown()
 
diff --git a/RNS/Packet.py b/RNS/Packet.py
index 77b1c9a..e196b3e 100755
--- a/RNS/Packet.py
+++ b/RNS/Packet.py
@@ -185,27 +185,33 @@ class Packet:
 
 
     def unpack(self):
-        self.flags = self.raw[0]
-        self.hops  = self.raw[1]
+        try:
+            self.flags = self.raw[0]
+            self.hops  = self.raw[1]
 
-        self.header_type      = (self.flags & 0b11000000) >> 6
-        self.transport_type   = (self.flags & 0b00110000) >> 4
-        self.destination_type = (self.flags & 0b00001100) >> 2
-        self.packet_type      = (self.flags & 0b00000011)
+            self.header_type      = (self.flags & 0b11000000) >> 6
+            self.transport_type   = (self.flags & 0b00110000) >> 4
+            self.destination_type = (self.flags & 0b00001100) >> 2
+            self.packet_type      = (self.flags & 0b00000011)
 
-        if self.header_type == Packet.HEADER_2:
-            self.transport_id = self.raw[2:12]
-            self.destination_hash = self.raw[12:22]
-            self.context = ord(self.raw[22:23])
-            self.data = self.raw[23:]
-        else:
-            self.transport_id = None
-            self.destination_hash = self.raw[2:12]
-            self.context = ord(self.raw[12:13])
-            self.data = self.raw[13:]
+            if self.header_type == Packet.HEADER_2:
+                self.transport_id = self.raw[2:12]
+                self.destination_hash = self.raw[12:22]
+                self.context = ord(self.raw[22:23])
+                self.data = self.raw[23:]
+            else:
+                self.transport_id = None
+                self.destination_hash = self.raw[2:12]
+                self.context = ord(self.raw[12:13])
+                self.data = self.raw[13:]
 
-        self.packed = False
-        self.update_hash()
+            self.packed = False
+            self.update_hash()
+            return True
+
+        except Exception as e:
+            RNS.log("Received malformed packet, dropping it. The contained exception was: "+str(e), RNS.LOG_EXTREME)
+            return False
 
     def send(self):
         """
diff --git a/RNS/Transport.py b/RNS/Transport.py
index 0d397fb..55fb8d9 100755
--- a/RNS/Transport.py
+++ b/RNS/Transport.py
@@ -585,7 +585,9 @@ class Transport:
         Transport.jobs_locked = True
         
         packet = RNS.Packet(None, raw)
-        packet.unpack()
+        if not packet.unpack():
+            return
+            
         packet.receiving_interface = interface
         packet.hops += 1