From 70bd87e19d6c7cf98de83f87eb40a77487b908b7 Mon Sep 17 00:00:00 2001
From: Pierre LALET <pierre.lalet@cea.fr>
Date: Wed, 8 Mar 2017 08:29:57 +0100
Subject: [PATCH] Increase TCP.answers() robustness
---
scapy/layers/inet.py | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/scapy/layers/inet.py b/scapy/layers/inet.py
index b1c04232..f20bf1d2 100644
--- a/scapy/layers/inet.py
+++ b/scapy/layers/inet.py
@@ -521,14 +521,29 @@ class TCP(Packet):
def answers(self, other):
if not isinstance(other, TCP):
return 0
+ # RST packets don't get answers
+ if other.flags.R:
+ return 0
+ # We do not support the four-way handshakes with the SYN+ACK
+ # answer split in two packets (one ACK and one SYN): in that
+ # case the ACK will be seen as an answer, but not the SYN.
+ if self.flags.S:
+ # SYN packets without ACK are not answers
+ if not self.flags.A:
+ return 0
+ # SYN+ACK packets answer SYN packets
+ if not other.flags.S:
+ return 0
if conf.checkIPsrc:
if not ((self.sport == other.dport) and
(self.dport == other.sport)):
return 0
- if abs(other.ack - self.seq) > 2:
+ # Do not check ack value for SYN packets without ACK
+ if not (other.flags.S and not other.flags.A) \
+ and abs(other.ack - self.seq) > 2:
return 0
- # Do not check ack value for RST packets when ack is 0
- if self.flags.R and not self.ack:
+ # Do not check ack value for RST packets without ACK
+ if self.flags.R and not self.flags.A:
return 1
if abs(other.seq - self.ack) > 2 + len(other.payload):
return 0
--
GitLab