The error raised by wrong BPF filter syntax is uncaught when using AsyncSniffer. #3567
Description
Brief description
The error raised by wrong BPF filter syntax in AsyncSniffer is not caught.
Scapy version
2.4.5
Python version
3.9.7
Operating system
Linux 5.13.0-37-generic
Additional environment information
This behavior is only reproducible on Linux, it couldn't be reproduced on Windows.
I didn't try on MAC.
How to reproduce
Step 1:
Open scapy
Step 2:
Run the following lines of code:
e = AsyncSniffer(filter='adawdadadsadaaw')
e.start()
Step 3:
Observe that:
- the incorrect filter error is uncaught
- the AsyncSniffer doesn't capture packets
- e.running is True, even though there was an error raised and the AsyncSniffer dosen't catch anything.
Actual result
Exception in thread AsyncSniffer:
Traceback (most recent call last):
File "/usr/lib/python3.9/threading.py", line 973, in _bootstrap_inner
self.run()
File "/usr/lib/python3.9/threading.py", line 910, in run
self._target(*self._args, **self._kwargs)
File "/usr/local/lib/python3.9/dist-packages/scapy/sendrecv.py", line 1127, in _run
sniff_sockets[L2socket(type=ETH_P_ALL, iface=iface,
File "/usr/local/lib/python3.9/dist-packages/scapy/arch/linux.py", line 497, in __init__
attach_filter(self.ins, filter, self.iface)
File "/usr/local/lib/python3.9/dist-packages/scapy/arch/linux.py", line 166, in attach_filter
bp = compile_filter(bpf_filter, iface)
File "/usr/local/lib/python3.9/dist-packages/scapy/arch/common.py", line 156, in compile_filter
raise Scapy_Exception(
scapy.error.Scapy_Exception: Failed to compile filter expression adawdadadsadaaw (-1)
Expected result
The error should be caught.
For lack of a better section, I will add more info here:
After a brief investigation, this behavior might be caused by the fact that:
File scapy/scapy/arch/linux.py line 498, there is a try-except, whose except catches only ImportErrors:
if filter is not None:
try:
attach_filter(self.ins, filter, self.iface)
except ImportError as ex:
log_runtime.error("Cannot set filter: %s", ex)
If the except is edited to catch all exceptions, the error is caught and the problematic behavior is eliminated.
if filter is not None:
try:
attach_filter(self.ins, filter, self.iface)
except Exception as ex:
log_runtime.error("Cannot set filter: %s", ex)
Example after modification:
>>> e = AsyncSniffer(filter='adawdadadsadaaw')
>>> e.start()
>>> ERROR: Cannot set filter: Failed to compile filter expression adawdadadsadaaw (-1)
>>>
>>> e.stop()
<Sniffed: TCP:35 UDP:0 ICMP:0 Other:0>
>>>
Related resources
No response