RecursionError in email.utils.parseaddr

[baltsers]

Bug report

We did a fuzzing test on Python3.9.15, a recursion error happened.

from email.utils import *
import email
import email.utils
import re

class demoCls():

    def __init__(self):
        pass

    def demoFunc(self, arg):
        try:
            ret = email.utils.parseaddr(arg)
        except (AttributeError, LookupError, OSError, TypeError, UnicodeEncodeError, ValueError):
            pass

with open("data.txt","r") as f:
    addr = f.readline()
    dc = demoCls()
    dc.demoFunc(addr)

code

The input value:

%usel�ayQ�WexQeGM4R:::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4:::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set:::::::::::::::::::::�����:::::::::::::�:::::::::::::::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::::::::::::::::::::set::::::::::::::::::::::::::::::::::�::::::::::::�_threshold2qR)phqzE7C4::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set:::::::::::::::::::::�����:::::::::::::�::::::::::::::::::::::::::::::::E7C4:::::::::::::::::::::::::::::set:::::::::::::::::::::�����:::::::::::::�::::::::::::�_threshold2qR)phqz

input

Bug info

Traceback (most recent call last):
  File "/root/fuzzVuls/Python3.9.15/email.utils.parseaddr/1#email#utils#parseaddr.py", line 20, in <module>
    dc.demoFunc(addr)
  File "/root/fuzzVuls/Python3.9.15/email.utils.parseaddr/1#email#utils#parseaddr.py", line 13, in demoFunc
    ret = email.utils.parseaddr(arg)
  File "/root/anaconda3/lib/python3.9/email/utils.py", line 212, in parseaddr
    addrs = _AddressList(addr).addresslist
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 513, in __init__
    self.addresslist = self.getaddrlist()
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 257, in getaddrlist
    ad = self.getaddress()
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 300, in getaddress
    returnlist = returnlist + self.getaddress()
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 300, in getaddress
    returnlist = returnlist + self.getaddress()
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 300, in getaddress
    returnlist = returnlist + self.getaddress()
  [Previous line repeated 989 more times]
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 267, in getaddress
    self.gotonext()
  File "/root/anaconda3/lib/python3.9/email/_parseaddr.py", line 239, in gotonext
    while self.pos < len(self.field):
RecursionError: maximum recursion depth exceeded while calling a Python object

My environment

CPython: 3.9.15
Ubuntu: 18.0.4 (x86 64)

[zware]

Can you explain why this is a problem that needs to be fixed? If you give pathological input to a function, an exception is not an unexpected result.

Also note that this can be reproduced with just the following:

from email.utils import parseaddr
parseaddr(':' * 100_000)

Please put some effort into reducing your reproducers to the smallest possible code before posting an issue.

[terryjreedy]

The RecursionError is not a bug when the (modifiable) recursion limit is reached. Nor is using recursion in our code, given that we have documented that our code has (undocumented) input size limits. So, not a bug.

There could possibly be a performance feaure request. returnlist = returnlist + self.getaddress() is the only direct recursion in getaddress. It is triggered by ':'. If there are no indirectly recursive calls, getaddress could be made tail recursive and thence iterative. (But not quite trivially.) However, given that parseaddr(':' * n) is ('', '') for n up to 1022 (on my machine in IDLE with default sys, 1023 raises RecursionError), I suspect that the default stack limit is sufficient for nearly all uses of Python's email module. If not, one can raise the stacklimit in code.

EDIT: replace incorrect statement and misleading example with corrected statement.