Add linter to check for catastrophic backtracking in Python re module

[mschwager]

• Catastrophic backtracking
• Preventing Regular Expression Denial of Service (ReDoS)

Some Python examples with catastrophic backtracking:

import re


bad_string = 'a' * 64 + '!'
bad_regexs = [
    r'(a+)+',
    r'([a-zA-Z]+)*',
    r'(a|aa)+',
    r'(a|a?)+',
    r'(.*a){20}',
]

boom = [
    re.search(bad_regex, bad_string)
    for bad_regex in bad_regexs
]

We'll need a way to parse regex patterns in a programmatic way (convert to NFA?). From here we can analyze patterns in re calls and check for catastrophic behavior. The prevention document above lists a few initial behaviors to search for.