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198 lines
5.3 KiB
198 lines
5.3 KiB
# frozen_string_literal: true
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class SpamCheck
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include Redisable
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include ActionView::Helpers::TextHelper
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# Threshold over which two Nilsimsa values are considered
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# to refer to the same text
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NILSIMSA_COMPARE_THRESHOLD = 95
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# Nilsimsa doesn't work well on small inputs, so below
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# this size, we check only for exact matches with MD5
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NILSIMSA_MIN_SIZE = 10
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# How long to keep the trail of digests between updates,
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# there is no reason to store it forever
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EXPIRE_SET_AFTER = 1.week.seconds
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# How many digests to keep in an account's trail. If it's
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# too small, spam could rotate around different message templates
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MAX_TRAIL_SIZE = 10
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# How many detected duplicates to allow through before
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# considering the message as spam
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THRESHOLD = 5
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def initialize(status)
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@account = status.account
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@status = status
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end
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def skip?
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disabled? || already_flagged? || trusted? || no_unsolicited_mentions? || solicited_reply?
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end
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def spam?
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if insufficient_data?
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false
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elsif nilsimsa?
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digests_over_threshold?('nilsimsa') { |_, other_digest| nilsimsa_compare_value(digest, other_digest) >= NILSIMSA_COMPARE_THRESHOLD }
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else
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digests_over_threshold?('md5') { |_, other_digest| other_digest == digest }
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end
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end
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def flag!
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auto_report_status!
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end
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def remember!
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# The scores in sorted sets don't actually have enough bits to hold an exact
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# value of our snowflake IDs, so we use it only for its ordering property. To
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# get the correct status ID back, we have to save it in the string value
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redis.zadd(redis_key, @status.id, digest_with_algorithm)
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redis.zremrangebyrank(redis_key, 0, -(MAX_TRAIL_SIZE + 1))
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redis.expire(redis_key, EXPIRE_SET_AFTER)
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end
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def reset!
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redis.del(redis_key)
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end
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def hashable_text
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return @hashable_text if defined?(@hashable_text)
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@hashable_text = @status.text
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@hashable_text = remove_mentions(@hashable_text)
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@hashable_text = strip_tags(@hashable_text) unless @status.local?
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@hashable_text = normalize_unicode(@status.spoiler_text + ' ' + @hashable_text)
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@hashable_text = remove_whitespace(@hashable_text)
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end
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def insufficient_data?
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hashable_text.blank?
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end
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def digest
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@digest ||= begin
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if nilsimsa?
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Nilsimsa.new(hashable_text).hexdigest
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else
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Digest::MD5.hexdigest(hashable_text)
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end
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end
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end
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def digest_with_algorithm
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if nilsimsa?
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['nilsimsa', digest, @status.id].join(':')
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else
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['md5', digest, @status.id].join(':')
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end
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end
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class << self
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def perform(status)
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spam_check = new(status)
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return if spam_check.skip?
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if spam_check.spam?
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spam_check.flag!
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else
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spam_check.remember!
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end
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end
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end
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private
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def disabled?
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!Setting.spam_check_enabled
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end
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def remove_mentions(text)
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return text.gsub(Account::MENTION_RE, '') if @status.local?
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Nokogiri::HTML.fragment(text).tap do |html|
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mentions = @status.mentions.map { |mention| ActivityPub::TagManager.instance.url_for(mention.account) }
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html.traverse do |element|
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element.unlink if element.name == 'a' && mentions.include?(element['href'])
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end
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end.to_s
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end
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def normalize_unicode(text)
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text.unicode_normalize(:nfkc).downcase
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end
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def remove_whitespace(text)
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text.gsub(/\s+/, ' ').strip
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end
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def auto_report_status!
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status_ids = Status.where(visibility: %i(public unlisted)).where(id: matching_status_ids).pluck(:id) + [@status.id] if @status.distributable?
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ReportService.new.call(Account.representative, @account, status_ids: status_ids, comment: I18n.t('spam_check.spam_detected'))
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end
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def already_flagged?
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@account.silenced? || @account.targeted_reports.unresolved.where(account_id: -99).exists?
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end
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def trusted?
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@account.trust_level > Account::TRUST_LEVELS[:untrusted]
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end
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def no_unsolicited_mentions?
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@status.mentions.all? { |mention| mention.silent? || (!@account.local? && !mention.account.local?) || mention.account.following?(@account) }
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end
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def solicited_reply?
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!@status.thread.nil? && @status.thread.mentions.where(account: @account).exists?
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end
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def nilsimsa_compare_value(first, second)
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first = [first].pack('H*')
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second = [second].pack('H*')
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bits = 0
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0.upto(31) do |i|
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bits += Nilsimsa::POPC[255 & (first[i].ord ^ second[i].ord)].ord
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end
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128 - bits # -128 <= Nilsimsa Compare Value <= 128
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end
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def nilsimsa?
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hashable_text.size > NILSIMSA_MIN_SIZE
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end
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def other_digests
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redis.zrange(redis_key, 0, -1)
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end
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def digests_over_threshold?(filter_algorithm)
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other_digests.select do |record|
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algorithm, other_digest, status_id = record.split(':')
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next unless algorithm == filter_algorithm
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yield algorithm, other_digest, status_id
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end.size >= THRESHOLD
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end
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def matching_status_ids
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if nilsimsa?
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other_digests.select { |record| record.start_with?('nilsimsa') && nilsimsa_compare_value(digest, record.split(':')[1]) >= NILSIMSA_COMPARE_THRESHOLD }.map { |record| record.split(':')[2] }.compact
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else
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other_digests.select { |record| record.start_with?('md5') && record.split(':')[1] == digest }.map { |record| record.split(':')[2] }.compact
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end
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end
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def redis_key
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@redis_key ||= "spam_check:#{@account.id}"
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end
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end
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