Change spam check to apply to local accounts and add a threshold (#11806)
Instead of detecting spam on first duplicate message, add a threshold of 5 such messages to reduce false positives
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@ -408,15 +408,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
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end
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def check_for_spam
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spam_check = SpamCheck.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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SpamCheck.perform(@status)
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end
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def forward_for_reply
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@ -4,9 +4,25 @@ 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_MIN_SIZE = 10
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EXPIRE_SET_AFTER = 1.week.seconds
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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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@ -21,9 +37,9 @@ class SpamCheck
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if insufficient_data?
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false
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elsif nilsimsa?
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any_other_digest?('nilsimsa') { |_, other_digest| nilsimsa_compare_value(digest, other_digest) >= NILSIMSA_COMPARE_THRESHOLD }
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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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any_other_digest?('md5') { |_, other_digest| other_digest == digest }
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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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@ -38,7 +54,7 @@ class SpamCheck
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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', '-10')
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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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@ -78,6 +94,20 @@ class SpamCheck
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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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@ -149,14 +179,14 @@ class SpamCheck
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redis.zrange(redis_key, 0, -1)
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end
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def any_other_digest?(filter_algorithm)
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other_digests.any? do |record|
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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
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end.size >= THRESHOLD
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end
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def matching_status_ids
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@ -33,6 +33,7 @@ class ProcessMentionsService < BaseService
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end
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status.save!
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check_for_spam(status)
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mentions.each { |mention| create_notification(mention) }
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end
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@ -61,4 +62,8 @@ class ProcessMentionsService < BaseService
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def resolve_account_service
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ResolveAccountService.new
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end
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def check_for_spam(status)
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SpamCheck.perform(status)
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end
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end
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@ -86,23 +86,33 @@ RSpec.describe SpamCheck do
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end
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it 'returns true for duplicate statuses to the same recipient' do
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status1 = status_with_html('@alice Hello')
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described_class.new(status1).remember!
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described_class::THRESHOLD.times do
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status1 = status_with_html('@alice Hello')
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described_class.new(status1).remember!
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end
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status2 = status_with_html('@alice Hello')
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expect(described_class.new(status2).spam?).to be true
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end
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it 'returns true for duplicate statuses to different recipients' do
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status1 = status_with_html('@alice Hello')
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described_class.new(status1).remember!
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described_class::THRESHOLD.times do
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status1 = status_with_html('@alice Hello')
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described_class.new(status1).remember!
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end
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status2 = status_with_html('@bob Hello')
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expect(described_class.new(status2).spam?).to be true
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end
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it 'returns true for nearly identical statuses with random numbers' do
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source_text = 'Sodium, atomic number 11, was first isolated by Humphry Davy in 1807. A chemical component of salt, he named it Na in honor of the saltiest region on earth, North America.'
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status1 = status_with_html('@alice ' + source_text + ' 1234')
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described_class.new(status1).remember!
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described_class::THRESHOLD.times do
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status1 = status_with_html('@alice ' + source_text + ' 1234')
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described_class.new(status1).remember!
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end
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status2 = status_with_html('@bob ' + source_text + ' 9568')
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expect(described_class.new(status2).spam?).to be true
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end
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@ -140,9 +150,9 @@ RSpec.describe SpamCheck do
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let(:redis_key) { spam_check.send(:redis_key) }
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it 'remembers' do
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expect do
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spam_check.remember!
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end.to change { Redis.current.exists(redis_key) }.from(false).to(true)
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expect(Redis.current.exists(redis_key)).to be true
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spam_check.remember!
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expect(Redis.current.exists(redis_key)).to be true
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end
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end
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@ -156,9 +166,9 @@ RSpec.describe SpamCheck do
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end
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it 'resets' do
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expect do
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spam_check.reset!
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end.to change { Redis.current.exists(redis_key) }.from(true).to(false)
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expect(Redis.current.exists(redis_key)).to be true
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spam_check.reset!
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expect(Redis.current.exists(redis_key)).to be false
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end
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end
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