119 lines
3.6 KiB
Ruby
119 lines
3.6 KiB
Ruby
# frozen_string_literal: true
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module Banzai
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module Filter
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# Sanitize HTML
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#
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# Extends HTML::Pipeline::SanitizationFilter with a custom whitelist.
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class SanitizationFilter < HTML::Pipeline::SanitizationFilter
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include Gitlab::Utils::StrongMemoize
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UNSAFE_PROTOCOLS = %w(data javascript vbscript).freeze
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TABLE_ALIGNMENT_PATTERN = /text-align: (?<alignment>center|left|right)/
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def whitelist
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strong_memoize(:whitelist) do
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customize_whitelist(super.deep_dup)
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end
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end
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private
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def customize_whitelist(whitelist)
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# Allow table alignment; we whitelist specific text-align values in a
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# transformer below
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whitelist[:attributes]['th'] = %w(style)
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whitelist[:attributes]['td'] = %w(style)
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whitelist[:css] = { properties: ['text-align'] }
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# Allow span elements
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whitelist[:elements].push('span')
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# Allow data-math-style attribute in order to support LaTeX formatting
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whitelist[:attributes]['code'] = %w(data-math-style)
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whitelist[:attributes]['pre'] = %w(data-math-style)
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# Allow html5 details/summary elements
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whitelist[:elements].push('details')
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whitelist[:elements].push('summary')
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# Allow abbr elements with title attribute
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whitelist[:elements].push('abbr')
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whitelist[:attributes]['abbr'] = %w(title)
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# Disallow `name` attribute globally, allow on `a`
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whitelist[:attributes][:all].delete('name')
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whitelist[:attributes]['a'].push('name')
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# Allow any protocol in `a` elements...
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whitelist[:protocols].delete('a')
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# ...but then remove links with unsafe protocols
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whitelist[:transformers].push(self.class.remove_unsafe_links)
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# Remove `rel` attribute from `a` elements
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whitelist[:transformers].push(self.class.remove_rel)
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# Remove any `style` properties not required for table alignment
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whitelist[:transformers].push(self.class.remove_unsafe_table_style)
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whitelist
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end
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class << self
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def remove_unsafe_links
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lambda do |env|
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node = env[:node]
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return unless node.name == 'a'
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return unless node.has_attribute?('href')
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begin
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node['href'] = node['href'].strip
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uri = Addressable::URI.parse(node['href'])
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return unless uri.scheme
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# Remove all invalid scheme characters before checking against the
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# list of unsafe protocols.
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#
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# See https://tools.ietf.org/html/rfc3986#section-3.1
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scheme = uri.scheme
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.strip
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.downcase
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.gsub(/[^A-Za-z0-9\+\.\-]+/, '')
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node.remove_attribute('href') if UNSAFE_PROTOCOLS.include?(scheme)
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rescue Addressable::URI::InvalidURIError
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node.remove_attribute('href')
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end
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end
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end
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def remove_rel
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lambda do |env|
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if env[:node_name] == 'a'
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env[:node].remove_attribute('rel')
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end
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end
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end
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def remove_unsafe_table_style
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lambda do |env|
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node = env[:node]
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return unless node.name == 'th' || node.name == 'td'
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return unless node.has_attribute?('style')
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if node['style'] =~ TABLE_ALIGNMENT_PATTERN
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node['style'] = "text-align: #{$~[:alignment]}"
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else
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node.remove_attribute('style')
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end
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end
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end
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end
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end
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end
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end
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