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client.rb
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# frozen_string_literal: true
module SMTPServer
class Client
extend HasPrometheusMetrics
include HasPrometheusMetrics
CRAM_MD5_DIGEST = OpenSSL::Digest.new("md5")
LOG_REDACTION_STRING = "[redacted]"
attr_reader :logging_enabled
attr_reader :credential
attr_reader :ip_address
attr_reader :recipients
attr_reader :headers
attr_reader :state
attr_reader :helo_name
def initialize(ip_address)
@logging_enabled = true
@ip_address = ip_address
@cr_present = false
@previous_cr_present = nil
if @ip_address
check_ip_address
@state = :welcome
else
@state = :preauth
end
transaction_reset
end
def check_ip_address
return unless @ip_address &&
Postal::Config.smtp_server.log_ip_address_exclusion_matcher &&
@ip_address =~ Regexp.new(Postal::Config.smtp_server.log_ip_address_exclusion_matcher)
@logging_enabled = false
end
def transaction_reset
@recipients = []
@mail_from = nil
@data = nil
@headers = nil
end
def trace_id
@trace_id ||= SecureRandom.alphanumeric(8).upcase
end
def handle(data)
if data[-1] == "\r"
@cr_present = true
data = data.chop # remove last character (\r)
else
# This doesn't use `logger` because that will be nil when logging is disabled
# and we always want to log this.
Postal.logger&.warn("Detected line with invalid line ending (missing <CR>)", trace_id: trace_id)
@cr_present = false
end
if @state == :preauth
return proxy(data)
end
logger&.debug "\e[32m<= #{sanitize_input_for_log(data.strip)}\e[0m"
if @proc
@proc.call(data)
else
handle_command(data)
end
ensure
@previous_cr_present = @cr_present
end
def finished?
@finished || false
end
def start_tls?
@start_tls || false
end
attr_writer :start_tls
def handle_command(data)
case data
when /^QUIT/i then quit
when /^STARTTLS/i then starttls
when /^EHLO/i then ehlo(data)
when /^HELO/i then helo(data)
when /^RSET/i then rset
when /^NOOP/i then noop
when /^AUTH PLAIN/i then auth_plain(data)
when /^AUTH LOGIN/i then auth_login(data)
when /^AUTH CRAM-MD5/i then auth_cram_md5(data)
when /^MAIL FROM/i then mail_from(data)
when /^RCPT TO/i then rcpt_to(data)
when /^DATA/i then data(data)
else
increment_error_count("invalid-command")
"502 Invalid/unsupported command"
end
end
def logger
return nil unless @logging_enabled
@logger ||= Postal.logger.create_tagged_logger(trace_id: trace_id)
end
private
def proxy(data)
# inet-protocol, client-ip, proxy-ip, client-port, proxy-port
if m = data.match(/\APROXY (.+) (.+) (.+) (.+) (.+)\z/)
@ip_address = m[2]
check_ip_address
@state = :welcome
logger&.debug "\e[35mClient identified as #{@ip_address}\e[0m"
increment_command_count("PROXY")
return "220 #{Postal::Config.postal.smtp_hostname} ESMTP Postal/#{trace_id}"
end
@finished = true
increment_error_count("proxy-error")
"502 Proxy Error"
end
def quit
@finished = true
"221 Closing Connection"
end
def starttls
if Postal::Config.smtp_server.tls_enabled?
@start_tls = true
@tls = true
increment_command_count("STARTLS")
"220 Ready to start TLS"
else
increment_error_count("tls-unavailable")
"502 TLS not available"
end
end
def ehlo(data)
@helo_name = data.strip.split(" ", 2)[1]
transaction_reset
@state = :welcomed
increment_command_count("EHLO")
[
"250-My capabilities are",
Postal::Config.smtp_server.tls_enabled? && !@tls ? "250-STARTTLS" : nil,
"250 AUTH CRAM-MD5 PLAIN LOGIN",
].compact
end
def helo(data)
@helo_name = data.strip.split(" ", 2)[1]
transaction_reset
@state = :welcomed
increment_command_count("HELO")
"250 #{Postal::Config.postal.smtp_hostname}"
end
def rset
transaction_reset
@state = :welcomed
increment_command_count("RSET")
"250 OK"
end
def noop
"250 OK"
end
def auth_plain(data)
increment_command_count("AUTH PLAIN")
handler = proc do |idata|
@proc = nil
idata = Base64.decode64(idata)
parts = idata.split("\0")
username = parts[-2]
password = parts[-1]
unless username && password
increment_error_count("missing-credentials")
next "535 Authenticated failed - protocol error"
end
authenticate(password)
end
data = data.gsub(/AUTH PLAIN ?/i, "")
if data.strip == ""
@proc = handler
@password_expected_next = true
"334"
else
handler.call(data)
end
end
def auth_login(data)
increment_command_count("AUTH LOGIN")
password_handler = proc do |idata|
@proc = nil
password = Base64.decode64(idata)
authenticate(password)
end
username_handler = proc do
@proc = password_handler
@password_expected_next = true
"334 UGFzc3dvcmQ6" # "Password:"
end
data = data.gsub(/AUTH LOGIN ?/i, "")
if data.strip == ""
@proc = username_handler
"334 VXNlcm5hbWU6" # "Username:"
else
username_handler.call(nil)
end
end
def authenticate(password)
if @credential = Credential.where(type: "SMTP", key: password).first
@credential.use
"235 Granted for #{@credential.server.organization.permalink}/#{@credential.server.permalink}"
else
logger&.warn "Authentication failure for #{@ip_address}"
increment_error_count("invalid-credentials")
"535 Invalid credential"
end
end
def auth_cram_md5(data)
increment_command_count("AUTH CRAM-MD5")
challenge = Digest::SHA1.hexdigest(Time.now.to_i.to_s + rand(100_000).to_s)
challenge = "<#{challenge[0, 20]}@#{Postal::Config.postal.smtp_hostname}>"
handler = proc do |idata|
@proc = nil
username, password = Base64.decode64(idata).split(" ", 2).map { |a| a.chomp }
org_permlink, server_permalink = username.split(/[\/_]/, 2)
server = ::Server.includes(:organization).where(organizations: { permalink: org_permlink }, permalink: server_permalink).first
if server.nil?
logger&.warn "Authentication failure for #{@ip_address} (no server found matching #{username})"
increment_error_count("invalid-credentials")
next "535 Denied"
end
grant = nil
server.credentials.where(type: "SMTP").each do |credential|
correct_response = OpenSSL::HMAC.hexdigest(CRAM_MD5_DIGEST, credential.key, challenge)
next unless password == correct_response
@credential = credential
@credential.use
logger&.debug "Authenticated with with credential #{credential.id}"
grant = "235 Granted for #{credential.server.organization.permalink}/#{credential.server.permalink}"
break
end
if grant.nil?
logger&.warn "Authentication failure for #{@ip_address} (invalid credential)"
increment_error_count("invalid-credentials")
next "535 Denied"
end
grant
end
@proc = handler
"334 " + Base64.encode64(challenge).gsub(/[\r\n]/, "")
end
def mail_from(data)
unless in_state(:welcomed, :mail_from_received)
increment_error_count("mail-from-out-of-order")
return "503 EHLO/HELO first please"
end
@state = :mail_from_received
transaction_reset
if data =~ /AUTH=/
# Discard AUTH= parameter and anything that follows.
# We don't need this parameter as we don't trust any client to set it
mail_from_line = data.sub(/ *AUTH=.*/, "")
else
mail_from_line = data
end
@mail_from = mail_from_line.gsub(/MAIL FROM\s*:\s*/i, "").gsub(/.*</, "").gsub(/>.*/, "").strip
"250 OK"
end
def rcpt_to(data)
unless in_state(:mail_from_received, :rcpt_to_received)
increment_error_count("rcpt-to-out-of-order")
return "503 EHLO/HELO and MAIL FROM first please"
end
rcpt_to = data.gsub(/RCPT TO\s*:\s*/i, "").gsub(/.*</, "").gsub(/>.*/, "").strip
if rcpt_to.blank?
increment_error_count("empty-rcpt-to")
return "501 RCPT TO should not be empty"
end
uname, domain = rcpt_to.split("@", 2)
if domain.blank?
increment_error_count("invalid-rcpt-to")
return "501 Invalid RCPT TO"
end
uname, tag = uname.split("+", 2)
if domain == Postal::Config.dns.return_path_domain || domain =~ /\A#{Regexp.escape(Postal::Config.dns.custom_return_path_prefix)}\./
# This is a return path
@state = :rcpt_to_received
if server = ::Server.where(token: uname).first
if server.suspended?
increment_error_count("server-suspended")
"535 Mail server has been suspended"
else
logger&.debug "Added bounce on server #{server.id}"
@recipients << [:bounce, rcpt_to, server]
"250 OK"
end
else
increment_error_count("invalid-server-token")
"550 Invalid server token"
end
elsif domain == Postal::Config.dns.route_domain
# This is an email direct to a route. This isn't actually supported yet.
@state = :rcpt_to_received
if route = Route.where(token: uname).first
if route.server.suspended?
increment_error_count("server-suspended")
"535 Mail server has been suspended"
elsif route.mode == "Reject"
increment_error_count("route-rejected")
"550 Route does not accept incoming messages"
else
logger&.debug "Added route #{route.id} to recipients (tag: #{tag.inspect})"
actual_rcpt_to = "#{route.name}#{tag ? "+#{tag}" : ''}@#{route.domain.name}"
@recipients << [:route, actual_rcpt_to, route.server, { route: route }]
"250 OK"
end
else
"550 Invalid route token"
end
elsif @credential
# This is outgoing mail for an authenticated user
@state = :rcpt_to_received
if @credential.server.suspended?
increment_error_count("server-suspended")
"535 Mail server has been suspended"
else
logger&.debug "Added external address '#{rcpt_to}'"
@recipients << [:credential, rcpt_to, @credential.server]
"250 OK"
end
elsif uname && domain && route = Route.find_by_name_and_domain(uname, domain)
# This is incoming mail for a route
@state = :rcpt_to_received
if route.server.suspended?
increment_error_count("server-suspended")
"535 Mail server has been suspended"
elsif route.mode == "Reject"
increment_error_count("route-rejection")
"550 Route does not accept incoming messages"
else
logger&.debug "Added route #{route.id} to recipients (tag: #{tag.inspect})"
@recipients << [:route, rcpt_to, route.server, { route: route }]
"250 OK"
end
else
# User is trying to relay but is not authenticated. Try to authenticate by IP address
@credential = Credential.where(type: "SMTP-IP").all.sort_by { |c| c.ipaddr&.prefix || 0 }.reverse.find do |credential|
credential.ipaddr.include?(@ip_address) || (credential.ipaddr.ipv4? && credential.ipaddr.ipv4_mapped.include?(@ip_address))
end
if @credential
# Retry with credential
@credential.use
rcpt_to(data)
else
increment_error_count("authentication-required")
logger&.warn "Authentication failure for #{@ip_address}"
"530 Authentication required"
end
end
end
def data(_data)
unless in_state(:rcpt_to_received)
increment_error_count("data-out-of-order")
return "503 HELO/EHLO, MAIL FROM and RCPT TO before sending data"
end
@data = String.new.force_encoding("BINARY")
@headers = {}
@receiving_headers = true
received_header = ReceivedHeader.generate(@credential&.server, @helo_name, @ip_address, :smtp)
.force_encoding("BINARY")
@data << "Received: #{received_header}\r\n"
@headers["received"] = [received_header]
handler = proc do |idata|
if idata == "." && @cr_present && @previous_cr_present
@logging_enabled = true
@proc = nil
finished
else
idata = idata.to_s.sub(/\A\.\./, ".")
if @credential&.server&.log_smtp_data?
# We want to log if enabled
else
logger&.debug "Not logging further message data."
@logging_enabled = false
end
if @receiving_headers
if idata&.length&.zero?
@receiving_headers = false
elsif idata.to_s =~ /^\s/
# This is a continuation of a header
if @header_key && @headers[@header_key.downcase] && @headers[@header_key.downcase].last
@headers[@header_key.downcase].last << idata.to_s
end
else
@header_key, value = idata.split(/:\s*/, 2)
@headers[@header_key.downcase] ||= []
@headers[@header_key.downcase] << value
end
end
@data << idata
@data << "\r\n"
nil
end
end
@proc = handler
"354 Go ahead"
end
def finished
if @data.bytesize > Postal::Config.smtp_server.max_message_size.megabytes.to_i
transaction_reset
@state = :welcomed
increment_error_count("message-too-large")
return format("552 Message too large (maximum size %dMB)", Postal::Config.smtp_server.max_message_size)
end
if @headers["received"].grep(/by #{Postal::Config.postal.smtp_hostname}/).count > 4
transaction_reset
@state = :welcomed
increment_error_count("loop-detected")
return "550 Loop detected"
end
authenticated_domain = nil
if @credential
authenticated_domain = @credential.server.find_authenticated_domain_from_headers(@headers)
if authenticated_domain.nil?
transaction_reset
@state = :welcomed
increment_error_count("from-name-invalid")
return "530 From/Sender name is not valid"
end
end
@recipients.each do |recipient|
type, rcpt_to, server, options = recipient
case type
when :credential
increment_message_count("outgoing")
# Outgoing messages are just inserted
message = server.message_db.new_message
message.rcpt_to = rcpt_to
message.mail_from = @mail_from
message.raw_message = @data
message.received_with_ssl = @tls
message.scope = "outgoing"
message.domain_id = authenticated_domain&.id
message.credential_id = @credential.id
message.save
when :bounce
increment_message_count("bounce")
if rp_route = server.routes.where(name: "__returnpath__").first
# If there's a return path route, we can use this to create the message
rp_route.create_messages do |msg|
msg.rcpt_to = rcpt_to
msg.mail_from = @mail_from
msg.raw_message = @data
msg.received_with_ssl = @tls
msg.bounce = 1
end
else
# There's no return path route, we just need to insert the mesage
# without going through the route.
message = server.message_db.new_message
message.rcpt_to = rcpt_to
message.mail_from = @mail_from
message.raw_message = @data
message.received_with_ssl = @tls
message.scope = "incoming"
message.bounce = 1
message.save
end
when :route
increment_message_count("incoming")
options[:route].create_messages do |msg|
msg.rcpt_to = rcpt_to
msg.mail_from = @mail_from
msg.raw_message = @data
msg.received_with_ssl = @tls
end
end
end
transaction_reset
@state = :welcomed
"250 OK"
end
def in_state(*states)
states.include?(@state)
end
def sanitize_input_for_log(data)
if @password_expected_next
@password_expected_next = false
if data =~ /\A[a-z0-9]{3,}=*\z/i
return LOG_REDACTION_STRING
end
end
data = data.dup
data.gsub!(/(.*AUTH \w+) (.*)\z/i) { "#{::Regexp.last_match(1)} #{LOG_REDACTION_STRING}" }
data
end
def increment_error_count(error)
increment_prometheus_counter :postal_smtp_server_client_errors, labels: { error: error }
end
def increment_command_count(command)
increment_prometheus_counter :postal_smtp_server_commands_total, labels: { command: command }
end
def increment_message_count(type)
increment_prometheus_counter :postal_smtp_server_messages_total, labels: {
type: type,
tls: @tls ? "yes" : "no"
}
end
class << self
def register_prometheus_metrics
register_prometheus_counter :postal_smtp_server_commands_total,
docstring: "The number of key commands received by the server",
labels: [:command]
register_prometheus_counter :postal_smtp_server_client_errors,
docstring: "The number of errors sent to a client",
labels: [:error]
register_prometheus_counter :postal_smtp_server_messages_total,
docstring: "The number of messages accepted by the SMTP server",
labels: [:type, :tls]
end
end
end
end