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Fix the fallback from UDP to TCP due to message truncation
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If truncation is detected, return immediately from decode so that
the UDP connection can be retried with TCP, instead of failing to
decode due to trying to decode a truncated response.

Fixes [Bug #13513]
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@jeremyevans
jeremyevans committed Nov 24, 2023
1 parent 09d141d commit 0de996d
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Showing 2 changed files with 176 additions and 2 deletions.
6 changes: 4 additions & 2 deletions lib/resolv.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -1533,13 +1533,15 @@ def Message.decode(m)
id, flag, qdcount, ancount, nscount, arcount =
msg.get_unpack('nnnnnn')
o.id = id
o.tc = (flag >> 9) & 1
o.rcode = flag & 15
return o unless o.tc.zero?

o.qr = (flag >> 15) & 1
o.opcode = (flag >> 11) & 15
o.aa = (flag >> 10) & 1
o.tc = (flag >> 9) & 1
o.rd = (flag >> 8) & 1
o.ra = (flag >> 7) & 1
o.rcode = flag & 15
(1..qdcount).each {
name, typeclass = msg.get_question
o.add_question(name, typeclass)
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172 changes: 172 additions & 0 deletions test/resolv/test_dns.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,16 @@ def teardown
BasicSocket.do_not_reverse_lookup = @save_do_not_reverse_lookup
end

def with_tcp(host, port)
t = TCPServer.new(host, port)
begin
t.listen(1)
yield t
ensure
t.close
end
end

def with_udp(host, port)
u = UDPSocket.new
begin
Expand Down Expand Up @@ -157,6 +167,168 @@ def test_query_ipv4_address
}
end

def test_query_ipv4_address_truncated_tcp_fallback
begin
OpenSSL
rescue LoadError
skip 'autoload problem. see [ruby-dev:45021][Bug #5786]'
end if defined?(OpenSSL)

num_records = 50

with_udp('127.0.0.1', 0) {|u|
_, server_port, _, server_address = u.addr
with_tcp('127.0.0.1', server_port) {|t|
client_thread = Thread.new {
Resolv::DNS.open(:nameserver_port => [[server_address, server_port]]) {|dns|
dns.getresources("foo.example.org", Resolv::DNS::Resource::IN::A)
}
}
udp_server_thread = Thread.new {
msg, (_, client_port, _, client_address) = Timeout.timeout(5) {u.recvfrom(4096)}
id, word2, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")
qr = (word2 & 0x8000) >> 15
opcode = (word2 & 0x7800) >> 11
aa = (word2 & 0x0400) >> 10
tc = (word2 & 0x0200) >> 9
rd = (word2 & 0x0100) >> 8
ra = (word2 & 0x0080) >> 7
z = (word2 & 0x0070) >> 4
rcode = word2 & 0x000f
rest = msg[12..-1]
assert_equal(0, qr) # 0:query 1:response
assert_equal(0, opcode) # 0:QUERY 1:IQUERY 2:STATUS
assert_equal(0, aa) # Authoritative Answer
assert_equal(0, tc) # TrunCation
assert_equal(1, rd) # Recursion Desired
assert_equal(0, ra) # Recursion Available
assert_equal(0, z) # Reserved for future use
assert_equal(0, rcode) # 0:No-error 1:Format-error 2:Server-failure 3:Name-Error 4:Not-Implemented 5:Refused
assert_equal(1, qdcount) # number of entries in the question section.
assert_equal(0, ancount) # number of entries in the answer section.
assert_equal(0, nscount) # number of entries in the authority records section.
assert_equal(0, arcount) # number of entries in the additional records section.
name = [3, "foo", 7, "example", 3, "org", 0].pack("Ca*Ca*Ca*C")
assert_operator(rest, :start_with?, name)
rest = rest[name.length..-1]
assert_equal(4, rest.length)
qtype, _ = rest.unpack("nn")
assert_equal(1, qtype) # A
assert_equal(1, qtype) # IN
id = id
qr = 1
opcode = opcode
aa = 0
tc = 1
rd = rd
ra = 1
z = 0
rcode = 0
qdcount = 0
ancount = num_records
nscount = 0
arcount = 0
word2 = (qr << 15) |
(opcode << 11) |
(aa << 10) |
(tc << 9) |
(rd << 8) |
(ra << 7) |
(z << 4) |
rcode
msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
type = 1
klass = 1
ttl = 3600
rdlength = 4
num_records.times do |i|
rdata = [192,0,2,i].pack("CCCC") # 192.0.2.x (TEST-NET address) RFC 3330
rr = [name, type, klass, ttl, rdlength, rdata].pack("a*nnNna*")
msg << rr
end
u.send(msg[0...512], 0, client_address, client_port)
}
tcp_server_thread = Thread.new {
ct = t.accept
msg = ct.recv(512)
msg.slice!(0..1) # Size (only for TCP)
id, word2, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")
qr = (word2 & 0x8000) >> 15
opcode = (word2 & 0x7800) >> 11
aa = (word2 & 0x0400) >> 10
tc = (word2 & 0x0200) >> 9
rd = (word2 & 0x0100) >> 8
ra = (word2 & 0x0080) >> 7
z = (word2 & 0x0070) >> 4
rcode = word2 & 0x000f
rest = msg[12..-1]
assert_equal(0, qr) # 0:query 1:response
assert_equal(0, opcode) # 0:QUERY 1:IQUERY 2:STATUS
assert_equal(0, aa) # Authoritative Answer
assert_equal(0, tc) # TrunCation
assert_equal(1, rd) # Recursion Desired
assert_equal(0, ra) # Recursion Available
assert_equal(0, z) # Reserved for future use
assert_equal(0, rcode) # 0:No-error 1:Format-error 2:Server-failure 3:Name-Error 4:Not-Implemented 5:Refused
assert_equal(1, qdcount) # number of entries in the question section.
assert_equal(0, ancount) # number of entries in the answer section.
assert_equal(0, nscount) # number of entries in the authority records section.
assert_equal(0, arcount) # number of entries in the additional records section.
name = [3, "foo", 7, "example", 3, "org", 0].pack("Ca*Ca*Ca*C")
assert_operator(rest, :start_with?, name)
rest = rest[name.length..-1]
assert_equal(4, rest.length)
qtype, _ = rest.unpack("nn")
assert_equal(1, qtype) # A
assert_equal(1, qtype) # IN
id = id
qr = 1
opcode = opcode
aa = 0
tc = 0
rd = rd
ra = 1
z = 0
rcode = 0
qdcount = 0
ancount = num_records
nscount = 0
arcount = 0
word2 = (qr << 15) |
(opcode << 11) |
(aa << 10) |
(tc << 9) |
(rd << 8) |
(ra << 7) |
(z << 4) |
rcode
msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
type = 1
klass = 1
ttl = 3600
rdlength = 4
num_records.times do |i|
rdata = [192,0,2,i].pack("CCCC") # 192.0.2.x (TEST-NET address) RFC 3330
rr = [name, type, klass, ttl, rdlength, rdata].pack("a*nnNna*")
msg << rr
end
msg = "#{[msg.bytesize].pack("n")}#{msg}" # Prefix with size
ct.send(msg, 0)
ct.close
}
result, _ = assert_join_threads([client_thread, udp_server_thread, tcp_server_thread])
assert_instance_of(Array, result)
assert_equal(50, result.length)
result.each_with_index do |rr, i|
assert_instance_of(Resolv::DNS::Resource::IN::A, rr)
assert_instance_of(Resolv::IPv4, rr.address)
assert_equal("192.0.2.#{i}", rr.address.to_s)
assert_equal(3600, rr.ttl)
end
}
}
end

def test_query_ipv4_duplicate_responses
begin
OpenSSL
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