From 0d9ad0a8445e7ba6e8bf9591257fa4457dda8321 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= <essen@ninenines.eu>
Date: Mon, 26 Nov 2018 11:52:27 +0100
Subject: Use the correct CRC32 algorithm for the PROXY header

Turns out it wasn't the plain CRC32 algorithm that should have
been used, whoops!

The implementation was adapted from pseudo code from
Thomas Cioppettini.

I've renamed the PROXY header building option value for
checksum from crc32 to crc32c and updated the documentation.
There is no support for plain crc32 checksums.
---
 src/ranch_proxy_header.erl | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

(limited to 'src/ranch_proxy_header.erl')

diff --git a/src/ranch_proxy_header.erl b/src/ranch_proxy_header.erl
index 837ce2d..081157f 100644
--- a/src/ranch_proxy_header.erl
+++ b/src/ranch_proxy_header.erl
@@ -48,7 +48,7 @@
 -export_type([proxy_info/0]).
 
 -type build_opts() :: #{
-	checksum => crc32,
+	checksum => crc32c,
 	padding => pos_integer() %% >= 3
 }.
 
@@ -482,6 +482,18 @@ parse_v2_test() ->
 		Path/binary, 0:Padding,
 		"GET / HTTP/1.1\r\n">>),
 	ok.
+
+parse_v2_regression_test() ->
+	%% Real packet received from AWS. We confirm that the CRC32C
+	%% check succeeds only (in other words that ok is returned).
+	{ok, _, <<>>} = parse(<<
+		13, 10, 13, 10, 0, 13, 10, 81, 85, 73, 84, 10, 33, 17, 0, 84,
+		172, 31, 7, 113, 172, 31, 10, 31, 200, 242, 0, 80, 3, 0, 4,
+		232, 214, 137, 45, 234, 0, 23, 1, 118, 112, 99, 101, 45, 48,
+		56, 100, 50, 98, 102, 49, 53, 102, 97, 99, 53, 48, 48, 49, 99,
+		57, 4, 0, 36, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>>),
+	ok.
 -endif.
 
 parse_tlv(Rest, 0, Info, _) ->
@@ -497,8 +509,8 @@ parse_tlv(<<16#3, TLVLen:16, CRC32C:32, Rest/bits>>, Len0, Info, Header) when TL
 	Len = Len0 - TLVLen - 3,
 	BeforeLen = byte_size(Header) - Len - TLVLen,
 	<<Before:BeforeLen/binary, _:32, After:Len/binary>> = Header,
-	%% The initial CRC is erlang:crc32(<<"\r\n\r\n\0\r\nQUIT\n", 2:4, 1:4>>).
-	case erlang:crc32(1302506282, [Before, <<0:32>>, After]) of
+	%% The initial CRC is ranch_crc32c:crc32c(<<"\r\n\r\n\0\r\nQUIT\n", 2:4, 1:4>>).
+	case ranch_crc32c:crc32c(2900412422, [Before, <<0:32>>, After]) of
 		CRC32C ->
 			parse_tlv(Rest, Len, Info, Header);
 		_ ->
@@ -591,7 +603,7 @@ header(ProxyInfo=#{version := 2, command := proxy,
 	Addresses = addresses(ProxyInfo),
 	TLVs = tlvs(ProxyInfo, Opts),
 	ExtraLen = case Opts of
-		#{checksum := crc32} -> 7;
+		#{checksum := crc32c} -> 7;
 		_ -> 0
 	end,
 	Len = iolist_size(Addresses) + iolist_size(TLVs) + ExtraLen,
@@ -603,8 +615,8 @@ header(ProxyInfo=#{version := 2, command := proxy,
 		TLVs
 	],
 	case Opts of
-		#{checksum := crc32} ->
-			CRC32C = erlang:crc32([Header, <<16#3, 4:16, 0:32>>]),
+		#{checksum := crc32c} ->
+			CRC32C = ranch_crc32c:crc32c([Header, <<16#3, 4:16, 0:32>>]),
 			[Header, <<16#3, 4:16, CRC32C:32>>];
 		_ ->
 			Header
@@ -849,7 +861,7 @@ v2_checksum_test() ->
 		dest_address => {10, 11, 12, 13},
 		dest_port => 23456
 	},
-	{ok, Test, <<>>} = parse(iolist_to_binary(header(Test, #{checksum => crc32}))),
+	{ok, Test, <<>>} = parse(iolist_to_binary(header(Test, #{checksum => crc32c}))),
 	ok.
 
 v2_padding_test() ->
-- 
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