From 052af4a8072bbbd3bfe7edf46fe3c1b350f71f08 Mon Sep 17 00:00:00 2001 From: Jordan Whited Date: Fri, 24 Mar 2023 16:23:42 -0700 Subject: [PATCH] tun: use correct IP header comparisons in tcpGRO() and tcpPacketsCanCoalesce() tcpGRO() was using an incorrect IPv4 more fragments bit mask. tcpPacketsCanCoalesce() was not distinguishing tcp6 from tcp4, and TTL values were not compared. TTL values should be equal at the IP layer, otherwise the packets should not coalesce. This tracks with the kernel. Reviewed-by: Denton Gentry Signed-off-by: Jordan Whited Signed-off-by: Jason A. Donenfeld --- tun/tcp_offload_linux.go | 35 ++++++++---- tun/tcp_offload_linux_test.go | 100 ++++++++++++++++++++++++++++++++-- 2 files changed, 119 insertions(+), 16 deletions(-) diff --git a/tun/tcp_offload_linux.go b/tun/tcp_offload_linux.go index 4912efd..39a7180 100644 --- a/tun/tcp_offload_linux.go +++ b/tun/tcp_offload_linux.go @@ -189,14 +189,29 @@ func tcpPacketsCanCoalesce(pkt []byte, iphLen, tcphLen uint8, seq uint32, pshSet return coalesceUnavailable } } - if pkt[1] != pktTarget[1] { - // cannot coalesce with unequal ToS values - return coalesceUnavailable - } - if pkt[6]>>5 != pktTarget[6]>>5 { - // cannot coalesce with unequal DF or reserved bits. MF is checked - // further up the stack. - return coalesceUnavailable + if pkt[0]>>4 == 6 { + if pkt[0] != pktTarget[0] || pkt[1]>>4 != pktTarget[1]>>4 { + // cannot coalesce with unequal Traffic class values + return coalesceUnavailable + } + if pkt[7] != pktTarget[7] { + // cannot coalesce with unequal Hop limit values + return coalesceUnavailable + } + } else { + if pkt[1] != pktTarget[1] { + // cannot coalesce with unequal ToS values + return coalesceUnavailable + } + if pkt[6]>>5 != pktTarget[6]>>5 { + // cannot coalesce with unequal DF or reserved bits. MF is checked + // further up the stack. + return coalesceUnavailable + } + if pkt[8] != pktTarget[8] { + // cannot coalesce with unequal TTL values + return coalesceUnavailable + } } // seq adjacency lhsLen := item.gsoSize @@ -366,7 +381,7 @@ func coalesceTCPPackets(mode canCoalesce, pkt []byte, pktBuffsIndex int, gsoSize } const ( - ipv4FlagMoreFragments = 0x80 + ipv4FlagMoreFragments uint8 = 0x20 ) const ( @@ -409,7 +424,7 @@ func tcpGRO(bufs [][]byte, offset int, pktI int, table *tcpGROTable, isV6 bool) return false } if !isV6 { - if pkt[6]&ipv4FlagMoreFragments != 0 || (pkt[6]<<3 != 0 || pkt[7] != 0) { + if pkt[6]&ipv4FlagMoreFragments != 0 || pkt[6]<<3 != 0 || pkt[7] != 0 { // no GRO support for fragmented segments for now return false } diff --git a/tun/tcp_offload_linux_test.go b/tun/tcp_offload_linux_test.go index 046e177..9160e18 100644 --- a/tun/tcp_offload_linux_test.go +++ b/tun/tcp_offload_linux_test.go @@ -28,19 +28,23 @@ var ( ip6PortC = netip.MustParseAddrPort("[2001:db8::3]:1") ) -func tcp4Packet(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segmentSize, seq uint32) []byte { +func tcp4PacketMutateIPFields(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segmentSize, seq uint32, ipFn func(*header.IPv4Fields)) []byte { totalLen := 40 + segmentSize b := make([]byte, offset+int(totalLen), 65535) ipv4H := header.IPv4(b[offset:]) srcAs4 := srcIPPort.Addr().As4() dstAs4 := dstIPPort.Addr().As4() - ipv4H.Encode(&header.IPv4Fields{ + ipFields := &header.IPv4Fields{ SrcAddr: tcpip.Address(srcAs4[:]), DstAddr: tcpip.Address(dstAs4[:]), Protocol: unix.IPPROTO_TCP, TTL: 64, TotalLength: uint16(totalLen), - }) + } + if ipFn != nil { + ipFn(ipFields) + } + ipv4H.Encode(ipFields) tcpH := header.TCP(b[offset+20:]) tcpH.Encode(&header.TCPFields{ SrcPort: srcIPPort.Port(), @@ -57,19 +61,27 @@ func tcp4Packet(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segm return b } -func tcp6Packet(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segmentSize, seq uint32) []byte { +func tcp4Packet(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segmentSize, seq uint32) []byte { + return tcp4PacketMutateIPFields(srcIPPort, dstIPPort, flags, segmentSize, seq, nil) +} + +func tcp6PacketMutateIPFields(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segmentSize, seq uint32, ipFn func(*header.IPv6Fields)) []byte { totalLen := 60 + segmentSize b := make([]byte, offset+int(totalLen), 65535) ipv6H := header.IPv6(b[offset:]) srcAs16 := srcIPPort.Addr().As16() dstAs16 := dstIPPort.Addr().As16() - ipv6H.Encode(&header.IPv6Fields{ + ipFields := &header.IPv6Fields{ SrcAddr: tcpip.Address(srcAs16[:]), DstAddr: tcpip.Address(dstAs16[:]), TransportProtocol: unix.IPPROTO_TCP, HopLimit: 64, PayloadLength: uint16(segmentSize + 20), - }) + } + if ipFn != nil { + ipFn(ipFields) + } + ipv6H.Encode(ipFields) tcpH := header.TCP(b[offset+40:]) tcpH.Encode(&header.TCPFields{ SrcPort: srcIPPort.Port(), @@ -85,6 +97,10 @@ func tcp6Packet(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segm return b } +func tcp6Packet(srcIPPort, dstIPPort netip.AddrPort, flags header.TCPFlags, segmentSize, seq uint32) []byte { + return tcp6PacketMutateIPFields(srcIPPort, dstIPPort, flags, segmentSize, seq, nil) +} + func Test_handleVirtioRead(t *testing.T) { tests := []struct { name string @@ -245,6 +261,78 @@ func Test_handleGRO(t *testing.T) { []int{340}, false, }, + { + "tcp4 unequal TTL", + [][]byte{ + tcp4Packet(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 1), + tcp4PacketMutateIPFields(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 101, func(fields *header.IPv4Fields) { + fields.TTL++ + }), + }, + []int{0, 1}, + []int{140, 140}, + false, + }, + { + "tcp4 unequal ToS", + [][]byte{ + tcp4Packet(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 1), + tcp4PacketMutateIPFields(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 101, func(fields *header.IPv4Fields) { + fields.TOS++ + }), + }, + []int{0, 1}, + []int{140, 140}, + false, + }, + { + "tcp4 unequal flags more fragments set", + [][]byte{ + tcp4Packet(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 1), + tcp4PacketMutateIPFields(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 101, func(fields *header.IPv4Fields) { + fields.Flags = 1 + }), + }, + []int{0, 1}, + []int{140, 140}, + false, + }, + { + "tcp4 unequal flags DF set", + [][]byte{ + tcp4Packet(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 1), + tcp4PacketMutateIPFields(ip4PortA, ip4PortB, header.TCPFlagAck, 100, 101, func(fields *header.IPv4Fields) { + fields.Flags = 2 + }), + }, + []int{0, 1}, + []int{140, 140}, + false, + }, + { + "tcp6 unequal hop limit", + [][]byte{ + tcp6Packet(ip6PortA, ip6PortB, header.TCPFlagAck, 100, 1), + tcp6PacketMutateIPFields(ip6PortA, ip6PortB, header.TCPFlagAck, 100, 101, func(fields *header.IPv6Fields) { + fields.HopLimit++ + }), + }, + []int{0, 1}, + []int{160, 160}, + false, + }, + { + "tcp6 unequal traffic class", + [][]byte{ + tcp6Packet(ip6PortA, ip6PortB, header.TCPFlagAck, 100, 1), + tcp6PacketMutateIPFields(ip6PortA, ip6PortB, header.TCPFlagAck, 100, 101, func(fields *header.IPv6Fields) { + fields.TrafficClass++ + }), + }, + []int{0, 1}, + []int{160, 160}, + false, + }, } for _, tt := range tests {