diff options
Diffstat (limited to 'pkg/tcpip/network/ipv4/icmp.go')
| -rw-r--r-- | pkg/tcpip/network/ipv4/icmp.go | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/pkg/tcpip/network/ipv4/icmp.go b/pkg/tcpip/network/ipv4/icmp.go index 9b5e37fee..58a19e74a 100644 --- a/pkg/tcpip/network/ipv4/icmp.go +++ b/pkg/tcpip/network/ipv4/icmp.go @@ -290,6 +290,13 @@ type icmpReasonProtoUnreachable struct{} func (*icmpReasonProtoUnreachable) isICMPReason() {} +// icmpReasonTTLExceeded is an error where a packet's time to live exceeded in +// transit to its final destination, as per RFC 792 page 6, Time Exceeded +// Message. +type icmpReasonTTLExceeded struct{} + +func (*icmpReasonTTLExceeded) isICMPReason() {} + // icmpReasonReassemblyTimeout is an error where insufficient fragments are // received to complete reassembly of a packet within a configured time after // the reception of the first-arriving fragment of that packet. @@ -342,11 +349,31 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi return nil } + // If we hit a TTL Exceeded error, then we know we are operating as a router. + // As per RFC 792 page 6, Time Exceeded Message, + // + // If the gateway processing a datagram finds the time to live field + // is zero it must discard the datagram. The gateway may also notify + // the source host via the time exceeded message. + // + // ... + // + // Code 0 may be received from a gateway. ... + // + // Note, Code 0 is the TTL exceeded error. + // + // If we are operating as a router/gateway, don't use the packet's destination + // address as the response's source address as we should not not own the + // destination address of a packet we are forwarding. + localAddr := origIPHdrDst + if _, ok := reason.(*icmpReasonTTLExceeded); ok { + localAddr = "" + } // Even if we were able to receive a packet from some remote, we may not have // a route to it - the remote may be blocked via routing rules. We must always // consult our routing table and find a route to the remote before sending any // packet. - route, err := p.stack.FindRoute(pkt.NICID, origIPHdrDst, origIPHdrSrc, ProtocolNumber, false /* multicastLoop */) + route, err := p.stack.FindRoute(pkt.NICID, localAddr, origIPHdrSrc, ProtocolNumber, false /* multicastLoop */) if err != nil { return err } @@ -454,6 +481,10 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi icmpHdr.SetType(header.ICMPv4DstUnreachable) icmpHdr.SetCode(header.ICMPv4ProtoUnreachable) counter = sent.DstUnreachable + case *icmpReasonTTLExceeded: + icmpHdr.SetType(header.ICMPv4TimeExceeded) + icmpHdr.SetCode(header.ICMPv4TTLExceeded) + counter = sent.TimeExceeded case *icmpReasonReassemblyTimeout: icmpHdr.SetType(header.ICMPv4TimeExceeded) icmpHdr.SetCode(header.ICMPv4ReassemblyTimeout) |