diff options
Diffstat (limited to 'pkg/tcpip/transport/tcp/accept.go')
| -rw-r--r-- | pkg/tcpip/transport/tcp/accept.go | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go index e9c5099ea..0802e984e 100644 --- a/pkg/tcpip/transport/tcp/accept.go +++ b/pkg/tcpip/transport/tcp/accept.go @@ -143,6 +143,15 @@ func decSynRcvdCount() { synRcvdCount.Unlock() } +// synCookiesInUse() returns true if the synRcvdCount is greater than +// SynRcvdCountThreshold. +func synCookiesInUse() bool { + synRcvdCount.Lock() + v := synRcvdCount.value + synRcvdCount.Unlock() + return v >= SynRcvdCountThreshold +} + // newListenContext creates a new listen context. func newListenContext(stk *stack.Stack, listenEP *endpoint, rcvWnd seqnum.Size, v6only bool, netProto tcpip.NetworkProtocolNumber) *listenContext { l := &listenContext{ @@ -446,6 +455,27 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) { return } + if !synCookiesInUse() { + // Send a reset as this is an ACK for which there is no + // half open connections and we are not using cookies + // yet. + // + // The only time we should reach here when a connection + // was opened and closed really quickly and a delayed + // ACK was received from the sender. + replyWithReset(s) + return + } + + // Since SYN cookies are in use this is potentially an ACK to a + // SYN-ACK we sent but don't have a half open connection state + // as cookies are being used to protect against a potential SYN + // flood. In such cases validate the cookie and if valid create + // a fully connected endpoint and deliver to the accept queue. + // + // If not, silently drop the ACK to avoid leaking information + // when under a potential syn flood attack. + // // Validate the cookie. data, ok := ctx.isCookieValid(s.id, s.ackNumber-1, s.sequenceNumber-1) if !ok || int(data) >= len(mssTable) { |