/*- * Copyright (c) 2001 Daniel Hartmeier * Copyright (c) 2002 - 2008 Henning Brauer * Copyright (c) 2012 Gleb Smirnoff * Copyright (c) 2015, 2016 Nicira, Inc. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * - Redistributions in binary form must reproduce the above * copyright notice, this list of conditions and the following * disclaimer in the documentation and/or other materials provided * with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Effort sponsored in part by the Defense Advanced Research Projects * Agency (DARPA) and Air Force Research Laboratory, Air Force * Materiel Command, USAF, under agreement number F30602-01-2-0537. * * $OpenBSD: pf.c,v 1.634 2009/02/27 12:37:45 henning Exp $ */ #include #include "conntrack-private.h" #include "conntrack-tp.h" #include "coverage.h" #include "ct-dpif.h" #include "dp-packet.h" #include "util.h" COVERAGE_DEFINE(conntrack_tcp_seq_chk_bypass); COVERAGE_DEFINE(conntrack_tcp_seq_chk_failed); COVERAGE_DEFINE(conntrack_invalid_tcp_flags); struct tcp_peer { uint32_t seqlo; /* Max sequence number sent */ uint32_t seqhi; /* Max the other end ACKd + win */ uint16_t max_win; /* largest window (pre scaling) */ uint8_t wscale; /* window scaling factor */ enum ct_dpif_tcp_state state; }; struct conn_tcp { struct conn up; struct tcp_peer peer[2]; /* 'conn' lock protected. */ }; enum { TCPOPT_EOL, TCPOPT_NOP, TCPOPT_WINDOW = 3, }; /* TCP sequence numbers are 32 bit integers operated * on with modular arithmetic. These macros can be * used to compare such integers. */ #define SEQ_LT(a,b) INT_MOD_LT(a, b) #define SEQ_LEQ(a,b) INT_MOD_LEQ(a, b) #define SEQ_GT(a,b) INT_MOD_GT(a, b) #define SEQ_GEQ(a,b) INT_MOD_GEQ(a, b) #define SEQ_MIN(a, b) INT_MOD_MIN(a, b) #define SEQ_MAX(a, b) INT_MOD_MAX(a, b) static struct conn_tcp* conn_tcp_cast(const struct conn* conn) { return CONTAINER_OF(conn, struct conn_tcp, up); } /* pf does this in in pf_normalize_tcp(), and it is called only if scrub * is enabled. We're not scrubbing, but this check seems reasonable. */ static bool tcp_invalid_flags(uint16_t flags) { if (flags & TCP_SYN) { if (flags & TCP_RST || flags & TCP_FIN) { return true; } } else { /* Illegal packet */ if (!(flags & (TCP_ACK|TCP_RST))) { return true; } } if (!(flags & TCP_ACK)) { /* These flags are only valid if ACK is set */ if ((flags & TCP_FIN) || (flags & TCP_PSH) || (flags & TCP_URG)) { return true; } } return false; } #define TCP_MAX_WSCALE 14 #define CT_WSCALE_FLAG 0x80 #define CT_WSCALE_UNKNOWN 0x40 #define CT_WSCALE_MASK 0xf static uint8_t tcp_get_wscale(const struct tcp_header *tcp) { int len = TCP_OFFSET(tcp->tcp_ctl) * 4 - sizeof *tcp; const uint8_t *opt = (const uint8_t *)(tcp + 1); uint8_t wscale = 0; uint8_t optlen; while (len >= 3) { switch (*opt) { case TCPOPT_EOL: return wscale; case TCPOPT_NOP: opt++; len--; break; case TCPOPT_WINDOW: wscale = MIN(opt[2], TCP_MAX_WSCALE); wscale |= CT_WSCALE_FLAG; /* fall through */ default: optlen = opt[1]; if (optlen < 2) { optlen = 2; } len -= optlen; opt += optlen; } } return wscale; } static bool tcp_bypass_seq_chk(struct conntrack *ct) { if (!conntrack_get_tcp_seq_chk(ct)) { COVERAGE_INC(conntrack_tcp_seq_chk_bypass); return true; } return false; } static enum ct_update_res tcp_conn_update(struct conntrack *ct, struct conn *conn_, struct dp_packet *pkt, bool reply, long long now) { struct conn_tcp *conn = conn_tcp_cast(conn_); struct tcp_header *tcp = dp_packet_l4(pkt); /* The peer that sent 'pkt' */ struct tcp_peer *src = &conn->peer[reply ? 1 : 0]; /* The peer that should receive 'pkt' */ struct tcp_peer *dst = &conn->peer[reply ? 0 : 1]; uint8_t sws = 0, dws = 0; uint16_t tcp_flags = TCP_FLAGS(tcp->tcp_ctl); uint16_t win = ntohs(tcp->tcp_winsz); uint32_t ack, end, seq, orig_seq; uint32_t p_len = dp_packet_get_tcp_payload_length(pkt); if (tcp_invalid_flags(tcp_flags)) { COVERAGE_INC(conntrack_invalid_tcp_flags); return CT_UPDATE_INVALID; } if ((tcp_flags & (TCP_SYN | TCP_ACK)) == TCP_SYN) { if (dst->state >= CT_DPIF_TCPS_FIN_WAIT_2 && src->state >= CT_DPIF_TCPS_FIN_WAIT_2) { src->state = dst->state = CT_DPIF_TCPS_CLOSED; return CT_UPDATE_NEW; } else if (src->state <= CT_DPIF_TCPS_SYN_SENT) { src->state = CT_DPIF_TCPS_SYN_SENT; conn_update_expiration(ct, &conn->up, CT_TM_TCP_FIRST_PACKET, now); return CT_UPDATE_VALID_NEW; } } if (src->wscale & CT_WSCALE_FLAG && dst->wscale & CT_WSCALE_FLAG && !(tcp_flags & TCP_SYN)) { sws = src->wscale & CT_WSCALE_MASK; dws = dst->wscale & CT_WSCALE_MASK; } else if (src->wscale & CT_WSCALE_UNKNOWN && dst->wscale & CT_WSCALE_UNKNOWN && !(tcp_flags & TCP_SYN)) { sws = TCP_MAX_WSCALE; dws = TCP_MAX_WSCALE; } /* * Sequence tracking algorithm from Guido van Rooij's paper: * http://www.madison-gurkha.com/publications/tcp_filtering/ * tcp_filtering.ps */ orig_seq = seq = ntohl(get_16aligned_be32(&tcp->tcp_seq)); bool check_ackskew = true; if (src->state < CT_DPIF_TCPS_SYN_SENT) { /* First packet from this end. Set its state */ ack = ntohl(get_16aligned_be32(&tcp->tcp_ack)); end = seq + p_len; if (tcp_flags & TCP_SYN) { end++; if (dst->wscale & CT_WSCALE_FLAG) { src->wscale = tcp_get_wscale(tcp); if (src->wscale & CT_WSCALE_FLAG) { /* Remove scale factor from initial window */ sws = src->wscale & CT_WSCALE_MASK; win = DIV_ROUND_UP((uint32_t) win, 1 << sws); dws = dst->wscale & CT_WSCALE_MASK; } else { /* fixup other window */ dst->max_win <<= dst->wscale & CT_WSCALE_MASK; /* in case of a retrans SYN|ACK */ dst->wscale = 0; } } } if (tcp_flags & TCP_FIN) { end++; } src->seqlo = seq; src->state = CT_DPIF_TCPS_SYN_SENT; /* * May need to slide the window (seqhi may have been set by * the crappy stack check or if we picked up the connection * after establishment) */ if (src->seqhi == 1 || SEQ_GEQ(end + MAX(1, dst->max_win << dws), src->seqhi)) { src->seqhi = end + MAX(1, dst->max_win << dws); /* We are either picking up a new connection or a connection which * was already in place. We are more permissive in terms of * ackskew checking in these cases. */ check_ackskew = false; } if (win > src->max_win) { src->max_win = win; } } else { ack = ntohl(get_16aligned_be32(&tcp->tcp_ack)); end = seq + p_len; if (tcp_flags & TCP_SYN) { end++; } if (tcp_flags & TCP_FIN) { end++; } } if ((tcp_flags & TCP_ACK) == 0) { /* Let it pass through the ack skew check */ ack = dst->seqlo; } else if ((ack == 0 && (tcp_flags & (TCP_ACK|TCP_RST)) == (TCP_ACK|TCP_RST)) /* broken tcp stacks do not set ack */) { /* Many stacks (ours included) will set the ACK number in an * FIN|ACK if the SYN times out -- no sequence to ACK. */ ack = dst->seqlo; } if (seq == end) { /* Ease sequencing restrictions on no data packets */ seq = src->seqlo; end = seq; } int ackskew = check_ackskew ? dst->seqlo - ack : 0; #define MAXACKWINDOW (0xffff + 1500) /* 1500 is an arbitrary fudge factor */ if ((SEQ_GEQ(src->seqhi, end) /* Last octet inside other's window space */ && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws)) /* Retrans: not more than one window back */ && (ackskew >= -MAXACKWINDOW) /* Acking not more than one reassembled fragment backwards */ && (ackskew <= (MAXACKWINDOW << sws)) /* Acking not more than one window forward */ && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo))) || tcp_bypass_seq_chk(ct)) { /* Require an exact/+1 sequence match on resets when possible */ /* update max window */ if (src->max_win < win) { src->max_win = win; } /* synchronize sequencing */ if (SEQ_GT(end, src->seqlo)) { src->seqlo = end; } /* slide the window of what the other end can send */ if (SEQ_GEQ(ack + (win << sws), dst->seqhi)) { dst->seqhi = ack + MAX((win << sws), 1); } /* update states */ if (tcp_flags & TCP_SYN && src->state < CT_DPIF_TCPS_SYN_SENT) { src->state = CT_DPIF_TCPS_SYN_SENT; } if (tcp_flags & TCP_FIN && src->state < CT_DPIF_TCPS_CLOSING) { src->state = CT_DPIF_TCPS_CLOSING; } if (tcp_flags & TCP_ACK) { if (dst->state == CT_DPIF_TCPS_SYN_SENT) { dst->state = CT_DPIF_TCPS_ESTABLISHED; } else if (dst->state == CT_DPIF_TCPS_CLOSING) { dst->state = CT_DPIF_TCPS_FIN_WAIT_2; } } if (tcp_flags & TCP_RST) { src->state = dst->state = CT_DPIF_TCPS_TIME_WAIT; } if (src->state >= CT_DPIF_TCPS_FIN_WAIT_2 && dst->state >= CT_DPIF_TCPS_FIN_WAIT_2) { conn_update_expiration(ct, &conn->up, CT_TM_TCP_CLOSED, now); } else if (src->state >= CT_DPIF_TCPS_CLOSING && dst->state >= CT_DPIF_TCPS_CLOSING) { conn_update_expiration(ct, &conn->up, CT_TM_TCP_FIN_WAIT, now); } else if (src->state < CT_DPIF_TCPS_ESTABLISHED || dst->state < CT_DPIF_TCPS_ESTABLISHED) { conn_update_expiration(ct, &conn->up, CT_TM_TCP_OPENING, now); } else if (src->state >= CT_DPIF_TCPS_CLOSING || dst->state >= CT_DPIF_TCPS_CLOSING) { conn_update_expiration(ct, &conn->up, CT_TM_TCP_CLOSING, now); } else { conn_update_expiration(ct, &conn->up, CT_TM_TCP_ESTABLISHED, now); } } else if ((dst->state < CT_DPIF_TCPS_SYN_SENT || dst->state >= CT_DPIF_TCPS_FIN_WAIT_2 || src->state >= CT_DPIF_TCPS_FIN_WAIT_2) && SEQ_GEQ(src->seqhi + MAXACKWINDOW, end) /* Within a window forward of the originating packet */ && SEQ_GEQ(seq, src->seqlo - MAXACKWINDOW)) { /* Within a window backward of the originating packet */ /* * This currently handles three situations: * 1) Stupid stacks will shotgun SYNs before their peer * replies. * 2) When PF catches an already established stream (the * firewall rebooted, the state table was flushed, routes * changed...) * 3) Packets get funky immediately after the connection * closes (this should catch Solaris spurious ACK|FINs * that web servers like to spew after a close) * * This must be a little more careful than the above code * since packet floods will also be caught here. We don't * update the TTL here to mitigate the damage of a packet * flood and so the same code can handle awkward establishment * and a loosened connection close. * In the establishment case, a correct peer response will * validate the connection, go through the normal state code * and keep updating the state TTL. */ /* update max window */ if (src->max_win < win) { src->max_win = win; } /* synchronize sequencing */ if (SEQ_GT(end, src->seqlo)) { src->seqlo = end; } /* slide the window of what the other end can send */ if (SEQ_GEQ(ack + (win << sws), dst->seqhi)) { dst->seqhi = ack + MAX((win << sws), 1); } /* * Cannot set dst->seqhi here since this could be a shotgunned * SYN and not an already established connection. */ if (tcp_flags & TCP_FIN && src->state < CT_DPIF_TCPS_CLOSING) { src->state = CT_DPIF_TCPS_CLOSING; } if (tcp_flags & TCP_RST) { src->state = dst->state = CT_DPIF_TCPS_TIME_WAIT; } } else { COVERAGE_INC(conntrack_tcp_seq_chk_failed); return CT_UPDATE_INVALID; } return CT_UPDATE_VALID; } static bool tcp_valid_new(struct dp_packet *pkt) { struct tcp_header *tcp = dp_packet_l4(pkt); uint16_t tcp_flags = TCP_FLAGS(tcp->tcp_ctl); if (tcp_invalid_flags(tcp_flags)) { return false; } /* A syn+ack is not allowed to create a connection. We want to allow * totally new connections (syn) or already established, not partially * open (syn+ack). */ if ((tcp_flags & TCP_SYN) && (tcp_flags & TCP_ACK)) { return false; } return true; } static struct conn * tcp_new_conn(struct conntrack *ct, struct dp_packet *pkt, long long now, uint32_t tp_id) { struct conn_tcp* newconn = NULL; struct tcp_header *tcp = dp_packet_l4(pkt); struct tcp_peer *src, *dst; uint16_t tcp_flags = TCP_FLAGS(tcp->tcp_ctl); newconn = xzalloc(sizeof *newconn); src = &newconn->peer[0]; dst = &newconn->peer[1]; src->seqlo = ntohl(get_16aligned_be32(&tcp->tcp_seq)); src->seqhi = src->seqlo + dp_packet_get_tcp_payload_length(pkt) + 1; if (tcp_flags & TCP_SYN) { src->seqhi++; src->wscale = tcp_get_wscale(tcp); } else { src->wscale = CT_WSCALE_UNKNOWN; dst->wscale = CT_WSCALE_UNKNOWN; } src->max_win = MAX(ntohs(tcp->tcp_winsz), 1); if (src->wscale & CT_WSCALE_MASK) { /* Remove scale factor from initial window */ uint8_t sws = src->wscale & CT_WSCALE_MASK; src->max_win = DIV_ROUND_UP((uint32_t) src->max_win, 1 << sws); } if (tcp_flags & TCP_FIN) { src->seqhi++; } dst->seqhi = 1; dst->max_win = 1; src->state = CT_DPIF_TCPS_SYN_SENT; dst->state = CT_DPIF_TCPS_CLOSED; newconn->up.tp_id = tp_id; conn_init_expiration(ct, &newconn->up, CT_TM_TCP_FIRST_PACKET, now); return &newconn->up; } static uint8_t tcp_peer_to_protoinfo_flags(const struct tcp_peer *peer) { uint8_t res = 0; if (peer->wscale & CT_WSCALE_FLAG) { res |= CT_DPIF_TCPF_WINDOW_SCALE; } if (peer->wscale & CT_WSCALE_UNKNOWN) { res |= CT_DPIF_TCPF_BE_LIBERAL; } return res; } static void tcp_conn_get_protoinfo(const struct conn *conn_, struct ct_dpif_protoinfo *protoinfo) { const struct conn_tcp *conn = conn_tcp_cast(conn_); protoinfo->proto = IPPROTO_TCP; protoinfo->tcp.state_orig = conn->peer[0].state; protoinfo->tcp.state_reply = conn->peer[1].state; protoinfo->tcp.wscale_orig = conn->peer[0].wscale & CT_WSCALE_MASK; protoinfo->tcp.wscale_reply = conn->peer[1].wscale & CT_WSCALE_MASK; protoinfo->tcp.flags_orig = tcp_peer_to_protoinfo_flags(&conn->peer[0]); protoinfo->tcp.flags_reply = tcp_peer_to_protoinfo_flags(&conn->peer[1]); } struct ct_l4_proto ct_proto_tcp = { .new_conn = tcp_new_conn, .valid_new = tcp_valid_new, .conn_update = tcp_conn_update, .conn_get_protoinfo = tcp_conn_get_protoinfo, };