From 30c2a48ca19a4a28bcd61627066178633f160f5a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?fengbojiang=28=E5=A7=9C=E5=87=A4=E6=B3=A2=29?=
 <fengbojiang@tencent.com>
Date: Fri, 22 Nov 2019 16:16:34 +0800
Subject: [PATCH] Resource exhaustion in TCP reassembly.

Corresponding upstream changeset from
https://www.freebsd.org/security/advisories/FreeBSD-SA-18:08.tcp.asc.
---
 freebsd/netinet/tcp_reass.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/freebsd/netinet/tcp_reass.c b/freebsd/netinet/tcp_reass.c
index a22fb3081..c72991f62 100644
--- a/freebsd/netinet/tcp_reass.c
+++ b/freebsd/netinet/tcp_reass.c
@@ -89,6 +89,11 @@ SYSCTL_UMA_CUR(_net_inet_tcp_reass, OID_AUTO, cursegments, 0,
     &tcp_reass_zone,
     "Global number of TCP Segments currently in Reassembly Queue");
 
+static u_int tcp_reass_maxqueuelen = 100;
+SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, maxqueuelen, CTLFLAG_RWTUN,
+    &tcp_reass_maxqueuelen, 0,
+    "Maximum number of TCP Segments per Reassembly Queue");
+
 /* Initialize TCP reassembly queue */
 static void
 tcp_reass_zone_change(void *tag)
@@ -168,6 +173,10 @@ tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
 	 * socket receive buffer determines our advertised window and grows
 	 * automatically when socket buffer autotuning is enabled. Use it as the
 	 * basis for our queue limit.
+	 *
+	 * However, allow the user to specify a ceiling for the number of
+	 * segments in each queue.
+	 *
 	 * Always let the missing segment through which caused this queue.
 	 * NB: Access to the socket buffer is left intentionally unlocked as we
 	 * can tolerate stale information here.
@@ -178,7 +187,8 @@ tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
 	 * is understood.
 	 */
 	if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
-	    tp->t_segqlen >= (so->so_rcv.sb_hiwat / tp->t_maxseg) + 1) {
+	    tp->t_segqlen >= min((so->so_rcv.sb_hiwat / tp->t_maxseg) + 1,
+	    tcp_reass_maxqueuelen)) {
 		TCPSTAT_INC(tcps_rcvreassfull);
 		*tlenp = 0;
 		if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {