diff options
authorJonathan T. Looney <jtl@FreeBSD.org>2018-08-06 17:48:46 +0000
committerJonathan T. Looney <jtl@FreeBSD.org>2018-08-06 17:48:46 +0000
commitee6b9658b71cbfce89447d6bdbb278987258ec31 (patch)
parent3cf76440d26778ad6a0a9bd4273bb4da01e8e491 (diff)
Address concerns about CPU usage while doing TCP reassembly.
Currently, the per-queue limit is a function of the receive buffer size and the MSS. In certain cases (such as connections with large receive buffers), the per-queue segment limit can be quite large. Because we process segments as a linked list, large queues may not perform acceptably. The better long-term solution is to make the queue more efficient. But, in the short-term, we can provide a way for a system administrator to set the maximum queue size. We set the default queue limit to 100. This is an effort to balance performance with a sane resource limit. Depending on their environment, goals, etc., an administrator may choose to modify this limit in either direction. Approved by: so Security: FreeBSD-SA-18:08.tcp Security: CVE-2018-6922
Notes: svn path=/releng/11.1/; revision=337388
2 files changed, 25 insertions, 1 deletions
diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index 8c7171666fd0..05a352c88f52 100644
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -445,6 +445,20 @@ no reseeding will occur.
Reseeding should not be necessary, and will break
recycling for a few minutes.
+.It Va reass.cursegments
+The current total number of segments present in all reassembly queues.
+.It Va reass.maxsegments
+The maximum limit on the total number of segments across all reassembly
+The limit can be adjusted as a tunable.
+.It Va reass.maxqueuelen
+The maximum number of segments allowed in each reassembly queue.
+By default, the system chooses a limit based on each TCP connection's
+receive buffer size and maximum segment size (MSS).
+The actual limit applied to a session's reassembly queue will be the lower of
+the system-calculated automatic limit and the user-specified
+.Va reass.maxqueuelen
.It Va rexmit_min , rexmit_slop
Adjust the retransmit timer calculation for
.Tn TCP .
diff --git a/sys/netinet/tcp_reass.c b/sys/netinet/tcp_reass.c
index a22fb3081d6d..c72991f622c2 100644
--- a/sys/netinet/tcp_reass.c
+++ b/sys/netinet/tcp_reass.c
@@ -89,6 +89,11 @@ SYSCTL_UMA_CUR(_net_inet_tcp_reass, OID_AUTO, cursegments, 0,
"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)) {
*tlenp = 0;
if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {