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Date:      Thu, 2 Jan 2020 13:55:11 +0000 (UTC)
From:      Michael Tuexen <tuexen@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r356270 - head/sys/netinet
Message-ID:  <202001021355.002DtBZC000426@repo.freebsd.org>
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Author: tuexen
Date: Thu Jan  2 13:55:10 2020
New Revision: 356270
URL: https://svnweb.freebsd.org/changeset/base/356270

Log:
  Improve input validation of the spp_pathmtu field in the
  SCTP_PEER_ADDR_PARAMS socket option. The code in the stack assumes
  sane values for the MTU.
  
  This issue was found by running an instance of syzkaller.
  
  MFC after:		1 week

Modified:
  head/sys/netinet/sctp.h
  head/sys/netinet/sctp_usrreq.c

Modified: head/sys/netinet/sctp.h
==============================================================================
--- head/sys/netinet/sctp.h	Thu Jan  2 11:02:09 2020	(r356269)
+++ head/sys/netinet/sctp.h	Thu Jan  2 13:55:10 2020	(r356270)
@@ -1,3 +1,4 @@
+
 /*-
  * SPDX-License-Identifier: BSD-3-Clause
  *
@@ -585,8 +586,10 @@ struct sctp_error_auth_invalid_hmac {
 #define SCTP_MOBILITY_PRIM_DELETED       0x00000004
 
 
-#define SCTP_SMALLEST_PMTU 512	/* smallest pmtu allowed when disabling PMTU
-				 * discovery */
+/* Smallest PMTU allowed when disabling PMTU discovery */
+#define SCTP_SMALLEST_PMTU 512
+/* Largest PMTU allowed when disabling PMTU discovery */
+#define SCTP_LARGEST_PMTU  65536
 
 #undef SCTP_PACKED
 

Modified: head/sys/netinet/sctp_usrreq.c
==============================================================================
--- head/sys/netinet/sctp_usrreq.c	Thu Jan  2 11:02:09 2020	(r356269)
+++ head/sys/netinet/sctp_usrreq.c	Thu Jan  2 13:55:10 2020	(r356270)
@@ -5363,6 +5363,14 @@ sctp_setopt(struct socket *so, int optname, void *optv
 				SCTP_LTRACE_ERR_RET(inp, NULL, NULL, SCTP_FROM_SCTP_USRREQ, EINVAL);
 				return (EINVAL);
 			}
+			if ((paddrp->spp_flags & SPP_PMTUD_DISABLE) &&
+			    ((paddrp->spp_pathmtu < SCTP_SMALLEST_PMTU) ||
+			    (paddrp->spp_pathmtu > SCTP_LARGEST_PMTU))) {
+				if (stcb)
+					SCTP_TCB_UNLOCK(stcb);
+				SCTP_LTRACE_ERR_RET(inp, NULL, NULL, SCTP_FROM_SCTP_USRREQ, EINVAL);
+				return (EINVAL);
+			}
 
 			if (stcb != NULL) {
 				/************************TCB SPECIFIC SET ******************/
@@ -5394,7 +5402,7 @@ sctp_setopt(struct socket *so, int optname, void *optv
 							sctp_timer_start(SCTP_TIMER_TYPE_HEARTBEAT, inp, stcb, net);
 						}
 					}
-					if ((paddrp->spp_flags & SPP_PMTUD_DISABLE) && (paddrp->spp_pathmtu >= SCTP_SMALLEST_PMTU)) {
+					if (paddrp->spp_flags & SPP_PMTUD_DISABLE) {
 						if (SCTP_OS_TIMER_PENDING(&net->pmtu_timer.timer)) {
 							sctp_timer_stop(SCTP_TIMER_TYPE_PATHMTURAISE, inp, stcb, net,
 							    SCTP_FROM_SCTP_USRREQ + SCTP_LOC_11);
@@ -5536,7 +5544,7 @@ sctp_setopt(struct socket *so, int optname, void *optv
 						}
 						sctp_stcb_feature_on(inp, stcb, SCTP_PCB_FLAGS_DONOT_HEARTBEAT);
 					}
-					if ((paddrp->spp_flags & SPP_PMTUD_DISABLE) && (paddrp->spp_pathmtu >= SCTP_SMALLEST_PMTU)) {
+					if (paddrp->spp_flags & SPP_PMTUD_DISABLE) {
 						TAILQ_FOREACH(net, &stcb->asoc.nets, sctp_next) {
 							if (SCTP_OS_TIMER_PENDING(&net->pmtu_timer.timer)) {
 								sctp_timer_stop(SCTP_TIMER_TYPE_PATHMTURAISE, inp, stcb, net,
@@ -5635,9 +5643,7 @@ sctp_setopt(struct socket *so, int optname, void *optv
 						inp->sctp_ep.default_mtu = 0;
 						sctp_feature_off(inp, SCTP_PCB_FLAGS_DO_NOT_PMTUD);
 					} else if (paddrp->spp_flags & SPP_PMTUD_DISABLE) {
-						if (paddrp->spp_pathmtu >= SCTP_SMALLEST_PMTU) {
-							inp->sctp_ep.default_mtu = paddrp->spp_pathmtu;
-						}
+						inp->sctp_ep.default_mtu = paddrp->spp_pathmtu;
 						sctp_feature_on(inp, SCTP_PCB_FLAGS_DO_NOT_PMTUD);
 					}
 					if (paddrp->spp_flags & SPP_DSCP) {

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