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Date:      Tue, 14 Aug 2018 17:19:49 +0000 (UTC)
From:      "Jonathan T. Looney" <jtl@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r337778 - head/sys/netinet
Message-ID:  <201808141719.w7EHJnas011158@repo.freebsd.org>
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Author: jtl
Date: Tue Aug 14 17:19:49 2018
New Revision: 337778
URL: https://svnweb.freebsd.org/changeset/base/337778

Log:
  Add a global limit on the number of IPv4 fragments.
  
  The IP reassembly fragment limit is based on the number of mbuf clusters,
  which are a global resource. However, the limit is currently applied
  on a per-VNET basis. Given enough VNETs (or given sufficient customization
  of enough VNETs), it is possible that the sum of all the VNET limits
  will exceed the number of mbuf clusters available in the system.
  
  Given the fact that the fragment limit is intended (at least in part) to
  regulate access to a global resource, the fragment limit should
  be applied on a global basis.
  
  VNET-specific limits can be adjusted by modifying the
  net.inet.ip.maxfragpackets and net.inet.ip.maxfragsperpacket
  sysctls.
  
  To disable fragment reassembly globally, set net.inet.ip.maxfrags to 0.
  To disable fragment reassembly for a particular VNET, set
  net.inet.ip.maxfragpackets to 0.
  
  Reviewed by:	jhb
  Security:	FreeBSD-SA-18:10.ip
  Security:	CVE-2018-6923

Modified:
  head/sys/netinet/ip_reass.c

Modified: head/sys/netinet/ip_reass.c
==============================================================================
--- head/sys/netinet/ip_reass.c	Tue Aug 14 17:19:11 2018	(r337777)
+++ head/sys/netinet/ip_reass.c	Tue Aug 14 17:19:49 2018	(r337778)
@@ -110,6 +110,15 @@ ipq_drop(struct ipqhead *head, struct ipq *fp)
 	ipq_free(head, fp);
 }
 
+static int		maxfrags;
+static volatile u_int	nfrags;
+SYSCTL_INT(_net_inet_ip, OID_AUTO, maxfrags, CTLFLAG_RW,
+    &maxfrags, 0,
+    "Maximum number of IPv4 fragments allowed across all reassembly queues");
+SYSCTL_UINT(_net_inet_ip, OID_AUTO, curfrags, CTLFLAG_RD,
+    __DEVOLATILE(u_int *, &nfrags), 0,
+    "Current number of IPv4 fragments across all reassembly queues");
+
 VNET_DEFINE_STATIC(uma_zone_t, ipq_zone);
 #define	V_ipq_zone	VNET(ipq_zone)
 SYSCTL_PROC(_net_inet_ip, OID_AUTO, maxfragpackets, CTLFLAG_VNET |
@@ -146,7 +155,7 @@ ip_reass(struct mbuf *m)
 	struct mbuf *p, *q, *nq, *t;
 	struct ipq *fp;
 	struct ipqhead *head;
-	int i, hlen, next;
+	int i, hlen, next, tmpmax;
 	u_int8_t ecn, ecn0;
 	uint32_t hash, hashkey[3];
 #ifdef	RSS
@@ -156,8 +165,12 @@ ip_reass(struct mbuf *m)
 	/*
 	 * If no reassembling or maxfragsperpacket are 0,
 	 * never accept fragments.
+	 * Also, drop packet if it would exceed the maximum
+	 * number of fragments.
 	 */
-	if (V_noreass == 1 || V_maxfragsperpacket == 0) {
+	tmpmax = maxfrags;
+	if (V_noreass == 1 || V_maxfragsperpacket == 0 ||
+	    (tmpmax >= 0 && atomic_load_int(&nfrags) >= (u_int)tmpmax)) {
 		IPSTAT_INC(ips_fragments);
 		IPSTAT_INC(ips_fragdropped);
 		m_freem(m);
@@ -241,6 +254,7 @@ ip_reass(struct mbuf *m)
 #endif
 		TAILQ_INSERT_HEAD(head, fp, ipq_list);
 		fp->ipq_nfrags = 1;
+		atomic_add_int(&nfrags, 1);
 		fp->ipq_ttl = IPFRAGTTL;
 		fp->ipq_p = ip->ip_p;
 		fp->ipq_id = ip->ip_id;
@@ -251,6 +265,7 @@ ip_reass(struct mbuf *m)
 		goto done;
 	} else {
 		fp->ipq_nfrags++;
+		atomic_add_int(&nfrags, 1);
 #ifdef MAC
 		mac_ipq_update(m, fp);
 #endif
@@ -327,6 +342,7 @@ ip_reass(struct mbuf *m)
 		m->m_nextpkt = nq;
 		IPSTAT_INC(ips_fragdropped);
 		fp->ipq_nfrags--;
+		atomic_subtract_int(&nfrags, 1);
 		m_freem(q);
 	}
 
@@ -392,6 +408,7 @@ ip_reass(struct mbuf *m)
 	while (m->m_pkthdr.csum_data & 0xffff0000)
 		m->m_pkthdr.csum_data = (m->m_pkthdr.csum_data & 0xffff) +
 		    (m->m_pkthdr.csum_data >> 16);
+	atomic_subtract_int(&nfrags, fp->ipq_nfrags);
 #ifdef MAC
 	mac_ipq_reassemble(fp, m);
 	mac_ipq_destroy(fp);
@@ -451,8 +468,10 @@ ip_reass(struct mbuf *m)
 
 dropfrag:
 	IPSTAT_INC(ips_fragdropped);
-	if (fp != NULL)
+	if (fp != NULL) {
 		fp->ipq_nfrags--;
+		atomic_subtract_int(&nfrags, 1);
+	}
 	m_freem(m);
 done:
 	IPQ_UNLOCK(hash);
@@ -479,9 +498,11 @@ ipreass_init(void)
 	    NULL, UMA_ALIGN_PTR, 0);
 	uma_zone_set_max(V_ipq_zone, nmbclusters / 32);
 
-	if (IS_DEFAULT_VNET(curvnet))
+	if (IS_DEFAULT_VNET(curvnet)) {
+		maxfrags = nmbclusters / 32;
 		EVENTHANDLER_REGISTER(nmbclusters_change, ipreass_zone_change,
 		    NULL, EVENTHANDLER_PRI_ANY);
+	}
 }
 
 /*
@@ -564,9 +585,19 @@ ipreass_drain_tomax(void)
 static void
 ipreass_zone_change(void *tag)
 {
+	VNET_ITERATOR_DECL(vnet_iter);
+	int max;
 
-	uma_zone_set_max(V_ipq_zone, nmbclusters / 32);
-	ipreass_drain_tomax();
+	maxfrags = nmbclusters / 32;
+	max = nmbclusters / 32;
+	VNET_LIST_RLOCK_NOSLEEP();
+	VNET_FOREACH(vnet_iter) {
+		CURVNET_SET(vnet_iter);
+		uma_zone_set_max(V_ipq_zone, max);
+		ipreass_drain_tomax();
+		CURVNET_RESTORE();
+	}
+	VNET_LIST_RUNLOCK_NOSLEEP();
 }
 
 /*
@@ -629,6 +660,7 @@ ipq_reuse(int start)
 			struct mbuf *m;
 
 			IPSTAT_ADD(ips_fragtimeout, fp->ipq_nfrags);
+			atomic_subtract_int(&nfrags, fp->ipq_nfrags);
 			while (fp->ipq_frags) {
 				m = fp->ipq_frags;
 				fp->ipq_frags = m->m_nextpkt;
@@ -653,6 +685,7 @@ ipq_free(struct ipqhead *fhp, struct ipq *fp)
 {
 	struct mbuf *q;
 
+	atomic_subtract_int(&nfrags, fp->ipq_nfrags);
 	while (fp->ipq_frags) {
 		q = fp->ipq_frags;
 		fp->ipq_frags = q->m_nextpkt;

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