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
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=337778
@ -110,6 +110,15 @@ ipq_drop(struct ipqhead *head, struct ipq *fp)
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ipq_free(head, fp);
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}
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static int maxfrags;
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static volatile u_int nfrags;
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SYSCTL_INT(_net_inet_ip, OID_AUTO, maxfrags, CTLFLAG_RW,
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&maxfrags, 0,
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"Maximum number of IPv4 fragments allowed across all reassembly queues");
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SYSCTL_UINT(_net_inet_ip, OID_AUTO, curfrags, CTLFLAG_RD,
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__DEVOLATILE(u_int *, &nfrags), 0,
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"Current number of IPv4 fragments across all reassembly queues");
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VNET_DEFINE_STATIC(uma_zone_t, ipq_zone);
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#define V_ipq_zone VNET(ipq_zone)
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SYSCTL_PROC(_net_inet_ip, OID_AUTO, maxfragpackets, CTLFLAG_VNET |
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@ -146,7 +155,7 @@ ip_reass(struct mbuf *m)
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struct mbuf *p, *q, *nq, *t;
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struct ipq *fp;
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struct ipqhead *head;
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int i, hlen, next;
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int i, hlen, next, tmpmax;
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u_int8_t ecn, ecn0;
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uint32_t hash, hashkey[3];
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#ifdef RSS
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@ -156,8 +165,12 @@ ip_reass(struct mbuf *m)
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/*
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* If no reassembling or maxfragsperpacket are 0,
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* never accept fragments.
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* Also, drop packet if it would exceed the maximum
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* number of fragments.
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*/
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if (V_noreass == 1 || V_maxfragsperpacket == 0) {
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tmpmax = maxfrags;
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if (V_noreass == 1 || V_maxfragsperpacket == 0 ||
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(tmpmax >= 0 && atomic_load_int(&nfrags) >= (u_int)tmpmax)) {
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IPSTAT_INC(ips_fragments);
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IPSTAT_INC(ips_fragdropped);
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m_freem(m);
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@ -241,6 +254,7 @@ ip_reass(struct mbuf *m)
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#endif
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TAILQ_INSERT_HEAD(head, fp, ipq_list);
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fp->ipq_nfrags = 1;
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atomic_add_int(&nfrags, 1);
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fp->ipq_ttl = IPFRAGTTL;
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fp->ipq_p = ip->ip_p;
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fp->ipq_id = ip->ip_id;
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@ -251,6 +265,7 @@ ip_reass(struct mbuf *m)
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goto done;
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} else {
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fp->ipq_nfrags++;
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atomic_add_int(&nfrags, 1);
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#ifdef MAC
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mac_ipq_update(m, fp);
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#endif
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@ -327,6 +342,7 @@ ip_reass(struct mbuf *m)
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m->m_nextpkt = nq;
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IPSTAT_INC(ips_fragdropped);
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fp->ipq_nfrags--;
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atomic_subtract_int(&nfrags, 1);
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m_freem(q);
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}
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@ -392,6 +408,7 @@ ip_reass(struct mbuf *m)
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while (m->m_pkthdr.csum_data & 0xffff0000)
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m->m_pkthdr.csum_data = (m->m_pkthdr.csum_data & 0xffff) +
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(m->m_pkthdr.csum_data >> 16);
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atomic_subtract_int(&nfrags, fp->ipq_nfrags);
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#ifdef MAC
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mac_ipq_reassemble(fp, m);
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mac_ipq_destroy(fp);
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@ -451,8 +468,10 @@ ip_reass(struct mbuf *m)
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dropfrag:
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IPSTAT_INC(ips_fragdropped);
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if (fp != NULL)
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if (fp != NULL) {
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fp->ipq_nfrags--;
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atomic_subtract_int(&nfrags, 1);
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}
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m_freem(m);
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done:
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IPQ_UNLOCK(hash);
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@ -479,9 +498,11 @@ ipreass_init(void)
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NULL, UMA_ALIGN_PTR, 0);
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uma_zone_set_max(V_ipq_zone, nmbclusters / 32);
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if (IS_DEFAULT_VNET(curvnet))
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if (IS_DEFAULT_VNET(curvnet)) {
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maxfrags = nmbclusters / 32;
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EVENTHANDLER_REGISTER(nmbclusters_change, ipreass_zone_change,
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NULL, EVENTHANDLER_PRI_ANY);
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}
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}
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/*
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@ -564,9 +585,19 @@ ipreass_drain_tomax(void)
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static void
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ipreass_zone_change(void *tag)
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{
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VNET_ITERATOR_DECL(vnet_iter);
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int max;
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uma_zone_set_max(V_ipq_zone, nmbclusters / 32);
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ipreass_drain_tomax();
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maxfrags = nmbclusters / 32;
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max = nmbclusters / 32;
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VNET_LIST_RLOCK_NOSLEEP();
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VNET_FOREACH(vnet_iter) {
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CURVNET_SET(vnet_iter);
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uma_zone_set_max(V_ipq_zone, max);
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ipreass_drain_tomax();
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CURVNET_RESTORE();
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}
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VNET_LIST_RUNLOCK_NOSLEEP();
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}
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/*
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@ -629,6 +660,7 @@ ipq_reuse(int start)
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struct mbuf *m;
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IPSTAT_ADD(ips_fragtimeout, fp->ipq_nfrags);
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atomic_subtract_int(&nfrags, fp->ipq_nfrags);
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while (fp->ipq_frags) {
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m = fp->ipq_frags;
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fp->ipq_frags = m->m_nextpkt;
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@ -653,6 +685,7 @@ ipq_free(struct ipqhead *fhp, struct ipq *fp)
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{
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struct mbuf *q;
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atomic_subtract_int(&nfrags, fp->ipq_nfrags);
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while (fp->ipq_frags) {
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q = fp->ipq_frags;
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fp->ipq_frags = q->m_nextpkt;
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