Implement a limit on on the number of IPv4 reassembly queues per bucket.
There is a hashing algorithm which should distribute IPv4 reassembly queues across the available buckets in a relatively even way. However, if there is a flaw in the hashing algorithm which allows a large number of IPv4 fragment reassembly queues to end up in a single bucket, a per- bucket limit could help mitigate the performance impact of this flaw. Implement such a limit, with a default of twice the maximum number of reassembly queues divided by the number of buckets. Recalculate the limit any time the maximum number of reassembly queues changes. However, allow the user to override the value using a sysctl (net.inet.ip.maxfragbucketsize). Reviewed by: jhb Security: FreeBSD-SA-18:10.ip Security: CVE-2018-6923
This commit is contained in:
Jonathan T. Looney
parent
e40369745c
commit
ff790bbad0
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=337780
@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/hash.h>
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#include <sys/mbuf.h>
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#include <sys/malloc.h>
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#include <sys/limits.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/sysctl.h>
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@ -70,6 +71,7 @@ SYSCTL_DECL(_net_inet_ip);
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struct ipqbucket {
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TAILQ_HEAD(ipqhead, ipq) head;
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struct mtx lock;
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int count;
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};
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VNET_DEFINE_STATIC(struct ipqbucket, ipq[IPREASS_NHASH]);
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@ -82,6 +84,9 @@ VNET_DEFINE_STATIC(uint32_t, ipq_hashseed);
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#define IPQ_UNLOCK(i) mtx_unlock(&V_ipq[i].lock)
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#define IPQ_LOCK_ASSERT(i) mtx_assert(&V_ipq[i].lock, MA_OWNED)
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VNET_DEFINE_STATIC(int, ipreass_maxbucketsize);
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#define V_ipreass_maxbucketsize VNET(ipreass_maxbucketsize)
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void ipreass_init(void);
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void ipreass_drain(void);
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void ipreass_slowtimo(void);
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@ -89,25 +94,26 @@ void ipreass_slowtimo(void);
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void ipreass_destroy(void);
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#endif
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static int sysctl_maxfragpackets(SYSCTL_HANDLER_ARGS);
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static int sysctl_maxfragbucketsize(SYSCTL_HANDLER_ARGS);
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static void ipreass_zone_change(void *);
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static void ipreass_drain_tomax(void);
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static void ipq_free(struct ipqhead *, struct ipq *);
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static void ipq_free(struct ipqbucket *, struct ipq *);
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static struct ipq * ipq_reuse(int);
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static inline void
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ipq_timeout(struct ipqhead *head, struct ipq *fp)
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ipq_timeout(struct ipqbucket *bucket, struct ipq *fp)
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{
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IPSTAT_ADD(ips_fragtimeout, fp->ipq_nfrags);
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ipq_free(head, fp);
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ipq_free(bucket, fp);
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}
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static inline void
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ipq_drop(struct ipqhead *head, struct ipq *fp)
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ipq_drop(struct ipqbucket *bucket, struct ipq *fp)
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{
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IPSTAT_ADD(ips_fragdropped, fp->ipq_nfrags);
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ipq_free(head, fp);
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ipq_free(bucket, fp);
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}
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static int maxfrags;
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@ -136,6 +142,10 @@ VNET_DEFINE_STATIC(int, maxfragsperpacket);
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SYSCTL_INT(_net_inet_ip, OID_AUTO, maxfragsperpacket, CTLFLAG_VNET | CTLFLAG_RW,
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&VNET_NAME(maxfragsperpacket), 0,
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"Maximum number of IPv4 fragments allowed per packet");
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SYSCTL_PROC(_net_inet_ip, OID_AUTO, maxfragbucketsize,
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CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_RW, NULL, 0,
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sysctl_maxfragbucketsize, "I",
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"Maximum number of IPv4 fragment reassembly queue entries per bucket");
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/*
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* Take incoming datagram fragment and try to reassemble it into
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@ -241,9 +251,12 @@ ip_reass(struct mbuf *m)
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* If first fragment to arrive, create a reassembly queue.
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*/
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if (fp == NULL) {
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fp = uma_zalloc(V_ipq_zone, M_NOWAIT);
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if (V_ipq[hash].count < V_ipreass_maxbucketsize)
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fp = uma_zalloc(V_ipq_zone, M_NOWAIT);
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if (fp == NULL)
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fp = ipq_reuse(hash);
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if (fp == NULL)
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goto dropfrag;
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#ifdef MAC
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if (mac_ipq_init(fp, M_NOWAIT) != 0) {
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uma_zfree(V_ipq_zone, fp);
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@ -253,6 +266,7 @@ ip_reass(struct mbuf *m)
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mac_ipq_create(m, fp);
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#endif
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TAILQ_INSERT_HEAD(head, fp, ipq_list);
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V_ipq[hash].count++;
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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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@ -360,7 +374,7 @@ ip_reass(struct mbuf *m)
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for (p = NULL, q = fp->ipq_frags; q; p = q, q = q->m_nextpkt) {
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if (ntohs(GETIP(q)->ip_off) != next) {
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if (fp->ipq_nfrags > V_maxfragsperpacket)
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ipq_drop(head, fp);
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ipq_drop(&V_ipq[hash], fp);
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goto done;
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}
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next += ntohs(GETIP(q)->ip_len);
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@ -368,7 +382,7 @@ ip_reass(struct mbuf *m)
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/* Make sure the last packet didn't have the IP_MF flag */
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if (p->m_flags & M_IP_FRAG) {
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if (fp->ipq_nfrags > V_maxfragsperpacket)
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ipq_drop(head, fp);
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ipq_drop(&V_ipq[hash], fp);
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goto done;
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}
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@ -379,7 +393,7 @@ ip_reass(struct mbuf *m)
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ip = GETIP(q);
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if (next + (ip->ip_hl << 2) > IP_MAXPACKET) {
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IPSTAT_INC(ips_toolong);
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ipq_drop(head, fp);
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ipq_drop(&V_ipq[hash], fp);
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goto done;
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}
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@ -423,6 +437,7 @@ ip_reass(struct mbuf *m)
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ip->ip_src = fp->ipq_src;
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ip->ip_dst = fp->ipq_dst;
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TAILQ_REMOVE(head, fp, ipq_list);
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V_ipq[hash].count--;
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uma_zfree(V_ipq_zone, fp);
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m->m_len += (ip->ip_hl << 2);
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m->m_data -= (ip->ip_hl << 2);
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@ -486,17 +501,21 @@ ip_reass(struct mbuf *m)
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void
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ipreass_init(void)
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{
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int max;
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for (int i = 0; i < IPREASS_NHASH; i++) {
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TAILQ_INIT(&V_ipq[i].head);
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mtx_init(&V_ipq[i].lock, "IP reassembly", NULL,
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MTX_DEF | MTX_DUPOK);
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V_ipq[i].count = 0;
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}
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V_ipq_hashseed = arc4random();
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V_maxfragsperpacket = 16;
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V_ipq_zone = uma_zcreate("ipq", sizeof(struct ipq), NULL, NULL, NULL,
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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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max = nmbclusters / 32;
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max = uma_zone_set_max(V_ipq_zone, max);
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V_ipreass_maxbucketsize = imax(max / (IPREASS_NHASH / 2), 1);
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if (IS_DEFAULT_VNET(curvnet)) {
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maxfrags = nmbclusters / 32;
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@ -517,7 +536,7 @@ ipreass_slowtimo(void)
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IPQ_LOCK(i);
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TAILQ_FOREACH_SAFE(fp, &V_ipq[i].head, ipq_list, tmp)
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if (--fp->ipq_ttl == 0)
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ipq_timeout(&V_ipq[i].head, fp);
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ipq_timeout(&V_ipq[i], fp);
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IPQ_UNLOCK(i);
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}
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}
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@ -532,7 +551,10 @@ ipreass_drain(void)
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for (int i = 0; i < IPREASS_NHASH; i++) {
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IPQ_LOCK(i);
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while(!TAILQ_EMPTY(&V_ipq[i].head))
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ipq_drop(&V_ipq[i].head, TAILQ_FIRST(&V_ipq[i].head));
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ipq_drop(&V_ipq[i], TAILQ_FIRST(&V_ipq[i].head));
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KASSERT(V_ipq[i].count == 0,
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("%s: V_ipq[%d] count %d (V_ipq=%p)", __func__, i,
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V_ipq[i].count, V_ipq));
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IPQ_UNLOCK(i);
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}
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}
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@ -560,8 +582,22 @@ ipreass_destroy(void)
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static void
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ipreass_drain_tomax(void)
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{
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struct ipq *fp;
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int target;
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/*
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* Make sure each bucket is under the new limit. If
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* necessary, drop enough of the oldest elements from
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* each bucket to get under the new limit.
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*/
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for (int i = 0; i < IPREASS_NHASH; i++) {
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IPQ_LOCK(i);
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while (V_ipq[i].count > V_ipreass_maxbucketsize &&
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(fp = TAILQ_LAST(&V_ipq[i].head, ipqhead)) != NULL)
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ipq_timeout(&V_ipq[i], fp);
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IPQ_UNLOCK(i);
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}
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/*
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* If we are over the maximum number of fragments,
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* drain off enough to get down to the new limit,
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@ -570,13 +606,11 @@ ipreass_drain_tomax(void)
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*/
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target = uma_zone_get_max(V_ipq_zone);
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while (uma_zone_get_cur(V_ipq_zone) > target) {
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struct ipq *fp;
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for (int i = 0; i < IPREASS_NHASH; i++) {
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IPQ_LOCK(i);
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fp = TAILQ_LAST(&V_ipq[i].head, ipqhead);
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if (fp != NULL)
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ipq_timeout(&V_ipq[i].head, fp);
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ipq_timeout(&V_ipq[i], fp);
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IPQ_UNLOCK(i);
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}
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}
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@ -593,7 +627,8 @@ ipreass_zone_change(void *tag)
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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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max = uma_zone_set_max(V_ipq_zone, max);
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V_ipreass_maxbucketsize = imax(max / (IPREASS_NHASH / 2), 1);
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ipreass_drain_tomax();
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CURVNET_RESTORE();
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}
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@ -625,6 +660,7 @@ sysctl_maxfragpackets(SYSCTL_HANDLER_ARGS)
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* and place an extreme upper bound.
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*/
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max = uma_zone_set_max(V_ipq_zone, max);
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V_ipreass_maxbucketsize = imax(max / (IPREASS_NHASH / 2), 1);
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ipreass_drain_tomax();
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V_noreass = 0;
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} else if (max == 0) {
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@ -633,6 +669,7 @@ sysctl_maxfragpackets(SYSCTL_HANDLER_ARGS)
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} else if (max == -1) {
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V_noreass = 0;
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uma_zone_set_max(V_ipq_zone, 0);
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V_ipreass_maxbucketsize = INT_MAX;
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} else
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return (EINVAL);
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return (0);
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@ -646,16 +683,15 @@ static struct ipq *
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ipq_reuse(int start)
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{
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struct ipq *fp;
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int i;
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int bucket, i;
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IPQ_LOCK_ASSERT(start);
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for (i = start;; i++) {
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if (i == IPREASS_NHASH)
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i = 0;
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if (i != start && IPQ_TRYLOCK(i) == 0)
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for (i = 0; i < IPREASS_NHASH; i++) {
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bucket = (start + i) % IPREASS_NHASH;
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if (bucket != start && IPQ_TRYLOCK(bucket) == 0)
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continue;
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fp = TAILQ_LAST(&V_ipq[i].head, ipqhead);
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fp = TAILQ_LAST(&V_ipq[bucket].head, ipqhead);
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if (fp) {
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struct mbuf *m;
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@ -666,22 +702,24 @@ ipq_reuse(int start)
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fp->ipq_frags = m->m_nextpkt;
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m_freem(m);
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}
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TAILQ_REMOVE(&V_ipq[i].head, fp, ipq_list);
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if (i != start)
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IPQ_UNLOCK(i);
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IPQ_LOCK_ASSERT(start);
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return (fp);
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TAILQ_REMOVE(&V_ipq[bucket].head, fp, ipq_list);
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V_ipq[bucket].count--;
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if (bucket != start)
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IPQ_UNLOCK(bucket);
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break;
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}
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if (i != start)
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IPQ_UNLOCK(i);
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if (bucket != start)
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IPQ_UNLOCK(bucket);
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}
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IPQ_LOCK_ASSERT(start);
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return (fp);
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}
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/*
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* Free a fragment reassembly header and all associated datagrams.
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*/
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static void
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ipq_free(struct ipqhead *fhp, struct ipq *fp)
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ipq_free(struct ipqbucket *bucket, struct ipq *fp)
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{
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struct mbuf *q;
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@ -691,6 +729,26 @@ ipq_free(struct ipqhead *fhp, struct ipq *fp)
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fp->ipq_frags = q->m_nextpkt;
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m_freem(q);
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}
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TAILQ_REMOVE(fhp, fp, ipq_list);
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TAILQ_REMOVE(&bucket->head, fp, ipq_list);
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bucket->count--;
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uma_zfree(V_ipq_zone, fp);
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}
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/*
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* Get or set the maximum number of reassembly queues per bucket.
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*/
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static int
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sysctl_maxfragbucketsize(SYSCTL_HANDLER_ARGS)
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{
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int error, max;
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max = V_ipreass_maxbucketsize;
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error = sysctl_handle_int(oidp, &max, 0, req);
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if (error || !req->newptr)
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return (error);
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if (max <= 0)
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return (EINVAL);
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V_ipreass_maxbucketsize = max;
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ipreass_drain_tomax();
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return (0);
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}
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