2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * The IP fragmentation functionality.
8 * Version: $Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $
10 * Authors: Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
11 * Alan Cox <Alan.Cox@linux.org>
14 * Alan Cox : Split from ip.c , see ip_input.c for history.
15 * David S. Miller : Begin massive cleanup...
16 * Andi Kleen : Add sysctls.
17 * xxxx : Overlapfrag bug.
18 * Ultima : ip_expire() kernel panic.
19 * Bill Hawes : Frag accounting and evictor fixes.
20 * John McDonald : 0 length frag bug.
21 * Alexey Kuznetsov: SMP races, threading, cleanup.
22 * Patrick McHardy : LRU queue of frag heads for evictor.
25 #include <linux/compiler.h>
26 #include <linux/module.h>
27 #include <linux/types.h>
29 #include <linux/jiffies.h>
30 #include <linux/skbuff.h>
31 #include <linux/list.h>
33 #include <linux/icmp.h>
34 #include <linux/netdevice.h>
35 #include <linux/jhash.h>
36 #include <linux/random.h>
40 #include <net/checksum.h>
41 #include <net/inetpeer.h>
42 #include <net/inet_frag.h>
43 #include <linux/tcp.h>
44 #include <linux/udp.h>
45 #include <linux/inet.h>
46 #include <linux/netfilter_ipv4.h>
48 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
49 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
50 * as well. Or notify me, at least. --ANK
53 int sysctl_ipfrag_max_dist __read_mostly = 64;
57 struct inet_skb_parm h;
61 #define FRAG_CB(skb) ((struct ipfrag_skb_cb*)((skb)->cb))
63 /* Describe an entry in the "incomplete datagrams" queue. */
65 struct inet_frag_queue q;
74 struct inet_peer *peer;
77 struct inet_frags_ctl ip4_frags_ctl __read_mostly = {
79 * Fragment cache limits. We will commit 256K at one time. Should we
80 * cross that limit we will prune down to 192K. This should cope with
81 * even the most extreme cases without allowing an attacker to
82 * measurably harm machine performance.
84 .high_thresh = 256 * 1024,
85 .low_thresh = 192 * 1024,
88 * Important NOTE! Fragment queue must be destroyed before MSL expires.
89 * RFC791 is wrong proposing to prolongate timer each fragment arrival
92 .timeout = IP_FRAG_TIME,
93 .secret_interval = 10 * 60 * HZ,
96 static struct inet_frags ip4_frags;
98 int ip_frag_nqueues(void)
100 return ip4_frags.nqueues;
103 int ip_frag_mem(void)
105 return atomic_read(&ip4_frags.mem);
108 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
109 struct net_device *dev);
111 static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
113 return jhash_3words((__force u32)id << 16 | prot,
114 (__force u32)saddr, (__force u32)daddr,
115 ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1);
118 static void ipfrag_secret_rebuild(unsigned long dummy)
120 unsigned long now = jiffies;
123 write_lock(&ip4_frags.lock);
124 get_random_bytes(&ip4_frags.rnd, sizeof(u32));
125 for (i = 0; i < INETFRAGS_HASHSZ; i++) {
127 struct hlist_node *p, *n;
129 hlist_for_each_entry_safe(q, p, n, &ip4_frags.hash[i], q.list) {
130 unsigned int hval = ipqhashfn(q->id, q->saddr,
131 q->daddr, q->protocol);
134 hlist_del(&q->q.list);
136 /* Relink to new hash chain. */
137 hlist_add_head(&q->q.list, &ip4_frags.hash[hval]);
141 write_unlock(&ip4_frags.lock);
143 mod_timer(&ip4_frags.secret_timer, now + ip4_frags_ctl.secret_interval);
146 /* Memory Tracking Functions. */
147 static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work)
150 *work -= skb->truesize;
151 atomic_sub(skb->truesize, &ip4_frags.mem);
155 static __inline__ void frag_free_queue(struct ipq *qp, int *work)
158 *work -= sizeof(struct ipq);
159 atomic_sub(sizeof(struct ipq), &ip4_frags.mem);
163 static __inline__ struct ipq *frag_alloc_queue(void)
165 struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);
169 atomic_add(sizeof(struct ipq), &ip4_frags.mem);
174 /* Destruction primitives. */
176 /* Complete destruction of ipq. */
177 static void ip_frag_destroy(struct ipq *qp, int *work)
181 BUG_TRAP(qp->q.last_in&COMPLETE);
182 BUG_TRAP(del_timer(&qp->q.timer) == 0);
185 inet_putpeer(qp->peer);
187 /* Release all fragment data. */
188 fp = qp->q.fragments;
190 struct sk_buff *xp = fp->next;
192 frag_kfree_skb(fp, work);
196 /* Finally, release the queue descriptor itself. */
197 frag_free_queue(qp, work);
200 static __inline__ void ipq_put(struct ipq *ipq, int *work)
202 if (atomic_dec_and_test(&ipq->q.refcnt))
203 ip_frag_destroy(ipq, work);
206 /* Kill ipq entry. It is not destroyed immediately,
207 * because caller (and someone more) holds reference count.
209 static void ipq_kill(struct ipq *ipq)
211 inet_frag_kill(&ipq->q, &ip4_frags);
214 /* Memory limiting on fragments. Evictor trashes the oldest
215 * fragment queue until we are back under the threshold.
217 static void ip_evictor(void)
220 struct list_head *tmp;
223 work = atomic_read(&ip4_frags.mem) - ip4_frags_ctl.low_thresh;
228 read_lock(&ip4_frags.lock);
229 if (list_empty(&ip4_frags.lru_list)) {
230 read_unlock(&ip4_frags.lock);
233 tmp = ip4_frags.lru_list.next;
234 qp = list_entry(tmp, struct ipq, q.lru_list);
235 atomic_inc(&qp->q.refcnt);
236 read_unlock(&ip4_frags.lock);
238 spin_lock(&qp->q.lock);
239 if (!(qp->q.last_in&COMPLETE))
241 spin_unlock(&qp->q.lock);
244 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
249 * Oops, a fragment queue timed out. Kill it and send an ICMP reply.
251 static void ip_expire(unsigned long arg)
253 struct ipq *qp = (struct ipq *) arg;
255 spin_lock(&qp->q.lock);
257 if (qp->q.last_in & COMPLETE)
262 IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
263 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
265 if ((qp->q.last_in&FIRST_IN) && qp->q.fragments != NULL) {
266 struct sk_buff *head = qp->q.fragments;
267 /* Send an ICMP "Fragment Reassembly Timeout" message. */
268 if ((head->dev = dev_get_by_index(&init_net, qp->iif)) != NULL) {
269 icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
274 spin_unlock(&qp->q.lock);
278 /* Creation primitives. */
280 static struct ipq *ip_frag_intern(struct ipq *qp_in)
284 struct hlist_node *n;
288 write_lock(&ip4_frags.lock);
289 hash = ipqhashfn(qp_in->id, qp_in->saddr, qp_in->daddr,
292 /* With SMP race we have to recheck hash table, because
293 * such entry could be created on other cpu, while we
294 * promoted read lock to write lock.
296 hlist_for_each_entry(qp, n, &ip4_frags.hash[hash], q.list) {
297 if (qp->id == qp_in->id &&
298 qp->saddr == qp_in->saddr &&
299 qp->daddr == qp_in->daddr &&
300 qp->protocol == qp_in->protocol &&
301 qp->user == qp_in->user) {
302 atomic_inc(&qp->q.refcnt);
303 write_unlock(&ip4_frags.lock);
304 qp_in->q.last_in |= COMPLETE;
305 ipq_put(qp_in, NULL);
312 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout))
313 atomic_inc(&qp->q.refcnt);
315 atomic_inc(&qp->q.refcnt);
316 hlist_add_head(&qp->q.list, &ip4_frags.hash[hash]);
317 INIT_LIST_HEAD(&qp->q.lru_list);
318 list_add_tail(&qp->q.lru_list, &ip4_frags.lru_list);
320 write_unlock(&ip4_frags.lock);
324 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
325 static struct ipq *ip_frag_create(struct iphdr *iph, u32 user)
329 if ((qp = frag_alloc_queue()) == NULL)
332 qp->protocol = iph->protocol;
335 qp->saddr = iph->saddr;
336 qp->daddr = iph->daddr;
340 qp->q.fragments = NULL;
342 qp->peer = sysctl_ipfrag_max_dist ? inet_getpeer(iph->saddr, 1) : NULL;
344 /* Initialize a timer for this entry. */
345 init_timer(&qp->q.timer);
346 qp->q.timer.data = (unsigned long) qp; /* pointer to queue */
347 qp->q.timer.function = ip_expire; /* expire function */
348 spin_lock_init(&qp->q.lock);
349 atomic_set(&qp->q.refcnt, 1);
351 return ip_frag_intern(qp);
354 LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
358 /* Find the correct entry in the "incomplete datagrams" queue for
359 * this IP datagram, and create new one, if nothing is found.
361 static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
364 __be32 saddr = iph->saddr;
365 __be32 daddr = iph->daddr;
366 __u8 protocol = iph->protocol;
369 struct hlist_node *n;
371 read_lock(&ip4_frags.lock);
372 hash = ipqhashfn(id, saddr, daddr, protocol);
373 hlist_for_each_entry(qp, n, &ip4_frags.hash[hash], q.list) {
375 qp->saddr == saddr &&
376 qp->daddr == daddr &&
377 qp->protocol == protocol &&
379 atomic_inc(&qp->q.refcnt);
380 read_unlock(&ip4_frags.lock);
384 read_unlock(&ip4_frags.lock);
386 return ip_frag_create(iph, user);
389 /* Is the fragment too far ahead to be part of ipq? */
390 static inline int ip_frag_too_far(struct ipq *qp)
392 struct inet_peer *peer = qp->peer;
393 unsigned int max = sysctl_ipfrag_max_dist;
394 unsigned int start, end;
402 end = atomic_inc_return(&peer->rid);
405 rc = qp->q.fragments && (end - start) > max;
408 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
414 static int ip_frag_reinit(struct ipq *qp)
418 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout)) {
419 atomic_inc(&qp->q.refcnt);
423 fp = qp->q.fragments;
425 struct sk_buff *xp = fp->next;
426 frag_kfree_skb(fp, NULL);
433 qp->q.fragments = NULL;
439 /* Add new segment to existing queue. */
440 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
442 struct sk_buff *prev, *next;
443 struct net_device *dev;
448 if (qp->q.last_in & COMPLETE)
451 if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
452 unlikely(ip_frag_too_far(qp)) &&
453 unlikely(err = ip_frag_reinit(qp))) {
458 offset = ntohs(ip_hdr(skb)->frag_off);
459 flags = offset & ~IP_OFFSET;
461 offset <<= 3; /* offset is in 8-byte chunks */
462 ihl = ip_hdrlen(skb);
464 /* Determine the position of this fragment. */
465 end = offset + skb->len - ihl;
468 /* Is this the final fragment? */
469 if ((flags & IP_MF) == 0) {
470 /* If we already have some bits beyond end
471 * or have different end, the segment is corrrupted.
473 if (end < qp->q.len ||
474 ((qp->q.last_in & LAST_IN) && end != qp->q.len))
476 qp->q.last_in |= LAST_IN;
481 if (skb->ip_summed != CHECKSUM_UNNECESSARY)
482 skb->ip_summed = CHECKSUM_NONE;
484 if (end > qp->q.len) {
485 /* Some bits beyond end -> corruption. */
486 if (qp->q.last_in & LAST_IN)
495 if (pskb_pull(skb, ihl) == NULL)
498 err = pskb_trim_rcsum(skb, end - offset);
502 /* Find out which fragments are in front and at the back of us
503 * in the chain of fragments so far. We must know where to put
504 * this fragment, right?
507 for (next = qp->q.fragments; next != NULL; next = next->next) {
508 if (FRAG_CB(next)->offset >= offset)
513 /* We found where to put this one. Check for overlap with
514 * preceding fragment, and, if needed, align things so that
515 * any overlaps are eliminated.
518 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
526 if (!pskb_pull(skb, i))
528 if (skb->ip_summed != CHECKSUM_UNNECESSARY)
529 skb->ip_summed = CHECKSUM_NONE;
535 while (next && FRAG_CB(next)->offset < end) {
536 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
539 /* Eat head of the next overlapped fragment
540 * and leave the loop. The next ones cannot overlap.
542 if (!pskb_pull(next, i))
544 FRAG_CB(next)->offset += i;
546 if (next->ip_summed != CHECKSUM_UNNECESSARY)
547 next->ip_summed = CHECKSUM_NONE;
550 struct sk_buff *free_it = next;
552 /* Old fragment is completely overridden with
560 qp->q.fragments = next;
562 qp->q.meat -= free_it->len;
563 frag_kfree_skb(free_it, NULL);
567 FRAG_CB(skb)->offset = offset;
569 /* Insert this fragment in the chain of fragments. */
574 qp->q.fragments = skb;
578 qp->iif = dev->ifindex;
581 qp->q.stamp = skb->tstamp;
582 qp->q.meat += skb->len;
583 atomic_add(skb->truesize, &ip4_frags.mem);
585 qp->q.last_in |= FIRST_IN;
587 if (qp->q.last_in == (FIRST_IN | LAST_IN) && qp->q.meat == qp->q.len)
588 return ip_frag_reasm(qp, prev, dev);
590 write_lock(&ip4_frags.lock);
591 list_move_tail(&qp->q.lru_list, &ip4_frags.lru_list);
592 write_unlock(&ip4_frags.lock);
601 /* Build a new IP datagram from all its fragments. */
603 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
604 struct net_device *dev)
607 struct sk_buff *fp, *head = qp->q.fragments;
614 /* Make the one we just received the head. */
617 fp = skb_clone(head, GFP_ATOMIC);
622 fp->next = head->next;
625 skb_morph(head, qp->q.fragments);
626 head->next = qp->q.fragments->next;
628 kfree_skb(qp->q.fragments);
629 qp->q.fragments = head;
632 BUG_TRAP(head != NULL);
633 BUG_TRAP(FRAG_CB(head)->offset == 0);
635 /* Allocate a new buffer for the datagram. */
636 ihlen = ip_hdrlen(head);
637 len = ihlen + qp->q.len;
643 /* Head of list must not be cloned. */
645 if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
648 /* If the first fragment is fragmented itself, we split
649 * it to two chunks: the first with data and paged part
650 * and the second, holding only fragments. */
651 if (skb_shinfo(head)->frag_list) {
652 struct sk_buff *clone;
655 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
657 clone->next = head->next;
659 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
660 skb_shinfo(head)->frag_list = NULL;
661 for (i=0; i<skb_shinfo(head)->nr_frags; i++)
662 plen += skb_shinfo(head)->frags[i].size;
663 clone->len = clone->data_len = head->data_len - plen;
664 head->data_len -= clone->len;
665 head->len -= clone->len;
667 clone->ip_summed = head->ip_summed;
668 atomic_add(clone->truesize, &ip4_frags.mem);
671 skb_shinfo(head)->frag_list = head->next;
672 skb_push(head, head->data - skb_network_header(head));
673 atomic_sub(head->truesize, &ip4_frags.mem);
675 for (fp=head->next; fp; fp = fp->next) {
676 head->data_len += fp->len;
677 head->len += fp->len;
678 if (head->ip_summed != fp->ip_summed)
679 head->ip_summed = CHECKSUM_NONE;
680 else if (head->ip_summed == CHECKSUM_COMPLETE)
681 head->csum = csum_add(head->csum, fp->csum);
682 head->truesize += fp->truesize;
683 atomic_sub(fp->truesize, &ip4_frags.mem);
688 head->tstamp = qp->q.stamp;
692 iph->tot_len = htons(len);
693 IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
694 qp->q.fragments = NULL;
698 LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing "
704 "Oversized IP packet from %d.%d.%d.%d.\n",
707 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
711 /* Process an incoming IP datagram fragment. */
712 int ip_defrag(struct sk_buff *skb, u32 user)
716 IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);
718 /* Start by cleaning up the memory. */
719 if (atomic_read(&ip4_frags.mem) > ip4_frags_ctl.high_thresh)
722 /* Lookup (or create) queue header */
723 if ((qp = ip_find(ip_hdr(skb), user)) != NULL) {
726 spin_lock(&qp->q.lock);
728 ret = ip_frag_queue(qp, skb);
730 spin_unlock(&qp->q.lock);
735 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
740 void __init ipfrag_init(void)
742 init_timer(&ip4_frags.secret_timer);
743 ip4_frags.secret_timer.function = ipfrag_secret_rebuild;
744 ip4_frags.secret_timer.expires = jiffies + ip4_frags_ctl.secret_interval;
745 add_timer(&ip4_frags.secret_timer);
747 ip4_frags.ctl = &ip4_frags_ctl;
748 inet_frags_init(&ip4_frags);
751 EXPORT_SYMBOL(ip_defrag);