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 unsigned int ip4_hashfn(struct inet_frag_queue *q)
122 ipq = container_of(q, struct ipq, q);
123 return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
126 /* Memory Tracking Functions. */
127 static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work)
130 *work -= skb->truesize;
131 atomic_sub(skb->truesize, &ip4_frags.mem);
135 static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
139 qp = container_of(q, struct ipq, q);
141 inet_putpeer(qp->peer);
145 static __inline__ struct ipq *frag_alloc_queue(void)
147 struct ipq *qp = kzalloc(sizeof(struct ipq), GFP_ATOMIC);
151 atomic_add(sizeof(struct ipq), &ip4_frags.mem);
156 /* Destruction primitives. */
158 static __inline__ void ipq_put(struct ipq *ipq)
160 inet_frag_put(&ipq->q, &ip4_frags);
163 /* Kill ipq entry. It is not destroyed immediately,
164 * because caller (and someone more) holds reference count.
166 static void ipq_kill(struct ipq *ipq)
168 inet_frag_kill(&ipq->q, &ip4_frags);
171 /* Memory limiting on fragments. Evictor trashes the oldest
172 * fragment queue until we are back under the threshold.
174 static void ip_evictor(void)
178 evicted = inet_frag_evictor(&ip4_frags);
180 IP_ADD_STATS_BH(IPSTATS_MIB_REASMFAILS, evicted);
184 * Oops, a fragment queue timed out. Kill it and send an ICMP reply.
186 static void ip_expire(unsigned long arg)
188 struct ipq *qp = (struct ipq *) arg;
190 spin_lock(&qp->q.lock);
192 if (qp->q.last_in & COMPLETE)
197 IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
198 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
200 if ((qp->q.last_in&FIRST_IN) && qp->q.fragments != NULL) {
201 struct sk_buff *head = qp->q.fragments;
202 /* Send an ICMP "Fragment Reassembly Timeout" message. */
203 if ((head->dev = dev_get_by_index(&init_net, qp->iif)) != NULL) {
204 icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
209 spin_unlock(&qp->q.lock);
213 /* Creation primitives. */
215 static struct ipq *ip_frag_intern(struct ipq *qp_in)
219 struct hlist_node *n;
223 write_lock(&ip4_frags.lock);
224 hash = ipqhashfn(qp_in->id, qp_in->saddr, qp_in->daddr,
227 /* With SMP race we have to recheck hash table, because
228 * such entry could be created on other cpu, while we
229 * promoted read lock to write lock.
231 hlist_for_each_entry(qp, n, &ip4_frags.hash[hash], q.list) {
232 if (qp->id == qp_in->id &&
233 qp->saddr == qp_in->saddr &&
234 qp->daddr == qp_in->daddr &&
235 qp->protocol == qp_in->protocol &&
236 qp->user == qp_in->user) {
237 atomic_inc(&qp->q.refcnt);
238 write_unlock(&ip4_frags.lock);
239 qp_in->q.last_in |= COMPLETE;
247 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout))
248 atomic_inc(&qp->q.refcnt);
250 atomic_inc(&qp->q.refcnt);
251 hlist_add_head(&qp->q.list, &ip4_frags.hash[hash]);
252 INIT_LIST_HEAD(&qp->q.lru_list);
253 list_add_tail(&qp->q.lru_list, &ip4_frags.lru_list);
255 write_unlock(&ip4_frags.lock);
259 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
260 static struct ipq *ip_frag_create(struct iphdr *iph, u32 user)
264 if ((qp = frag_alloc_queue()) == NULL)
267 qp->protocol = iph->protocol;
269 qp->saddr = iph->saddr;
270 qp->daddr = iph->daddr;
272 qp->peer = sysctl_ipfrag_max_dist ? inet_getpeer(iph->saddr, 1) : NULL;
274 /* Initialize a timer for this entry. */
275 init_timer(&qp->q.timer);
276 qp->q.timer.data = (unsigned long) qp; /* pointer to queue */
277 qp->q.timer.function = ip_expire; /* expire function */
278 spin_lock_init(&qp->q.lock);
279 atomic_set(&qp->q.refcnt, 1);
281 return ip_frag_intern(qp);
284 LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
288 /* Find the correct entry in the "incomplete datagrams" queue for
289 * this IP datagram, and create new one, if nothing is found.
291 static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
294 __be32 saddr = iph->saddr;
295 __be32 daddr = iph->daddr;
296 __u8 protocol = iph->protocol;
299 struct hlist_node *n;
301 read_lock(&ip4_frags.lock);
302 hash = ipqhashfn(id, saddr, daddr, protocol);
303 hlist_for_each_entry(qp, n, &ip4_frags.hash[hash], q.list) {
305 qp->saddr == saddr &&
306 qp->daddr == daddr &&
307 qp->protocol == protocol &&
309 atomic_inc(&qp->q.refcnt);
310 read_unlock(&ip4_frags.lock);
314 read_unlock(&ip4_frags.lock);
316 return ip_frag_create(iph, user);
319 /* Is the fragment too far ahead to be part of ipq? */
320 static inline int ip_frag_too_far(struct ipq *qp)
322 struct inet_peer *peer = qp->peer;
323 unsigned int max = sysctl_ipfrag_max_dist;
324 unsigned int start, end;
332 end = atomic_inc_return(&peer->rid);
335 rc = qp->q.fragments && (end - start) > max;
338 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
344 static int ip_frag_reinit(struct ipq *qp)
348 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout)) {
349 atomic_inc(&qp->q.refcnt);
353 fp = qp->q.fragments;
355 struct sk_buff *xp = fp->next;
356 frag_kfree_skb(fp, NULL);
363 qp->q.fragments = NULL;
369 /* Add new segment to existing queue. */
370 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
372 struct sk_buff *prev, *next;
373 struct net_device *dev;
378 if (qp->q.last_in & COMPLETE)
381 if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
382 unlikely(ip_frag_too_far(qp)) &&
383 unlikely(err = ip_frag_reinit(qp))) {
388 offset = ntohs(ip_hdr(skb)->frag_off);
389 flags = offset & ~IP_OFFSET;
391 offset <<= 3; /* offset is in 8-byte chunks */
392 ihl = ip_hdrlen(skb);
394 /* Determine the position of this fragment. */
395 end = offset + skb->len - ihl;
398 /* Is this the final fragment? */
399 if ((flags & IP_MF) == 0) {
400 /* If we already have some bits beyond end
401 * or have different end, the segment is corrrupted.
403 if (end < qp->q.len ||
404 ((qp->q.last_in & LAST_IN) && end != qp->q.len))
406 qp->q.last_in |= LAST_IN;
411 if (skb->ip_summed != CHECKSUM_UNNECESSARY)
412 skb->ip_summed = CHECKSUM_NONE;
414 if (end > qp->q.len) {
415 /* Some bits beyond end -> corruption. */
416 if (qp->q.last_in & LAST_IN)
425 if (pskb_pull(skb, ihl) == NULL)
428 err = pskb_trim_rcsum(skb, end - offset);
432 /* Find out which fragments are in front and at the back of us
433 * in the chain of fragments so far. We must know where to put
434 * this fragment, right?
437 for (next = qp->q.fragments; next != NULL; next = next->next) {
438 if (FRAG_CB(next)->offset >= offset)
443 /* We found where to put this one. Check for overlap with
444 * preceding fragment, and, if needed, align things so that
445 * any overlaps are eliminated.
448 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
456 if (!pskb_pull(skb, i))
458 if (skb->ip_summed != CHECKSUM_UNNECESSARY)
459 skb->ip_summed = CHECKSUM_NONE;
465 while (next && FRAG_CB(next)->offset < end) {
466 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
469 /* Eat head of the next overlapped fragment
470 * and leave the loop. The next ones cannot overlap.
472 if (!pskb_pull(next, i))
474 FRAG_CB(next)->offset += i;
476 if (next->ip_summed != CHECKSUM_UNNECESSARY)
477 next->ip_summed = CHECKSUM_NONE;
480 struct sk_buff *free_it = next;
482 /* Old fragment is completely overridden with
490 qp->q.fragments = next;
492 qp->q.meat -= free_it->len;
493 frag_kfree_skb(free_it, NULL);
497 FRAG_CB(skb)->offset = offset;
499 /* Insert this fragment in the chain of fragments. */
504 qp->q.fragments = skb;
508 qp->iif = dev->ifindex;
511 qp->q.stamp = skb->tstamp;
512 qp->q.meat += skb->len;
513 atomic_add(skb->truesize, &ip4_frags.mem);
515 qp->q.last_in |= FIRST_IN;
517 if (qp->q.last_in == (FIRST_IN | LAST_IN) && qp->q.meat == qp->q.len)
518 return ip_frag_reasm(qp, prev, dev);
520 write_lock(&ip4_frags.lock);
521 list_move_tail(&qp->q.lru_list, &ip4_frags.lru_list);
522 write_unlock(&ip4_frags.lock);
531 /* Build a new IP datagram from all its fragments. */
533 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
534 struct net_device *dev)
537 struct sk_buff *fp, *head = qp->q.fragments;
544 /* Make the one we just received the head. */
547 fp = skb_clone(head, GFP_ATOMIC);
552 fp->next = head->next;
555 skb_morph(head, qp->q.fragments);
556 head->next = qp->q.fragments->next;
558 kfree_skb(qp->q.fragments);
559 qp->q.fragments = head;
562 BUG_TRAP(head != NULL);
563 BUG_TRAP(FRAG_CB(head)->offset == 0);
565 /* Allocate a new buffer for the datagram. */
566 ihlen = ip_hdrlen(head);
567 len = ihlen + qp->q.len;
573 /* Head of list must not be cloned. */
575 if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
578 /* If the first fragment is fragmented itself, we split
579 * it to two chunks: the first with data and paged part
580 * and the second, holding only fragments. */
581 if (skb_shinfo(head)->frag_list) {
582 struct sk_buff *clone;
585 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
587 clone->next = head->next;
589 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
590 skb_shinfo(head)->frag_list = NULL;
591 for (i=0; i<skb_shinfo(head)->nr_frags; i++)
592 plen += skb_shinfo(head)->frags[i].size;
593 clone->len = clone->data_len = head->data_len - plen;
594 head->data_len -= clone->len;
595 head->len -= clone->len;
597 clone->ip_summed = head->ip_summed;
598 atomic_add(clone->truesize, &ip4_frags.mem);
601 skb_shinfo(head)->frag_list = head->next;
602 skb_push(head, head->data - skb_network_header(head));
603 atomic_sub(head->truesize, &ip4_frags.mem);
605 for (fp=head->next; fp; fp = fp->next) {
606 head->data_len += fp->len;
607 head->len += fp->len;
608 if (head->ip_summed != fp->ip_summed)
609 head->ip_summed = CHECKSUM_NONE;
610 else if (head->ip_summed == CHECKSUM_COMPLETE)
611 head->csum = csum_add(head->csum, fp->csum);
612 head->truesize += fp->truesize;
613 atomic_sub(fp->truesize, &ip4_frags.mem);
618 head->tstamp = qp->q.stamp;
622 iph->tot_len = htons(len);
623 IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
624 qp->q.fragments = NULL;
628 LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing "
634 "Oversized IP packet from %d.%d.%d.%d.\n",
637 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
641 /* Process an incoming IP datagram fragment. */
642 int ip_defrag(struct sk_buff *skb, u32 user)
646 IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);
648 /* Start by cleaning up the memory. */
649 if (atomic_read(&ip4_frags.mem) > ip4_frags_ctl.high_thresh)
652 /* Lookup (or create) queue header */
653 if ((qp = ip_find(ip_hdr(skb), user)) != NULL) {
656 spin_lock(&qp->q.lock);
658 ret = ip_frag_queue(qp, skb);
660 spin_unlock(&qp->q.lock);
665 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
670 void __init ipfrag_init(void)
672 ip4_frags.ctl = &ip4_frags_ctl;
673 ip4_frags.hashfn = ip4_hashfn;
674 ip4_frags.destructor = ip4_frag_free;
675 ip4_frags.skb_free = NULL;
676 ip4_frags.qsize = sizeof(struct ipq);
677 inet_frags_init(&ip4_frags);
680 EXPORT_SYMBOL(ip_defrag);