1 /*
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.
5 *
6 * The IP fragmentation functionality.
7 *
8 * Version: $Id: ip_fragment.c,v 1.53 2000/12/08 17:15:53 davem Exp $
9 *
10 * Authors: Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
11 * Alan Cox <Alan.Cox@linux.org>
12 *
13 * Fixes:
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 */
23
24 #include <linux/config.h>
25 #include <linux/types.h>
26 #include <linux/mm.h>
27 #include <linux/sched.h>
28 #include <linux/skbuff.h>
29 #include <linux/ip.h>
30 #include <linux/icmp.h>
31 #include <linux/netdevice.h>
32 #include <net/sock.h>
33 #include <net/ip.h>
34 #include <net/icmp.h>
35 #include <net/checksum.h>
36 #include <linux/tcp.h>
37 #include <linux/udp.h>
38 #include <linux/inet.h>
39 #include <linux/netfilter_ipv4.h>
40
41 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
42 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
43 * as well. Or notify me, at least. --ANK
44 */
45
46 /* Fragment cache limits. We will commit 256K at one time. Should we
47 * cross that limit we will prune down to 192K. This should cope with
48 * even the most extreme cases without allowing an attacker to measurably
49 * harm machine performance.
50 */
51 int sysctl_ipfrag_high_thresh = 256*1024;
52 int sysctl_ipfrag_low_thresh = 192*1024;
53
54 /* Important NOTE! Fragment queue must be destroyed before MSL expires.
55 * RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL.
56 */
57 int sysctl_ipfrag_time = IP_FRAG_TIME;
58
59 struct ipfrag_skb_cb
60 {
61 struct inet_skb_parm h;
62 int offset;
63 };
64
65 #define FRAG_CB(skb) ((struct ipfrag_skb_cb*)((skb)->cb))
66
67 /* Describe an entry in the "incomplete datagrams" queue. */
68 struct ipq {
69 struct ipq *next; /* linked list pointers */
70 u32 saddr;
71 u32 daddr;
72 u16 id;
73 u8 protocol;
74 u8 last_in;
75 #define COMPLETE 4
76 #define FIRST_IN 2
77 #define LAST_IN 1
78
79 struct sk_buff *fragments; /* linked list of received fragments */
80 int len; /* total length of original datagram */
81 int meat;
82 spinlock_t lock;
83 atomic_t refcnt;
84 struct timer_list timer; /* when will this queue expire? */
85 struct ipq **pprev;
86 int iif; /* Device index - for icmp replies */
87 };
88
89 /* Hash table. */
90
91 #define IPQ_HASHSZ 64
92
93 /* Per-bucket lock is easy to add now. */
94 static struct ipq *ipq_hash[IPQ_HASHSZ];
95 static rwlock_t ipfrag_lock = RW_LOCK_UNLOCKED;
96 int ip_frag_nqueues = 0;
97
98 static __inline__ void __ipq_unlink(struct ipq *qp)
99 {
100 if(qp->next)
101 qp->next->pprev = qp->pprev;
102 *qp->pprev = qp->next;
103 ip_frag_nqueues--;
104 }
105
106 static __inline__ void ipq_unlink(struct ipq *ipq)
107 {
108 write_lock(&ipfrag_lock);
109 __ipq_unlink(ipq);
110 write_unlock(&ipfrag_lock);
111 }
112
113 /*
114 * Was: ((((id) >> 1) ^ (saddr) ^ (daddr) ^ (prot)) & (IPQ_HASHSZ - 1))
115 *
116 * I see, I see evil hand of bigendian mafia. On Intel all the packets hit
117 * one hash bucket with this hash function. 8)
118 */
119 static __inline__ unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot)
120 {
121 unsigned int h = saddr ^ daddr;
122
123 h ^= (h>>16)^id;
124 h ^= (h>>8)^prot;
125 return h & (IPQ_HASHSZ - 1);
126 }
127
128
129 atomic_t ip_frag_mem = ATOMIC_INIT(0); /* Memory used for fragments */
130
131 /* Memory Tracking Functions. */
132 extern __inline__ void frag_kfree_skb(struct sk_buff *skb)
133 {
134 atomic_sub(skb->truesize, &ip_frag_mem);
135 kfree_skb(skb);
136 }
137
138 extern __inline__ void frag_free_queue(struct ipq *qp)
139 {
140 atomic_sub(sizeof(struct ipq), &ip_frag_mem);
141 kfree(qp);
142 }
143
144 extern __inline__ struct ipq *frag_alloc_queue(void)
145 {
146 struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);
147
148 if(!qp)
149 return NULL;
150 atomic_add(sizeof(struct ipq), &ip_frag_mem);
151 return qp;
152 }
153
154
155 /* Destruction primitives. */
156
157 /* Complete destruction of ipq. */
158 static void ip_frag_destroy(struct ipq *qp)
159 {
160 struct sk_buff *fp;
161
162 BUG_TRAP(qp->last_in&COMPLETE);
163 BUG_TRAP(del_timer(&qp->timer) == 0);
164
165 /* Release all fragment data. */
166 fp = qp->fragments;
167 while (fp) {
168 struct sk_buff *xp = fp->next;
169
170 frag_kfree_skb(fp);
171 fp = xp;
172 }
173
174 /* Finally, release the queue descriptor itself. */
175 frag_free_queue(qp);
176 }
177
178 static __inline__ void ipq_put(struct ipq *ipq)
179 {
180 if (atomic_dec_and_test(&ipq->refcnt))
181 ip_frag_destroy(ipq);
182 }
183
184 /* Kill ipq entry. It is not destroyed immediately,
185 * because caller (and someone more) holds reference count.
186 */
187 static __inline__ void ipq_kill(struct ipq *ipq)
188 {
189 if (del_timer(&ipq->timer))
190 atomic_dec(&ipq->refcnt);
191
192 if (!(ipq->last_in & COMPLETE)) {
193 ipq_unlink(ipq);
194 atomic_dec(&ipq->refcnt);
195 ipq->last_in |= COMPLETE;
196 }
197 }
198
199 /* Memory limiting on fragments. Evictor trashes the oldest
200 * fragment queue until we are back under the low threshold.
201 */
202 static void ip_evictor(void)
203 {
204 int i, progress;
205
206 do {
207 if (atomic_read(&ip_frag_mem) <= sysctl_ipfrag_low_thresh)
208 return;
209 progress = 0;
210 /* FIXME: Make LRU queue of frag heads. -DaveM */
211 for (i = 0; i < IPQ_HASHSZ; i++) {
212 struct ipq *qp;
213 if (ipq_hash[i] == NULL)
214 continue;
215
216 write_lock(&ipfrag_lock);
217 if ((qp = ipq_hash[i]) != NULL) {
218 /* find the oldest queue for this hash bucket */
219 while (qp->next)
220 qp = qp->next;
221 __ipq_unlink(qp);
222 write_unlock(&ipfrag_lock);
223
224 spin_lock(&qp->lock);
225 if (del_timer(&qp->timer))
226 atomic_dec(&qp->refcnt);
227 qp->last_in |= COMPLETE;
228 spin_unlock(&qp->lock);
229
230 ipq_put(qp);
231 IP_INC_STATS_BH(IpReasmFails);
232 progress = 1;
233 continue;
234 }
235 write_unlock(&ipfrag_lock);
236 }
237 } while (progress);
238 }
239
240 /*
241 * Oops, a fragment queue timed out. Kill it and send an ICMP reply.
242 */
243 static void ip_expire(unsigned long arg)
244 {
245 struct ipq *qp = (struct ipq *) arg;
246
247 spin_lock(&qp->lock);
248
249 if (qp->last_in & COMPLETE)
250 goto out;
251
252 ipq_kill(qp);
253
254 IP_INC_STATS_BH(IpReasmTimeout);
255 IP_INC_STATS_BH(IpReasmFails);
256
257 if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) {
258 struct sk_buff *head = qp->fragments;
259
260 /* Send an ICMP "Fragment Reassembly Timeout" message. */
261 if ((head->dev = dev_get_by_index(qp->iif)) != NULL) {
262 icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
263 dev_put(head->dev);
264 }
265 }
266 out:
267 spin_unlock(&qp->lock);
268 ipq_put(qp);
269 }
270
271 /* Creation primitives. */
272
273 static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
274 {
275 struct ipq *qp;
276
277 write_lock(&ipfrag_lock);
278 #ifdef CONFIG_SMP
279 /* With SMP race we have to recheck hash table, because
280 * such entry could be created on other cpu, while we
281 * promoted read lock to write lock.
282 */
283 for(qp = ipq_hash[hash]; qp; qp = qp->next) {
284 if(qp->id == qp_in->id &&
285 qp->saddr == qp_in->saddr &&
286 qp->daddr == qp_in->daddr &&
287 qp->protocol == qp_in->protocol) {
288 atomic_inc(&qp->refcnt);
289 write_unlock(&ipfrag_lock);
290 qp_in->last_in |= COMPLETE;
291 ipq_put(qp_in);
292 return qp;
293 }
294 }
295 #endif
296 qp = qp_in;
297
298 if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time))
299 atomic_inc(&qp->refcnt);
300
301 atomic_inc(&qp->refcnt);
302 if((qp->next = ipq_hash[hash]) != NULL)
303 qp->next->pprev = &qp->next;
304 ipq_hash[hash] = qp;
305 qp->pprev = &ipq_hash[hash];
306 ip_frag_nqueues++;
307 write_unlock(&ipfrag_lock);
308 return qp;
309 }
310
311 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
312 static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph)
313 {
314 struct ipq *qp;
315
316 if ((qp = frag_alloc_queue()) == NULL)
317 goto out_nomem;
318
319 qp->protocol = iph->protocol;
320 qp->last_in = 0;
321 qp->id = iph->id;
322 qp->saddr = iph->saddr;
323 qp->daddr = iph->daddr;
324 qp->len = 0;
325 qp->meat = 0;
326 qp->fragments = NULL;
327 qp->iif = 0;
328
329 /* Initialize a timer for this entry. */
330 init_timer(&qp->timer);
331 qp->timer.data = (unsigned long) qp; /* pointer to queue */
332 qp->timer.function = ip_expire; /* expire function */
333 qp->lock = SPIN_LOCK_UNLOCKED;
334 atomic_set(&qp->refcnt, 1);
335
336 return ip_frag_intern(hash, qp);
337
338 out_nomem:
339 NETDEBUG(printk(KERN_ERR "ip_frag_create: no memory left !\n"));
340 return NULL;
341 }
342
343 /* Find the correct entry in the "incomplete datagrams" queue for
344 * this IP datagram, and create new one, if nothing is found.
345 */
346 static inline struct ipq *ip_find(struct iphdr *iph)
347 {
348 __u16 id = iph->id;
349 __u32 saddr = iph->saddr;
350 __u32 daddr = iph->daddr;
351 __u8 protocol = iph->protocol;
352 unsigned int hash = ipqhashfn(id, saddr, daddr, protocol);
353 struct ipq *qp;
354
355 read_lock(&ipfrag_lock);
356 for(qp = ipq_hash[hash]; qp; qp = qp->next) {
357 if(qp->id == id &&
358 qp->saddr == saddr &&
359 qp->daddr == daddr &&
360 qp->protocol == protocol) {
361 atomic_inc(&qp->refcnt);
362 read_unlock(&ipfrag_lock);
363 return qp;
364 }
365 }
366 read_unlock(&ipfrag_lock);
367
368 return ip_frag_create(hash, iph);
369 }
370
371 /* Add new segment to existing queue. */
372 static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
373 {
374 struct iphdr *iph = skb->nh.iph;
375 struct sk_buff *prev, *next;
376 int flags, offset;
377 int ihl, end;
378
379 if (qp->last_in & COMPLETE)
380 goto err;
381
382 offset = ntohs(iph->frag_off);
383 flags = offset & ~IP_OFFSET;
384 offset &= IP_OFFSET;
385 offset <<= 3; /* offset is in 8-byte chunks */
386 ihl = iph->ihl * 4;
387
388 /* Determine the position of this fragment. */
389 end = offset + (ntohs(iph->tot_len) - ihl);
390
391 /* Is this the final fragment? */
392 if ((flags & IP_MF) == 0) {
393 /* If we already have some bits beyond end
394 * or have different end, the segment is corrrupted.
395 */
396 if (end < qp->len ||
397 ((qp->last_in & LAST_IN) && end != qp->len))
398 goto err;
399 qp->last_in |= LAST_IN;
400 qp->len = end;
401 } else {
402 if (end&7) {
403 end &= ~7;
404 if (skb->ip_summed != CHECKSUM_UNNECESSARY)
405 skb->ip_summed = CHECKSUM_NONE;
406 }
407 if (end > qp->len) {
408 /* Some bits beyond end -> corruption. */
409 if (qp->last_in & LAST_IN)
410 goto err;
411 qp->len = end;
412 }
413 }
414 if (end == offset)
415 goto err;
416
417 /* Point into the IP datagram 'data' part. */
418 skb_pull(skb, (skb->nh.raw+ihl) - skb->data);
419 skb_trim(skb, end - offset);
420
421 /* Find out which fragments are in front and at the back of us
422 * in the chain of fragments so far. We must know where to put
423 * this fragment, right?
424 */
425 prev = NULL;
426 for(next = qp->fragments; next != NULL; next = next->next) {
427 if (FRAG_CB(next)->offset >= offset)
428 break; /* bingo! */
429 prev = next;
430 }
431
432 /* We found where to put this one. Check for overlap with
433 * preceding fragment, and, if needed, align things so that
434 * any overlaps are eliminated.
435 */
436 if (prev) {
437 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
438
439 if (i > 0) {
440 offset += i;
441 if (end <= offset)
442 goto err;
443 skb_pull(skb, i);
444 if (skb->ip_summed != CHECKSUM_UNNECESSARY)
445 skb->ip_summed = CHECKSUM_NONE;
446 }
447 }
448
449 while (next && FRAG_CB(next)->offset < end) {
450 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
451
452 if (i < next->len) {
453 /* Eat head of the next overlapped fragment
454 * and leave the loop. The next ones cannot overlap.
455 */
456 FRAG_CB(next)->offset += i;
457 skb_pull(next, i);
458 qp->meat -= i;
459 if (next->ip_summed != CHECKSUM_UNNECESSARY)
460 next->ip_summed = CHECKSUM_NONE;
461 break;
462 } else {
463 struct sk_buff *free_it = next;
464
465 /* Old fragmnet is completely overridden with
466 * new one drop it.
467 */
468 next = next->next;
469
470 if (prev)
471 prev->next = next;
472 else
473 qp->fragments = next;
474
475 qp->meat -= free_it->len;
476 frag_kfree_skb(free_it);
477 }
478 }
479
480 FRAG_CB(skb)->offset = offset;
481
482 /* Insert this fragment in the chain of fragments. */
483 skb->next = next;
484 if (prev)
485 prev->next = skb;
486 else
487 qp->fragments = skb;
488
489 if (skb->dev)
490 qp->iif = skb->dev->ifindex;
491 skb->dev = NULL;
492 qp->meat += skb->len;
493 atomic_add(skb->truesize, &ip_frag_mem);
494 if (offset == 0)
495 qp->last_in |= FIRST_IN;
496
497 return;
498
499 err:
500 kfree_skb(skb);
501 }
502
503
504 /* Build a new IP datagram from all its fragments.
505 *
506 * FIXME: We copy here because we lack an effective way of handling lists
507 * of bits on input. Until the new skb data handling is in I'm not going
508 * to touch this with a bargepole.
509 */
510 static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev)
511 {
512 struct sk_buff *skb;
513 struct iphdr *iph;
514 struct sk_buff *fp, *head = qp->fragments;
515 int len;
516 int ihlen;
517
518 ipq_kill(qp);
519
520 BUG_TRAP(head != NULL);
521 BUG_TRAP(FRAG_CB(head)->offset == 0);
522
523 /* Allocate a new buffer for the datagram. */
524 ihlen = head->nh.iph->ihl*4;
525 len = ihlen + qp->len;
526
527 if(len > 65535)
528 goto out_oversize;
529
530 skb = dev_alloc_skb(len);
531 if (!skb)
532 goto out_nomem;
533
534 /* Fill in the basic details. */
535 skb->mac.raw = skb->data;
536 skb->nh.raw = skb->data;
537 FRAG_CB(skb)->h = FRAG_CB(head)->h;
538 skb->ip_summed = head->ip_summed;
539 skb->csum = 0;
540
541 /* Copy the original IP headers into the new buffer. */
542 memcpy(skb_put(skb, ihlen), head->nh.iph, ihlen);
543
544 /* Copy the data portions of all fragments into the new buffer. */
545 for (fp=head; fp; fp = fp->next) {
546 memcpy(skb_put(skb, fp->len), fp->data, fp->len);
547
548 if (skb->ip_summed != fp->ip_summed)
549 skb->ip_summed = CHECKSUM_NONE;
550 else if (skb->ip_summed == CHECKSUM_HW)
551 skb->csum = csum_add(skb->csum, fp->csum);
552 }
553
554 skb->dst = dst_clone(head->dst);
555 skb->pkt_type = head->pkt_type;
556 skb->protocol = head->protocol;
557 skb->dev = dev;
558
559 /*
560 * Clearly bogus, because security markings of the individual
561 * fragments should have been checked for consistency before
562 * gluing, and intermediate coalescing of fragments may have
563 * taken place in ip_defrag() before ip_glue() ever got called.
564 * If we're not going to do the consistency checking, we might
565 * as well take the value associated with the first fragment.
566 * --rct
567 */
568 skb->security = head->security;
569
570 #ifdef CONFIG_NETFILTER
571 /* Connection association is same as fragment (if any). */
572 skb->nfct = head->nfct;
573 nf_conntrack_get(skb->nfct);
574 #ifdef CONFIG_NETFILTER_DEBUG
575 skb->nf_debug = head->nf_debug;
576 #endif
577 #endif
578
579 /* Done with all fragments. Fixup the new IP header. */
580 iph = skb->nh.iph;
581 iph->frag_off = 0;
582 iph->tot_len = htons(len);
583 IP_INC_STATS_BH(IpReasmOKs);
584 return skb;
585
586 out_nomem:
587 NETDEBUG(printk(KERN_ERR
588 "IP: queue_glue: no memory for gluing queue %p\n",
589 qp));
590 goto out_fail;
591 out_oversize:
592 if (net_ratelimit())
593 printk(KERN_INFO
594 "Oversized IP packet from %d.%d.%d.%d.\n",
595 NIPQUAD(qp->saddr));
596 out_fail:
597 IP_INC_STATS_BH(IpReasmFails);
598 return NULL;
599 }
600
601 /* Process an incoming IP datagram fragment. */
602 struct sk_buff *ip_defrag(struct sk_buff *skb)
603 {
604 struct iphdr *iph = skb->nh.iph;
605 struct ipq *qp;
606 struct net_device *dev;
607
608 IP_INC_STATS_BH(IpReasmReqds);
609
610 /* Start by cleaning up the memory. */
611 if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh)
612 ip_evictor();
613
614 dev = skb->dev;
615
616 /* Lookup (or create) queue header */
617 if ((qp = ip_find(iph)) != NULL) {
618 struct sk_buff *ret = NULL;
619
620 spin_lock(&qp->lock);
621
622 ip_frag_queue(qp, skb);
623
624 if (qp->last_in == (FIRST_IN|LAST_IN) &&
625 qp->meat == qp->len)
626 ret = ip_frag_reasm(qp, dev);
627
628 spin_unlock(&qp->lock);
629 ipq_put(qp);
630 return ret;
631 }
632
633 IP_INC_STATS_BH(IpReasmFails);
634 kfree_skb(skb);
635 return NULL;
636 }
637
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