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*/
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 * Authors: Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
9 * Alan Cox <Alan.Cox@linux.org>
10 *
11 * Fixes:
12 * Alan Cox : Split from ip.c , see ip_input.c for history.
13 */
14
15 #include <linux/types.h>
16 #include <linux/mm.h>
17 #include <linux/sched.h>
18 #include <linux/skbuff.h>
19 #include <linux/ip.h>
20 #include <linux/icmp.h>
21 #include <linux/netdevice.h>
22 #include <net/sock.h>
23 #include <net/ip.h>
24 #include <net/icmp.h>
25 #include <linux/tcp.h>
26 #include <linux/udp.h>
27 #include <linux/firewall.h>
28 #include <linux/ip_fw.h>
29 #include <net/checksum.h>
30
31 /*
32 * Fragment cache limits. We will commit 256K at one time. Should we
33 * cross that limit we will prune down to 192K. This should cope with
34 * even the most extreme cases without allowing an attacker to measurably
35 * harm machine performance.
36 */
37
38 #define IPFRAG_HIGH_THRESH (256*1024)
39 #define IPFRAG_LOW_THRESH (192*1024)
40
41 /*
42 * This fragment handler is a bit of a heap. On the other hand it works quite
43 * happily and handles things quite well.
44 */
45
46 static struct ipq *ipqueue = NULL; /* IP fragment queue */
47
48 atomic_t ip_frag_mem = 0; /* Memory used for fragments */
49
50 /*
51 * Memory Tracking Functions
52 */
53
54 extern __inline__ void frag_kfree_skb(struct sk_buff *skb, int type)
/* ![[next]](../icons/right.png)
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*/
55 {
56 atomic_sub(skb->truesize, &ip_frag_mem);
57 kfree_skb(skb,type);
58 }
59
60 extern __inline__ void frag_kfree_s(void *ptr, int len)
/* ![[previous]](../icons/left.png)
*/
61 {
62 atomic_sub(len, &ip_frag_mem);
63 kfree_s(ptr,len);
64 }
65
66 extern __inline__ void *frag_kmalloc(int size, int pri)
/* */
67 {
68 void *vp=kmalloc(size,pri);
69 if(!vp)
70 return NULL;
71 atomic_add(size, &ip_frag_mem);
72 return vp;
73 }
74
75 /*
76 * Create a new fragment entry.
77 */
78
79 static struct ipfrag *ip_frag_create(int offset, int end, struct sk_buff *skb, unsigned char *ptr)
/* */
80 {
81 struct ipfrag *fp;
82 unsigned long flags;
83
84 fp = (struct ipfrag *) frag_kmalloc(sizeof(struct ipfrag), GFP_ATOMIC);
85 if (fp == NULL)
86 {
87 NETDEBUG(printk("IP: frag_create: no memory left !\n"));
88 return(NULL);
89 }
90 memset(fp, 0, sizeof(struct ipfrag));
91
92 /* Fill in the structure. */
93 fp->offset = offset;
94 fp->end = end;
95 fp->len = end - offset;
96 fp->skb = skb;
97 fp->ptr = ptr;
98
99 /*
100 * Charge for the SKB as well.
101 */
102
103 save_flags(flags);
104 cli();
105 ip_frag_mem+=skb->truesize;
106 restore_flags(flags);
107
108 return(fp);
109 }
110
111
112 /*
113 * Find the correct entry in the "incomplete datagrams" queue for
114 * this IP datagram, and return the queue entry address if found.
115 */
116
117 static struct ipq *ip_find(struct iphdr *iph)
/* */
118 {
119 struct ipq *qp;
120 struct ipq *qplast;
121
122 cli();
123 qplast = NULL;
124 for(qp = ipqueue; qp != NULL; qplast = qp, qp = qp->next)
125 {
126 if (iph->id== qp->iph->id && iph->saddr == qp->iph->saddr &&
127 iph->daddr == qp->iph->daddr && iph->protocol == qp->iph->protocol)
128 {
129 del_timer(&qp->timer); /* So it doesn't vanish on us. The timer will be reset anyway */
130 sti();
131 return(qp);
132 }
133 }
134 sti();
135 return(NULL);
136 }
137
138
139 /*
140 * Remove an entry from the "incomplete datagrams" queue, either
141 * because we completed, reassembled and processed it, or because
142 * it timed out.
143 */
144
145 static void ip_free(struct ipq *qp)
/* */
146 {
147 struct ipfrag *fp;
148 struct ipfrag *xp;
149
150 /*
151 * Stop the timer for this entry.
152 */
153
154 del_timer(&qp->timer);
155
156 /* Remove this entry from the "incomplete datagrams" queue. */
157 cli();
158 if (qp->prev == NULL)
159 {
160 ipqueue = qp->next;
161 if (ipqueue != NULL)
162 ipqueue->prev = NULL;
163 }
164 else
165 {
166 qp->prev->next = qp->next;
167 if (qp->next != NULL)
168 qp->next->prev = qp->prev;
169 }
170
171 /* Release all fragment data. */
172
173 fp = qp->fragments;
174 while (fp != NULL)
175 {
176 xp = fp->next;
177 IS_SKB(fp->skb);
178 frag_kfree_skb(fp->skb,FREE_READ);
179 frag_kfree_s(fp, sizeof(struct ipfrag));
180 fp = xp;
181 }
182
183 /* Release the IP header. */
184 frag_kfree_s(qp->iph, 64 + 8);
185
186 /* Finally, release the queue descriptor itself. */
187 frag_kfree_s(qp, sizeof(struct ipq));
188 sti();
189 }
190
191
192 /*
193 * Oops- a fragment queue timed out. Kill it and send an ICMP reply.
194 */
195
196 static void ip_expire(unsigned long arg)
/* */
197 {
198 struct ipq *qp;
199
200 qp = (struct ipq *)arg;
201
202 /*
203 * Send an ICMP "Fragment Reassembly Timeout" message.
204 */
205
206 ip_statistics.IpReasmTimeout++;
207 ip_statistics.IpReasmFails++;
208 /* This if is always true... shrug */
209 if(qp->fragments!=NULL)
210 icmp_send(qp->fragments->skb,ICMP_TIME_EXCEEDED,
211 ICMP_EXC_FRAGTIME, 0, qp->dev);
212
213 /*
214 * Nuke the fragment queue.
215 */
216 ip_free(qp);
217 }
218
219 /*
220 * Memory limiting on fragments. Evictor trashes the oldest
221 * fragment queue until we are back under the low threshold
222 */
223
224 static void ip_evictor(void)
/* */
225 {
226 while(ip_frag_mem>IPFRAG_LOW_THRESH)
227 {
228 if(!ipqueue)
229 panic("ip_evictor: memcount");
230 ip_free(ipqueue);
231 }
232 }
233
234 /*
235 * Add an entry to the 'ipq' queue for a newly received IP datagram.
236 * We will (hopefully :-) receive all other fragments of this datagram
237 * in time, so we just create a queue for this datagram, in which we
238 * will insert the received fragments at their respective positions.
239 */
240
241 static struct ipq *ip_create(struct sk_buff *skb, struct iphdr *iph, struct device *dev)
/* */
242 {
243 struct ipq *qp;
244 int ihlen;
245
246 qp = (struct ipq *) frag_kmalloc(sizeof(struct ipq), GFP_ATOMIC);
247 if (qp == NULL)
248 {
249 NETDEBUG(printk("IP: create: no memory left !\n"));
250 return(NULL);
251 }
252 memset(qp, 0, sizeof(struct ipq));
253
254 /*
255 * Allocate memory for the IP header (plus 8 octets for ICMP).
256 */
257
258 ihlen = iph->ihl * 4;
259 qp->iph = (struct iphdr *) frag_kmalloc(64 + 8, GFP_ATOMIC);
260 if (qp->iph == NULL)
261 {
262 NETDEBUG(printk("IP: create: no memory left !\n"));
263 frag_kfree_s(qp, sizeof(struct ipq));
264 return(NULL);
265 }
266
267 memcpy(qp->iph, iph, ihlen + 8);
268 qp->len = 0;
269 qp->ihlen = ihlen;
270 qp->fragments = NULL;
271 qp->dev = dev;
272
273 /* Start a timer for this entry. */
274 qp->timer.expires = jiffies + IP_FRAG_TIME; /* about 30 seconds */
275 qp->timer.data = (unsigned long) qp; /* pointer to queue */
276 qp->timer.function = ip_expire; /* expire function */
277 add_timer(&qp->timer);
278
279 /* Add this entry to the queue. */
280 qp->prev = NULL;
281 cli();
282 qp->next = ipqueue;
283 if (qp->next != NULL)
284 qp->next->prev = qp;
285 ipqueue = qp;
286 sti();
287 return(qp);
288 }
289
290
291 /*
292 * See if a fragment queue is complete.
293 */
294
295 static int ip_done(struct ipq *qp)
/* */
296 {
297 struct ipfrag *fp;
298 int offset;
299
300 /* Only possible if we received the final fragment. */
301 if (qp->len == 0)
302 return(0);
303
304 /* Check all fragment offsets to see if they connect. */
305 fp = qp->fragments;
306 offset = 0;
307 while (fp != NULL)
308 {
309 if (fp->offset > offset)
310 return(0); /* fragment(s) missing */
311 offset = fp->end;
312 fp = fp->next;
313 }
314
315 /* All fragments are present. */
316 return(1);
317 }
318
319
320 /*
321 * Build a new IP datagram from all its fragments.
322 *
323 * FIXME: We copy here because we lack an effective way of handling lists
324 * of bits on input. Until the new skb data handling is in I'm not going
325 * to touch this with a bargepole.
326 */
327
328 static struct sk_buff *ip_glue(struct ipq *qp)
/* */
329 {
330 struct sk_buff *skb;
331 struct iphdr *iph;
332 struct ipfrag *fp;
333 unsigned char *ptr;
334 int count, len;
335
336 /*
337 * Allocate a new buffer for the datagram.
338 */
339 len = qp->ihlen + qp->len;
340
341 if ((skb = dev_alloc_skb(len)) == NULL)
342 {
343 ip_statistics.IpReasmFails++;
344 NETDEBUG(printk("IP: queue_glue: no memory for gluing queue %p\n", qp));
345 ip_free(qp);
346 return(NULL);
347 }
348
349 /* Fill in the basic details. */
350 skb_put(skb,len);
351 skb->h.raw = skb->data;
352 skb->free = 1;
353
354 /* Copy the original IP headers into the new buffer. */
355 ptr = (unsigned char *) skb->h.raw;
356 memcpy(ptr, ((unsigned char *) qp->iph), qp->ihlen);
357 ptr += qp->ihlen;
358
359 count = 0;
360
361 /* Copy the data portions of all fragments into the new buffer. */
362 fp = qp->fragments;
363 while(fp != NULL)
364 {
365 if(count+fp->len > skb->len)
366 {
367 NETDEBUG(printk("Invalid fragment list: Fragment over size.\n"));
368 ip_free(qp);
369 frag_kfree_skb(skb,FREE_WRITE);
370 ip_statistics.IpReasmFails++;
371 return NULL;
372 }
373 memcpy((ptr + fp->offset), fp->ptr, fp->len);
374 count += fp->len;
375 fp = fp->next;
376 }
377
378 /* We glued together all fragments, so remove the queue entry. */
379 ip_free(qp);
380
381 /* Done with all fragments. Fixup the new IP header. */
382 iph = skb->h.iph;
383 iph->frag_off = 0;
384 iph->tot_len = htons((iph->ihl * 4) + count);
385 skb->ip_hdr = iph;
386
387 ip_statistics.IpReasmOKs++;
388 return(skb);
389 }
390
391
392 /*
393 * Process an incoming IP datagram fragment.
394 */
395
396 struct sk_buff *ip_defrag(struct iphdr *iph, struct sk_buff *skb, struct device *dev)
/* */
397 {
398 struct ipfrag *prev, *next, *tmp;
399 struct ipfrag *tfp;
400 struct ipq *qp;
401 struct sk_buff *skb2;
402 unsigned char *ptr;
403 int flags, offset;
404 int i, ihl, end;
405
406 ip_statistics.IpReasmReqds++;
407
408 /*
409 * Start by cleaning up the memory
410 */
411
412 if(ip_frag_mem>IPFRAG_HIGH_THRESH)
413 ip_evictor();
414 /*
415 * Find the entry of this IP datagram in the "incomplete datagrams" queue.
416 */
417
418 qp = ip_find(iph);
419
420 /* Is this a non-fragmented datagram? */
421 offset = ntohs(iph->frag_off);
422 flags = offset & ~IP_OFFSET;
423 offset &= IP_OFFSET;
424 if (((flags & IP_MF) == 0) && (offset == 0))
425 {
426 if (qp != NULL)
427 ip_free(qp); /* Huh? How could this exist?? */
428 return(skb);
429 }
430
431 offset <<= 3; /* offset is in 8-byte chunks */
432 ihl = iph->ihl * 4;
433
434 /*
435 * If the queue already existed, keep restarting its timer as long
436 * as we still are receiving fragments. Otherwise, create a fresh
437 * queue entry.
438 */
439
440 if (qp != NULL)
441 {
442 /* ANK. If the first fragment is received,
443 * we should remember the correct IP header (with options)
444 */
445 if (offset == 0)
446 {
447 qp->ihlen = ihl;
448 memcpy(qp->iph, iph, ihl+8);
449 }
450 del_timer(&qp->timer);
451 qp->timer.expires = jiffies + IP_FRAG_TIME; /* about 30 seconds */
452 qp->timer.data = (unsigned long) qp; /* pointer to queue */
453 qp->timer.function = ip_expire; /* expire function */
454 add_timer(&qp->timer);
455 }
456 else
457 {
458 /*
459 * If we failed to create it, then discard the frame
460 */
461 if ((qp = ip_create(skb, iph, dev)) == NULL)
462 {
463 skb->sk = NULL;
464 frag_kfree_skb(skb, FREE_READ);
465 ip_statistics.IpReasmFails++;
466 return NULL;
467 }
468 }
469
470 /*
471 * Determine the position of this fragment.
472 */
473
474 end = offset + ntohs(iph->tot_len) - ihl;
475
476 /*
477 * Point into the IP datagram 'data' part.
478 */
479
480 ptr = skb->data + ihl;
481
482 /*
483 * Is this the final fragment?
484 */
485
486 if ((flags & IP_MF) == 0)
487 qp->len = end;
488
489 /*
490 * Find out which fragments are in front and at the back of us
491 * in the chain of fragments so far. We must know where to put
492 * this fragment, right?
493 */
494
495 prev = NULL;
496 for(next = qp->fragments; next != NULL; next = next->next)
497 {
498 if (next->offset > offset)
499 break; /* bingo! */
500 prev = next;
501 }
502
503 /*
504 * We found where to put this one.
505 * Check for overlap with preceding fragment, and, if needed,
506 * align things so that any overlaps are eliminated.
507 */
508 if (prev != NULL && offset < prev->end)
509 {
510 i = prev->end - offset;
511 offset += i; /* ptr into datagram */
512 ptr += i; /* ptr into fragment data */
513 }
514
515 /*
516 * Look for overlap with succeeding segments.
517 * If we can merge fragments, do it.
518 */
519
520 for(tmp=next; tmp != NULL; tmp = tfp)
521 {
522 tfp = tmp->next;
523 if (tmp->offset >= end)
524 break; /* no overlaps at all */
525
526 i = end - next->offset; /* overlap is 'i' bytes */
527 tmp->len -= i; /* so reduce size of */
528 tmp->offset += i; /* next fragment */
529 tmp->ptr += i;
530 /*
531 * If we get a frag size of <= 0, remove it and the packet
532 * that it goes with.
533 */
534 if (tmp->len <= 0)
535 {
536 if (tmp->prev != NULL)
537 tmp->prev->next = tmp->next;
538 else
539 qp->fragments = tmp->next;
540
541 if (tfp->next != NULL)
542 tmp->next->prev = tmp->prev;
543
544 next=tfp; /* We have killed the original next frame */
545
546 frag_kfree_skb(tmp->skb,FREE_READ);
547 frag_kfree_s(tmp, sizeof(struct ipfrag));
548 }
549 }
550
551 /*
552 * Insert this fragment in the chain of fragments.
553 */
554
555 tfp = NULL;
556 tfp = ip_frag_create(offset, end, skb, ptr);
557
558 /*
559 * No memory to save the fragment - so throw the lot
560 */
561
562 if (!tfp)
563 {
564 skb->sk = NULL;
565 frag_kfree_skb(skb, FREE_READ);
566 return NULL;
567 }
568 tfp->prev = prev;
569 tfp->next = next;
570 if (prev != NULL)
571 prev->next = tfp;
572 else
573 qp->fragments = tfp;
574
575 if (next != NULL)
576 next->prev = tfp;
577
578 /*
579 * OK, so we inserted this new fragment into the chain.
580 * Check if we now have a full IP datagram which we can
581 * bump up to the IP layer...
582 */
583
584 if (ip_done(qp))
585 {
586 skb2 = ip_glue(qp); /* glue together the fragments */
587 return(skb2);
588 }
589 return(NULL);
590 }
591
592
593 /*
594 * This IP datagram is too large to be sent in one piece. Break it up into
595 * smaller pieces (each of size equal to the MAC header plus IP header plus
596 * a block of the data of the original IP data part) that will yet fit in a
597 * single device frame, and queue such a frame for sending by calling the
598 * ip_queue_xmit(). Note that this is recursion, and bad things will happen
599 * if this function causes a loop...
600 *
601 * Yes this is inefficient, feel free to submit a quicker one.
602 *
603 */
604
605 void ip_fragment(struct sock *sk, struct sk_buff *skb, struct device *dev, int is_frag)
/* ![[last]](../icons/n_last.png)
*/
606 {
607 struct iphdr *iph;
608 unsigned char *raw;
609 unsigned char *ptr;
610 struct sk_buff *skb2;
611 int left, mtu, hlen, len;
612 int offset;
613
614 /*
615 * Point into the IP datagram header.
616 */
617
618 raw = skb->data;
619 #if 0
620 iph = (struct iphdr *) (raw + dev->hard_header_len);
621 skb->ip_hdr = iph;
622 #else
623 iph = skb->ip_hdr;
624 #endif
625
626 /*
627 * Setup starting values.
628 */
629
630 hlen = iph->ihl * 4;
631 left = ntohs(iph->tot_len) - hlen; /* Space per frame */
632 hlen += dev->hard_header_len; /* Total header size */
633 mtu = (dev->mtu - hlen); /* Size of data space */
634 ptr = (raw + hlen); /* Where to start from */
635
636 /*
637 * Check for any "DF" flag. [DF means do not fragment]
638 */
639
640 if (ntohs(iph->frag_off) & IP_DF)
641 {
642 ip_statistics.IpFragFails++;
643 NETDEBUG(printk("ip_queue_xmit: frag needed\n"));
644 return;
645 }
646
647 /*
648 * The protocol doesn't seem to say what to do in the case that the
649 * frame + options doesn't fit the mtu. As it used to fall down dead
650 * in this case we were fortunate it didn't happen
651 */
652
653 if(mtu<8)
654 {
655 /* It's wrong but it's better than nothing */
656 icmp_send(skb,ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED,dev->mtu, dev);
657 ip_statistics.IpFragFails++;
658 return;
659 }
660
661 /*
662 * Fragment the datagram.
663 */
664
665 /*
666 * The initial offset is 0 for a complete frame. When
667 * fragmenting fragments it's wherever this one starts.
668 */
669
670 if (is_frag & 2)
671 offset = (ntohs(iph->frag_off) & IP_OFFSET) << 3;
672 else
673 offset = 0;
674
675
676 /*
677 * Keep copying data until we run out.
678 */
679
680 while(left > 0)
681 {
682 len = left;
683 /* IF: it doesn't fit, use 'mtu' - the data space left */
684 if (len > mtu)
685 len = mtu;
686 /* IF: we are not sending upto and including the packet end
687 then align the next start on an eight byte boundary */
688 if (len < left)
689 {
690 len/=8;
691 len*=8;
692 }
693 /*
694 * Allocate buffer.
695 */
696
697 if ((skb2 = alloc_skb(len + hlen+15,GFP_ATOMIC)) == NULL)
698 {
699 NETDEBUG(printk("IP: frag: no memory for new fragment!\n"));
700 ip_statistics.IpFragFails++;
701 return;
702 }
703
704 /*
705 * Set up data on packet
706 */
707
708 skb2->arp = skb->arp;
709 if(skb->free==0)
710 printk("IP fragmenter: BUG free!=1 in fragmenter\n");
711 skb2->free = 1;
712 skb_put(skb2,len + hlen);
713 skb2->h.raw=(char *) skb2->data;
714 /*
715 * Charge the memory for the fragment to any owner
716 * it might possess
717 */
718
719 if (sk)
720 {
721 atomic_add(skb2->truesize, &sk->wmem_alloc);
722 skb2->sk=sk;
723 }
724 skb2->raddr = skb->raddr; /* For rebuild_header - must be here */
725
726 /*
727 * Copy the packet header into the new buffer.
728 */
729
730 memcpy(skb2->h.raw, raw, hlen);
731
732 /*
733 * Copy a block of the IP datagram.
734 */
735 memcpy(skb2->h.raw + hlen, ptr, len);
736 left -= len;
737
738 skb2->h.raw+=dev->hard_header_len;
739
740 /*
741 * Fill in the new header fields.
742 */
743 iph = (struct iphdr *)(skb2->h.raw/*+dev->hard_header_len*/);
744 iph->frag_off = htons((offset >> 3));
745 skb2->ip_hdr = iph;
746
747 /* ANK: dirty, but effective trick. Upgrade options only if
748 * the segment to be fragmented was THE FIRST (otherwise,
749 * options are already fixed) and make it ONCE
750 * on the initial skb, so that all the following fragments
751 * will inherit fixed options.
752 */
753 if (offset == 0)
754 ip_options_fragment(skb);
755
756 /*
757 * Added AC : If we are fragmenting a fragment thats not the
758 * last fragment then keep MF on each bit
759 */
760 if (left > 0 || (is_frag & 1))
761 iph->frag_off |= htons(IP_MF);
762 ptr += len;
763 offset += len;
764
765 /*
766 * Put this fragment into the sending queue.
767 */
768
769 ip_statistics.IpFragCreates++;
770
771 ip_queue_xmit(sk, dev, skb2, 2);
772 }
773 ip_statistics.IpFragOKs++;
774 }
775
776
![[bottom]](../icons/n_bottom.png){kind=icon}
*/