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 1.59 2002/01/12 07:54:56 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 * Patrick McHardy : LRU queue of frag heads for evictor. 23 */ 24 25 #include <linux/compiler.h> 26 #include <linux/module.h> 27 #include <linux/types.h> 28 #include <linux/mm.h> 29 #include <linux/jiffies.h> 30 #include <linux/skbuff.h> 31 #include <linux/list.h> 32 #include <linux/ip.h> 33 #include <linux/icmp.h> 34 #include <linux/netdevice.h> 35 #include <linux/jhash.h> 36 #include <linux/random.h> 37 #include <net/sock.h> 38 #include <net/ip.h> 39 #include <net/icmp.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> 47 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 51 */ 52 53 int sysctl_ipfrag_max_dist __read_mostly = 64; 54 55 struct ipfrag_skb_cb 56 { 57 struct inet_skb_parm h; 58 int offset; 59 }; 60 61 #define FRAG_CB(skb) ((struct ipfrag_skb_cb*)((skb)->cb)) 62 63 /* Describe an entry in the "incomplete datagrams" queue. */ 64 struct ipq { 65 struct inet_frag_queue q; 66 67 u32 user; 68 __be32 saddr; 69 __be32 daddr; 70 __be16 id; 71 u8 protocol; 72 int iif; 73 unsigned int rid; 74 struct inet_peer *peer; 75 }; 76 77 struct inet_frags_ctl ip4_frags_ctl __read_mostly = { 78 /* 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. 83 */ 84 .high_thresh = 256 * 1024, 85 .low_thresh = 192 * 1024, 86 87 /* 88 * Important NOTE! Fragment queue must be destroyed before MSL expires. 89 * RFC791 is wrong proposing to prolongate timer each fragment arrival 90 * by TTL. 91 */ 92 .timeout = IP_FRAG_TIME, 93 .secret_interval = 10 * 60 * HZ, 94 }; 95 96 static struct inet_frags ip4_frags; 97 98 int ip_frag_nqueues(void) 99 { 100 return ip4_frags.nqueues; 101 } 102 103 int ip_frag_mem(void) 104 { 105 return atomic_read(&ip4_frags.mem); 106 } 107 108 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev, 109 struct net_device *dev); 110 111 static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot) 112 { 113 return jhash_3words((__force u32)id << 16 | prot, 114 (__force u32)saddr, (__force u32)daddr, 115 ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1); 116 } 117 118 static unsigned int ip4_hashfn(struct inet_frag_queue *q) 119 { 120 struct ipq *ipq; 121 122 ipq = container_of(q, struct ipq, q); 123 return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol); 124 } 125 126 /* Memory Tracking Functions. */ 127 static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work) 128 { 129 if (work) 130 *work -= skb->truesize; 131 atomic_sub(skb->truesize, &ip4_frags.mem); 132 kfree_skb(skb); 133 } 134 135 static __inline__ void ip4_frag_free(struct inet_frag_queue *q) 136 { 137 struct ipq *qp; 138 139 qp = container_of(q, struct ipq, q); 140 if (qp->peer) 141 inet_putpeer(qp->peer); 142 kfree(qp); 143 } 144 145 static __inline__ struct ipq *frag_alloc_queue(void) 146 { 147 struct ipq *qp = kzalloc(sizeof(struct ipq), GFP_ATOMIC); 148 149 if (!qp) 150 return NULL; 151 atomic_add(sizeof(struct ipq), &ip4_frags.mem); 152 return qp; 153 } 154 155 156 /* Destruction primitives. */ 157 158 static __inline__ void ipq_put(struct ipq *ipq) 159 { 160 inet_frag_put(&ipq->q, &ip4_frags); 161 } 162 163 /* Kill ipq entry. It is not destroyed immediately, 164 * because caller (and someone more) holds reference count. 165 */ 166 static void ipq_kill(struct ipq *ipq) 167 { 168 inet_frag_kill(&ipq->q, &ip4_frags); 169 } 170 171 /* Memory limiting on fragments. Evictor trashes the oldest 172 * fragment queue until we are back under the threshold. 173 */ 174 static void ip_evictor(void) 175 { 176 int evicted; 177 178 evicted = inet_frag_evictor(&ip4_frags); 179 if (evicted) 180 IP_ADD_STATS_BH(IPSTATS_MIB_REASMFAILS, evicted); 181 } 182 183 /* 184 * Oops, a fragment queue timed out. Kill it and send an ICMP reply. 185 */ 186 static void ip_expire(unsigned long arg) 187 { 188 struct ipq *qp = (struct ipq *) arg; 189 190 spin_lock(&qp->q.lock); 191 192 if (qp->q.last_in & COMPLETE) 193 goto out; 194 195 ipq_kill(qp); 196 197 IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT); 198 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 199 200 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); 205 dev_put(head->dev); 206 } 207 } 208 out: 209 spin_unlock(&qp->q.lock); 210 ipq_put(qp); 211 } 212 213 /* Creation primitives. */ 214 215 static struct ipq *ip_frag_intern(struct ipq *qp_in) 216 { 217 struct ipq *qp; 218 #ifdef CONFIG_SMP 219 struct hlist_node *n; 220 #endif 221 unsigned int hash; 222 223 write_lock(&ip4_frags.lock); 224 hash = ipqhashfn(qp_in->id, qp_in->saddr, qp_in->daddr, 225 qp_in->protocol); 226 #ifdef CONFIG_SMP 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. 230 */ 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; 240 ipq_put(qp_in); 241 return qp; 242 } 243 } 244 #endif 245 qp = qp_in; 246 247 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout)) 248 atomic_inc(&qp->q.refcnt); 249 250 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); 254 ip4_frags.nqueues++; 255 write_unlock(&ip4_frags.lock); 256 return qp; 257 } 258 259 /* 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) 261 { 262 struct ipq *qp; 263 264 if ((qp = frag_alloc_queue()) == NULL) 265 goto out_nomem; 266 267 qp->protocol = iph->protocol; 268 qp->id = iph->id; 269 qp->saddr = iph->saddr; 270 qp->daddr = iph->daddr; 271 qp->user = user; 272 qp->peer = sysctl_ipfrag_max_dist ? inet_getpeer(iph->saddr, 1) : NULL; 273 274 /* 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); 280 281 return ip_frag_intern(qp); 282 283 out_nomem: 284 LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n"); 285 return NULL; 286 } 287 288 /* Find the correct entry in the "incomplete datagrams" queue for 289 * this IP datagram, and create new one, if nothing is found. 290 */ 291 static inline struct ipq *ip_find(struct iphdr *iph, u32 user) 292 { 293 __be16 id = iph->id; 294 __be32 saddr = iph->saddr; 295 __be32 daddr = iph->daddr; 296 __u8 protocol = iph->protocol; 297 unsigned int hash; 298 struct ipq *qp; 299 struct hlist_node *n; 300 301 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) { 304 if (qp->id == id && 305 qp->saddr == saddr && 306 qp->daddr == daddr && 307 qp->protocol == protocol && 308 qp->user == user) { 309 atomic_inc(&qp->q.refcnt); 310 read_unlock(&ip4_frags.lock); 311 return qp; 312 } 313 } 314 read_unlock(&ip4_frags.lock); 315 316 return ip_frag_create(iph, user); 317 } 318 319 /* Is the fragment too far ahead to be part of ipq? */ 320 static inline int ip_frag_too_far(struct ipq *qp) 321 { 322 struct inet_peer *peer = qp->peer; 323 unsigned int max = sysctl_ipfrag_max_dist; 324 unsigned int start, end; 325 326 int rc; 327 328 if (!peer || !max) 329 return 0; 330 331 start = qp->rid; 332 end = atomic_inc_return(&peer->rid); 333 qp->rid = end; 334 335 rc = qp->q.fragments && (end - start) > max; 336 337 if (rc) { 338 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 339 } 340 341 return rc; 342 } 343 344 static int ip_frag_reinit(struct ipq *qp) 345 { 346 struct sk_buff *fp; 347 348 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout)) { 349 atomic_inc(&qp->q.refcnt); 350 return -ETIMEDOUT; 351 } 352 353 fp = qp->q.fragments; 354 do { 355 struct sk_buff *xp = fp->next; 356 frag_kfree_skb(fp, NULL); 357 fp = xp; 358 } while (fp); 359 360 qp->q.last_in = 0; 361 qp->q.len = 0; 362 qp->q.meat = 0; 363 qp->q.fragments = NULL; 364 qp->iif = 0; 365 366 return 0; 367 } 368 369 /* Add new segment to existing queue. */ 370 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) 371 { 372 struct sk_buff *prev, *next; 373 struct net_device *dev; 374 int flags, offset; 375 int ihl, end; 376 int err = -ENOENT; 377 378 if (qp->q.last_in & COMPLETE) 379 goto err; 380 381 if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) && 382 unlikely(ip_frag_too_far(qp)) && 383 unlikely(err = ip_frag_reinit(qp))) { 384 ipq_kill(qp); 385 goto err; 386 } 387 388 offset = ntohs(ip_hdr(skb)->frag_off); 389 flags = offset & ~IP_OFFSET; 390 offset &= IP_OFFSET; 391 offset <<= 3; /* offset is in 8-byte chunks */ 392 ihl = ip_hdrlen(skb); 393 394 /* Determine the position of this fragment. */ 395 end = offset + skb->len - ihl; 396 err = -EINVAL; 397 398 /* 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. 402 */ 403 if (end < qp->q.len || 404 ((qp->q.last_in & LAST_IN) && end != qp->q.len)) 405 goto err; 406 qp->q.last_in |= LAST_IN; 407 qp->q.len = end; 408 } else { 409 if (end&7) { 410 end &= ~7; 411 if (skb->ip_summed != CHECKSUM_UNNECESSARY) 412 skb->ip_summed = CHECKSUM_NONE; 413 } 414 if (end > qp->q.len) { 415 /* Some bits beyond end -> corruption. */ 416 if (qp->q.last_in & LAST_IN) 417 goto err; 418 qp->q.len = end; 419 } 420 } 421 if (end == offset) 422 goto err; 423 424 err = -ENOMEM; 425 if (pskb_pull(skb, ihl) == NULL) 426 goto err; 427 428 err = pskb_trim_rcsum(skb, end - offset); 429 if (err) 430 goto err; 431 432 /* 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? 435 */ 436 prev = NULL; 437 for (next = qp->q.fragments; next != NULL; next = next->next) { 438 if (FRAG_CB(next)->offset >= offset) 439 break; /* bingo! */ 440 prev = next; 441 } 442 443 /* 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. 446 */ 447 if (prev) { 448 int i = (FRAG_CB(prev)->offset + prev->len) - offset; 449 450 if (i > 0) { 451 offset += i; 452 err = -EINVAL; 453 if (end <= offset) 454 goto err; 455 err = -ENOMEM; 456 if (!pskb_pull(skb, i)) 457 goto err; 458 if (skb->ip_summed != CHECKSUM_UNNECESSARY) 459 skb->ip_summed = CHECKSUM_NONE; 460 } 461 } 462 463 err = -ENOMEM; 464 465 while (next && FRAG_CB(next)->offset < end) { 466 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */ 467 468 if (i < next->len) { 469 /* Eat head of the next overlapped fragment 470 * and leave the loop. The next ones cannot overlap. 471 */ 472 if (!pskb_pull(next, i)) 473 goto err; 474 FRAG_CB(next)->offset += i; 475 qp->q.meat -= i; 476 if (next->ip_summed != CHECKSUM_UNNECESSARY) 477 next->ip_summed = CHECKSUM_NONE; 478 break; 479 } else { 480 struct sk_buff *free_it = next; 481 482 /* Old fragment is completely overridden with 483 * new one drop it. 484 */ 485 next = next->next; 486 487 if (prev) 488 prev->next = next; 489 else 490 qp->q.fragments = next; 491 492 qp->q.meat -= free_it->len; 493 frag_kfree_skb(free_it, NULL); 494 } 495 } 496 497 FRAG_CB(skb)->offset = offset; 498 499 /* Insert this fragment in the chain of fragments. */ 500 skb->next = next; 501 if (prev) 502 prev->next = skb; 503 else 504 qp->q.fragments = skb; 505 506 dev = skb->dev; 507 if (dev) { 508 qp->iif = dev->ifindex; 509 skb->dev = NULL; 510 } 511 qp->q.stamp = skb->tstamp; 512 qp->q.meat += skb->len; 513 atomic_add(skb->truesize, &ip4_frags.mem); 514 if (offset == 0) 515 qp->q.last_in |= FIRST_IN; 516 517 if (qp->q.last_in == (FIRST_IN | LAST_IN) && qp->q.meat == qp->q.len) 518 return ip_frag_reasm(qp, prev, dev); 519 520 write_lock(&ip4_frags.lock); 521 list_move_tail(&qp->q.lru_list, &ip4_frags.lru_list); 522 write_unlock(&ip4_frags.lock); 523 return -EINPROGRESS; 524 525 err: 526 kfree_skb(skb); 527 return err; 528 } 529 530 531 /* Build a new IP datagram from all its fragments. */ 532 533 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev, 534 struct net_device *dev) 535 { 536 struct iphdr *iph; 537 struct sk_buff *fp, *head = qp->q.fragments; 538 int len; 539 int ihlen; 540 int err; 541 542 ipq_kill(qp); 543 544 /* Make the one we just received the head. */ 545 if (prev) { 546 head = prev->next; 547 fp = skb_clone(head, GFP_ATOMIC); 548 549 if (!fp) 550 goto out_nomem; 551 552 fp->next = head->next; 553 prev->next = fp; 554 555 skb_morph(head, qp->q.fragments); 556 head->next = qp->q.fragments->next; 557 558 kfree_skb(qp->q.fragments); 559 qp->q.fragments = head; 560 } 561 562 BUG_TRAP(head != NULL); 563 BUG_TRAP(FRAG_CB(head)->offset == 0); 564 565 /* Allocate a new buffer for the datagram. */ 566 ihlen = ip_hdrlen(head); 567 len = ihlen + qp->q.len; 568 569 err = -E2BIG; 570 if (len > 65535) 571 goto out_oversize; 572 573 /* Head of list must not be cloned. */ 574 err = -ENOMEM; 575 if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) 576 goto out_nomem; 577 578 /* 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; 583 int i, plen = 0; 584 585 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL) 586 goto out_nomem; 587 clone->next = head->next; 588 head->next = clone; 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; 596 clone->csum = 0; 597 clone->ip_summed = head->ip_summed; 598 atomic_add(clone->truesize, &ip4_frags.mem); 599 } 600 601 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); 604 605 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); 614 } 615 616 head->next = NULL; 617 head->dev = dev; 618 head->tstamp = qp->q.stamp; 619 620 iph = ip_hdr(head); 621 iph->frag_off = 0; 622 iph->tot_len = htons(len); 623 IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS); 624 qp->q.fragments = NULL; 625 return 0; 626 627 out_nomem: 628 LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing " 629 "queue %p\n", qp); 630 goto out_fail; 631 out_oversize: 632 if (net_ratelimit()) 633 printk(KERN_INFO 634 "Oversized IP packet from %d.%d.%d.%d.\n", 635 NIPQUAD(qp->saddr)); 636 out_fail: 637 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 638 return err; 639 } 640 641 /* Process an incoming IP datagram fragment. */ 642 int ip_defrag(struct sk_buff *skb, u32 user) 643 { 644 struct ipq *qp; 645 646 IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS); 647 648 /* Start by cleaning up the memory. */ 649 if (atomic_read(&ip4_frags.mem) > ip4_frags_ctl.high_thresh) 650 ip_evictor(); 651 652 /* Lookup (or create) queue header */ 653 if ((qp = ip_find(ip_hdr(skb), user)) != NULL) { 654 int ret; 655 656 spin_lock(&qp->q.lock); 657 658 ret = ip_frag_queue(qp, skb); 659 660 spin_unlock(&qp->q.lock); 661 ipq_put(qp); 662 return ret; 663 } 664 665 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 666 kfree_skb(skb); 667 return -ENOMEM; 668 } 669 670 void __init ipfrag_init(void) 671 { 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); 678 } 679 680 EXPORT_SYMBOL(ip_defrag); 681