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 struct ip4_create_arg { 112 struct iphdr *iph; 113 u32 user; 114 }; 115 116 static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot) 117 { 118 return jhash_3words((__force u32)id << 16 | prot, 119 (__force u32)saddr, (__force u32)daddr, 120 ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1); 121 } 122 123 static unsigned int ip4_hashfn(struct inet_frag_queue *q) 124 { 125 struct ipq *ipq; 126 127 ipq = container_of(q, struct ipq, q); 128 return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol); 129 } 130 131 static int ip4_frag_match(struct inet_frag_queue *q, void *a) 132 { 133 struct ipq *qp; 134 struct ip4_create_arg *arg = a; 135 136 qp = container_of(q, struct ipq, q); 137 return (qp->id == arg->iph->id && 138 qp->saddr == arg->iph->saddr && 139 qp->daddr == arg->iph->daddr && 140 qp->protocol == arg->iph->protocol && 141 qp->user == arg->user); 142 } 143 144 /* Memory Tracking Functions. */ 145 static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work) 146 { 147 if (work) 148 *work -= skb->truesize; 149 atomic_sub(skb->truesize, &ip4_frags.mem); 150 kfree_skb(skb); 151 } 152 153 static void ip4_frag_init(struct inet_frag_queue *q, void *a) 154 { 155 struct ipq *qp = container_of(q, struct ipq, q); 156 struct ip4_create_arg *arg = a; 157 158 qp->protocol = arg->iph->protocol; 159 qp->id = arg->iph->id; 160 qp->saddr = arg->iph->saddr; 161 qp->daddr = arg->iph->daddr; 162 qp->user = arg->user; 163 qp->peer = sysctl_ipfrag_max_dist ? 164 inet_getpeer(arg->iph->saddr, 1) : NULL; 165 } 166 167 static __inline__ void ip4_frag_free(struct inet_frag_queue *q) 168 { 169 struct ipq *qp; 170 171 qp = container_of(q, struct ipq, q); 172 if (qp->peer) 173 inet_putpeer(qp->peer); 174 } 175 176 177 /* Destruction primitives. */ 178 179 static __inline__ void ipq_put(struct ipq *ipq) 180 { 181 inet_frag_put(&ipq->q, &ip4_frags); 182 } 183 184 /* Kill ipq entry. It is not destroyed immediately, 185 * because caller (and someone more) holds reference count. 186 */ 187 static void ipq_kill(struct ipq *ipq) 188 { 189 inet_frag_kill(&ipq->q, &ip4_frags); 190 } 191 192 /* Memory limiting on fragments. Evictor trashes the oldest 193 * fragment queue until we are back under the threshold. 194 */ 195 static void ip_evictor(void) 196 { 197 int evicted; 198 199 evicted = inet_frag_evictor(&ip4_frags); 200 if (evicted) 201 IP_ADD_STATS_BH(IPSTATS_MIB_REASMFAILS, evicted); 202 } 203 204 /* 205 * Oops, a fragment queue timed out. Kill it and send an ICMP reply. 206 */ 207 static void ip_expire(unsigned long arg) 208 { 209 struct ipq *qp; 210 211 qp = container_of((struct inet_frag_queue *) arg, struct ipq, q); 212 213 spin_lock(&qp->q.lock); 214 215 if (qp->q.last_in & COMPLETE) 216 goto out; 217 218 ipq_kill(qp); 219 220 IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT); 221 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 222 223 if ((qp->q.last_in&FIRST_IN) && qp->q.fragments != NULL) { 224 struct sk_buff *head = qp->q.fragments; 225 /* Send an ICMP "Fragment Reassembly Timeout" message. */ 226 if ((head->dev = dev_get_by_index(&init_net, qp->iif)) != NULL) { 227 icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0); 228 dev_put(head->dev); 229 } 230 } 231 out: 232 spin_unlock(&qp->q.lock); 233 ipq_put(qp); 234 } 235 236 /* Find the correct entry in the "incomplete datagrams" queue for 237 * this IP datagram, and create new one, if nothing is found. 238 */ 239 static inline struct ipq *ip_find(struct iphdr *iph, u32 user) 240 { 241 struct inet_frag_queue *q; 242 struct ip4_create_arg arg; 243 unsigned int hash; 244 245 arg.iph = iph; 246 arg.user = user; 247 hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol); 248 249 q = inet_frag_find(&ip4_frags, &arg, hash); 250 if (q == NULL) 251 goto out_nomem; 252 253 return container_of(q, struct ipq, q); 254 255 out_nomem: 256 LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n"); 257 return NULL; 258 } 259 260 /* Is the fragment too far ahead to be part of ipq? */ 261 static inline int ip_frag_too_far(struct ipq *qp) 262 { 263 struct inet_peer *peer = qp->peer; 264 unsigned int max = sysctl_ipfrag_max_dist; 265 unsigned int start, end; 266 267 int rc; 268 269 if (!peer || !max) 270 return 0; 271 272 start = qp->rid; 273 end = atomic_inc_return(&peer->rid); 274 qp->rid = end; 275 276 rc = qp->q.fragments && (end - start) > max; 277 278 if (rc) { 279 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 280 } 281 282 return rc; 283 } 284 285 static int ip_frag_reinit(struct ipq *qp) 286 { 287 struct sk_buff *fp; 288 289 if (!mod_timer(&qp->q.timer, jiffies + ip4_frags_ctl.timeout)) { 290 atomic_inc(&qp->q.refcnt); 291 return -ETIMEDOUT; 292 } 293 294 fp = qp->q.fragments; 295 do { 296 struct sk_buff *xp = fp->next; 297 frag_kfree_skb(fp, NULL); 298 fp = xp; 299 } while (fp); 300 301 qp->q.last_in = 0; 302 qp->q.len = 0; 303 qp->q.meat = 0; 304 qp->q.fragments = NULL; 305 qp->iif = 0; 306 307 return 0; 308 } 309 310 /* Add new segment to existing queue. */ 311 static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) 312 { 313 struct sk_buff *prev, *next; 314 struct net_device *dev; 315 int flags, offset; 316 int ihl, end; 317 int err = -ENOENT; 318 319 if (qp->q.last_in & COMPLETE) 320 goto err; 321 322 if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) && 323 unlikely(ip_frag_too_far(qp)) && 324 unlikely(err = ip_frag_reinit(qp))) { 325 ipq_kill(qp); 326 goto err; 327 } 328 329 offset = ntohs(ip_hdr(skb)->frag_off); 330 flags = offset & ~IP_OFFSET; 331 offset &= IP_OFFSET; 332 offset <<= 3; /* offset is in 8-byte chunks */ 333 ihl = ip_hdrlen(skb); 334 335 /* Determine the position of this fragment. */ 336 end = offset + skb->len - ihl; 337 err = -EINVAL; 338 339 /* Is this the final fragment? */ 340 if ((flags & IP_MF) == 0) { 341 /* If we already have some bits beyond end 342 * or have different end, the segment is corrrupted. 343 */ 344 if (end < qp->q.len || 345 ((qp->q.last_in & LAST_IN) && end != qp->q.len)) 346 goto err; 347 qp->q.last_in |= LAST_IN; 348 qp->q.len = end; 349 } else { 350 if (end&7) { 351 end &= ~7; 352 if (skb->ip_summed != CHECKSUM_UNNECESSARY) 353 skb->ip_summed = CHECKSUM_NONE; 354 } 355 if (end > qp->q.len) { 356 /* Some bits beyond end -> corruption. */ 357 if (qp->q.last_in & LAST_IN) 358 goto err; 359 qp->q.len = end; 360 } 361 } 362 if (end == offset) 363 goto err; 364 365 err = -ENOMEM; 366 if (pskb_pull(skb, ihl) == NULL) 367 goto err; 368 369 err = pskb_trim_rcsum(skb, end - offset); 370 if (err) 371 goto err; 372 373 /* Find out which fragments are in front and at the back of us 374 * in the chain of fragments so far. We must know where to put 375 * this fragment, right? 376 */ 377 prev = NULL; 378 for (next = qp->q.fragments; next != NULL; next = next->next) { 379 if (FRAG_CB(next)->offset >= offset) 380 break; /* bingo! */ 381 prev = next; 382 } 383 384 /* We found where to put this one. Check for overlap with 385 * preceding fragment, and, if needed, align things so that 386 * any overlaps are eliminated. 387 */ 388 if (prev) { 389 int i = (FRAG_CB(prev)->offset + prev->len) - offset; 390 391 if (i > 0) { 392 offset += i; 393 err = -EINVAL; 394 if (end <= offset) 395 goto err; 396 err = -ENOMEM; 397 if (!pskb_pull(skb, i)) 398 goto err; 399 if (skb->ip_summed != CHECKSUM_UNNECESSARY) 400 skb->ip_summed = CHECKSUM_NONE; 401 } 402 } 403 404 err = -ENOMEM; 405 406 while (next && FRAG_CB(next)->offset < end) { 407 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */ 408 409 if (i < next->len) { 410 /* Eat head of the next overlapped fragment 411 * and leave the loop. The next ones cannot overlap. 412 */ 413 if (!pskb_pull(next, i)) 414 goto err; 415 FRAG_CB(next)->offset += i; 416 qp->q.meat -= i; 417 if (next->ip_summed != CHECKSUM_UNNECESSARY) 418 next->ip_summed = CHECKSUM_NONE; 419 break; 420 } else { 421 struct sk_buff *free_it = next; 422 423 /* Old fragment is completely overridden with 424 * new one drop it. 425 */ 426 next = next->next; 427 428 if (prev) 429 prev->next = next; 430 else 431 qp->q.fragments = next; 432 433 qp->q.meat -= free_it->len; 434 frag_kfree_skb(free_it, NULL); 435 } 436 } 437 438 FRAG_CB(skb)->offset = offset; 439 440 /* Insert this fragment in the chain of fragments. */ 441 skb->next = next; 442 if (prev) 443 prev->next = skb; 444 else 445 qp->q.fragments = skb; 446 447 dev = skb->dev; 448 if (dev) { 449 qp->iif = dev->ifindex; 450 skb->dev = NULL; 451 } 452 qp->q.stamp = skb->tstamp; 453 qp->q.meat += skb->len; 454 atomic_add(skb->truesize, &ip4_frags.mem); 455 if (offset == 0) 456 qp->q.last_in |= FIRST_IN; 457 458 if (qp->q.last_in == (FIRST_IN | LAST_IN) && qp->q.meat == qp->q.len) 459 return ip_frag_reasm(qp, prev, dev); 460 461 write_lock(&ip4_frags.lock); 462 list_move_tail(&qp->q.lru_list, &ip4_frags.lru_list); 463 write_unlock(&ip4_frags.lock); 464 return -EINPROGRESS; 465 466 err: 467 kfree_skb(skb); 468 return err; 469 } 470 471 472 /* Build a new IP datagram from all its fragments. */ 473 474 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev, 475 struct net_device *dev) 476 { 477 struct iphdr *iph; 478 struct sk_buff *fp, *head = qp->q.fragments; 479 int len; 480 int ihlen; 481 int err; 482 483 ipq_kill(qp); 484 485 /* Make the one we just received the head. */ 486 if (prev) { 487 head = prev->next; 488 fp = skb_clone(head, GFP_ATOMIC); 489 if (!fp) 490 goto out_nomem; 491 492 fp->next = head->next; 493 prev->next = fp; 494 495 skb_morph(head, qp->q.fragments); 496 head->next = qp->q.fragments->next; 497 498 kfree_skb(qp->q.fragments); 499 qp->q.fragments = head; 500 } 501 502 BUG_TRAP(head != NULL); 503 BUG_TRAP(FRAG_CB(head)->offset == 0); 504 505 /* Allocate a new buffer for the datagram. */ 506 ihlen = ip_hdrlen(head); 507 len = ihlen + qp->q.len; 508 509 err = -E2BIG; 510 if (len > 65535) 511 goto out_oversize; 512 513 /* Head of list must not be cloned. */ 514 if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) 515 goto out_nomem; 516 517 /* If the first fragment is fragmented itself, we split 518 * it to two chunks: the first with data and paged part 519 * and the second, holding only fragments. */ 520 if (skb_shinfo(head)->frag_list) { 521 struct sk_buff *clone; 522 int i, plen = 0; 523 524 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL) 525 goto out_nomem; 526 clone->next = head->next; 527 head->next = clone; 528 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list; 529 skb_shinfo(head)->frag_list = NULL; 530 for (i=0; i<skb_shinfo(head)->nr_frags; i++) 531 plen += skb_shinfo(head)->frags[i].size; 532 clone->len = clone->data_len = head->data_len - plen; 533 head->data_len -= clone->len; 534 head->len -= clone->len; 535 clone->csum = 0; 536 clone->ip_summed = head->ip_summed; 537 atomic_add(clone->truesize, &ip4_frags.mem); 538 } 539 540 skb_shinfo(head)->frag_list = head->next; 541 skb_push(head, head->data - skb_network_header(head)); 542 atomic_sub(head->truesize, &ip4_frags.mem); 543 544 for (fp=head->next; fp; fp = fp->next) { 545 head->data_len += fp->len; 546 head->len += fp->len; 547 if (head->ip_summed != fp->ip_summed) 548 head->ip_summed = CHECKSUM_NONE; 549 else if (head->ip_summed == CHECKSUM_COMPLETE) 550 head->csum = csum_add(head->csum, fp->csum); 551 head->truesize += fp->truesize; 552 atomic_sub(fp->truesize, &ip4_frags.mem); 553 } 554 555 head->next = NULL; 556 head->dev = dev; 557 head->tstamp = qp->q.stamp; 558 559 iph = ip_hdr(head); 560 iph->frag_off = 0; 561 iph->tot_len = htons(len); 562 IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS); 563 qp->q.fragments = NULL; 564 return 0; 565 566 out_nomem: 567 LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing " 568 "queue %p\n", qp); 569 err = -ENOMEM; 570 goto out_fail; 571 out_oversize: 572 if (net_ratelimit()) 573 printk(KERN_INFO 574 "Oversized IP packet from %d.%d.%d.%d.\n", 575 NIPQUAD(qp->saddr)); 576 out_fail: 577 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 578 return err; 579 } 580 581 /* Process an incoming IP datagram fragment. */ 582 int ip_defrag(struct sk_buff *skb, u32 user) 583 { 584 struct ipq *qp; 585 586 IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS); 587 588 /* Start by cleaning up the memory. */ 589 if (atomic_read(&ip4_frags.mem) > ip4_frags_ctl.high_thresh) 590 ip_evictor(); 591 592 /* Lookup (or create) queue header */ 593 if ((qp = ip_find(ip_hdr(skb), user)) != NULL) { 594 int ret; 595 596 spin_lock(&qp->q.lock); 597 598 ret = ip_frag_queue(qp, skb); 599 600 spin_unlock(&qp->q.lock); 601 ipq_put(qp); 602 return ret; 603 } 604 605 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS); 606 kfree_skb(skb); 607 return -ENOMEM; 608 } 609 610 void __init ipfrag_init(void) 611 { 612 ip4_frags.ctl = &ip4_frags_ctl; 613 ip4_frags.hashfn = ip4_hashfn; 614 ip4_frags.constructor = ip4_frag_init; 615 ip4_frags.destructor = ip4_frag_free; 616 ip4_frags.skb_free = NULL; 617 ip4_frags.qsize = sizeof(struct ipq); 618 ip4_frags.match = ip4_frag_match; 619 ip4_frags.frag_expire = ip_expire; 620 inet_frags_init(&ip4_frags); 621 } 622 623 EXPORT_SYMBOL(ip_defrag); 624