net/ipv4/inet_fragment.c

   1 /*
   2  * inet fragments management
   3  *
   4  *              This program is free software; you can redistribute it and/or
   5  *              modify it under the terms of the GNU General Public License
   6  *              as published by the Free Software Foundation; either version
   7  *              2 of the License, or (at your option) any later version.
   8  *
   9  *              Authors:        Pavel Emelyanov <xemul@openvz.org>
  10  *                              Started as consolidation of ipv4/ip_fragment.c,
  11  *                              ipv6/reassembly. and ipv6 nf conntrack reassembly
  12  */
  13
  14 #include <linux/list.h>
  15 #include <linux/spinlock.h>
  16 #include <linux/module.h>
  17 #include <linux/timer.h>
  18 #include <linux/mm.h>
  19 #include <linux/random.h>
  20 #include <linux/skbuff.h>
  21 #include <linux/rtnetlink.h>
  22 #include <linux/slab.h>
  23
  24 #include <net/sock.h>
  25 #include <net/inet_frag.h>
  26 #include <net/inet_ecn.h>
  27 #include <net/ip.h>
  28 #include <net/ipv6.h>
  29
  30 /* Use skb->cb to track consecutive/adjacent fragments coming at
  31  * the end of the queue. Nodes in the rb-tree queue will
  32  * contain "runs" of one or more adjacent fragments.
  33  *
  34  * Invariants:
  35  * - next_frag is NULL at the tail of a "run";
  36  * - the head of a "run" has the sum of all fragment lengths in frag_run_len.
  37  */
  38 struct ipfrag_skb_cb {
  39         union {
  40                 struct inet_skb_parm    h4;
  41                 struct inet6_skb_parm   h6;
  42         };
  43         struct sk_buff          *next_frag;
  44         int                     frag_run_len;
  45 };
  46
  47 #define FRAG_CB(skb)            ((struct ipfrag_skb_cb *)((skb)->cb))
  48
  49 static void fragcb_clear(struct sk_buff *skb)
  50 {
  51         RB_CLEAR_NODE(&skb->rbnode);
  52         FRAG_CB(skb)->next_frag = NULL;
  53         FRAG_CB(skb)->frag_run_len = skb->len;
  54 }
  55
  56 /* Append skb to the last "run". */
  57 static void fragrun_append_to_last(struct inet_frag_queue *q,
  58                                    struct sk_buff *skb)
  59 {
  60         fragcb_clear(skb);
  61
  62         FRAG_CB(q->last_run_head)->frag_run_len += skb->len;
  63         FRAG_CB(q->fragments_tail)->next_frag = skb;
  64         q->fragments_tail = skb;
  65 }
  66
  67 /* Create a new "run" with the skb. */
  68 static void fragrun_create(struct inet_frag_queue *q, struct sk_buff *skb)
  69 {
  70         BUILD_BUG_ON(sizeof(struct ipfrag_skb_cb) > sizeof(skb->cb));
  71         fragcb_clear(skb);
  72
  73         if (q->last_run_head)
  74                 rb_link_node(&skb->rbnode, &q->last_run_head->rbnode,
  75                              &q->last_run_head->rbnode.rb_right);
  76         else
  77                 rb_link_node(&skb->rbnode, NULL, &q->rb_fragments.rb_node);
  78         rb_insert_color(&skb->rbnode, &q->rb_fragments);
  79
  80         q->fragments_tail = skb;
  81         q->last_run_head = skb;
  82 }
  83
  84 /* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
  85  * Value : 0xff if frame should be dropped.
  86  *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
  87  */
  88 const u8 ip_frag_ecn_table[16] = {
  89         /* at least one fragment had CE, and others ECT_0 or ECT_1 */
  90         [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]                      = INET_ECN_CE,
  91         [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]                      = INET_ECN_CE,
  92         [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]   = INET_ECN_CE,
  93
  94         /* invalid combinations : drop frame */
  95         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
  96         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
  97         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
  98         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
  99         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
 100         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
 101         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
 102 };
 103 EXPORT_SYMBOL(ip_frag_ecn_table);
 104
 105 int inet_frags_init(struct inet_frags *f)
 106 {
 107         f->frags_cachep = kmem_cache_create(f->frags_cache_name, f->qsize, 0, 0,
 108                                             NULL);
 109         if (!f->frags_cachep)
 110                 return -ENOMEM;
 111
 112         return 0;
 113 }
 114 EXPORT_SYMBOL(inet_frags_init);
 115
 116 void inet_frags_fini(struct inet_frags *f)
 117 {
 118         /* We must wait that all inet_frag_destroy_rcu() have completed. */
 119         rcu_barrier();
 120
 121         kmem_cache_destroy(f->frags_cachep);
 122         f->frags_cachep = NULL;
 123 }
 124 EXPORT_SYMBOL(inet_frags_fini);
 125
 126 static void inet_frags_free_cb(void *ptr, void *arg)
 127 {
 128         struct inet_frag_queue *fq = ptr;
 129
 130         /* If we can not cancel the timer, it means this frag_queue
 131          * is already disappearing, we have nothing to do.
 132          * Otherwise, we own a refcount until the end of this function.
 133          */
 134         if (!del_timer(&fq->timer))
 135                 return;
 136
 137         spin_lock_bh(&fq->lock);
 138         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 139                 fq->flags |= INET_FRAG_COMPLETE;
 140                 atomic_dec(&fq->refcnt);
 141         }
 142         spin_unlock_bh(&fq->lock);
 143
 144         inet_frag_put(fq);
 145 }
 146
 147 void inet_frags_exit_net(struct netns_frags *nf)
 148 {
 149         nf->high_thresh = 0; /* prevent creation of new frags */
 150
 151         rhashtable_free_and_destroy(&nf->rhashtable, inet_frags_free_cb, NULL);
 152 }
 153 EXPORT_SYMBOL(inet_frags_exit_net);
 154
 155 void inet_frag_kill(struct inet_frag_queue *fq)
 156 {
 157         if (del_timer(&fq->timer))
 158                 atomic_dec(&fq->refcnt);
 159
 160         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 161                 struct netns_frags *nf = fq->net;
 162
 163                 fq->flags |= INET_FRAG_COMPLETE;
 164                 rhashtable_remove_fast(&nf->rhashtable, &fq->node, nf->f->rhash_params);
 165                 atomic_dec(&fq->refcnt);
 166         }
 167 }
 168 EXPORT_SYMBOL(inet_frag_kill);
 169
 170 static void inet_frag_destroy_rcu(struct rcu_head *head)
 171 {
 172         struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
 173                                                  rcu);
 174         struct inet_frags *f = q->net->f;
 175
 176         if (f->destructor)
 177                 f->destructor(q);
 178         kmem_cache_free(f->frags_cachep, q);
 179 }
 180
 181 unsigned int inet_frag_rbtree_purge(struct rb_root *root)
 182 {
 183         struct rb_node *p = rb_first(root);
 184         unsigned int sum = 0;
 185
 186         while (p) {
 187                 struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
 188
 189                 p = rb_next(p);
 190                 rb_erase(&skb->rbnode, root);
 191                 while (skb) {
 192                         struct sk_buff *next = FRAG_CB(skb)->next_frag;
 193
 194                         sum += skb->truesize;
 195                         kfree_skb(skb);
 196                         skb = next;
 197                 }
 198         }
 199         return sum;
 200 }
 201 EXPORT_SYMBOL(inet_frag_rbtree_purge);
 202
 203 void inet_frag_destroy(struct inet_frag_queue *q)
 204 {
 205         struct sk_buff *fp;
 206         struct netns_frags *nf;
 207         unsigned int sum, sum_truesize = 0;
 208         struct inet_frags *f;
 209
 210         WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
 211         WARN_ON(del_timer(&q->timer) != 0);
 212
 213         /* Release all fragment data. */
 214         fp = q->fragments;
 215         nf = q->net;
 216         f = nf->f;
 217         if (fp) {
 218                 do {
 219                         struct sk_buff *xp = fp->next;
 220
 221                         sum_truesize += fp->truesize;
 222                         kfree_skb(fp);
 223                         fp = xp;
 224                 } while (fp);
 225         } else {
 226                 sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments);
 227         }
 228         sum = sum_truesize + f->qsize;
 229
 230         call_rcu(&q->rcu, inet_frag_destroy_rcu);
 231
 232         sub_frag_mem_limit(nf, sum);
 233 }
 234 EXPORT_SYMBOL(inet_frag_destroy);
 235
 236 static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
 237                                                struct inet_frags *f,
 238                                                void *arg)
 239 {
 240         struct inet_frag_queue *q;
 241
 242         if (!nf->high_thresh || frag_mem_limit(nf) > nf->high_thresh)
 243                 return NULL;
 244
 245         q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
 246         if (!q)
 247                 return NULL;
 248
 249         q->net = nf;
 250         f->constructor(q, arg);
 251         add_frag_mem_limit(nf, f->qsize);
 252
 253         setup_timer(&q->timer, f->frag_expire, (unsigned long)q);
 254         spin_lock_init(&q->lock);
 255         atomic_set(&q->refcnt, 3);
 256
 257         return q;
 258 }
 259
 260 static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
 261                                                 void *arg,
 262                                                 struct inet_frag_queue **prev)
 263 {
 264         struct inet_frags *f = nf->f;
 265         struct inet_frag_queue *q;
 266
 267         q = inet_frag_alloc(nf, f, arg);
 268         if (!q) {
 269                 *prev = ERR_PTR(-ENOMEM);
 270                 return NULL;
 271         }
 272         mod_timer(&q->timer, jiffies + nf->timeout);
 273
 274         *prev = rhashtable_lookup_get_insert_key(&nf->rhashtable, &q->key,
 275                                                  &q->node, f->rhash_params);
 276         if (*prev) {
 277                 q->flags |= INET_FRAG_COMPLETE;
 278                 inet_frag_kill(q);
 279                 inet_frag_destroy(q);
 280                 return NULL;
 281         }
 282         return q;
 283 }
 284 EXPORT_SYMBOL(inet_frag_create);
 285
 286 /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
 287 struct inet_frag_queue *inet_frag_find(struct netns_frags *nf, void *key)
 288 {
 289         struct inet_frag_queue *fq = NULL, *prev;
 290
 291         rcu_read_lock();
 292         prev = rhashtable_lookup(&nf->rhashtable, key, nf->f->rhash_params);
 293         if (!prev)
 294                 fq = inet_frag_create(nf, key, &prev);
 295         if (prev && !IS_ERR(prev)) {
 296                 fq = prev;
 297                 if (!atomic_inc_not_zero(&fq->refcnt))
 298                         fq = NULL;
 299         }
 300         rcu_read_unlock();
 301         return fq;
 302 }
 303 EXPORT_SYMBOL(inet_frag_find);
 304
 305 int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
 306                            int offset, int end)
 307 {
 308         struct sk_buff *last = q->fragments_tail;
 309
 310         /* RFC5722, Section 4, amended by Errata ID : 3089
 311          *                          When reassembling an IPv6 datagram, if
 312          *   one or more its constituent fragments is determined to be an
 313          *   overlapping fragment, the entire datagram (and any constituent
 314          *   fragments) MUST be silently discarded.
 315          *
 316          * Duplicates, however, should be ignored (i.e. skb dropped, but the
 317          * queue/fragments kept for later reassembly).
 318          */
 319         if (!last)
 320                 fragrun_create(q, skb);  /* First fragment. */
 321         else if (last->ip_defrag_offset + last->len < end) {
 322                 /* This is the common case: skb goes to the end. */
 323                 /* Detect and discard overlaps. */
 324                 if (offset < last->ip_defrag_offset + last->len)
 325                         return IPFRAG_OVERLAP;
 326                 if (offset == last->ip_defrag_offset + last->len)
 327                         fragrun_append_to_last(q, skb);
 328                 else
 329                         fragrun_create(q, skb);
 330         } else {
 331                 /* Binary search. Note that skb can become the first fragment,
 332                  * but not the last (covered above).
 333                  */
 334                 struct rb_node **rbn, *parent;
 335
 336                 rbn = &q->rb_fragments.rb_node;
 337                 do {
 338                         struct sk_buff *curr;
 339                         int curr_run_end;
 340
 341                         parent = *rbn;
 342                         curr = rb_to_skb(parent);
 343                         curr_run_end = curr->ip_defrag_offset +
 344                                         FRAG_CB(curr)->frag_run_len;
 345                         if (end <= curr->ip_defrag_offset)
 346                                 rbn = &parent->rb_left;
 347                         else if (offset >= curr_run_end)
 348                                 rbn = &parent->rb_right;
 349                         else if (offset >= curr->ip_defrag_offset &&
 350                                  end <= curr_run_end)
 351                                 return IPFRAG_DUP;
 352                         else
 353                                 return IPFRAG_OVERLAP;
 354                 } while (*rbn);
 355                 /* Here we have parent properly set, and rbn pointing to
 356                  * one of its NULL left/right children. Insert skb.
 357                  */
 358                 fragcb_clear(skb);
 359                 rb_link_node(&skb->rbnode, parent, rbn);
 360                 rb_insert_color(&skb->rbnode, &q->rb_fragments);
 361         }
 362
 363         skb->ip_defrag_offset = offset;
 364
 365         return IPFRAG_OK;
 366 }
 367 EXPORT_SYMBOL(inet_frag_queue_insert);
 368
 369 void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
 370                               struct sk_buff *parent)
 371 {
 372         struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
 373         struct sk_buff **nextp;
 374         int delta;
 375
 376         if (head != skb) {
 377                 fp = skb_clone(skb, GFP_ATOMIC);
 378                 if (!fp)
 379                         return NULL;
 380                 FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
 381                 if (RB_EMPTY_NODE(&skb->rbnode))
 382                         FRAG_CB(parent)->next_frag = fp;
 383                 else
 384                         rb_replace_node(&skb->rbnode, &fp->rbnode,
 385                                         &q->rb_fragments);
 386                 if (q->fragments_tail == skb)
 387                         q->fragments_tail = fp;
 388                 skb_morph(skb, head);
 389                 FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
 390                 rb_replace_node(&head->rbnode, &skb->rbnode,
 391                                 &q->rb_fragments);
 392                 consume_skb(head);
 393                 head = skb;
 394         }
 395         WARN_ON(head->ip_defrag_offset != 0);
 396
 397         delta = -head->truesize;
 398
 399         /* Head of list must not be cloned. */
 400         if (skb_unclone(head, GFP_ATOMIC))
 401                 return NULL;
 402
 403         delta += head->truesize;
 404         if (delta)
 405                 add_frag_mem_limit(q->net, delta);
 406
 407         /* If the first fragment is fragmented itself, we split
 408          * it to two chunks: the first with data and paged part
 409          * and the second, holding only fragments.
 410          */
 411         if (skb_has_frag_list(head)) {
 412                 struct sk_buff *clone;
 413                 int i, plen = 0;
 414
 415                 clone = alloc_skb(0, GFP_ATOMIC);
 416                 if (!clone)
 417                         return NULL;
 418                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 419                 skb_frag_list_init(head);
 420                 for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
 421                         plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
 422                 clone->data_len = head->data_len - plen;
 423                 clone->len = clone->data_len;
 424                 head->truesize += clone->truesize;
 425                 clone->csum = 0;
 426                 clone->ip_summed = head->ip_summed;
 427                 add_frag_mem_limit(q->net, clone->truesize);
 428                 skb_shinfo(head)->frag_list = clone;
 429                 nextp = &clone->next;
 430         } else {
 431                 nextp = &skb_shinfo(head)->frag_list;
 432         }
 433
 434         return nextp;
 435 }
 436 EXPORT_SYMBOL(inet_frag_reasm_prepare);
 437
 438 void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
 439                             void *reasm_data)
 440 {
 441         struct sk_buff **nextp = (struct sk_buff **)reasm_data;
 442         struct rb_node *rbn;
 443         struct sk_buff *fp;
 444
 445         skb_push(head, head->data - skb_network_header(head));
 446
 447         /* Traverse the tree in order, to build frag_list. */
 448         fp = FRAG_CB(head)->next_frag;
 449         rbn = rb_next(&head->rbnode);
 450         rb_erase(&head->rbnode, &q->rb_fragments);
 451         while (rbn || fp) {
 452                 /* fp points to the next sk_buff in the current run;
 453                  * rbn points to the next run.
 454                  */
 455                 /* Go through the current run. */
 456                 while (fp) {
 457                         *nextp = fp;
 458                         nextp = &fp->next;
 459                         fp->prev = NULL;
 460                         memset(&fp->rbnode, 0, sizeof(fp->rbnode));
 461                         fp->sk = NULL;
 462                         head->data_len += fp->len;
 463                         head->len += fp->len;
 464                         if (head->ip_summed != fp->ip_summed)
 465                                 head->ip_summed = CHECKSUM_NONE;
 466                         else if (head->ip_summed == CHECKSUM_COMPLETE)
 467                                 head->csum = csum_add(head->csum, fp->csum);
 468                         head->truesize += fp->truesize;
 469                         fp = FRAG_CB(fp)->next_frag;
 470                 }
 471                 /* Move to the next run. */
 472                 if (rbn) {
 473                         struct rb_node *rbnext = rb_next(rbn);
 474
 475                         fp = rb_to_skb(rbn);
 476                         rb_erase(rbn, &q->rb_fragments);
 477                         rbn = rbnext;
 478                 }
 479         }
 480         sub_frag_mem_limit(q->net, head->truesize);
 481
 482         *nextp = NULL;
 483         head->next = NULL;
 484         head->prev = NULL;
 485         head->tstamp = q->stamp;
 486 }
 487 EXPORT_SYMBOL(inet_frag_reasm_finish);
 488
 489 struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
 490 {
 491         struct sk_buff *head;
 492
 493         if (q->fragments) {
 494                 head = q->fragments;
 495                 q->fragments = head->next;
 496         } else {
 497                 struct sk_buff *skb;
 498
 499                 head = skb_rb_first(&q->rb_fragments);
 500                 if (!head)
 501                         return NULL;
 502                 skb = FRAG_CB(head)->next_frag;
 503                 if (skb)
 504                         rb_replace_node(&head->rbnode, &skb->rbnode,
 505                                         &q->rb_fragments);
 506                 else
 507                         rb_erase(&head->rbnode, &q->rb_fragments);
 508                 memset(&head->rbnode, 0, sizeof(head->rbnode));
 509                 barrier();
 510         }
 511         if (head == q->fragments_tail)
 512                 q->fragments_tail = NULL;
 513
 514         sub_frag_mem_limit(q->net, head->truesize);
 515
 516         return head;
 517 }
 518 EXPORT_SYMBOL(inet_frag_pull_head);