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