net/ipv4/inet_fragment.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * inet fragments management
   4  *
   5  *              Authors:        Pavel Emelyanov <xemul@openvz.org>
   6  *                              Started as consolidation of ipv4/ip_fragment.c,
   7  *                              ipv6/reassembly. and ipv6 nf conntrack reassembly
   8  */
   9
  10 #include <linux/list.h>
  11 #include <linux/spinlock.h>
  12 #include <linux/module.h>
  13 #include <linux/timer.h>
  14 #include <linux/mm.h>
  15 #include <linux/random.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/rtnetlink.h>
  18 #include <linux/slab.h>
  19 #include <linux/rhashtable.h>
  20
  21 #include <net/sock.h>
  22 #include <net/inet_frag.h>
  23 #include <net/inet_ecn.h>
  24 #include <net/ip.h>
  25 #include <net/ipv6.h>
  26
  27 /* Use skb->cb to track consecutive/adjacent fragments coming at
  28  * the end of the queue. Nodes in the rb-tree queue will
  29  * contain "runs" of one or more adjacent fragments.
  30  *
  31  * Invariants:
  32  * - next_frag is NULL at the tail of a "run";
  33  * - the head of a "run" has the sum of all fragment lengths in frag_run_len.
  34  */
  35 struct ipfrag_skb_cb {
  36         union {
  37                 struct inet_skb_parm    h4;
  38                 struct inet6_skb_parm   h6;
  39         };
  40         struct sk_buff          *next_frag;
  41         int                     frag_run_len;
  42 };
  43
  44 #define FRAG_CB(skb)            ((struct ipfrag_skb_cb *)((skb)->cb))
  45
  46 static void fragcb_clear(struct sk_buff *skb)
  47 {
  48         RB_CLEAR_NODE(&skb->rbnode);
  49         FRAG_CB(skb)->next_frag = NULL;
  50         FRAG_CB(skb)->frag_run_len = skb->len;
  51 }
  52
  53 /* Append skb to the last "run". */
  54 static void fragrun_append_to_last(struct inet_frag_queue *q,
  55                                    struct sk_buff *skb)
  56 {
  57         fragcb_clear(skb);
  58
  59         FRAG_CB(q->last_run_head)->frag_run_len += skb->len;
  60         FRAG_CB(q->fragments_tail)->next_frag = skb;
  61         q->fragments_tail = skb;
  62 }
  63
  64 /* Create a new "run" with the skb. */
  65 static void fragrun_create(struct inet_frag_queue *q, struct sk_buff *skb)
  66 {
  67         BUILD_BUG_ON(sizeof(struct ipfrag_skb_cb) > sizeof(skb->cb));
  68         fragcb_clear(skb);
  69
  70         if (q->last_run_head)
  71                 rb_link_node(&skb->rbnode, &q->last_run_head->rbnode,
  72                              &q->last_run_head->rbnode.rb_right);
  73         else
  74                 rb_link_node(&skb->rbnode, NULL, &q->rb_fragments.rb_node);
  75         rb_insert_color(&skb->rbnode, &q->rb_fragments);
  76
  77         q->fragments_tail = skb;
  78         q->last_run_head = skb;
  79 }
  80
  81 /* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
  82  * Value : 0xff if frame should be dropped.
  83  *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
  84  */
  85 const u8 ip_frag_ecn_table[16] = {
  86         /* at least one fragment had CE, and others ECT_0 or ECT_1 */
  87         [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]                      = INET_ECN_CE,
  88         [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]                      = INET_ECN_CE,
  89         [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]   = INET_ECN_CE,
  90
  91         /* invalid combinations : drop frame */
  92         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
  93         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
  94         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
  95         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
  96         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
  97         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
  98         [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
  99 };
 100 EXPORT_SYMBOL(ip_frag_ecn_table);
 101
 102 int inet_frags_init(struct inet_frags *f)
 103 {
 104         f->frags_cachep = kmem_cache_create(f->frags_cache_name, f->qsize, 0, 0,
 105                                             NULL);
 106         if (!f->frags_cachep)
 107                 return -ENOMEM;
 108
 109         refcount_set(&f->refcnt, 1);
 110         init_completion(&f->completion);
 111         return 0;
 112 }
 113 EXPORT_SYMBOL(inet_frags_init);
 114
 115 void inet_frags_fini(struct inet_frags *f)
 116 {
 117         if (refcount_dec_and_test(&f->refcnt))
 118                 complete(&f->completion);
 119
 120         wait_for_completion(&f->completion);
 121
 122         kmem_cache_destroy(f->frags_cachep);
 123         f->frags_cachep = NULL;
 124 }
 125 EXPORT_SYMBOL(inet_frags_fini);
 126
 127 /* called from rhashtable_free_and_destroy() at netns_frags dismantle */
 128 static void inet_frags_free_cb(void *ptr, void *arg)
 129 {
 130         struct inet_frag_queue *fq = ptr;
 131         int count;
 132
 133         count = del_timer_sync(&fq->timer) ? 1 : 0;
 134
 135         spin_lock_bh(&fq->lock);
 136         fq->flags |= INET_FRAG_DROP;
 137         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 138                 fq->flags |= INET_FRAG_COMPLETE;
 139                 count++;
 140         } else if (fq->flags & INET_FRAG_HASH_DEAD) {
 141                 count++;
 142         }
 143         spin_unlock_bh(&fq->lock);
 144
 145         if (refcount_sub_and_test(count, &fq->refcnt))
 146                 inet_frag_destroy(fq);
 147 }
 148
 149 static LLIST_HEAD(fqdir_free_list);
 150
 151 static void fqdir_free_fn(struct work_struct *work)
 152 {
 153         struct llist_node *kill_list;
 154         struct fqdir *fqdir, *tmp;
 155         struct inet_frags *f;
 156
 157         /* Atomically snapshot the list of fqdirs to free */
 158         kill_list = llist_del_all(&fqdir_free_list);
 159
 160         /* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
 161          * have completed, since they need to dereference fqdir.
 162          * Would it not be nice to have kfree_rcu_barrier() ? :)
 163          */
 164         rcu_barrier();
 165
 166         llist_for_each_entry_safe(fqdir, tmp, kill_list, free_list) {
 167                 f = fqdir->f;
 168                 if (refcount_dec_and_test(&f->refcnt))
 169                         complete(&f->completion);
 170
 171                 kfree(fqdir);
 172         }
 173 }
 174
 175 static DECLARE_WORK(fqdir_free_work, fqdir_free_fn);
 176
 177 static void fqdir_work_fn(struct work_struct *work)
 178 {
 179         struct fqdir *fqdir = container_of(work, struct fqdir, destroy_work);
 180
 181         rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL);
 182
 183         if (llist_add(&fqdir->free_list, &fqdir_free_list))
 184                 queue_work(system_wq, &fqdir_free_work);
 185 }
 186
 187 int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
 188 {
 189         struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
 190         int res;
 191
 192         if (!fqdir)
 193                 return -ENOMEM;
 194         fqdir->f = f;
 195         fqdir->net = net;
 196         res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
 197         if (res < 0) {
 198                 kfree(fqdir);
 199                 return res;
 200         }
 201         refcount_inc(&f->refcnt);
 202         *fqdirp = fqdir;
 203         return 0;
 204 }
 205 EXPORT_SYMBOL(fqdir_init);
 206
 207 static struct workqueue_struct *inet_frag_wq;
 208
 209 static int __init inet_frag_wq_init(void)
 210 {
 211         inet_frag_wq = create_workqueue("inet_frag_wq");
 212         if (!inet_frag_wq)
 213                 panic("Could not create inet frag workq");
 214         return 0;
 215 }
 216
 217 pure_initcall(inet_frag_wq_init);
 218
 219 void fqdir_exit(struct fqdir *fqdir)
 220 {
 221         INIT_WORK(&fqdir->destroy_work, fqdir_work_fn);
 222         queue_work(inet_frag_wq, &fqdir->destroy_work);
 223 }
 224 EXPORT_SYMBOL(fqdir_exit);
 225
 226 void inet_frag_kill(struct inet_frag_queue *fq)
 227 {
 228         if (del_timer(&fq->timer))
 229                 refcount_dec(&fq->refcnt);
 230
 231         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 232                 struct fqdir *fqdir = fq->fqdir;
 233
 234                 fq->flags |= INET_FRAG_COMPLETE;
 235                 rcu_read_lock();
 236                 /* The RCU read lock provides a memory barrier
 237                  * guaranteeing that if fqdir->dead is false then
 238                  * the hash table destruction will not start until
 239                  * after we unlock.  Paired with fqdir_pre_exit().
 240                  */
 241                 if (!READ_ONCE(fqdir->dead)) {
 242                         rhashtable_remove_fast(&fqdir->rhashtable, &fq->node,
 243                                                fqdir->f->rhash_params);
 244                         refcount_dec(&fq->refcnt);
 245                 } else {
 246                         fq->flags |= INET_FRAG_HASH_DEAD;
 247                 }
 248                 rcu_read_unlock();
 249         }
 250 }
 251 EXPORT_SYMBOL(inet_frag_kill);
 252
 253 static void inet_frag_destroy_rcu(struct rcu_head *head)
 254 {
 255         struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
 256                                                  rcu);
 257         struct inet_frags *f = q->fqdir->f;
 258
 259         if (f->destructor)
 260                 f->destructor(q);
 261         kmem_cache_free(f->frags_cachep, q);
 262 }
 263
 264 unsigned int inet_frag_rbtree_purge(struct rb_root *root,
 265                                     enum skb_drop_reason reason)
 266 {
 267         struct rb_node *p = rb_first(root);
 268         unsigned int sum = 0;
 269
 270         while (p) {
 271                 struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
 272
 273                 p = rb_next(p);
 274                 rb_erase(&skb->rbnode, root);
 275                 while (skb) {
 276                         struct sk_buff *next = FRAG_CB(skb)->next_frag;
 277
 278                         sum += skb->truesize;
 279                         kfree_skb_reason(skb, reason);
 280                         skb = next;
 281                 }
 282         }
 283         return sum;
 284 }
 285 EXPORT_SYMBOL(inet_frag_rbtree_purge);
 286
 287 void inet_frag_destroy(struct inet_frag_queue *q)
 288 {
 289         unsigned int sum, sum_truesize = 0;
 290         enum skb_drop_reason reason;
 291         struct inet_frags *f;
 292         struct fqdir *fqdir;
 293
 294         WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
 295         reason = (q->flags & INET_FRAG_DROP) ?
 296                         SKB_DROP_REASON_FRAG_REASM_TIMEOUT :
 297                         SKB_CONSUMED;
 298         WARN_ON(del_timer(&q->timer) != 0);
 299
 300         /* Release all fragment data. */
 301         fqdir = q->fqdir;
 302         f = fqdir->f;
 303         sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments, reason);
 304         sum = sum_truesize + f->qsize;
 305
 306         call_rcu(&q->rcu, inet_frag_destroy_rcu);
 307
 308         sub_frag_mem_limit(fqdir, sum);
 309 }
 310 EXPORT_SYMBOL(inet_frag_destroy);
 311
 312 static struct inet_frag_queue *inet_frag_alloc(struct fqdir *fqdir,
 313                                                struct inet_frags *f,
 314                                                void *arg)
 315 {
 316         struct inet_frag_queue *q;
 317
 318         q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
 319         if (!q)
 320                 return NULL;
 321
 322         q->fqdir = fqdir;
 323         f->constructor(q, arg);
 324         add_frag_mem_limit(fqdir, f->qsize);
 325
 326         timer_setup(&q->timer, f->frag_expire, 0);
 327         spin_lock_init(&q->lock);
 328         refcount_set(&q->refcnt, 3);
 329
 330         return q;
 331 }
 332
 333 static struct inet_frag_queue *inet_frag_create(struct fqdir *fqdir,
 334                                                 void *arg,
 335                                                 struct inet_frag_queue **prev)
 336 {
 337         struct inet_frags *f = fqdir->f;
 338         struct inet_frag_queue *q;
 339
 340         q = inet_frag_alloc(fqdir, f, arg);
 341         if (!q) {
 342                 *prev = ERR_PTR(-ENOMEM);
 343                 return NULL;
 344         }
 345         mod_timer(&q->timer, jiffies + fqdir->timeout);
 346
 347         *prev = rhashtable_lookup_get_insert_key(&fqdir->rhashtable, &q->key,
 348                                                  &q->node, f->rhash_params);
 349         if (*prev) {
 350                 q->flags |= INET_FRAG_COMPLETE;
 351                 inet_frag_kill(q);
 352                 inet_frag_destroy(q);
 353                 return NULL;
 354         }
 355         return q;
 356 }
 357
 358 /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
 359 struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key)
 360 {
 361         /* This pairs with WRITE_ONCE() in fqdir_pre_exit(). */
 362         long high_thresh = READ_ONCE(fqdir->high_thresh);
 363         struct inet_frag_queue *fq = NULL, *prev;
 364
 365         if (!high_thresh || frag_mem_limit(fqdir) > high_thresh)
 366                 return NULL;
 367
 368         rcu_read_lock();
 369
 370         prev = rhashtable_lookup(&fqdir->rhashtable, key, fqdir->f->rhash_params);
 371         if (!prev)
 372                 fq = inet_frag_create(fqdir, key, &prev);
 373         if (!IS_ERR_OR_NULL(prev)) {
 374                 fq = prev;
 375                 if (!refcount_inc_not_zero(&fq->refcnt))
 376                         fq = NULL;
 377         }
 378         rcu_read_unlock();
 379         return fq;
 380 }
 381 EXPORT_SYMBOL(inet_frag_find);
 382
 383 int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
 384                            int offset, int end)
 385 {
 386         struct sk_buff *last = q->fragments_tail;
 387
 388         /* RFC5722, Section 4, amended by Errata ID : 3089
 389          *                          When reassembling an IPv6 datagram, if
 390          *   one or more its constituent fragments is determined to be an
 391          *   overlapping fragment, the entire datagram (and any constituent
 392          *   fragments) MUST be silently discarded.
 393          *
 394          * Duplicates, however, should be ignored (i.e. skb dropped, but the
 395          * queue/fragments kept for later reassembly).
 396          */
 397         if (!last)
 398                 fragrun_create(q, skb);  /* First fragment. */
 399         else if (last->ip_defrag_offset + last->len < end) {
 400                 /* This is the common case: skb goes to the end. */
 401                 /* Detect and discard overlaps. */
 402                 if (offset < last->ip_defrag_offset + last->len)
 403                         return IPFRAG_OVERLAP;
 404                 if (offset == last->ip_defrag_offset + last->len)
 405                         fragrun_append_to_last(q, skb);
 406                 else
 407                         fragrun_create(q, skb);
 408         } else {
 409                 /* Binary search. Note that skb can become the first fragment,
 410                  * but not the last (covered above).
 411                  */
 412                 struct rb_node **rbn, *parent;
 413
 414                 rbn = &q->rb_fragments.rb_node;
 415                 do {
 416                         struct sk_buff *curr;
 417                         int curr_run_end;
 418
 419                         parent = *rbn;
 420                         curr = rb_to_skb(parent);
 421                         curr_run_end = curr->ip_defrag_offset +
 422                                         FRAG_CB(curr)->frag_run_len;
 423                         if (end <= curr->ip_defrag_offset)
 424                                 rbn = &parent->rb_left;
 425                         else if (offset >= curr_run_end)
 426                                 rbn = &parent->rb_right;
 427                         else if (offset >= curr->ip_defrag_offset &&
 428                                  end <= curr_run_end)
 429                                 return IPFRAG_DUP;
 430                         else
 431                                 return IPFRAG_OVERLAP;
 432                 } while (*rbn);
 433                 /* Here we have parent properly set, and rbn pointing to
 434                  * one of its NULL left/right children. Insert skb.
 435                  */
 436                 fragcb_clear(skb);
 437                 rb_link_node(&skb->rbnode, parent, rbn);
 438                 rb_insert_color(&skb->rbnode, &q->rb_fragments);
 439         }
 440
 441         skb->ip_defrag_offset = offset;
 442
 443         return IPFRAG_OK;
 444 }
 445 EXPORT_SYMBOL(inet_frag_queue_insert);
 446
 447 void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
 448                               struct sk_buff *parent)
 449 {
 450         struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
 451         struct sk_buff **nextp;
 452         int delta;
 453
 454         if (head != skb) {
 455                 fp = skb_clone(skb, GFP_ATOMIC);
 456                 if (!fp)
 457                         return NULL;
 458                 FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
 459                 if (RB_EMPTY_NODE(&skb->rbnode))
 460                         FRAG_CB(parent)->next_frag = fp;
 461                 else
 462                         rb_replace_node(&skb->rbnode, &fp->rbnode,
 463                                         &q->rb_fragments);
 464                 if (q->fragments_tail == skb)
 465                         q->fragments_tail = fp;
 466                 skb_morph(skb, head);
 467                 FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
 468                 rb_replace_node(&head->rbnode, &skb->rbnode,
 469                                 &q->rb_fragments);
 470                 consume_skb(head);
 471                 head = skb;
 472         }
 473         WARN_ON(head->ip_defrag_offset != 0);
 474
 475         delta = -head->truesize;
 476
 477         /* Head of list must not be cloned. */
 478         if (skb_unclone(head, GFP_ATOMIC))
 479                 return NULL;
 480
 481         delta += head->truesize;
 482         if (delta)
 483                 add_frag_mem_limit(q->fqdir, delta);
 484
 485         /* If the first fragment is fragmented itself, we split
 486          * it to two chunks: the first with data and paged part
 487          * and the second, holding only fragments.
 488          */
 489         if (skb_has_frag_list(head)) {
 490                 struct sk_buff *clone;
 491                 int i, plen = 0;
 492
 493                 clone = alloc_skb(0, GFP_ATOMIC);
 494                 if (!clone)
 495                         return NULL;
 496                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 497                 skb_frag_list_init(head);
 498                 for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
 499                         plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
 500                 clone->data_len = head->data_len - plen;
 501                 clone->len = clone->data_len;
 502                 head->truesize += clone->truesize;
 503                 clone->csum = 0;
 504                 clone->ip_summed = head->ip_summed;
 505                 add_frag_mem_limit(q->fqdir, clone->truesize);
 506                 skb_shinfo(head)->frag_list = clone;
 507                 nextp = &clone->next;
 508         } else {
 509                 nextp = &skb_shinfo(head)->frag_list;
 510         }
 511
 512         return nextp;
 513 }
 514 EXPORT_SYMBOL(inet_frag_reasm_prepare);
 515
 516 void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
 517                             void *reasm_data, bool try_coalesce)
 518 {
 519         struct sk_buff **nextp = reasm_data;
 520         struct rb_node *rbn;
 521         struct sk_buff *fp;
 522         int sum_truesize;
 523
 524         skb_push(head, head->data - skb_network_header(head));
 525
 526         /* Traverse the tree in order, to build frag_list. */
 527         fp = FRAG_CB(head)->next_frag;
 528         rbn = rb_next(&head->rbnode);
 529         rb_erase(&head->rbnode, &q->rb_fragments);
 530
 531         sum_truesize = head->truesize;
 532         while (rbn || fp) {
 533                 /* fp points to the next sk_buff in the current run;
 534                  * rbn points to the next run.
 535                  */
 536                 /* Go through the current run. */
 537                 while (fp) {
 538                         struct sk_buff *next_frag = FRAG_CB(fp)->next_frag;
 539                         bool stolen;
 540                         int delta;
 541
 542                         sum_truesize += fp->truesize;
 543                         if (head->ip_summed != fp->ip_summed)
 544                                 head->ip_summed = CHECKSUM_NONE;
 545                         else if (head->ip_summed == CHECKSUM_COMPLETE)
 546                                 head->csum = csum_add(head->csum, fp->csum);
 547
 548                         if (try_coalesce && skb_try_coalesce(head, fp, &stolen,
 549                                                              &delta)) {
 550                                 kfree_skb_partial(fp, stolen);
 551                         } else {
 552                                 fp->prev = NULL;
 553                                 memset(&fp->rbnode, 0, sizeof(fp->rbnode));
 554                                 fp->sk = NULL;
 555
 556                                 head->data_len += fp->len;
 557                                 head->len += fp->len;
 558                                 head->truesize += fp->truesize;
 559
 560                                 *nextp = fp;
 561                                 nextp = &fp->next;
 562                         }
 563
 564                         fp = next_frag;
 565                 }
 566                 /* Move to the next run. */
 567                 if (rbn) {
 568                         struct rb_node *rbnext = rb_next(rbn);
 569
 570                         fp = rb_to_skb(rbn);
 571                         rb_erase(rbn, &q->rb_fragments);
 572                         rbn = rbnext;
 573                 }
 574         }
 575         sub_frag_mem_limit(q->fqdir, sum_truesize);
 576
 577         *nextp = NULL;
 578         skb_mark_not_on_list(head);
 579         head->prev = NULL;
 580         head->tstamp = q->stamp;
 581         head->mono_delivery_time = q->mono_delivery_time;
 582 }
 583 EXPORT_SYMBOL(inet_frag_reasm_finish);
 584
 585 struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
 586 {
 587         struct sk_buff *head, *skb;
 588
 589         head = skb_rb_first(&q->rb_fragments);
 590         if (!head)
 591                 return NULL;
 592         skb = FRAG_CB(head)->next_frag;
 593         if (skb)
 594                 rb_replace_node(&head->rbnode, &skb->rbnode,
 595                                 &q->rb_fragments);
 596         else
 597                 rb_erase(&head->rbnode, &q->rb_fragments);
 598         memset(&head->rbnode, 0, sizeof(head->rbnode));
 599         barrier();
 600
 601         if (head == q->fragments_tail)
 602                 q->fragments_tail = NULL;
 603
 604         sub_frag_mem_limit(q->fqdir, head->truesize);
 605
 606         return head;
 607 }
 608 EXPORT_SYMBOL(inet_frag_pull_head);