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         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 137                 fq->flags |= INET_FRAG_COMPLETE;
 138                 count++;
 139         } else if (fq->flags & INET_FRAG_HASH_DEAD) {
 140                 count++;
 141         }
 142         spin_unlock_bh(&fq->lock);
 143
 144         if (refcount_sub_and_test(count, &fq->refcnt))
 145                 inet_frag_destroy(fq);
 146 }
 147
 148 static LLIST_HEAD(fqdir_free_list);
 149
 150 static void fqdir_free_fn(struct work_struct *work)
 151 {
 152         struct llist_node *kill_list;
 153         struct fqdir *fqdir, *tmp;
 154         struct inet_frags *f;
 155
 156         /* Atomically snapshot the list of fqdirs to free */
 157         kill_list = llist_del_all(&fqdir_free_list);
 158
 159         /* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
 160          * have completed, since they need to dereference fqdir.
 161          * Would it not be nice to have kfree_rcu_barrier() ? :)
 162          */
 163         rcu_barrier();
 164
 165         llist_for_each_entry_safe(fqdir, tmp, kill_list, free_list) {
 166                 f = fqdir->f;
 167                 if (refcount_dec_and_test(&f->refcnt))
 168                         complete(&f->completion);
 169
 170                 kfree(fqdir);
 171         }
 172 }
 173
 174 static DECLARE_WORK(fqdir_free_work, fqdir_free_fn);
 175
 176 static void fqdir_work_fn(struct work_struct *work)
 177 {
 178         struct fqdir *fqdir = container_of(work, struct fqdir, destroy_work);
 179
 180         rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL);
 181
 182         if (llist_add(&fqdir->free_list, &fqdir_free_list))
 183                 queue_work(system_wq, &fqdir_free_work);
 184 }
 185
 186 int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
 187 {
 188         struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
 189         int res;
 190
 191         if (!fqdir)
 192                 return -ENOMEM;
 193         fqdir->f = f;
 194         fqdir->net = net;
 195         res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
 196         if (res < 0) {
 197                 kfree(fqdir);
 198                 return res;
 199         }
 200         refcount_inc(&f->refcnt);
 201         *fqdirp = fqdir;
 202         return 0;
 203 }
 204 EXPORT_SYMBOL(fqdir_init);
 205
 206 static struct workqueue_struct *inet_frag_wq;
 207
 208 static int __init inet_frag_wq_init(void)
 209 {
 210         inet_frag_wq = create_workqueue("inet_frag_wq");
 211         if (!inet_frag_wq)
 212                 panic("Could not create inet frag workq");
 213         return 0;
 214 }
 215
 216 pure_initcall(inet_frag_wq_init);
 217
 218 void fqdir_exit(struct fqdir *fqdir)
 219 {
 220         INIT_WORK(&fqdir->destroy_work, fqdir_work_fn);
 221         queue_work(inet_frag_wq, &fqdir->destroy_work);
 222 }
 223 EXPORT_SYMBOL(fqdir_exit);
 224
 225 void inet_frag_kill(struct inet_frag_queue *fq)
 226 {
 227         if (del_timer(&fq->timer))
 228                 refcount_dec(&fq->refcnt);
 229
 230         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 231                 struct fqdir *fqdir = fq->fqdir;
 232
 233                 fq->flags |= INET_FRAG_COMPLETE;
 234                 rcu_read_lock();
 235                 /* The RCU read lock provides a memory barrier
 236                  * guaranteeing that if fqdir->dead is false then
 237                  * the hash table destruction will not start until
 238                  * after we unlock.  Paired with fqdir_pre_exit().
 239                  */
 240                 if (!READ_ONCE(fqdir->dead)) {
 241                         rhashtable_remove_fast(&fqdir->rhashtable, &fq->node,
 242                                                fqdir->f->rhash_params);
 243                         refcount_dec(&fq->refcnt);
 244                 } else {
 245                         fq->flags |= INET_FRAG_HASH_DEAD;
 246                 }
 247                 rcu_read_unlock();
 248         }
 249 }
 250 EXPORT_SYMBOL(inet_frag_kill);
 251
 252 static void inet_frag_destroy_rcu(struct rcu_head *head)
 253 {
 254         struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
 255                                                  rcu);
 256         struct inet_frags *f = q->fqdir->f;
 257
 258         if (f->destructor)
 259                 f->destructor(q);
 260         kmem_cache_free(f->frags_cachep, q);
 261 }
 262
 263 unsigned int inet_frag_rbtree_purge(struct rb_root *root)
 264 {
 265         struct rb_node *p = rb_first(root);
 266         unsigned int sum = 0;
 267
 268         while (p) {
 269                 struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
 270
 271                 p = rb_next(p);
 272                 rb_erase(&skb->rbnode, root);
 273                 while (skb) {
 274                         struct sk_buff *next = FRAG_CB(skb)->next_frag;
 275
 276                         sum += skb->truesize;
 277                         kfree_skb(skb);
 278                         skb = next;
 279                 }
 280         }
 281         return sum;
 282 }
 283 EXPORT_SYMBOL(inet_frag_rbtree_purge);
 284
 285 void inet_frag_destroy(struct inet_frag_queue *q)
 286 {
 287         struct fqdir *fqdir;
 288         unsigned int sum, sum_truesize = 0;
 289         struct inet_frags *f;
 290
 291         WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
 292         WARN_ON(del_timer(&q->timer) != 0);
 293
 294         /* Release all fragment data. */
 295         fqdir = q->fqdir;
 296         f = fqdir->f;
 297         sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments);
 298         sum = sum_truesize + f->qsize;
 299
 300         call_rcu(&q->rcu, inet_frag_destroy_rcu);
 301
 302         sub_frag_mem_limit(fqdir, sum);
 303 }
 304 EXPORT_SYMBOL(inet_frag_destroy);
 305
 306 static struct inet_frag_queue *inet_frag_alloc(struct fqdir *fqdir,
 307                                                struct inet_frags *f,
 308                                                void *arg)
 309 {
 310         struct inet_frag_queue *q;
 311
 312         q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
 313         if (!q)
 314                 return NULL;
 315
 316         q->fqdir = fqdir;
 317         f->constructor(q, arg);
 318         add_frag_mem_limit(fqdir, f->qsize);
 319
 320         timer_setup(&q->timer, f->frag_expire, 0);
 321         spin_lock_init(&q->lock);
 322         refcount_set(&q->refcnt, 3);
 323
 324         return q;
 325 }
 326
 327 static struct inet_frag_queue *inet_frag_create(struct fqdir *fqdir,
 328                                                 void *arg,
 329                                                 struct inet_frag_queue **prev)
 330 {
 331         struct inet_frags *f = fqdir->f;
 332         struct inet_frag_queue *q;
 333
 334         q = inet_frag_alloc(fqdir, f, arg);
 335         if (!q) {
 336                 *prev = ERR_PTR(-ENOMEM);
 337                 return NULL;
 338         }
 339         mod_timer(&q->timer, jiffies + fqdir->timeout);
 340
 341         *prev = rhashtable_lookup_get_insert_key(&fqdir->rhashtable, &q->key,
 342                                                  &q->node, f->rhash_params);
 343         if (*prev) {
 344                 q->flags |= INET_FRAG_COMPLETE;
 345                 inet_frag_kill(q);
 346                 inet_frag_destroy(q);
 347                 return NULL;
 348         }
 349         return q;
 350 }
 351
 352 /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
 353 struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key)
 354 {
 355         /* This pairs with WRITE_ONCE() in fqdir_pre_exit(). */
 356         long high_thresh = READ_ONCE(fqdir->high_thresh);
 357         struct inet_frag_queue *fq = NULL, *prev;
 358
 359         if (!high_thresh || frag_mem_limit(fqdir) > high_thresh)
 360                 return NULL;
 361
 362         rcu_read_lock();
 363
 364         prev = rhashtable_lookup(&fqdir->rhashtable, key, fqdir->f->rhash_params);
 365         if (!prev)
 366                 fq = inet_frag_create(fqdir, key, &prev);
 367         if (!IS_ERR_OR_NULL(prev)) {
 368                 fq = prev;
 369                 if (!refcount_inc_not_zero(&fq->refcnt))
 370                         fq = NULL;
 371         }
 372         rcu_read_unlock();
 373         return fq;
 374 }
 375 EXPORT_SYMBOL(inet_frag_find);
 376
 377 int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
 378                            int offset, int end)
 379 {
 380         struct sk_buff *last = q->fragments_tail;
 381
 382         /* RFC5722, Section 4, amended by Errata ID : 3089
 383          *                          When reassembling an IPv6 datagram, if
 384          *   one or more its constituent fragments is determined to be an
 385          *   overlapping fragment, the entire datagram (and any constituent
 386          *   fragments) MUST be silently discarded.
 387          *
 388          * Duplicates, however, should be ignored (i.e. skb dropped, but the
 389          * queue/fragments kept for later reassembly).
 390          */
 391         if (!last)
 392                 fragrun_create(q, skb);  /* First fragment. */
 393         else if (last->ip_defrag_offset + last->len < end) {
 394                 /* This is the common case: skb goes to the end. */
 395                 /* Detect and discard overlaps. */
 396                 if (offset < last->ip_defrag_offset + last->len)
 397                         return IPFRAG_OVERLAP;
 398                 if (offset == last->ip_defrag_offset + last->len)
 399                         fragrun_append_to_last(q, skb);
 400                 else
 401                         fragrun_create(q, skb);
 402         } else {
 403                 /* Binary search. Note that skb can become the first fragment,
 404                  * but not the last (covered above).
 405                  */
 406                 struct rb_node **rbn, *parent;
 407
 408                 rbn = &q->rb_fragments.rb_node;
 409                 do {
 410                         struct sk_buff *curr;
 411                         int curr_run_end;
 412
 413                         parent = *rbn;
 414                         curr = rb_to_skb(parent);
 415                         curr_run_end = curr->ip_defrag_offset +
 416                                         FRAG_CB(curr)->frag_run_len;
 417                         if (end <= curr->ip_defrag_offset)
 418                                 rbn = &parent->rb_left;
 419                         else if (offset >= curr_run_end)
 420                                 rbn = &parent->rb_right;
 421                         else if (offset >= curr->ip_defrag_offset &&
 422                                  end <= curr_run_end)
 423                                 return IPFRAG_DUP;
 424                         else
 425                                 return IPFRAG_OVERLAP;
 426                 } while (*rbn);
 427                 /* Here we have parent properly set, and rbn pointing to
 428                  * one of its NULL left/right children. Insert skb.
 429                  */
 430                 fragcb_clear(skb);
 431                 rb_link_node(&skb->rbnode, parent, rbn);
 432                 rb_insert_color(&skb->rbnode, &q->rb_fragments);
 433         }
 434
 435         skb->ip_defrag_offset = offset;
 436
 437         return IPFRAG_OK;
 438 }
 439 EXPORT_SYMBOL(inet_frag_queue_insert);
 440
 441 void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
 442                               struct sk_buff *parent)
 443 {
 444         struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
 445         struct sk_buff **nextp;
 446         int delta;
 447
 448         if (head != skb) {
 449                 fp = skb_clone(skb, GFP_ATOMIC);
 450                 if (!fp)
 451                         return NULL;
 452                 FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
 453                 if (RB_EMPTY_NODE(&skb->rbnode))
 454                         FRAG_CB(parent)->next_frag = fp;
 455                 else
 456                         rb_replace_node(&skb->rbnode, &fp->rbnode,
 457                                         &q->rb_fragments);
 458                 if (q->fragments_tail == skb)
 459                         q->fragments_tail = fp;
 460                 skb_morph(skb, head);
 461                 FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
 462                 rb_replace_node(&head->rbnode, &skb->rbnode,
 463                                 &q->rb_fragments);
 464                 consume_skb(head);
 465                 head = skb;
 466         }
 467         WARN_ON(head->ip_defrag_offset != 0);
 468
 469         delta = -head->truesize;
 470
 471         /* Head of list must not be cloned. */
 472         if (skb_unclone(head, GFP_ATOMIC))
 473                 return NULL;
 474
 475         delta += head->truesize;
 476         if (delta)
 477                 add_frag_mem_limit(q->fqdir, delta);
 478
 479         /* If the first fragment is fragmented itself, we split
 480          * it to two chunks: the first with data and paged part
 481          * and the second, holding only fragments.
 482          */
 483         if (skb_has_frag_list(head)) {
 484                 struct sk_buff *clone;
 485                 int i, plen = 0;
 486
 487                 clone = alloc_skb(0, GFP_ATOMIC);
 488                 if (!clone)
 489                         return NULL;
 490                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 491                 skb_frag_list_init(head);
 492                 for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
 493                         plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
 494                 clone->data_len = head->data_len - plen;
 495                 clone->len = clone->data_len;
 496                 head->truesize += clone->truesize;
 497                 clone->csum = 0;
 498                 clone->ip_summed = head->ip_summed;
 499                 add_frag_mem_limit(q->fqdir, clone->truesize);
 500                 skb_shinfo(head)->frag_list = clone;
 501                 nextp = &clone->next;
 502         } else {
 503                 nextp = &skb_shinfo(head)->frag_list;
 504         }
 505
 506         return nextp;
 507 }
 508 EXPORT_SYMBOL(inet_frag_reasm_prepare);
 509
 510 void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
 511                             void *reasm_data, bool try_coalesce)
 512 {
 513         struct sk_buff **nextp = (struct sk_buff **)reasm_data;
 514         struct rb_node *rbn;
 515         struct sk_buff *fp;
 516         int sum_truesize;
 517
 518         skb_push(head, head->data - skb_network_header(head));
 519
 520         /* Traverse the tree in order, to build frag_list. */
 521         fp = FRAG_CB(head)->next_frag;
 522         rbn = rb_next(&head->rbnode);
 523         rb_erase(&head->rbnode, &q->rb_fragments);
 524
 525         sum_truesize = head->truesize;
 526         while (rbn || fp) {
 527                 /* fp points to the next sk_buff in the current run;
 528                  * rbn points to the next run.
 529                  */
 530                 /* Go through the current run. */
 531                 while (fp) {
 532                         struct sk_buff *next_frag = FRAG_CB(fp)->next_frag;
 533                         bool stolen;
 534                         int delta;
 535
 536                         sum_truesize += fp->truesize;
 537                         if (head->ip_summed != fp->ip_summed)
 538                                 head->ip_summed = CHECKSUM_NONE;
 539                         else if (head->ip_summed == CHECKSUM_COMPLETE)
 540                                 head->csum = csum_add(head->csum, fp->csum);
 541
 542                         if (try_coalesce && skb_try_coalesce(head, fp, &stolen,
 543                                                              &delta)) {
 544                                 kfree_skb_partial(fp, stolen);
 545                         } else {
 546                                 fp->prev = NULL;
 547                                 memset(&fp->rbnode, 0, sizeof(fp->rbnode));
 548                                 fp->sk = NULL;
 549
 550                                 head->data_len += fp->len;
 551                                 head->len += fp->len;
 552                                 head->truesize += fp->truesize;
 553
 554                                 *nextp = fp;
 555                                 nextp = &fp->next;
 556                         }
 557
 558                         fp = next_frag;
 559                 }
 560                 /* Move to the next run. */
 561                 if (rbn) {
 562                         struct rb_node *rbnext = rb_next(rbn);
 563
 564                         fp = rb_to_skb(rbn);
 565                         rb_erase(rbn, &q->rb_fragments);
 566                         rbn = rbnext;
 567                 }
 568         }
 569         sub_frag_mem_limit(q->fqdir, sum_truesize);
 570
 571         *nextp = NULL;
 572         skb_mark_not_on_list(head);
 573         head->prev = NULL;
 574         head->tstamp = q->stamp;
 575         head->mono_delivery_time = q->mono_delivery_time;
 576 }
 577 EXPORT_SYMBOL(inet_frag_reasm_finish);
 578
 579 struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
 580 {
 581         struct sk_buff *head, *skb;
 582
 583         head = skb_rb_first(&q->rb_fragments);
 584         if (!head)
 585                 return NULL;
 586         skb = FRAG_CB(head)->next_frag;
 587         if (skb)
 588                 rb_replace_node(&head->rbnode, &skb->rbnode,
 589                                 &q->rb_fragments);
 590         else
 591                 rb_erase(&head->rbnode, &q->rb_fragments);
 592         memset(&head->rbnode, 0, sizeof(head->rbnode));
 593         barrier();
 594
 595         if (head == q->fragments_tail)
 596                 q->fragments_tail = NULL;
 597
 598         sub_frag_mem_limit(q->fqdir, head->truesize);
 599
 600         return head;
 601 }
 602 EXPORT_SYMBOL(inet_frag_pull_head);