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