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         return 0;
 110 }
 111 EXPORT_SYMBOL(inet_frags_init);
 112
 113 void inet_frags_fini(struct inet_frags *f)
 114 {
 115         /* We must wait that all inet_frag_destroy_rcu() have completed. */
 116         rcu_barrier();
 117
 118         kmem_cache_destroy(f->frags_cachep);
 119         f->frags_cachep = NULL;
 120 }
 121 EXPORT_SYMBOL(inet_frags_fini);
 122
 123 static void inet_frags_free_cb(void *ptr, void *arg)
 124 {
 125         struct inet_frag_queue *fq = ptr;
 126
 127         /* If we can not cancel the timer, it means this frag_queue
 128          * is already disappearing, we have nothing to do.
 129          * Otherwise, we own a refcount until the end of this function.
 130          */
 131         if (!del_timer(&fq->timer))
 132                 return;
 133
 134         spin_lock_bh(&fq->lock);
 135         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 136                 fq->flags |= INET_FRAG_COMPLETE;
 137                 refcount_dec(&fq->refcnt);
 138         }
 139         spin_unlock_bh(&fq->lock);
 140
 141         inet_frag_put(fq);
 142 }
 143
 144 void inet_frags_exit_net(struct netns_frags *nf)
 145 {
 146         nf->high_thresh = 0; /* prevent creation of new frags */
 147
 148         rhashtable_free_and_destroy(&nf->rhashtable, inet_frags_free_cb, NULL);
 149 }
 150 EXPORT_SYMBOL(inet_frags_exit_net);
 151
 152 void inet_frag_kill(struct inet_frag_queue *fq)
 153 {
 154         if (del_timer(&fq->timer))
 155                 refcount_dec(&fq->refcnt);
 156
 157         if (!(fq->flags & INET_FRAG_COMPLETE)) {
 158                 struct netns_frags *nf = fq->net;
 159
 160                 fq->flags |= INET_FRAG_COMPLETE;
 161                 rhashtable_remove_fast(&nf->rhashtable, &fq->node, nf->f->rhash_params);
 162                 refcount_dec(&fq->refcnt);
 163         }
 164 }
 165 EXPORT_SYMBOL(inet_frag_kill);
 166
 167 static void inet_frag_destroy_rcu(struct rcu_head *head)
 168 {
 169         struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
 170                                                  rcu);
 171         struct inet_frags *f = q->net->f;
 172
 173         if (f->destructor)
 174                 f->destructor(q);
 175         kmem_cache_free(f->frags_cachep, q);
 176 }
 177
 178 unsigned int inet_frag_rbtree_purge(struct rb_root *root)
 179 {
 180         struct rb_node *p = rb_first(root);
 181         unsigned int sum = 0;
 182
 183         while (p) {
 184                 struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
 185
 186                 p = rb_next(p);
 187                 rb_erase(&skb->rbnode, root);
 188                 while (skb) {
 189                         struct sk_buff *next = FRAG_CB(skb)->next_frag;
 190
 191                         sum += skb->truesize;
 192                         kfree_skb(skb);
 193                         skb = next;
 194                 }
 195         }
 196         return sum;
 197 }
 198 EXPORT_SYMBOL(inet_frag_rbtree_purge);
 199
 200 void inet_frag_destroy(struct inet_frag_queue *q)
 201 {
 202         struct netns_frags *nf;
 203         unsigned int sum, sum_truesize = 0;
 204         struct inet_frags *f;
 205
 206         WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
 207         WARN_ON(del_timer(&q->timer) != 0);
 208
 209         /* Release all fragment data. */
 210         nf = q->net;
 211         f = nf->f;
 212         sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments);
 213         sum = sum_truesize + f->qsize;
 214
 215         call_rcu(&q->rcu, inet_frag_destroy_rcu);
 216
 217         sub_frag_mem_limit(nf, sum);
 218 }
 219 EXPORT_SYMBOL(inet_frag_destroy);
 220
 221 static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
 222                                                struct inet_frags *f,
 223                                                void *arg)
 224 {
 225         struct inet_frag_queue *q;
 226
 227         q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
 228         if (!q)
 229                 return NULL;
 230
 231         q->net = nf;
 232         f->constructor(q, arg);
 233         add_frag_mem_limit(nf, f->qsize);
 234
 235         timer_setup(&q->timer, f->frag_expire, 0);
 236         spin_lock_init(&q->lock);
 237         refcount_set(&q->refcnt, 3);
 238
 239         return q;
 240 }
 241
 242 static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
 243                                                 void *arg,
 244                                                 struct inet_frag_queue **prev)
 245 {
 246         struct inet_frags *f = nf->f;
 247         struct inet_frag_queue *q;
 248
 249         q = inet_frag_alloc(nf, f, arg);
 250         if (!q) {
 251                 *prev = ERR_PTR(-ENOMEM);
 252                 return NULL;
 253         }
 254         mod_timer(&q->timer, jiffies + nf->timeout);
 255
 256         *prev = rhashtable_lookup_get_insert_key(&nf->rhashtable, &q->key,
 257                                                  &q->node, f->rhash_params);
 258         if (*prev) {
 259                 q->flags |= INET_FRAG_COMPLETE;
 260                 inet_frag_kill(q);
 261                 inet_frag_destroy(q);
 262                 return NULL;
 263         }
 264         return q;
 265 }
 266
 267 /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
 268 struct inet_frag_queue *inet_frag_find(struct netns_frags *nf, void *key)
 269 {
 270         struct inet_frag_queue *fq = NULL, *prev;
 271
 272         if (!nf->high_thresh || frag_mem_limit(nf) > nf->high_thresh)
 273                 return NULL;
 274
 275         rcu_read_lock();
 276
 277         prev = rhashtable_lookup(&nf->rhashtable, key, nf->f->rhash_params);
 278         if (!prev)
 279                 fq = inet_frag_create(nf, key, &prev);
 280         if (prev && !IS_ERR(prev)) {
 281                 fq = prev;
 282                 if (!refcount_inc_not_zero(&fq->refcnt))
 283                         fq = NULL;
 284         }
 285         rcu_read_unlock();
 286         return fq;
 287 }
 288 EXPORT_SYMBOL(inet_frag_find);
 289
 290 int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
 291                            int offset, int end)
 292 {
 293         struct sk_buff *last = q->fragments_tail;
 294
 295         /* RFC5722, Section 4, amended by Errata ID : 3089
 296          *                          When reassembling an IPv6 datagram, if
 297          *   one or more its constituent fragments is determined to be an
 298          *   overlapping fragment, the entire datagram (and any constituent
 299          *   fragments) MUST be silently discarded.
 300          *
 301          * Duplicates, however, should be ignored (i.e. skb dropped, but the
 302          * queue/fragments kept for later reassembly).
 303          */
 304         if (!last)
 305                 fragrun_create(q, skb);  /* First fragment. */
 306         else if (last->ip_defrag_offset + last->len < end) {
 307                 /* This is the common case: skb goes to the end. */
 308                 /* Detect and discard overlaps. */
 309                 if (offset < last->ip_defrag_offset + last->len)
 310                         return IPFRAG_OVERLAP;
 311                 if (offset == last->ip_defrag_offset + last->len)
 312                         fragrun_append_to_last(q, skb);
 313                 else
 314                         fragrun_create(q, skb);
 315         } else {
 316                 /* Binary search. Note that skb can become the first fragment,
 317                  * but not the last (covered above).
 318                  */
 319                 struct rb_node **rbn, *parent;
 320
 321                 rbn = &q->rb_fragments.rb_node;
 322                 do {
 323                         struct sk_buff *curr;
 324                         int curr_run_end;
 325
 326                         parent = *rbn;
 327                         curr = rb_to_skb(parent);
 328                         curr_run_end = curr->ip_defrag_offset +
 329                                         FRAG_CB(curr)->frag_run_len;
 330                         if (end <= curr->ip_defrag_offset)
 331                                 rbn = &parent->rb_left;
 332                         else if (offset >= curr_run_end)
 333                                 rbn = &parent->rb_right;
 334                         else if (offset >= curr->ip_defrag_offset &&
 335                                  end <= curr_run_end)
 336                                 return IPFRAG_DUP;
 337                         else
 338                                 return IPFRAG_OVERLAP;
 339                 } while (*rbn);
 340                 /* Here we have parent properly set, and rbn pointing to
 341                  * one of its NULL left/right children. Insert skb.
 342                  */
 343                 fragcb_clear(skb);
 344                 rb_link_node(&skb->rbnode, parent, rbn);
 345                 rb_insert_color(&skb->rbnode, &q->rb_fragments);
 346         }
 347
 348         skb->ip_defrag_offset = offset;
 349
 350         return IPFRAG_OK;
 351 }
 352 EXPORT_SYMBOL(inet_frag_queue_insert);
 353
 354 void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
 355                               struct sk_buff *parent)
 356 {
 357         struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
 358         struct sk_buff **nextp;
 359         int delta;
 360
 361         if (head != skb) {
 362                 fp = skb_clone(skb, GFP_ATOMIC);
 363                 if (!fp)
 364                         return NULL;
 365                 FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
 366                 if (RB_EMPTY_NODE(&skb->rbnode))
 367                         FRAG_CB(parent)->next_frag = fp;
 368                 else
 369                         rb_replace_node(&skb->rbnode, &fp->rbnode,
 370                                         &q->rb_fragments);
 371                 if (q->fragments_tail == skb)
 372                         q->fragments_tail = fp;
 373                 skb_morph(skb, head);
 374                 FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
 375                 rb_replace_node(&head->rbnode, &skb->rbnode,
 376                                 &q->rb_fragments);
 377                 consume_skb(head);
 378                 head = skb;
 379         }
 380         WARN_ON(head->ip_defrag_offset != 0);
 381
 382         delta = -head->truesize;
 383
 384         /* Head of list must not be cloned. */
 385         if (skb_unclone(head, GFP_ATOMIC))
 386                 return NULL;
 387
 388         delta += head->truesize;
 389         if (delta)
 390                 add_frag_mem_limit(q->net, delta);
 391
 392         /* If the first fragment is fragmented itself, we split
 393          * it to two chunks: the first with data and paged part
 394          * and the second, holding only fragments.
 395          */
 396         if (skb_has_frag_list(head)) {
 397                 struct sk_buff *clone;
 398                 int i, plen = 0;
 399
 400                 clone = alloc_skb(0, GFP_ATOMIC);
 401                 if (!clone)
 402                         return NULL;
 403                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 404                 skb_frag_list_init(head);
 405                 for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
 406                         plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
 407                 clone->data_len = head->data_len - plen;
 408                 clone->len = clone->data_len;
 409                 head->truesize += clone->truesize;
 410                 clone->csum = 0;
 411                 clone->ip_summed = head->ip_summed;
 412                 add_frag_mem_limit(q->net, clone->truesize);
 413                 skb_shinfo(head)->frag_list = clone;
 414                 nextp = &clone->next;
 415         } else {
 416                 nextp = &skb_shinfo(head)->frag_list;
 417         }
 418
 419         return nextp;
 420 }
 421 EXPORT_SYMBOL(inet_frag_reasm_prepare);
 422
 423 void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
 424                             void *reasm_data)
 425 {
 426         struct sk_buff **nextp = (struct sk_buff **)reasm_data;
 427         struct rb_node *rbn;
 428         struct sk_buff *fp;
 429
 430         skb_push(head, head->data - skb_network_header(head));
 431
 432         /* Traverse the tree in order, to build frag_list. */
 433         fp = FRAG_CB(head)->next_frag;
 434         rbn = rb_next(&head->rbnode);
 435         rb_erase(&head->rbnode, &q->rb_fragments);
 436         while (rbn || fp) {
 437                 /* fp points to the next sk_buff in the current run;
 438                  * rbn points to the next run.
 439                  */
 440                 /* Go through the current run. */
 441                 while (fp) {
 442                         *nextp = fp;
 443                         nextp = &fp->next;
 444                         fp->prev = NULL;
 445                         memset(&fp->rbnode, 0, sizeof(fp->rbnode));
 446                         fp->sk = NULL;
 447                         head->data_len += fp->len;
 448                         head->len += fp->len;
 449                         if (head->ip_summed != fp->ip_summed)
 450                                 head->ip_summed = CHECKSUM_NONE;
 451                         else if (head->ip_summed == CHECKSUM_COMPLETE)
 452                                 head->csum = csum_add(head->csum, fp->csum);
 453                         head->truesize += fp->truesize;
 454                         fp = FRAG_CB(fp)->next_frag;
 455                 }
 456                 /* Move to the next run. */
 457                 if (rbn) {
 458                         struct rb_node *rbnext = rb_next(rbn);
 459
 460                         fp = rb_to_skb(rbn);
 461                         rb_erase(rbn, &q->rb_fragments);
 462                         rbn = rbnext;
 463                 }
 464         }
 465         sub_frag_mem_limit(q->net, head->truesize);
 466
 467         *nextp = NULL;
 468         skb_mark_not_on_list(head);
 469         head->prev = NULL;
 470         head->tstamp = q->stamp;
 471 }
 472 EXPORT_SYMBOL(inet_frag_reasm_finish);
 473
 474 struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
 475 {
 476         struct sk_buff *head, *skb;
 477
 478         head = skb_rb_first(&q->rb_fragments);
 479         if (!head)
 480                 return NULL;
 481         skb = FRAG_CB(head)->next_frag;
 482         if (skb)
 483                 rb_replace_node(&head->rbnode, &skb->rbnode,
 484                                 &q->rb_fragments);
 485         else
 486                 rb_erase(&head->rbnode, &q->rb_fragments);
 487         memset(&head->rbnode, 0, sizeof(head->rbnode));
 488         barrier();
 489
 490         if (head == q->fragments_tail)
 491                 q->fragments_tail = NULL;
 492
 493         sub_frag_mem_limit(q->net, head->truesize);
 494
 495         return head;
 496 }
 497 EXPORT_SYMBOL(inet_frag_pull_head);