kernel/bpf/lpm_trie.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Longest prefix match list implementation
   4  *
   5  * Copyright (c) 2016,2017 Daniel Mack
   6  * Copyright (c) 2016 David Herrmann
   7  */
   8
   9 #include <linux/bpf.h>
  10 #include <linux/btf.h>
  11 #include <linux/err.h>
  12 #include <linux/slab.h>
  13 #include <linux/spinlock.h>
  14 #include <linux/vmalloc.h>
  15 #include <net/ipv6.h>
  16 #include <uapi/linux/btf.h>
  17
  18 /* Intermediate node */
  19 #define LPM_TREE_NODE_FLAG_IM BIT(0)
  20
  21 struct lpm_trie_node;
  22
  23 struct lpm_trie_node {
  24         struct rcu_head rcu;
  25         struct lpm_trie_node __rcu      *child[2];
  26         u32                             prefixlen;
  27         u32                             flags;
  28         u8                              data[];
  29 };
  30
  31 struct lpm_trie {
  32         struct bpf_map                  map;
  33         struct lpm_trie_node __rcu      *root;
  34         size_t                          n_entries;
  35         size_t                          max_prefixlen;
  36         size_t                          data_size;
  37         spinlock_t                      lock;
  38 };
  39
  40 /* This trie implements a longest prefix match algorithm that can be used to
  41  * match IP addresses to a stored set of ranges.
  42  *
  43  * Data stored in @data of struct bpf_lpm_key and struct lpm_trie_node is
  44  * interpreted as big endian, so data[0] stores the most significant byte.
  45  *
  46  * Match ranges are internally stored in instances of struct lpm_trie_node
  47  * which each contain their prefix length as well as two pointers that may
  48  * lead to more nodes containing more specific matches. Each node also stores
  49  * a value that is defined by and returned to userspace via the update_elem
  50  * and lookup functions.
  51  *
  52  * For instance, let's start with a trie that was created with a prefix length
  53  * of 32, so it can be used for IPv4 addresses, and one single element that
  54  * matches 192.168.0.0/16. The data array would hence contain
  55  * [0xc0, 0xa8, 0x00, 0x00] in big-endian notation. This documentation will
  56  * stick to IP-address notation for readability though.
  57  *
  58  * As the trie is empty initially, the new node (1) will be places as root
  59  * node, denoted as (R) in the example below. As there are no other node, both
  60  * child pointers are %NULL.
  61  *
  62  *              +----------------+
  63  *              |       (1)  (R) |
  64  *              | 192.168.0.0/16 |
  65  *              |    value: 1    |
  66  *              |   [0]    [1]   |
  67  *              +----------------+
  68  *
  69  * Next, let's add a new node (2) matching 192.168.0.0/24. As there is already
  70  * a node with the same data and a smaller prefix (ie, a less specific one),
  71  * node (2) will become a child of (1). In child index depends on the next bit
  72  * that is outside of what (1) matches, and that bit is 0, so (2) will be
  73  * child[0] of (1):
  74  *
  75  *              +----------------+
  76  *              |       (1)  (R) |
  77  *              | 192.168.0.0/16 |
  78  *              |    value: 1    |
  79  *              |   [0]    [1]   |
  80  *              +----------------+
  81  *                   |
  82  *    +----------------+
  83  *    |       (2)      |
  84  *    | 192.168.0.0/24 |
  85  *    |    value: 2    |
  86  *    |   [0]    [1]   |
  87  *    +----------------+
  88  *
  89  * The child[1] slot of (1) could be filled with another node which has bit #17
  90  * (the next bit after the ones that (1) matches on) set to 1. For instance,
  91  * 192.168.128.0/24:
  92  *
  93  *              +----------------+
  94  *              |       (1)  (R) |
  95  *              | 192.168.0.0/16 |
  96  *              |    value: 1    |
  97  *              |   [0]    [1]   |
  98  *              +----------------+
  99  *                   |      |
 100  *    +----------------+  +------------------+
 101  *    |       (2)      |  |        (3)       |
 102  *    | 192.168.0.0/24 |  | 192.168.128.0/24 |
 103  *    |    value: 2    |  |     value: 3     |
 104  *    |   [0]    [1]   |  |    [0]    [1]    |
 105  *    +----------------+  +------------------+
 106  *
 107  * Let's add another node (4) to the game for 192.168.1.0/24. In order to place
 108  * it, node (1) is looked at first, and because (4) of the semantics laid out
 109  * above (bit #17 is 0), it would normally be attached to (1) as child[0].
 110  * However, that slot is already allocated, so a new node is needed in between.
 111  * That node does not have a value attached to it and it will never be
 112  * returned to users as result of a lookup. It is only there to differentiate
 113  * the traversal further. It will get a prefix as wide as necessary to
 114  * distinguish its two children:
 115  *
 116  *                      +----------------+
 117  *                      |       (1)  (R) |
 118  *                      | 192.168.0.0/16 |
 119  *                      |    value: 1    |
 120  *                      |   [0]    [1]   |
 121  *                      +----------------+
 122  *                           |      |
 123  *            +----------------+  +------------------+
 124  *            |       (4)  (I) |  |        (3)       |
 125  *            | 192.168.0.0/23 |  | 192.168.128.0/24 |
 126  *            |    value: ---  |  |     value: 3     |
 127  *            |   [0]    [1]   |  |    [0]    [1]    |
 128  *            +----------------+  +------------------+
 129  *                 |      |
 130  *  +----------------+  +----------------+
 131  *  |       (2)      |  |       (5)      |
 132  *  | 192.168.0.0/24 |  | 192.168.1.0/24 |
 133  *  |    value: 2    |  |     value: 5   |
 134  *  |   [0]    [1]   |  |   [0]    [1]   |
 135  *  +----------------+  +----------------+
 136  *
 137  * 192.168.1.1/32 would be a child of (5) etc.
 138  *
 139  * An intermediate node will be turned into a 'real' node on demand. In the
 140  * example above, (4) would be re-used if 192.168.0.0/23 is added to the trie.
 141  *
 142  * A fully populated trie would have a height of 32 nodes, as the trie was
 143  * created with a prefix length of 32.
 144  *
 145  * The lookup starts at the root node. If the current node matches and if there
 146  * is a child that can be used to become more specific, the trie is traversed
 147  * downwards. The last node in the traversal that is a non-intermediate one is
 148  * returned.
 149  */
 150
 151 static inline int extract_bit(const u8 *data, size_t index)
 152 {
 153         return !!(data[index / 8] & (1 << (7 - (index % 8))));
 154 }
 155
 156 /**
 157  * longest_prefix_match() - determine the longest prefix
 158  * @trie:       The trie to get internal sizes from
 159  * @node:       The node to operate on
 160  * @key:        The key to compare to @node
 161  *
 162  * Determine the longest prefix of @node that matches the bits in @key.
 163  */
 164 static size_t longest_prefix_match(const struct lpm_trie *trie,
 165                                    const struct lpm_trie_node *node,
 166                                    const struct bpf_lpm_trie_key *key)
 167 {
 168         u32 limit = min(node->prefixlen, key->prefixlen);
 169         u32 prefixlen = 0, i = 0;
 170
 171         BUILD_BUG_ON(offsetof(struct lpm_trie_node, data) % sizeof(u32));
 172         BUILD_BUG_ON(offsetof(struct bpf_lpm_trie_key, data) % sizeof(u32));
 173
 174 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && defined(CONFIG_64BIT)
 175
 176         /* data_size >= 16 has very small probability.
 177          * We do not use a loop for optimal code generation.
 178          */
 179         if (trie->data_size >= 8) {
 180                 u64 diff = be64_to_cpu(*(__be64 *)node->data ^
 181                                        *(__be64 *)key->data);
 182
 183                 prefixlen = 64 - fls64(diff);
 184                 if (prefixlen >= limit)
 185                         return limit;
 186                 if (diff)
 187                         return prefixlen;
 188                 i = 8;
 189         }
 190 #endif
 191
 192         while (trie->data_size >= i + 4) {
 193                 u32 diff = be32_to_cpu(*(__be32 *)&node->data[i] ^
 194                                        *(__be32 *)&key->data[i]);
 195
 196                 prefixlen += 32 - fls(diff);
 197                 if (prefixlen >= limit)
 198                         return limit;
 199                 if (diff)
 200                         return prefixlen;
 201                 i += 4;
 202         }
 203
 204         if (trie->data_size >= i + 2) {
 205                 u16 diff = be16_to_cpu(*(__be16 *)&node->data[i] ^
 206                                        *(__be16 *)&key->data[i]);
 207
 208                 prefixlen += 16 - fls(diff);
 209                 if (prefixlen >= limit)
 210                         return limit;
 211                 if (diff)
 212                         return prefixlen;
 213                 i += 2;
 214         }
 215
 216         if (trie->data_size >= i + 1) {
 217                 prefixlen += 8 - fls(node->data[i] ^ key->data[i]);
 218
 219                 if (prefixlen >= limit)
 220                         return limit;
 221         }
 222
 223         return prefixlen;
 224 }
 225
 226 /* Called from syscall or from eBPF program */
 227 static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 228 {
 229         struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
 230         struct lpm_trie_node *node, *found = NULL;
 231         struct bpf_lpm_trie_key *key = _key;
 232
 233         /* Start walking the trie from the root node ... */
 234
 235         for (node = rcu_dereference(trie->root); node;) {
 236                 unsigned int next_bit;
 237                 size_t matchlen;
 238
 239                 /* Determine the longest prefix of @node that matches @key.
 240                  * If it's the maximum possible prefix for this trie, we have
 241                  * an exact match and can return it directly.
 242                  */
 243                 matchlen = longest_prefix_match(trie, node, key);
 244                 if (matchlen == trie->max_prefixlen) {
 245                         found = node;
 246                         break;
 247                 }
 248
 249                 /* If the number of bits that match is smaller than the prefix
 250                  * length of @node, bail out and return the node we have seen
 251                  * last in the traversal (ie, the parent).
 252                  */
 253                 if (matchlen < node->prefixlen)
 254                         break;
 255
 256                 /* Consider this node as return candidate unless it is an
 257                  * artificially added intermediate one.
 258                  */
 259                 if (!(node->flags & LPM_TREE_NODE_FLAG_IM))
 260                         found = node;
 261
 262                 /* If the node match is fully satisfied, let's see if we can
 263                  * become more specific. Determine the next bit in the key and
 264                  * traverse down.
 265                  */
 266                 next_bit = extract_bit(key->data, node->prefixlen);
 267                 node = rcu_dereference(node->child[next_bit]);
 268         }
 269
 270         if (!found)
 271                 return NULL;
 272
 273         return found->data + trie->data_size;
 274 }
 275
 276 static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie,
 277                                                  const void *value)
 278 {
 279         struct lpm_trie_node *node;
 280         size_t size = sizeof(struct lpm_trie_node) + trie->data_size;
 281
 282         if (value)
 283                 size += trie->map.value_size;
 284
 285         node = bpf_map_kmalloc_node(&trie->map, size, GFP_ATOMIC | __GFP_NOWARN,
 286                                     trie->map.numa_node);
 287         if (!node)
 288                 return NULL;
 289
 290         node->flags = 0;
 291
 292         if (value)
 293                 memcpy(node->data + trie->data_size, value,
 294                        trie->map.value_size);
 295
 296         return node;
 297 }
 298
 299 /* Called from syscall or from eBPF program */
 300 static int trie_update_elem(struct bpf_map *map,
 301                             void *_key, void *value, u64 flags)
 302 {
 303         struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
 304         struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL;
 305         struct lpm_trie_node __rcu **slot;
 306         struct bpf_lpm_trie_key *key = _key;
 307         unsigned long irq_flags;
 308         unsigned int next_bit;
 309         size_t matchlen = 0;
 310         int ret = 0;
 311
 312         if (unlikely(flags > BPF_EXIST))
 313                 return -EINVAL;
 314
 315         if (key->prefixlen > trie->max_prefixlen)
 316                 return -EINVAL;
 317
 318         spin_lock_irqsave(&trie->lock, irq_flags);
 319
 320         /* Allocate and fill a new node */
 321
 322         if (trie->n_entries == trie->map.max_entries) {
 323                 ret = -ENOSPC;
 324                 goto out;
 325         }
 326
 327         new_node = lpm_trie_node_alloc(trie, value);
 328         if (!new_node) {
 329                 ret = -ENOMEM;
 330                 goto out;
 331         }
 332
 333         trie->n_entries++;
 334
 335         new_node->prefixlen = key->prefixlen;
 336         RCU_INIT_POINTER(new_node->child[0], NULL);
 337         RCU_INIT_POINTER(new_node->child[1], NULL);
 338         memcpy(new_node->data, key->data, trie->data_size);
 339
 340         /* Now find a slot to attach the new node. To do that, walk the tree
 341          * from the root and match as many bits as possible for each node until
 342          * we either find an empty slot or a slot that needs to be replaced by
 343          * an intermediate node.
 344          */
 345         slot = &trie->root;
 346
 347         while ((node = rcu_dereference_protected(*slot,
 348                                         lockdep_is_held(&trie->lock)))) {
 349                 matchlen = longest_prefix_match(trie, node, key);
 350
 351                 if (node->prefixlen != matchlen ||
 352                     node->prefixlen == key->prefixlen ||
 353                     node->prefixlen == trie->max_prefixlen)
 354                         break;
 355
 356                 next_bit = extract_bit(key->data, node->prefixlen);
 357                 slot = &node->child[next_bit];
 358         }
 359
 360         /* If the slot is empty (a free child pointer or an empty root),
 361          * simply assign the @new_node to that slot and be done.
 362          */
 363         if (!node) {
 364                 rcu_assign_pointer(*slot, new_node);
 365                 goto out;
 366         }
 367
 368         /* If the slot we picked already exists, replace it with @new_node
 369          * which already has the correct data array set.
 370          */
 371         if (node->prefixlen == matchlen) {
 372                 new_node->child[0] = node->child[0];
 373                 new_node->child[1] = node->child[1];
 374
 375                 if (!(node->flags & LPM_TREE_NODE_FLAG_IM))
 376                         trie->n_entries--;
 377
 378                 rcu_assign_pointer(*slot, new_node);
 379                 kfree_rcu(node, rcu);
 380
 381                 goto out;
 382         }
 383
 384         /* If the new node matches the prefix completely, it must be inserted
 385          * as an ancestor. Simply insert it between @node and *@slot.
 386          */
 387         if (matchlen == key->prefixlen) {
 388                 next_bit = extract_bit(node->data, matchlen);
 389                 rcu_assign_pointer(new_node->child[next_bit], node);
 390                 rcu_assign_pointer(*slot, new_node);
 391                 goto out;
 392         }
 393
 394         im_node = lpm_trie_node_alloc(trie, NULL);
 395         if (!im_node) {
 396                 ret = -ENOMEM;
 397                 goto out;
 398         }
 399
 400         im_node->prefixlen = matchlen;
 401         im_node->flags |= LPM_TREE_NODE_FLAG_IM;
 402         memcpy(im_node->data, node->data, trie->data_size);
 403
 404         /* Now determine which child to install in which slot */
 405         if (extract_bit(key->data, matchlen)) {
 406                 rcu_assign_pointer(im_node->child[0], node);
 407                 rcu_assign_pointer(im_node->child[1], new_node);
 408         } else {
 409                 rcu_assign_pointer(im_node->child[0], new_node);
 410                 rcu_assign_pointer(im_node->child[1], node);
 411         }
 412
 413         /* Finally, assign the intermediate node to the determined spot */
 414         rcu_assign_pointer(*slot, im_node);
 415
 416 out:
 417         if (ret) {
 418                 if (new_node)
 419                         trie->n_entries--;
 420
 421                 kfree(new_node);
 422                 kfree(im_node);
 423         }
 424
 425         spin_unlock_irqrestore(&trie->lock, irq_flags);
 426
 427         return ret;
 428 }
 429
 430 /* Called from syscall or from eBPF program */
 431 static int trie_delete_elem(struct bpf_map *map, void *_key)
 432 {
 433         struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
 434         struct bpf_lpm_trie_key *key = _key;
 435         struct lpm_trie_node __rcu **trim, **trim2;
 436         struct lpm_trie_node *node, *parent;
 437         unsigned long irq_flags;
 438         unsigned int next_bit;
 439         size_t matchlen = 0;
 440         int ret = 0;
 441
 442         if (key->prefixlen > trie->max_prefixlen)
 443                 return -EINVAL;
 444
 445         spin_lock_irqsave(&trie->lock, irq_flags);
 446
 447         /* Walk the tree looking for an exact key/length match and keeping
 448          * track of the path we traverse.  We will need to know the node
 449          * we wish to delete, and the slot that points to the node we want
 450          * to delete.  We may also need to know the nodes parent and the
 451          * slot that contains it.
 452          */
 453         trim = &trie->root;
 454         trim2 = trim;
 455         parent = NULL;
 456         while ((node = rcu_dereference_protected(
 457                        *trim, lockdep_is_held(&trie->lock)))) {
 458                 matchlen = longest_prefix_match(trie, node, key);
 459
 460                 if (node->prefixlen != matchlen ||
 461                     node->prefixlen == key->prefixlen)
 462                         break;
 463
 464                 parent = node;
 465                 trim2 = trim;
 466                 next_bit = extract_bit(key->data, node->prefixlen);
 467                 trim = &node->child[next_bit];
 468         }
 469
 470         if (!node || node->prefixlen != key->prefixlen ||
 471             node->prefixlen != matchlen ||
 472             (node->flags & LPM_TREE_NODE_FLAG_IM)) {
 473                 ret = -ENOENT;
 474                 goto out;
 475         }
 476
 477         trie->n_entries--;
 478
 479         /* If the node we are removing has two children, simply mark it
 480          * as intermediate and we are done.
 481          */
 482         if (rcu_access_pointer(node->child[0]) &&
 483             rcu_access_pointer(node->child[1])) {
 484                 node->flags |= LPM_TREE_NODE_FLAG_IM;
 485                 goto out;
 486         }
 487
 488         /* If the parent of the node we are about to delete is an intermediate
 489          * node, and the deleted node doesn't have any children, we can delete
 490          * the intermediate parent as well and promote its other child
 491          * up the tree.  Doing this maintains the invariant that all
 492          * intermediate nodes have exactly 2 children and that there are no
 493          * unnecessary intermediate nodes in the tree.
 494          */
 495         if (parent && (parent->flags & LPM_TREE_NODE_FLAG_IM) &&
 496             !node->child[0] && !node->child[1]) {
 497                 if (node == rcu_access_pointer(parent->child[0]))
 498                         rcu_assign_pointer(
 499                                 *trim2, rcu_access_pointer(parent->child[1]));
 500                 else
 501                         rcu_assign_pointer(
 502                                 *trim2, rcu_access_pointer(parent->child[0]));
 503                 kfree_rcu(parent, rcu);
 504                 kfree_rcu(node, rcu);
 505                 goto out;
 506         }
 507
 508         /* The node we are removing has either zero or one child. If there
 509          * is a child, move it into the removed node's slot then delete
 510          * the node.  Otherwise just clear the slot and delete the node.
 511          */
 512         if (node->child[0])
 513                 rcu_assign_pointer(*trim, rcu_access_pointer(node->child[0]));
 514         else if (node->child[1])
 515                 rcu_assign_pointer(*trim, rcu_access_pointer(node->child[1]));
 516         else
 517                 RCU_INIT_POINTER(*trim, NULL);
 518         kfree_rcu(node, rcu);
 519
 520 out:
 521         spin_unlock_irqrestore(&trie->lock, irq_flags);
 522
 523         return ret;
 524 }
 525
 526 #define LPM_DATA_SIZE_MAX       256
 527 #define LPM_DATA_SIZE_MIN       1
 528
 529 #define LPM_VAL_SIZE_MAX        (KMALLOC_MAX_SIZE - LPM_DATA_SIZE_MAX - \
 530                                  sizeof(struct lpm_trie_node))
 531 #define LPM_VAL_SIZE_MIN        1
 532
 533 #define LPM_KEY_SIZE(X)         (sizeof(struct bpf_lpm_trie_key) + (X))
 534 #define LPM_KEY_SIZE_MAX        LPM_KEY_SIZE(LPM_DATA_SIZE_MAX)
 535 #define LPM_KEY_SIZE_MIN        LPM_KEY_SIZE(LPM_DATA_SIZE_MIN)
 536
 537 #define LPM_CREATE_FLAG_MASK    (BPF_F_NO_PREALLOC | BPF_F_NUMA_NODE |  \
 538                                  BPF_F_ACCESS_MASK)
 539
 540 static struct bpf_map *trie_alloc(union bpf_attr *attr)
 541 {
 542         struct lpm_trie *trie;
 543
 544         if (!bpf_capable())
 545                 return ERR_PTR(-EPERM);
 546
 547         /* check sanity of attributes */
 548         if (attr->max_entries == 0 ||
 549             !(attr->map_flags & BPF_F_NO_PREALLOC) ||
 550             attr->map_flags & ~LPM_CREATE_FLAG_MASK ||
 551             !bpf_map_flags_access_ok(attr->map_flags) ||
 552             attr->key_size < LPM_KEY_SIZE_MIN ||
 553             attr->key_size > LPM_KEY_SIZE_MAX ||
 554             attr->value_size < LPM_VAL_SIZE_MIN ||
 555             attr->value_size > LPM_VAL_SIZE_MAX)
 556                 return ERR_PTR(-EINVAL);
 557
 558         trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
 559         if (!trie)
 560                 return ERR_PTR(-ENOMEM);
 561
 562         /* copy mandatory map attributes */
 563         bpf_map_init_from_attr(&trie->map, attr);
 564         trie->data_size = attr->key_size -
 565                           offsetof(struct bpf_lpm_trie_key, data);
 566         trie->max_prefixlen = trie->data_size * 8;
 567
 568         spin_lock_init(&trie->lock);
 569
 570         return &trie->map;
 571 }
 572
 573 static void trie_free(struct bpf_map *map)
 574 {
 575         struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
 576         struct lpm_trie_node __rcu **slot;
 577         struct lpm_trie_node *node;
 578
 579         /* Always start at the root and walk down to a node that has no
 580          * children. Then free that node, nullify its reference in the parent
 581          * and start over.
 582          */
 583
 584         for (;;) {
 585                 slot = &trie->root;
 586
 587                 for (;;) {
 588                         node = rcu_dereference_protected(*slot, 1);
 589                         if (!node)
 590                                 goto out;
 591
 592                         if (rcu_access_pointer(node->child[0])) {
 593                                 slot = &node->child[0];
 594                                 continue;
 595                         }
 596
 597                         if (rcu_access_pointer(node->child[1])) {
 598                                 slot = &node->child[1];
 599                                 continue;
 600                         }
 601
 602                         kfree(node);
 603                         RCU_INIT_POINTER(*slot, NULL);
 604                         break;
 605                 }
 606         }
 607
 608 out:
 609         kfree(trie);
 610 }
 611
 612 static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key)
 613 {
 614         struct lpm_trie_node *node, *next_node = NULL, *parent, *search_root;
 615         struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
 616         struct bpf_lpm_trie_key *key = _key, *next_key = _next_key;
 617         struct lpm_trie_node **node_stack = NULL;
 618         int err = 0, stack_ptr = -1;
 619         unsigned int next_bit;
 620         size_t matchlen;
 621
 622         /* The get_next_key follows postorder. For the 4 node example in
 623          * the top of this file, the trie_get_next_key() returns the following
 624          * one after another:
 625          *   192.168.0.0/24
 626          *   192.168.1.0/24
 627          *   192.168.128.0/24
 628          *   192.168.0.0/16
 629          *
 630          * The idea is to return more specific keys before less specific ones.
 631          */
 632
 633         /* Empty trie */
 634         search_root = rcu_dereference(trie->root);
 635         if (!search_root)
 636                 return -ENOENT;
 637
 638         /* For invalid key, find the leftmost node in the trie */
 639         if (!key || key->prefixlen > trie->max_prefixlen)
 640                 goto find_leftmost;
 641
 642         node_stack = kmalloc_array(trie->max_prefixlen,
 643                                    sizeof(struct lpm_trie_node *),
 644                                    GFP_ATOMIC | __GFP_NOWARN);
 645         if (!node_stack)
 646                 return -ENOMEM;
 647
 648         /* Try to find the exact node for the given key */
 649         for (node = search_root; node;) {
 650                 node_stack[++stack_ptr] = node;
 651                 matchlen = longest_prefix_match(trie, node, key);
 652                 if (node->prefixlen != matchlen ||
 653                     node->prefixlen == key->prefixlen)
 654                         break;
 655
 656                 next_bit = extract_bit(key->data, node->prefixlen);
 657                 node = rcu_dereference(node->child[next_bit]);
 658         }
 659         if (!node || node->prefixlen != key->prefixlen ||
 660             (node->flags & LPM_TREE_NODE_FLAG_IM))
 661                 goto find_leftmost;
 662
 663         /* The node with the exactly-matching key has been found,
 664          * find the first node in postorder after the matched node.
 665          */
 666         node = node_stack[stack_ptr];
 667         while (stack_ptr > 0) {
 668                 parent = node_stack[stack_ptr - 1];
 669                 if (rcu_dereference(parent->child[0]) == node) {
 670                         search_root = rcu_dereference(parent->child[1]);
 671                         if (search_root)
 672                                 goto find_leftmost;
 673                 }
 674                 if (!(parent->flags & LPM_TREE_NODE_FLAG_IM)) {
 675                         next_node = parent;
 676                         goto do_copy;
 677                 }
 678
 679                 node = parent;
 680                 stack_ptr--;
 681         }
 682
 683         /* did not find anything */
 684         err = -ENOENT;
 685         goto free_stack;
 686
 687 find_leftmost:
 688         /* Find the leftmost non-intermediate node, all intermediate nodes
 689          * have exact two children, so this function will never return NULL.
 690          */
 691         for (node = search_root; node;) {
 692                 if (node->flags & LPM_TREE_NODE_FLAG_IM) {
 693                         node = rcu_dereference(node->child[0]);
 694                 } else {
 695                         next_node = node;
 696                         node = rcu_dereference(node->child[0]);
 697                         if (!node)
 698                                 node = rcu_dereference(next_node->child[1]);
 699                 }
 700         }
 701 do_copy:
 702         next_key->prefixlen = next_node->prefixlen;
 703         memcpy((void *)next_key + offsetof(struct bpf_lpm_trie_key, data),
 704                next_node->data, trie->data_size);
 705 free_stack:
 706         kfree(node_stack);
 707         return err;
 708 }
 709
 710 static int trie_check_btf(const struct bpf_map *map,
 711                           const struct btf *btf,
 712                           const struct btf_type *key_type,
 713                           const struct btf_type *value_type)
 714 {
 715         /* Keys must have struct bpf_lpm_trie_key embedded. */
 716         return BTF_INFO_KIND(key_type->info) != BTF_KIND_STRUCT ?
 717                -EINVAL : 0;
 718 }
 719
 720 static int trie_map_btf_id;
 721 const struct bpf_map_ops trie_map_ops = {
 722         .map_meta_equal = bpf_map_meta_equal,
 723         .map_alloc = trie_alloc,
 724         .map_free = trie_free,
 725         .map_get_next_key = trie_get_next_key,
 726         .map_lookup_elem = trie_lookup_elem,
 727         .map_update_elem = trie_update_elem,
 728         .map_delete_elem = trie_delete_elem,
 729         .map_check_btf = trie_check_btf,
 730         .map_btf_name = "lpm_trie",
 731         .map_btf_id = &trie_map_btf_id,
 732 };