517 строки
14 KiB
C
517 строки
14 KiB
C
/*
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* Longest prefix match list implementation
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*
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* Copyright (c) 2016,2017 Daniel Mack
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* Copyright (c) 2016 David Herrmann
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*
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* This file is subject to the terms and conditions of version 2 of the GNU
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* General Public License. See the file COPYING in the main directory of the
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* Linux distribution for more details.
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*/
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#include <linux/bpf.h>
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#include <linux/err.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/vmalloc.h>
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#include <net/ipv6.h>
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/* Intermediate node */
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#define LPM_TREE_NODE_FLAG_IM BIT(0)
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struct lpm_trie_node;
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struct lpm_trie_node {
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struct rcu_head rcu;
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struct lpm_trie_node __rcu *child[2];
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u32 prefixlen;
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u32 flags;
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u8 data[0];
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};
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struct lpm_trie {
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struct bpf_map map;
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struct lpm_trie_node __rcu *root;
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size_t n_entries;
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size_t max_prefixlen;
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size_t data_size;
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raw_spinlock_t lock;
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};
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/* This trie implements a longest prefix match algorithm that can be used to
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* match IP addresses to a stored set of ranges.
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*
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* Data stored in @data of struct bpf_lpm_key and struct lpm_trie_node is
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* interpreted as big endian, so data[0] stores the most significant byte.
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*
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* Match ranges are internally stored in instances of struct lpm_trie_node
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* which each contain their prefix length as well as two pointers that may
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* lead to more nodes containing more specific matches. Each node also stores
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* a value that is defined by and returned to userspace via the update_elem
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* and lookup functions.
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*
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* For instance, let's start with a trie that was created with a prefix length
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* of 32, so it can be used for IPv4 addresses, and one single element that
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* matches 192.168.0.0/16. The data array would hence contain
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* [0xc0, 0xa8, 0x00, 0x00] in big-endian notation. This documentation will
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* stick to IP-address notation for readability though.
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*
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* As the trie is empty initially, the new node (1) will be places as root
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* node, denoted as (R) in the example below. As there are no other node, both
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* child pointers are %NULL.
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*
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* +----------------+
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* | (1) (R) |
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* | 192.168.0.0/16 |
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* | value: 1 |
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* | [0] [1] |
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* +----------------+
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*
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* Next, let's add a new node (2) matching 192.168.0.0/24. As there is already
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* a node with the same data and a smaller prefix (ie, a less specific one),
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* node (2) will become a child of (1). In child index depends on the next bit
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* that is outside of what (1) matches, and that bit is 0, so (2) will be
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* child[0] of (1):
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*
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* +----------------+
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* | (1) (R) |
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* | 192.168.0.0/16 |
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* | value: 1 |
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* | [0] [1] |
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* +----------------+
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* |
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* +----------------+
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* | (2) |
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* | 192.168.0.0/24 |
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* | value: 2 |
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* | [0] [1] |
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* +----------------+
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*
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* The child[1] slot of (1) could be filled with another node which has bit #17
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* (the next bit after the ones that (1) matches on) set to 1. For instance,
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* 192.168.128.0/24:
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*
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* +----------------+
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* | (1) (R) |
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* | 192.168.0.0/16 |
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* | value: 1 |
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* | [0] [1] |
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* +----------------+
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* | |
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* +----------------+ +------------------+
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* | (2) | | (3) |
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* | 192.168.0.0/24 | | 192.168.128.0/24 |
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* | value: 2 | | value: 3 |
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* | [0] [1] | | [0] [1] |
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* +----------------+ +------------------+
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*
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* Let's add another node (4) to the game for 192.168.1.0/24. In order to place
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* it, node (1) is looked at first, and because (4) of the semantics laid out
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* above (bit #17 is 0), it would normally be attached to (1) as child[0].
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* However, that slot is already allocated, so a new node is needed in between.
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* That node does not have a value attached to it and it will never be
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* returned to users as result of a lookup. It is only there to differentiate
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* the traversal further. It will get a prefix as wide as necessary to
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* distinguish its two children:
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*
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* +----------------+
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* | (1) (R) |
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* | 192.168.0.0/16 |
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* | value: 1 |
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* | [0] [1] |
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* +----------------+
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* | |
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* +----------------+ +------------------+
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* | (4) (I) | | (3) |
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* | 192.168.0.0/23 | | 192.168.128.0/24 |
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* | value: --- | | value: 3 |
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* | [0] [1] | | [0] [1] |
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* +----------------+ +------------------+
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* | |
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* +----------------+ +----------------+
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* | (2) | | (5) |
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* | 192.168.0.0/24 | | 192.168.1.0/24 |
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* | value: 2 | | value: 5 |
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* | [0] [1] | | [0] [1] |
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* +----------------+ +----------------+
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*
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* 192.168.1.1/32 would be a child of (5) etc.
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*
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* An intermediate node will be turned into a 'real' node on demand. In the
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* example above, (4) would be re-used if 192.168.0.0/23 is added to the trie.
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*
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* A fully populated trie would have a height of 32 nodes, as the trie was
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* created with a prefix length of 32.
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*
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* The lookup starts at the root node. If the current node matches and if there
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* is a child that can be used to become more specific, the trie is traversed
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* downwards. The last node in the traversal that is a non-intermediate one is
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* returned.
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*/
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static inline int extract_bit(const u8 *data, size_t index)
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{
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return !!(data[index / 8] & (1 << (7 - (index % 8))));
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}
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/**
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* longest_prefix_match() - determine the longest prefix
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* @trie: The trie to get internal sizes from
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* @node: The node to operate on
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* @key: The key to compare to @node
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*
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* Determine the longest prefix of @node that matches the bits in @key.
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*/
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static size_t longest_prefix_match(const struct lpm_trie *trie,
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const struct lpm_trie_node *node,
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const struct bpf_lpm_trie_key *key)
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{
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size_t prefixlen = 0;
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size_t i;
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for (i = 0; i < trie->data_size; i++) {
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size_t b;
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b = 8 - fls(node->data[i] ^ key->data[i]);
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prefixlen += b;
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if (prefixlen >= node->prefixlen || prefixlen >= key->prefixlen)
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return min(node->prefixlen, key->prefixlen);
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if (b < 8)
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break;
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}
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return prefixlen;
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}
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/* Called from syscall or from eBPF program */
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static void *trie_lookup_elem(struct bpf_map *map, void *_key)
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{
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struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
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struct lpm_trie_node *node, *found = NULL;
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struct bpf_lpm_trie_key *key = _key;
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/* Start walking the trie from the root node ... */
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for (node = rcu_dereference(trie->root); node;) {
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unsigned int next_bit;
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size_t matchlen;
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/* Determine the longest prefix of @node that matches @key.
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* If it's the maximum possible prefix for this trie, we have
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* an exact match and can return it directly.
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*/
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matchlen = longest_prefix_match(trie, node, key);
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if (matchlen == trie->max_prefixlen) {
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found = node;
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break;
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}
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/* If the number of bits that match is smaller than the prefix
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* length of @node, bail out and return the node we have seen
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* last in the traversal (ie, the parent).
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*/
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if (matchlen < node->prefixlen)
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break;
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/* Consider this node as return candidate unless it is an
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* artificially added intermediate one.
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*/
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if (!(node->flags & LPM_TREE_NODE_FLAG_IM))
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found = node;
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/* If the node match is fully satisfied, let's see if we can
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* become more specific. Determine the next bit in the key and
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* traverse down.
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*/
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next_bit = extract_bit(key->data, node->prefixlen);
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node = rcu_dereference(node->child[next_bit]);
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}
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if (!found)
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return NULL;
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return found->data + trie->data_size;
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}
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static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie,
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const void *value)
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{
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struct lpm_trie_node *node;
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size_t size = sizeof(struct lpm_trie_node) + trie->data_size;
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if (value)
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size += trie->map.value_size;
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node = kmalloc(size, GFP_ATOMIC | __GFP_NOWARN);
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if (!node)
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return NULL;
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node->flags = 0;
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if (value)
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memcpy(node->data + trie->data_size, value,
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trie->map.value_size);
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return node;
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}
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/* Called from syscall or from eBPF program */
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static int trie_update_elem(struct bpf_map *map,
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void *_key, void *value, u64 flags)
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{
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struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
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struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL;
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struct lpm_trie_node __rcu **slot;
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struct bpf_lpm_trie_key *key = _key;
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unsigned long irq_flags;
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unsigned int next_bit;
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size_t matchlen = 0;
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int ret = 0;
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if (unlikely(flags > BPF_EXIST))
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return -EINVAL;
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if (key->prefixlen > trie->max_prefixlen)
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return -EINVAL;
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raw_spin_lock_irqsave(&trie->lock, irq_flags);
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/* Allocate and fill a new node */
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if (trie->n_entries == trie->map.max_entries) {
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ret = -ENOSPC;
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goto out;
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}
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new_node = lpm_trie_node_alloc(trie, value);
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if (!new_node) {
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ret = -ENOMEM;
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goto out;
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}
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trie->n_entries++;
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new_node->prefixlen = key->prefixlen;
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RCU_INIT_POINTER(new_node->child[0], NULL);
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RCU_INIT_POINTER(new_node->child[1], NULL);
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memcpy(new_node->data, key->data, trie->data_size);
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/* Now find a slot to attach the new node. To do that, walk the tree
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* from the root and match as many bits as possible for each node until
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* we either find an empty slot or a slot that needs to be replaced by
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* an intermediate node.
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*/
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slot = &trie->root;
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while ((node = rcu_dereference_protected(*slot,
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lockdep_is_held(&trie->lock)))) {
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matchlen = longest_prefix_match(trie, node, key);
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if (node->prefixlen != matchlen ||
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node->prefixlen == key->prefixlen ||
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node->prefixlen == trie->max_prefixlen)
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break;
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next_bit = extract_bit(key->data, node->prefixlen);
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slot = &node->child[next_bit];
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}
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/* If the slot is empty (a free child pointer or an empty root),
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* simply assign the @new_node to that slot and be done.
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*/
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if (!node) {
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rcu_assign_pointer(*slot, new_node);
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goto out;
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}
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/* If the slot we picked already exists, replace it with @new_node
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* which already has the correct data array set.
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*/
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if (node->prefixlen == matchlen) {
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new_node->child[0] = node->child[0];
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new_node->child[1] = node->child[1];
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if (!(node->flags & LPM_TREE_NODE_FLAG_IM))
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trie->n_entries--;
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rcu_assign_pointer(*slot, new_node);
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kfree_rcu(node, rcu);
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goto out;
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}
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/* If the new node matches the prefix completely, it must be inserted
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* as an ancestor. Simply insert it between @node and *@slot.
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*/
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if (matchlen == key->prefixlen) {
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next_bit = extract_bit(node->data, matchlen);
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rcu_assign_pointer(new_node->child[next_bit], node);
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rcu_assign_pointer(*slot, new_node);
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goto out;
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}
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im_node = lpm_trie_node_alloc(trie, NULL);
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if (!im_node) {
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ret = -ENOMEM;
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goto out;
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}
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im_node->prefixlen = matchlen;
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im_node->flags |= LPM_TREE_NODE_FLAG_IM;
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memcpy(im_node->data, node->data, trie->data_size);
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/* Now determine which child to install in which slot */
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if (extract_bit(key->data, matchlen)) {
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rcu_assign_pointer(im_node->child[0], node);
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rcu_assign_pointer(im_node->child[1], new_node);
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} else {
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rcu_assign_pointer(im_node->child[0], new_node);
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rcu_assign_pointer(im_node->child[1], node);
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}
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/* Finally, assign the intermediate node to the determined spot */
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rcu_assign_pointer(*slot, im_node);
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out:
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if (ret) {
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if (new_node)
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trie->n_entries--;
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kfree(new_node);
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kfree(im_node);
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}
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raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
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return ret;
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}
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static int trie_delete_elem(struct bpf_map *map, void *key)
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{
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/* TODO */
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return -ENOSYS;
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}
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#define LPM_DATA_SIZE_MAX 256
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#define LPM_DATA_SIZE_MIN 1
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#define LPM_VAL_SIZE_MAX (KMALLOC_MAX_SIZE - LPM_DATA_SIZE_MAX - \
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sizeof(struct lpm_trie_node))
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#define LPM_VAL_SIZE_MIN 1
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#define LPM_KEY_SIZE(X) (sizeof(struct bpf_lpm_trie_key) + (X))
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#define LPM_KEY_SIZE_MAX LPM_KEY_SIZE(LPM_DATA_SIZE_MAX)
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#define LPM_KEY_SIZE_MIN LPM_KEY_SIZE(LPM_DATA_SIZE_MIN)
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static struct bpf_map *trie_alloc(union bpf_attr *attr)
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{
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struct lpm_trie *trie;
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u64 cost = sizeof(*trie), cost_per_node;
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int ret;
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if (!capable(CAP_SYS_ADMIN))
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return ERR_PTR(-EPERM);
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/* check sanity of attributes */
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if (attr->max_entries == 0 ||
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attr->map_flags != BPF_F_NO_PREALLOC ||
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attr->key_size < LPM_KEY_SIZE_MIN ||
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attr->key_size > LPM_KEY_SIZE_MAX ||
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attr->value_size < LPM_VAL_SIZE_MIN ||
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attr->value_size > LPM_VAL_SIZE_MAX)
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return ERR_PTR(-EINVAL);
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trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN);
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if (!trie)
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return ERR_PTR(-ENOMEM);
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/* copy mandatory map attributes */
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trie->map.map_type = attr->map_type;
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trie->map.key_size = attr->key_size;
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trie->map.value_size = attr->value_size;
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trie->map.max_entries = attr->max_entries;
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trie->map.map_flags = attr->map_flags;
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trie->data_size = attr->key_size -
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offsetof(struct bpf_lpm_trie_key, data);
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trie->max_prefixlen = trie->data_size * 8;
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cost_per_node = sizeof(struct lpm_trie_node) +
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attr->value_size + trie->data_size;
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cost += (u64) attr->max_entries * cost_per_node;
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if (cost >= U32_MAX - PAGE_SIZE) {
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ret = -E2BIG;
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goto out_err;
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}
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trie->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
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ret = bpf_map_precharge_memlock(trie->map.pages);
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if (ret)
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goto out_err;
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raw_spin_lock_init(&trie->lock);
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return &trie->map;
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out_err:
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kfree(trie);
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return ERR_PTR(ret);
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}
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static void trie_free(struct bpf_map *map)
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{
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struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
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struct lpm_trie_node __rcu **slot;
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struct lpm_trie_node *node;
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raw_spin_lock(&trie->lock);
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/* Always start at the root and walk down to a node that has no
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* children. Then free that node, nullify its reference in the parent
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* and start over.
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*/
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for (;;) {
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slot = &trie->root;
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for (;;) {
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node = rcu_dereference_protected(*slot,
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lockdep_is_held(&trie->lock));
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if (!node)
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goto unlock;
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if (rcu_access_pointer(node->child[0])) {
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slot = &node->child[0];
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continue;
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}
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if (rcu_access_pointer(node->child[1])) {
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slot = &node->child[1];
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continue;
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}
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kfree(node);
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RCU_INIT_POINTER(*slot, NULL);
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break;
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}
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}
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unlock:
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raw_spin_unlock(&trie->lock);
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}
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static int trie_get_next_key(struct bpf_map *map, void *key, void *next_key)
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|
{
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|
return -ENOTSUPP;
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|
}
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|
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const struct bpf_map_ops trie_map_ops = {
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.map_alloc = trie_alloc,
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|
.map_free = trie_free,
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|
.map_get_next_key = trie_get_next_key,
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|
.map_lookup_elem = trie_lookup_elem,
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|
.map_update_elem = trie_update_elem,
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|
.map_delete_elem = trie_delete_elem,
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|
};
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