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Linux/net/netfilter/nft_set_bitmap.c

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  1 /*
  2  * Copyright (c) 2017 Pablo Neira Ayuso <pablo@netfilter.org>
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU General Public License version 2 as
  6  * published by the Free Software Foundation.
  7  */
  8 
  9 #include <linux/kernel.h>
 10 #include <linux/init.h>
 11 #include <linux/module.h>
 12 #include <linux/list.h>
 13 #include <linux/netlink.h>
 14 #include <linux/netfilter.h>
 15 #include <linux/netfilter/nf_tables.h>
 16 #include <net/netfilter/nf_tables.h>
 17 
 18 struct nft_bitmap_elem {
 19         struct list_head        head;
 20         struct nft_set_ext      ext;
 21 };
 22 
 23 /* This bitmap uses two bits to represent one element. These two bits determine
 24  * the element state in the current and the future generation.
 25  *
 26  * An element can be in three states. The generation cursor is represented using
 27  * the ^ character, note that this cursor shifts on every succesful transaction.
 28  * If no transaction is going on, we observe all elements are in the following
 29  * state:
 30  *
 31  * 11 = this element is active in the current generation. In case of no updates,
 32  * ^    it stays active in the next generation.
 33  * 00 = this element is inactive in the current generation. In case of no
 34  * ^    updates, it stays inactive in the next generation.
 35  *
 36  * On transaction handling, we observe these two temporary states:
 37  *
 38  * 01 = this element is inactive in the current generation and it becomes active
 39  * ^    in the next one. This happens when the element is inserted but commit
 40  *      path has not yet been executed yet, so activation is still pending. On
 41  *      transaction abortion, the element is removed.
 42  * 10 = this element is active in the current generation and it becomes inactive
 43  * ^    in the next one. This happens when the element is deactivated but commit
 44  *      path has not yet been executed yet, so removal is still pending. On
 45  *      transation abortion, the next generation bit is reset to go back to
 46  *      restore its previous state.
 47  */
 48 struct nft_bitmap {
 49         struct  list_head       list;
 50         u16                     bitmap_size;
 51         u8                      bitmap[];
 52 };
 53 
 54 static inline void nft_bitmap_location(const struct nft_set *set,
 55                                        const void *key,
 56                                        u32 *idx, u32 *off)
 57 {
 58         u32 k;
 59 
 60         if (set->klen == 2)
 61                 k = *(u16 *)key;
 62         else
 63                 k = *(u8 *)key;
 64         k <<= 1;
 65 
 66         *idx = k / BITS_PER_BYTE;
 67         *off = k % BITS_PER_BYTE;
 68 }
 69 
 70 /* Fetch the two bits that represent the element and check if it is active based
 71  * on the generation mask.
 72  */
 73 static inline bool
 74 nft_bitmap_active(const u8 *bitmap, u32 idx, u32 off, u8 genmask)
 75 {
 76         return (bitmap[idx] & (0x3 << off)) & (genmask << off);
 77 }
 78 
 79 static bool nft_bitmap_lookup(const struct net *net, const struct nft_set *set,
 80                               const u32 *key, const struct nft_set_ext **ext)
 81 {
 82         const struct nft_bitmap *priv = nft_set_priv(set);
 83         u8 genmask = nft_genmask_cur(net);
 84         u32 idx, off;
 85 
 86         nft_bitmap_location(set, key, &idx, &off);
 87 
 88         return nft_bitmap_active(priv->bitmap, idx, off, genmask);
 89 }
 90 
 91 static struct nft_bitmap_elem *
 92 nft_bitmap_elem_find(const struct nft_set *set, struct nft_bitmap_elem *this,
 93                      u8 genmask)
 94 {
 95         const struct nft_bitmap *priv = nft_set_priv(set);
 96         struct nft_bitmap_elem *be;
 97 
 98         list_for_each_entry_rcu(be, &priv->list, head) {
 99                 if (memcmp(nft_set_ext_key(&be->ext),
100                            nft_set_ext_key(&this->ext), set->klen) ||
101                     !nft_set_elem_active(&be->ext, genmask))
102                         continue;
103 
104                 return be;
105         }
106         return NULL;
107 }
108 
109 static int nft_bitmap_insert(const struct net *net, const struct nft_set *set,
110                              const struct nft_set_elem *elem,
111                              struct nft_set_ext **ext)
112 {
113         struct nft_bitmap *priv = nft_set_priv(set);
114         struct nft_bitmap_elem *new = elem->priv, *be;
115         u8 genmask = nft_genmask_next(net);
116         u32 idx, off;
117 
118         be = nft_bitmap_elem_find(set, new, genmask);
119         if (be) {
120                 *ext = &be->ext;
121                 return -EEXIST;
122         }
123 
124         nft_bitmap_location(set, nft_set_ext_key(&new->ext), &idx, &off);
125         /* Enter 01 state. */
126         priv->bitmap[idx] |= (genmask << off);
127         list_add_tail_rcu(&new->head, &priv->list);
128 
129         return 0;
130 }
131 
132 static void nft_bitmap_remove(const struct net *net,
133                               const struct nft_set *set,
134                               const struct nft_set_elem *elem)
135 {
136         struct nft_bitmap *priv = nft_set_priv(set);
137         struct nft_bitmap_elem *be = elem->priv;
138         u8 genmask = nft_genmask_next(net);
139         u32 idx, off;
140 
141         nft_bitmap_location(set, nft_set_ext_key(&be->ext), &idx, &off);
142         /* Enter 00 state. */
143         priv->bitmap[idx] &= ~(genmask << off);
144         list_del_rcu(&be->head);
145 }
146 
147 static void nft_bitmap_activate(const struct net *net,
148                                 const struct nft_set *set,
149                                 const struct nft_set_elem *elem)
150 {
151         struct nft_bitmap *priv = nft_set_priv(set);
152         struct nft_bitmap_elem *be = elem->priv;
153         u8 genmask = nft_genmask_next(net);
154         u32 idx, off;
155 
156         nft_bitmap_location(set, nft_set_ext_key(&be->ext), &idx, &off);
157         /* Enter 11 state. */
158         priv->bitmap[idx] |= (genmask << off);
159         nft_set_elem_change_active(net, set, &be->ext);
160 }
161 
162 static bool nft_bitmap_flush(const struct net *net,
163                              const struct nft_set *set, void *_be)
164 {
165         struct nft_bitmap *priv = nft_set_priv(set);
166         u8 genmask = nft_genmask_next(net);
167         struct nft_bitmap_elem *be = _be;
168         u32 idx, off;
169 
170         nft_bitmap_location(set, nft_set_ext_key(&be->ext), &idx, &off);
171         /* Enter 10 state, similar to deactivation. */
172         priv->bitmap[idx] &= ~(genmask << off);
173         nft_set_elem_change_active(net, set, &be->ext);
174 
175         return true;
176 }
177 
178 static void *nft_bitmap_deactivate(const struct net *net,
179                                    const struct nft_set *set,
180                                    const struct nft_set_elem *elem)
181 {
182         struct nft_bitmap *priv = nft_set_priv(set);
183         struct nft_bitmap_elem *this = elem->priv, *be;
184         u8 genmask = nft_genmask_next(net);
185         u32 idx, off;
186 
187         nft_bitmap_location(set, elem->key.val.data, &idx, &off);
188 
189         be = nft_bitmap_elem_find(set, this, genmask);
190         if (!be)
191                 return NULL;
192 
193         /* Enter 10 state. */
194         priv->bitmap[idx] &= ~(genmask << off);
195         nft_set_elem_change_active(net, set, &be->ext);
196 
197         return be;
198 }
199 
200 static void nft_bitmap_walk(const struct nft_ctx *ctx,
201                             struct nft_set *set,
202                             struct nft_set_iter *iter)
203 {
204         const struct nft_bitmap *priv = nft_set_priv(set);
205         struct nft_bitmap_elem *be;
206         struct nft_set_elem elem;
207 
208         list_for_each_entry_rcu(be, &priv->list, head) {
209                 if (iter->count < iter->skip)
210                         goto cont;
211                 if (!nft_set_elem_active(&be->ext, iter->genmask))
212                         goto cont;
213 
214                 elem.priv = be;
215 
216                 iter->err = iter->fn(ctx, set, iter, &elem);
217 
218                 if (iter->err < 0)
219                         return;
220 cont:
221                 iter->count++;
222         }
223 }
224 
225 /* The bitmap size is pow(2, key length in bits) / bits per byte. This is
226  * multiplied by two since each element takes two bits. For 8 bit keys, the
227  * bitmap consumes 66 bytes. For 16 bit keys, 16388 bytes.
228  */
229 static inline u32 nft_bitmap_size(u32 klen)
230 {
231         return ((2 << ((klen * BITS_PER_BYTE) - 1)) / BITS_PER_BYTE) << 1;
232 }
233 
234 static inline u32 nft_bitmap_total_size(u32 klen)
235 {
236         return sizeof(struct nft_bitmap) + nft_bitmap_size(klen);
237 }
238 
239 static unsigned int nft_bitmap_privsize(const struct nlattr * const nla[],
240                                         const struct nft_set_desc *desc)
241 {
242         u32 klen = ntohl(nla_get_be32(nla[NFTA_SET_KEY_LEN]));
243 
244         return nft_bitmap_total_size(klen);
245 }
246 
247 static int nft_bitmap_init(const struct nft_set *set,
248                          const struct nft_set_desc *desc,
249                          const struct nlattr * const nla[])
250 {
251         struct nft_bitmap *priv = nft_set_priv(set);
252 
253         INIT_LIST_HEAD(&priv->list);
254         priv->bitmap_size = nft_bitmap_size(set->klen);
255 
256         return 0;
257 }
258 
259 static void nft_bitmap_destroy(const struct nft_set *set)
260 {
261         struct nft_bitmap *priv = nft_set_priv(set);
262         struct nft_bitmap_elem *be, *n;
263 
264         list_for_each_entry_safe(be, n, &priv->list, head)
265                 nft_set_elem_destroy(set, be, true);
266 }
267 
268 static bool nft_bitmap_estimate(const struct nft_set_desc *desc, u32 features,
269                                 struct nft_set_estimate *est)
270 {
271         /* Make sure bitmaps we don't get bitmaps larger than 16 Kbytes. */
272         if (desc->klen > 2)
273                 return false;
274 
275         est->size   = nft_bitmap_total_size(desc->klen);
276         est->lookup = NFT_SET_CLASS_O_1;
277         est->space  = NFT_SET_CLASS_O_1;
278 
279         return true;
280 }
281 
282 static struct nft_set_type nft_bitmap_type;
283 static struct nft_set_ops nft_bitmap_ops __read_mostly = {
284         .type           = &nft_bitmap_type,
285         .privsize       = nft_bitmap_privsize,
286         .elemsize       = offsetof(struct nft_bitmap_elem, ext),
287         .estimate       = nft_bitmap_estimate,
288         .init           = nft_bitmap_init,
289         .destroy        = nft_bitmap_destroy,
290         .insert         = nft_bitmap_insert,
291         .remove         = nft_bitmap_remove,
292         .deactivate     = nft_bitmap_deactivate,
293         .flush          = nft_bitmap_flush,
294         .activate       = nft_bitmap_activate,
295         .lookup         = nft_bitmap_lookup,
296         .walk           = nft_bitmap_walk,
297 };
298 
299 static struct nft_set_type nft_bitmap_type __read_mostly = {
300         .ops            = &nft_bitmap_ops,
301         .owner          = THIS_MODULE,
302 };
303 
304 static int __init nft_bitmap_module_init(void)
305 {
306         return nft_register_set(&nft_bitmap_type);
307 }
308 
309 static void __exit nft_bitmap_module_exit(void)
310 {
311         nft_unregister_set(&nft_bitmap_type);
312 }
313 
314 module_init(nft_bitmap_module_init);
315 module_exit(nft_bitmap_module_exit);
316 
317 MODULE_LICENSE("GPL");
318 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
319 MODULE_ALIAS_NFT_SET();
320 

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