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Linux/net/bridge/netfilter/ebt_among.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  *  ebt_among
  4  *
  5  *      Authors:
  6  *      Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
  7  *
  8  *  August, 2003
  9  *
 10  */
 11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 12 #include <linux/ip.h>
 13 #include <linux/if_arp.h>
 14 #include <linux/module.h>
 15 #include <linux/netfilter/x_tables.h>
 16 #include <linux/netfilter_bridge/ebtables.h>
 17 #include <linux/netfilter_bridge/ebt_among.h>
 18 
 19 static bool ebt_mac_wormhash_contains(const struct ebt_mac_wormhash *wh,
 20                                       const char *mac, __be32 ip)
 21 {
 22         /* You may be puzzled as to how this code works.
 23          * Some tricks were used, refer to
 24          *      include/linux/netfilter_bridge/ebt_among.h
 25          * as there you can find a solution of this mystery.
 26          */
 27         const struct ebt_mac_wormhash_tuple *p;
 28         int start, limit, i;
 29         uint32_t cmp[2] = { 0, 0 };
 30         int key = ((const unsigned char *)mac)[5];
 31 
 32         ether_addr_copy(((char *) cmp) + 2, mac);
 33         start = wh->table[key];
 34         limit = wh->table[key + 1];
 35         if (ip) {
 36                 for (i = start; i < limit; i++) {
 37                         p = &wh->pool[i];
 38                         if (cmp[1] == p->cmp[1] && cmp[0] == p->cmp[0])
 39                                 if (p->ip == 0 || p->ip == ip)
 40                                         return true;
 41                 }
 42         } else {
 43                 for (i = start; i < limit; i++) {
 44                         p = &wh->pool[i];
 45                         if (cmp[1] == p->cmp[1] && cmp[0] == p->cmp[0])
 46                                 if (p->ip == 0)
 47                                         return true;
 48                 }
 49         }
 50         return false;
 51 }
 52 
 53 static int ebt_mac_wormhash_check_integrity(const struct ebt_mac_wormhash
 54                                             *wh)
 55 {
 56         int i;
 57 
 58         for (i = 0; i < 256; i++) {
 59                 if (wh->table[i] > wh->table[i + 1])
 60                         return -0x100 - i;
 61                 if (wh->table[i] < 0)
 62                         return -0x200 - i;
 63                 if (wh->table[i] > wh->poolsize)
 64                         return -0x300 - i;
 65         }
 66         if (wh->table[256] > wh->poolsize)
 67                 return -0xc00;
 68         return 0;
 69 }
 70 
 71 static int get_ip_dst(const struct sk_buff *skb, __be32 *addr)
 72 {
 73         if (eth_hdr(skb)->h_proto == htons(ETH_P_IP)) {
 74                 const struct iphdr *ih;
 75                 struct iphdr _iph;
 76 
 77                 ih = skb_header_pointer(skb, 0, sizeof(_iph), &_iph);
 78                 if (ih == NULL)
 79                         return -1;
 80                 *addr = ih->daddr;
 81         } else if (eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
 82                 const struct arphdr *ah;
 83                 struct arphdr _arph;
 84                 const __be32 *bp;
 85                 __be32 buf;
 86 
 87                 ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
 88                 if (ah == NULL ||
 89                     ah->ar_pln != sizeof(__be32) ||
 90                     ah->ar_hln != ETH_ALEN)
 91                         return -1;
 92                 bp = skb_header_pointer(skb, sizeof(struct arphdr) +
 93                                         2 * ETH_ALEN + sizeof(__be32),
 94                                         sizeof(__be32), &buf);
 95                 if (bp == NULL)
 96                         return -1;
 97                 *addr = *bp;
 98         }
 99         return 0;
100 }
101 
102 static int get_ip_src(const struct sk_buff *skb, __be32 *addr)
103 {
104         if (eth_hdr(skb)->h_proto == htons(ETH_P_IP)) {
105                 const struct iphdr *ih;
106                 struct iphdr _iph;
107 
108                 ih = skb_header_pointer(skb, 0, sizeof(_iph), &_iph);
109                 if (ih == NULL)
110                         return -1;
111                 *addr = ih->saddr;
112         } else if (eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
113                 const struct arphdr *ah;
114                 struct arphdr _arph;
115                 const __be32 *bp;
116                 __be32 buf;
117 
118                 ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
119                 if (ah == NULL ||
120                     ah->ar_pln != sizeof(__be32) ||
121                     ah->ar_hln != ETH_ALEN)
122                         return -1;
123                 bp = skb_header_pointer(skb, sizeof(struct arphdr) +
124                                         ETH_ALEN, sizeof(__be32), &buf);
125                 if (bp == NULL)
126                         return -1;
127                 *addr = *bp;
128         }
129         return 0;
130 }
131 
132 static bool
133 ebt_among_mt(const struct sk_buff *skb, struct xt_action_param *par)
134 {
135         const struct ebt_among_info *info = par->matchinfo;
136         const char *dmac, *smac;
137         const struct ebt_mac_wormhash *wh_dst, *wh_src;
138         __be32 dip = 0, sip = 0;
139 
140         wh_dst = ebt_among_wh_dst(info);
141         wh_src = ebt_among_wh_src(info);
142 
143         if (wh_src) {
144                 smac = eth_hdr(skb)->h_source;
145                 if (get_ip_src(skb, &sip))
146                         return false;
147                 if (!(info->bitmask & EBT_AMONG_SRC_NEG)) {
148                         /* we match only if it contains */
149                         if (!ebt_mac_wormhash_contains(wh_src, smac, sip))
150                                 return false;
151                 } else {
152                         /* we match only if it DOES NOT contain */
153                         if (ebt_mac_wormhash_contains(wh_src, smac, sip))
154                                 return false;
155                 }
156         }
157 
158         if (wh_dst) {
159                 dmac = eth_hdr(skb)->h_dest;
160                 if (get_ip_dst(skb, &dip))
161                         return false;
162                 if (!(info->bitmask & EBT_AMONG_DST_NEG)) {
163                         /* we match only if it contains */
164                         if (!ebt_mac_wormhash_contains(wh_dst, dmac, dip))
165                                 return false;
166                 } else {
167                         /* we match only if it DOES NOT contain */
168                         if (ebt_mac_wormhash_contains(wh_dst, dmac, dip))
169                                 return false;
170                 }
171         }
172 
173         return true;
174 }
175 
176 static bool poolsize_invalid(const struct ebt_mac_wormhash *w)
177 {
178         return w && w->poolsize >= (INT_MAX / sizeof(struct ebt_mac_wormhash_tuple));
179 }
180 
181 static bool wormhash_offset_invalid(int off, unsigned int len)
182 {
183         if (off == 0) /* not present */
184                 return false;
185 
186         if (off < (int)sizeof(struct ebt_among_info) ||
187             off % __alignof__(struct ebt_mac_wormhash))
188                 return true;
189 
190         off += sizeof(struct ebt_mac_wormhash);
191 
192         return off > len;
193 }
194 
195 static bool wormhash_sizes_valid(const struct ebt_mac_wormhash *wh, int a, int b)
196 {
197         if (a == 0)
198                 a = sizeof(struct ebt_among_info);
199 
200         return ebt_mac_wormhash_size(wh) + a == b;
201 }
202 
203 static int ebt_among_mt_check(const struct xt_mtchk_param *par)
204 {
205         const struct ebt_among_info *info = par->matchinfo;
206         const struct ebt_entry_match *em =
207                 container_of(par->matchinfo, const struct ebt_entry_match, data);
208         unsigned int expected_length = sizeof(struct ebt_among_info);
209         const struct ebt_mac_wormhash *wh_dst, *wh_src;
210         int err;
211 
212         if (expected_length > em->match_size)
213                 return -EINVAL;
214 
215         if (wormhash_offset_invalid(info->wh_dst_ofs, em->match_size) ||
216             wormhash_offset_invalid(info->wh_src_ofs, em->match_size))
217                 return -EINVAL;
218 
219         wh_dst = ebt_among_wh_dst(info);
220         if (poolsize_invalid(wh_dst))
221                 return -EINVAL;
222 
223         expected_length += ebt_mac_wormhash_size(wh_dst);
224         if (expected_length > em->match_size)
225                 return -EINVAL;
226 
227         wh_src = ebt_among_wh_src(info);
228         if (poolsize_invalid(wh_src))
229                 return -EINVAL;
230 
231         if (info->wh_src_ofs < info->wh_dst_ofs) {
232                 if (!wormhash_sizes_valid(wh_src, info->wh_src_ofs, info->wh_dst_ofs))
233                         return -EINVAL;
234         } else {
235                 if (!wormhash_sizes_valid(wh_dst, info->wh_dst_ofs, info->wh_src_ofs))
236                         return -EINVAL;
237         }
238 
239         expected_length += ebt_mac_wormhash_size(wh_src);
240 
241         if (em->match_size != EBT_ALIGN(expected_length)) {
242                 pr_err_ratelimited("wrong size: %d against expected %d, rounded to %zd\n",
243                                    em->match_size, expected_length,
244                                    EBT_ALIGN(expected_length));
245                 return -EINVAL;
246         }
247         if (wh_dst && (err = ebt_mac_wormhash_check_integrity(wh_dst))) {
248                 pr_err_ratelimited("dst integrity fail: %x\n", -err);
249                 return -EINVAL;
250         }
251         if (wh_src && (err = ebt_mac_wormhash_check_integrity(wh_src))) {
252                 pr_err_ratelimited("src integrity fail: %x\n", -err);
253                 return -EINVAL;
254         }
255         return 0;
256 }
257 
258 static struct xt_match ebt_among_mt_reg __read_mostly = {
259         .name           = "among",
260         .revision       = 0,
261         .family         = NFPROTO_BRIDGE,
262         .match          = ebt_among_mt,
263         .checkentry     = ebt_among_mt_check,
264         .matchsize      = -1, /* special case */
265         .me             = THIS_MODULE,
266 };
267 
268 static int __init ebt_among_init(void)
269 {
270         return xt_register_match(&ebt_among_mt_reg);
271 }
272 
273 static void __exit ebt_among_fini(void)
274 {
275         xt_unregister_match(&ebt_among_mt_reg);
276 }
277 
278 module_init(ebt_among_init);
279 module_exit(ebt_among_fini);
280 MODULE_DESCRIPTION("Ebtables: Combined MAC/IP address list matching");
281 MODULE_LICENSE("GPL");
282 

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