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Linux/net/ipv6/netfilter/ip6t_hbh.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /* Kernel module to match Hop-by-Hop and Destination parameters. */
  3 
  4 /* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
  5  */
  6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  7 #include <linux/module.h>
  8 #include <linux/skbuff.h>
  9 #include <linux/ipv6.h>
 10 #include <linux/types.h>
 11 #include <net/checksum.h>
 12 #include <net/ipv6.h>
 13 
 14 #include <asm/byteorder.h>
 15 
 16 #include <linux/netfilter/x_tables.h>
 17 #include <linux/netfilter_ipv6/ip6_tables.h>
 18 #include <linux/netfilter_ipv6/ip6t_opts.h>
 19 
 20 MODULE_LICENSE("GPL");
 21 MODULE_DESCRIPTION("Xtables: IPv6 Hop-By-Hop and Destination Header match");
 22 MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");
 23 MODULE_ALIAS("ip6t_dst");
 24 
 25 /*
 26  *  (Type & 0xC0) >> 6
 27  *      0       -> ignorable
 28  *      1       -> must drop the packet
 29  *      2       -> send ICMP PARM PROB regardless and drop packet
 30  *      3       -> Send ICMP if not a multicast address and drop packet
 31  *  (Type & 0x20) >> 5
 32  *      0       -> invariant
 33  *      1       -> can change the routing
 34  *  (Type & 0x1F) Type
 35  *      0       -> Pad1 (only 1 byte!)
 36  *      1       -> PadN LENGTH info (total length = length + 2)
 37  *      C0 | 2  -> JUMBO 4 x x x x ( xxxx > 64k )
 38  *      5       -> RTALERT 2 x x
 39  */
 40 
 41 static struct xt_match hbh_mt6_reg[] __read_mostly;
 42 
 43 static bool
 44 hbh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 45 {
 46         struct ipv6_opt_hdr _optsh;
 47         const struct ipv6_opt_hdr *oh;
 48         const struct ip6t_opts *optinfo = par->matchinfo;
 49         unsigned int temp;
 50         unsigned int ptr = 0;
 51         unsigned int hdrlen = 0;
 52         bool ret = false;
 53         u8 _opttype;
 54         u8 _optlen;
 55         const u_int8_t *tp = NULL;
 56         const u_int8_t *lp = NULL;
 57         unsigned int optlen;
 58         int err;
 59 
 60         err = ipv6_find_hdr(skb, &ptr,
 61                             (par->match == &hbh_mt6_reg[0]) ?
 62                             NEXTHDR_HOP : NEXTHDR_DEST, NULL, NULL);
 63         if (err < 0) {
 64                 if (err != -ENOENT)
 65                         par->hotdrop = true;
 66                 return false;
 67         }
 68 
 69         oh = skb_header_pointer(skb, ptr, sizeof(_optsh), &_optsh);
 70         if (oh == NULL) {
 71                 par->hotdrop = true;
 72                 return false;
 73         }
 74 
 75         hdrlen = ipv6_optlen(oh);
 76         if (skb->len - ptr < hdrlen) {
 77                 /* Packet smaller than it's length field */
 78                 return false;
 79         }
 80 
 81         pr_debug("IPv6 OPTS LEN %u %u ", hdrlen, oh->hdrlen);
 82 
 83         pr_debug("len %02X %04X %02X ",
 84                  optinfo->hdrlen, hdrlen,
 85                  (!(optinfo->flags & IP6T_OPTS_LEN) ||
 86                   ((optinfo->hdrlen == hdrlen) ^
 87                    !!(optinfo->invflags & IP6T_OPTS_INV_LEN))));
 88 
 89         ret = (!(optinfo->flags & IP6T_OPTS_LEN) ||
 90                ((optinfo->hdrlen == hdrlen) ^
 91                 !!(optinfo->invflags & IP6T_OPTS_INV_LEN)));
 92 
 93         ptr += 2;
 94         hdrlen -= 2;
 95         if (!(optinfo->flags & IP6T_OPTS_OPTS)) {
 96                 return ret;
 97         } else {
 98                 pr_debug("Strict ");
 99                 pr_debug("#%d ", optinfo->optsnr);
100                 for (temp = 0; temp < optinfo->optsnr; temp++) {
101                         /* type field exists ? */
102                         if (hdrlen < 1)
103                                 break;
104                         tp = skb_header_pointer(skb, ptr, sizeof(_opttype),
105                                                 &_opttype);
106                         if (tp == NULL)
107                                 break;
108 
109                         /* Type check */
110                         if (*tp != (optinfo->opts[temp] & 0xFF00) >> 8) {
111                                 pr_debug("Tbad %02X %02X\n", *tp,
112                                          (optinfo->opts[temp] & 0xFF00) >> 8);
113                                 return false;
114                         } else {
115                                 pr_debug("Tok ");
116                         }
117                         /* Length check */
118                         if (*tp) {
119                                 u16 spec_len;
120 
121                                 /* length field exists ? */
122                                 if (hdrlen < 2)
123                                         break;
124                                 lp = skb_header_pointer(skb, ptr + 1,
125                                                         sizeof(_optlen),
126                                                         &_optlen);
127                                 if (lp == NULL)
128                                         break;
129                                 spec_len = optinfo->opts[temp] & 0x00FF;
130 
131                                 if (spec_len != 0x00FF && spec_len != *lp) {
132                                         pr_debug("Lbad %02X %04X\n", *lp,
133                                                  spec_len);
134                                         return false;
135                                 }
136                                 pr_debug("Lok ");
137                                 optlen = *lp + 2;
138                         } else {
139                                 pr_debug("Pad1\n");
140                                 optlen = 1;
141                         }
142 
143                         /* Step to the next */
144                         pr_debug("len%04X\n", optlen);
145 
146                         if ((ptr > skb->len - optlen || hdrlen < optlen) &&
147                             temp < optinfo->optsnr - 1) {
148                                 pr_debug("new pointer is too large!\n");
149                                 break;
150                         }
151                         ptr += optlen;
152                         hdrlen -= optlen;
153                 }
154                 if (temp == optinfo->optsnr)
155                         return ret;
156                 else
157                         return false;
158         }
159 
160         return false;
161 }
162 
163 static int hbh_mt6_check(const struct xt_mtchk_param *par)
164 {
165         const struct ip6t_opts *optsinfo = par->matchinfo;
166 
167         if (optsinfo->invflags & ~IP6T_OPTS_INV_MASK) {
168                 pr_debug("unknown flags %X\n", optsinfo->invflags);
169                 return -EINVAL;
170         }
171 
172         if (optsinfo->flags & IP6T_OPTS_NSTRICT) {
173                 pr_debug("Not strict - not implemented");
174                 return -EINVAL;
175         }
176 
177         return 0;
178 }
179 
180 static struct xt_match hbh_mt6_reg[] __read_mostly = {
181         {
182                 /* Note, hbh_mt6 relies on the order of hbh_mt6_reg */
183                 .name           = "hbh",
184                 .family         = NFPROTO_IPV6,
185                 .match          = hbh_mt6,
186                 .matchsize      = sizeof(struct ip6t_opts),
187                 .checkentry     = hbh_mt6_check,
188                 .me             = THIS_MODULE,
189         },
190         {
191                 .name           = "dst",
192                 .family         = NFPROTO_IPV6,
193                 .match          = hbh_mt6,
194                 .matchsize      = sizeof(struct ip6t_opts),
195                 .checkentry     = hbh_mt6_check,
196                 .me             = THIS_MODULE,
197         },
198 };
199 
200 static int __init hbh_mt6_init(void)
201 {
202         return xt_register_matches(hbh_mt6_reg, ARRAY_SIZE(hbh_mt6_reg));
203 }
204 
205 static void __exit hbh_mt6_exit(void)
206 {
207         xt_unregister_matches(hbh_mt6_reg, ARRAY_SIZE(hbh_mt6_reg));
208 }
209 
210 module_init(hbh_mt6_init);
211 module_exit(hbh_mt6_exit);
212 

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