net/ipv6/netfilter/ip6t_frag.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Kernel module to match FRAG 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 <linux/netfilter/x_tables.h>
  15 #include <linux/netfilter_ipv6/ip6_tables.h>
  16 #include <linux/netfilter_ipv6/ip6t_frag.h>
  17
  18 MODULE_LICENSE("GPL");
  19 MODULE_DESCRIPTION("Xtables: IPv6 fragment match");
  20 MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");
  21
  22 /* Returns 1 if the id is matched by the range, 0 otherwise */
  23 static inline bool
  24 id_match(u_int32_t min, u_int32_t max, u_int32_t id, bool invert)
  25 {
  26         bool r;
  27         pr_debug("id_match:%c 0x%x <= 0x%x <= 0x%x\n", invert ? '!' : ' ',
  28                  min, id, max);
  29         r = (id >= min && id <= max) ^ invert;
  30         pr_debug(" result %s\n", r ? "PASS" : "FAILED");
  31         return r;
  32 }
  33
  34 static bool
  35 frag_mt6(const struct sk_buff *skb, struct xt_action_param *par)
  36 {
  37         struct frag_hdr _frag;
  38         const struct frag_hdr *fh;
  39         const struct ip6t_frag *fraginfo = par->matchinfo;
  40         unsigned int ptr = 0;
  41         int err;
  42
  43         err = ipv6_find_hdr(skb, &ptr, NEXTHDR_FRAGMENT, NULL, NULL);
  44         if (err < 0) {
  45                 if (err != -ENOENT)
  46                         par->hotdrop = true;
  47                 return false;
  48         }
  49
  50         fh = skb_header_pointer(skb, ptr, sizeof(_frag), &_frag);
  51         if (fh == NULL) {
  52                 par->hotdrop = true;
  53                 return false;
  54         }
  55
  56         pr_debug("INFO %04X ", fh->frag_off);
  57         pr_debug("OFFSET %04X ", ntohs(fh->frag_off) & ~0x7);
  58         pr_debug("RES %02X %04X", fh->reserved, ntohs(fh->frag_off) & 0x6);
  59         pr_debug("MF %04X ", fh->frag_off & htons(IP6_MF));
  60         pr_debug("ID %u %08X\n", ntohl(fh->identification),
  61                  ntohl(fh->identification));
  62
  63         pr_debug("IPv6 FRAG id %02X ",
  64                  id_match(fraginfo->ids[0], fraginfo->ids[1],
  65                           ntohl(fh->identification),
  66                           !!(fraginfo->invflags & IP6T_FRAG_INV_IDS)));
  67         pr_debug("res %02X %02X%04X %02X ",
  68                  fraginfo->flags & IP6T_FRAG_RES, fh->reserved,
  69                  ntohs(fh->frag_off) & 0x6,
  70                  !((fraginfo->flags & IP6T_FRAG_RES) &&
  71                    (fh->reserved || (ntohs(fh->frag_off) & 0x06))));
  72         pr_debug("first %02X %02X %02X ",
  73                  fraginfo->flags & IP6T_FRAG_FST,
  74                  ntohs(fh->frag_off) & ~0x7,
  75                  !((fraginfo->flags & IP6T_FRAG_FST) &&
  76                    (ntohs(fh->frag_off) & ~0x7)));
  77         pr_debug("mf %02X %02X %02X ",
  78                  fraginfo->flags & IP6T_FRAG_MF,
  79                  ntohs(fh->frag_off) & IP6_MF,
  80                  !((fraginfo->flags & IP6T_FRAG_MF) &&
  81                    !((ntohs(fh->frag_off) & IP6_MF))));
  82         pr_debug("last %02X %02X %02X\n",
  83                  fraginfo->flags & IP6T_FRAG_NMF,
  84                  ntohs(fh->frag_off) & IP6_MF,
  85                  !((fraginfo->flags & IP6T_FRAG_NMF) &&
  86                    (ntohs(fh->frag_off) & IP6_MF)));
  87
  88         return id_match(fraginfo->ids[0], fraginfo->ids[1],
  89                          ntohl(fh->identification),
  90                          !!(fraginfo->invflags & IP6T_FRAG_INV_IDS)) &&
  91                 !((fraginfo->flags & IP6T_FRAG_RES) &&
  92                   (fh->reserved || (ntohs(fh->frag_off) & 0x6))) &&
  93                 !((fraginfo->flags & IP6T_FRAG_FST) &&
  94                   (ntohs(fh->frag_off) & ~0x7)) &&
  95                 !((fraginfo->flags & IP6T_FRAG_MF) &&
  96                   !(ntohs(fh->frag_off) & IP6_MF)) &&
  97                 !((fraginfo->flags & IP6T_FRAG_NMF) &&
  98                   (ntohs(fh->frag_off) & IP6_MF));
  99 }
 100
 101 static int frag_mt6_check(const struct xt_mtchk_param *par)
 102 {
 103         const struct ip6t_frag *fraginfo = par->matchinfo;
 104
 105         if (fraginfo->invflags & ~IP6T_FRAG_INV_MASK) {
 106                 pr_debug("unknown flags %X\n", fraginfo->invflags);
 107                 return -EINVAL;
 108         }
 109         return 0;
 110 }
 111
 112 static struct xt_match frag_mt6_reg __read_mostly = {
 113         .name           = "frag",
 114         .family         = NFPROTO_IPV6,
 115         .match          = frag_mt6,
 116         .matchsize      = sizeof(struct ip6t_frag),
 117         .checkentry     = frag_mt6_check,
 118         .me             = THIS_MODULE,
 119 };
 120
 121 static int __init frag_mt6_init(void)
 122 {
 123         return xt_register_match(&frag_mt6_reg);
 124 }
 125
 126 static void __exit frag_mt6_exit(void)
 127 {
 128         xt_unregister_match(&frag_mt6_reg);
 129 }
 130
 131 module_init(frag_mt6_init);
 132 module_exit(frag_mt6_exit);