1 /* 2 * xt_u32 - kernel module to match u32 packet content 3 * 4 * Original author: Don Cohen <don@isis.cs3-inc.com> 5 * (C) CC Computer Consultants GmbH, 2007 6 */ 7 8 #include <linux/module.h> 9 #include <linux/moduleparam.h> 10 #include <linux/spinlock.h> 11 #include <linux/skbuff.h> 12 #include <linux/types.h> 13 #include <linux/netfilter/x_tables.h> 14 #include <linux/netfilter/xt_u32.h> 15 16 static bool u32_match_it(const struct xt_u32 *data, 17 const struct sk_buff *skb) 18 { 19 const struct xt_u32_test *ct; 20 unsigned int testind; 21 unsigned int nnums; 22 unsigned int nvals; 23 unsigned int i; 24 __be32 n; 25 u_int32_t pos; 26 u_int32_t val; 27 u_int32_t at; 28 29 /* 30 * Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17" 31 * (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands. 32 */ 33 for (testind = 0; testind < data->ntests; ++testind) { 34 ct = &data->tests[testind]; 35 at = 0; 36 pos = ct->location[0].number; 37 38 if (skb->len < 4 || pos > skb->len - 4) 39 return false; 40 41 if (skb_copy_bits(skb, pos, &n, sizeof(n)) < 0) 42 BUG(); 43 val = ntohl(n); 44 nnums = ct->nnums; 45 46 /* Inner loop runs over "&", "<<", ">>" and "@" operands */ 47 for (i = 1; i < nnums; ++i) { 48 u_int32_t number = ct->location[i].number; 49 switch (ct->location[i].nextop) { 50 case XT_U32_AND: 51 val &= number; 52 break; 53 case XT_U32_LEFTSH: 54 val <<= number; 55 break; 56 case XT_U32_RIGHTSH: 57 val >>= number; 58 break; 59 case XT_U32_AT: 60 if (at + val < at) 61 return false; 62 at += val; 63 pos = number; 64 if (at + 4 < at || skb->len < at + 4 || 65 pos > skb->len - at - 4) 66 return false; 67 68 if (skb_copy_bits(skb, at + pos, &n, 69 sizeof(n)) < 0) 70 BUG(); 71 val = ntohl(n); 72 break; 73 } 74 } 75 76 /* Run over the "," and ":" operands */ 77 nvals = ct->nvalues; 78 for (i = 0; i < nvals; ++i) 79 if (ct->value[i].min <= val && val <= ct->value[i].max) 80 break; 81 82 if (i >= ct->nvalues) 83 return false; 84 } 85 86 return true; 87 } 88 89 static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par) 90 { 91 const struct xt_u32 *data = par->matchinfo; 92 bool ret; 93 94 ret = u32_match_it(data, skb); 95 return ret ^ data->invert; 96 } 97 98 static struct xt_match xt_u32_mt_reg __read_mostly = { 99 .name = "u32", 100 .revision = 0, 101 .family = NFPROTO_UNSPEC, 102 .match = u32_mt, 103 .matchsize = sizeof(struct xt_u32), 104 .me = THIS_MODULE, 105 }; 106 107 static int __init u32_mt_init(void) 108 { 109 return xt_register_match(&xt_u32_mt_reg); 110 } 111 112 static void __exit u32_mt_exit(void) 113 { 114 xt_unregister_match(&xt_u32_mt_reg); 115 } 116 117 module_init(u32_mt_init); 118 module_exit(u32_mt_exit); 119 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>"); 120 MODULE_DESCRIPTION("Xtables: arbitrary byte matching"); 121 MODULE_LICENSE("GPL"); 122 MODULE_ALIAS("ipt_u32"); 123 MODULE_ALIAS("ip6t_u32"); 124