1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * xt_u32 - kernel module to match u32 packet content 4 * 5 * Original author: Don Cohen <don@isis.cs3-inc.com> 6 * (C) CC Computer Consultants GmbH, 2007 7 */ 8 9 #include <linux/module.h> 10 #include <linux/moduleparam.h> 11 #include <linux/spinlock.h> 12 #include <linux/skbuff.h> 13 #include <linux/types.h> 14 #include <linux/netfilter/x_tables.h> 15 #include <linux/netfilter/xt_u32.h> 16 17 static bool u32_match_it(const struct xt_u32 *data, 18 const struct sk_buff *skb) 19 { 20 const struct xt_u32_test *ct; 21 unsigned int testind; 22 unsigned int nnums; 23 unsigned int nvals; 24 unsigned int i; 25 __be32 n; 26 u_int32_t pos; 27 u_int32_t val; 28 u_int32_t at; 29 30 /* 31 * Small example: "0 >> 28 == 4 && 8 & 0xFF0000 >> 16 = 6, 17" 32 * (=IPv4 and (TCP or UDP)). Outer loop runs over the "&&" operands. 33 */ 34 for (testind = 0; testind < data->ntests; ++testind) { 35 ct = &data->tests[testind]; 36 at = 0; 37 pos = ct->location[0].number; 38 39 if (skb->len < 4 || pos > skb->len - 4) 40 return false; 41 42 if (skb_copy_bits(skb, pos, &n, sizeof(n)) < 0) 43 BUG(); 44 val = ntohl(n); 45 nnums = ct->nnums; 46 47 /* Inner loop runs over "&", "<<", ">>" and "@" operands */ 48 for (i = 1; i < nnums; ++i) { 49 u_int32_t number = ct->location[i].number; 50 switch (ct->location[i].nextop) { 51 case XT_U32_AND: 52 val &= number; 53 break; 54 case XT_U32_LEFTSH: 55 val <<= number; 56 break; 57 case XT_U32_RIGHTSH: 58 val >>= number; 59 break; 60 case XT_U32_AT: 61 if (at + val < at) 62 return false; 63 at += val; 64 pos = number; 65 if (at + 4 < at || skb->len < at + 4 || 66 pos > skb->len - at - 4) 67 return false; 68 69 if (skb_copy_bits(skb, at + pos, &n, 70 sizeof(n)) < 0) 71 BUG(); 72 val = ntohl(n); 73 break; 74 } 75 } 76 77 /* Run over the "," and ":" operands */ 78 nvals = ct->nvalues; 79 for (i = 0; i < nvals; ++i) 80 if (ct->value[i].min <= val && val <= ct->value[i].max) 81 break; 82 83 if (i >= ct->nvalues) 84 return false; 85 } 86 87 return true; 88 } 89 90 static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par) 91 { 92 const struct xt_u32 *data = par->matchinfo; 93 bool ret; 94 95 ret = u32_match_it(data, skb); 96 return ret ^ data->invert; 97 } 98 99 static int u32_mt_checkentry(const struct xt_mtchk_param *par) 100 { 101 const struct xt_u32 *data = par->matchinfo; 102 const struct xt_u32_test *ct; 103 unsigned int i; 104 105 if (data->ntests > ARRAY_SIZE(data->tests)) 106 return -EINVAL; 107 108 for (i = 0; i < data->ntests; ++i) { 109 ct = &data->tests[i]; 110 111 if (ct->nnums > ARRAY_SIZE(ct->location) || 112 ct->nvalues > ARRAY_SIZE(ct->value)) 113 return -EINVAL; 114 } 115 116 return 0; 117 } 118 119 static struct xt_match xt_u32_mt_reg __read_mostly = { 120 .name = "u32", 121 .revision = 0, 122 .family = NFPROTO_UNSPEC, 123 .match = u32_mt, 124 .checkentry = u32_mt_checkentry, 125 .matchsize = sizeof(struct xt_u32), 126 .me = THIS_MODULE, 127 }; 128 129 static int __init u32_mt_init(void) 130 { 131 return xt_register_match(&xt_u32_mt_reg); 132 } 133 134 static void __exit u32_mt_exit(void) 135 { 136 xt_unregister_match(&xt_u32_mt_reg); 137 } 138 139 module_init(u32_mt_init); 140 module_exit(u32_mt_exit); 141 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>"); 142 MODULE_DESCRIPTION("Xtables: arbitrary byte matching"); 143 MODULE_LICENSE("GPL"); 144 MODULE_ALIAS("ipt_u32"); 145 MODULE_ALIAS("ip6t_u32"); 146