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Linux/net/netfilter/nf_conntrack_tftp.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /* (C) 2001-2002 Magnus Boden <mb@ozaba.mine.nu>
  3  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  4  */
  5 
  6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  7 
  8 #include <linux/module.h>
  9 #include <linux/moduleparam.h>
 10 #include <linux/in.h>
 11 #include <linux/udp.h>
 12 #include <linux/netfilter.h>
 13 
 14 #include <net/netfilter/nf_conntrack.h>
 15 #include <net/netfilter/nf_conntrack_tuple.h>
 16 #include <net/netfilter/nf_conntrack_expect.h>
 17 #include <net/netfilter/nf_conntrack_ecache.h>
 18 #include <net/netfilter/nf_conntrack_helper.h>
 19 #include <linux/netfilter/nf_conntrack_tftp.h>
 20 
 21 #define HELPER_NAME "tftp"
 22 
 23 MODULE_AUTHOR("Magnus Boden <mb@ozaba.mine.nu>");
 24 MODULE_DESCRIPTION("TFTP connection tracking helper");
 25 MODULE_LICENSE("GPL");
 26 MODULE_ALIAS("ip_conntrack_tftp");
 27 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
 28 
 29 #define MAX_PORTS 8
 30 static unsigned short ports[MAX_PORTS];
 31 static unsigned int ports_c;
 32 module_param_array(ports, ushort, &ports_c, 0400);
 33 MODULE_PARM_DESC(ports, "Port numbers of TFTP servers");
 34 
 35 unsigned int (*nf_nat_tftp_hook)(struct sk_buff *skb,
 36                                  enum ip_conntrack_info ctinfo,
 37                                  struct nf_conntrack_expect *exp) __read_mostly;
 38 EXPORT_SYMBOL_GPL(nf_nat_tftp_hook);
 39 
 40 static int tftp_help(struct sk_buff *skb,
 41                      unsigned int protoff,
 42                      struct nf_conn *ct,
 43                      enum ip_conntrack_info ctinfo)
 44 {
 45         const struct tftphdr *tfh;
 46         struct tftphdr _tftph;
 47         struct nf_conntrack_expect *exp;
 48         struct nf_conntrack_tuple *tuple;
 49         unsigned int ret = NF_ACCEPT;
 50         typeof(nf_nat_tftp_hook) nf_nat_tftp;
 51 
 52         tfh = skb_header_pointer(skb, protoff + sizeof(struct udphdr),
 53                                  sizeof(_tftph), &_tftph);
 54         if (tfh == NULL)
 55                 return NF_ACCEPT;
 56 
 57         switch (ntohs(tfh->opcode)) {
 58         case TFTP_OPCODE_READ:
 59         case TFTP_OPCODE_WRITE:
 60                 /* RRQ and WRQ works the same way */
 61                 nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 62                 nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 63 
 64                 exp = nf_ct_expect_alloc(ct);
 65                 if (exp == NULL) {
 66                         nf_ct_helper_log(skb, ct, "cannot alloc expectation");
 67                         return NF_DROP;
 68                 }
 69                 tuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
 70                 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
 71                                   nf_ct_l3num(ct),
 72                                   &tuple->src.u3, &tuple->dst.u3,
 73                                   IPPROTO_UDP, NULL, &tuple->dst.u.udp.port);
 74 
 75                 pr_debug("expect: ");
 76                 nf_ct_dump_tuple(&exp->tuple);
 77 
 78                 nf_nat_tftp = rcu_dereference(nf_nat_tftp_hook);
 79                 if (nf_nat_tftp && ct->status & IPS_NAT_MASK)
 80                         ret = nf_nat_tftp(skb, ctinfo, exp);
 81                 else if (nf_ct_expect_related(exp, 0) != 0) {
 82                         nf_ct_helper_log(skb, ct, "cannot add expectation");
 83                         ret = NF_DROP;
 84                 }
 85                 nf_ct_expect_put(exp);
 86                 break;
 87         case TFTP_OPCODE_DATA:
 88         case TFTP_OPCODE_ACK:
 89                 pr_debug("Data/ACK opcode\n");
 90                 break;
 91         case TFTP_OPCODE_ERROR:
 92                 pr_debug("Error opcode\n");
 93                 break;
 94         default:
 95                 pr_debug("Unknown opcode\n");
 96         }
 97         return ret;
 98 }
 99 
100 static struct nf_conntrack_helper tftp[MAX_PORTS * 2] __read_mostly;
101 
102 static const struct nf_conntrack_expect_policy tftp_exp_policy = {
103         .max_expected   = 1,
104         .timeout        = 5 * 60,
105 };
106 
107 static void __exit nf_conntrack_tftp_fini(void)
108 {
109         nf_conntrack_helpers_unregister(tftp, ports_c * 2);
110 }
111 
112 static int __init nf_conntrack_tftp_init(void)
113 {
114         int i, ret;
115 
116         NF_CT_HELPER_BUILD_BUG_ON(0);
117 
118         if (ports_c == 0)
119                 ports[ports_c++] = TFTP_PORT;
120 
121         for (i = 0; i < ports_c; i++) {
122                 nf_ct_helper_init(&tftp[2 * i], AF_INET, IPPROTO_UDP,
123                                   HELPER_NAME, TFTP_PORT, ports[i], i,
124                                   &tftp_exp_policy, 0, tftp_help, NULL,
125                                   THIS_MODULE);
126                 nf_ct_helper_init(&tftp[2 * i + 1], AF_INET6, IPPROTO_UDP,
127                                   HELPER_NAME, TFTP_PORT, ports[i], i,
128                                   &tftp_exp_policy, 0, tftp_help, NULL,
129                                   THIS_MODULE);
130         }
131 
132         ret = nf_conntrack_helpers_register(tftp, ports_c * 2);
133         if (ret < 0) {
134                 pr_err("failed to register helpers\n");
135                 return ret;
136         }
137         return 0;
138 }
139 
140 module_init(nf_conntrack_tftp_init);
141 module_exit(nf_conntrack_tftp_fini);
142 

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