net/netfilter/nfnetlink_hook.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (c) 2021 Red Hat GmbH
   4  *
   5  * Author: Florian Westphal <fw@strlen.de>
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/kernel.h>
  10 #include <linux/types.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/errno.h>
  13 #include <linux/netlink.h>
  14 #include <linux/slab.h>
  15
  16 #include <linux/netfilter.h>
  17
  18 #include <linux/netfilter/nfnetlink.h>
  19 #include <linux/netfilter/nfnetlink_hook.h>
  20
  21 #include <net/netfilter/nf_tables.h>
  22 #include <net/sock.h>
  23
  24 static const struct nla_policy nfnl_hook_nla_policy[NFNLA_HOOK_MAX + 1] = {
  25         [NFNLA_HOOK_HOOKNUM]    = { .type = NLA_U32 },
  26         [NFNLA_HOOK_PRIORITY]   = { .type = NLA_U32 },
  27         [NFNLA_HOOK_DEV]        = { .type = NLA_STRING,
  28                                     .len = IFNAMSIZ - 1 },
  29         [NFNLA_HOOK_FUNCTION_NAME] = { .type = NLA_NUL_STRING,
  30                                        .len = KSYM_NAME_LEN, },
  31         [NFNLA_HOOK_MODULE_NAME] = { .type = NLA_NUL_STRING,
  32                                      .len = MODULE_NAME_LEN, },
  33         [NFNLA_HOOK_CHAIN_INFO] = { .type = NLA_NESTED, },
  34 };
  35
  36 static int nf_netlink_dump_start_rcu(struct sock *nlsk, struct sk_buff *skb,
  37                                      const struct nlmsghdr *nlh,
  38                                      struct netlink_dump_control *c)
  39 {
  40         int err;
  41
  42         if (!try_module_get(THIS_MODULE))
  43                 return -EINVAL;
  44
  45         rcu_read_unlock();
  46         err = netlink_dump_start(nlsk, skb, nlh, c);
  47         rcu_read_lock();
  48         module_put(THIS_MODULE);
  49
  50         return err;
  51 }
  52
  53 struct nfnl_dump_hook_data {
  54         char devname[IFNAMSIZ];
  55         unsigned long headv;
  56         u8 hook;
  57 };
  58
  59 static int nfnl_hook_put_nft_chain_info(struct sk_buff *nlskb,
  60                                         const struct nfnl_dump_hook_data *ctx,
  61                                         unsigned int seq,
  62                                         const struct nf_hook_ops *ops)
  63 {
  64         struct net *net = sock_net(nlskb->sk);
  65         struct nlattr *nest, *nest2;
  66         struct nft_chain *chain;
  67         int ret = 0;
  68
  69         if (ops->hook_ops_type != NF_HOOK_OP_NF_TABLES)
  70                 return 0;
  71
  72         chain = ops->priv;
  73         if (WARN_ON_ONCE(!chain))
  74                 return 0;
  75
  76         if (!nft_is_active(net, chain))
  77                 return 0;
  78
  79         nest = nla_nest_start(nlskb, NFNLA_HOOK_CHAIN_INFO);
  80         if (!nest)
  81                 return -EMSGSIZE;
  82
  83         ret = nla_put_be32(nlskb, NFNLA_HOOK_INFO_TYPE,
  84                            htonl(NFNL_HOOK_TYPE_NFTABLES));
  85         if (ret)
  86                 goto cancel_nest;
  87
  88         nest2 = nla_nest_start(nlskb, NFNLA_HOOK_INFO_DESC);
  89         if (!nest2)
  90                 goto cancel_nest;
  91
  92         ret = nla_put_string(nlskb, NFTA_CHAIN_TABLE, chain->table->name);
  93         if (ret)
  94                 goto cancel_nest;
  95
  96         ret = nla_put_string(nlskb, NFTA_CHAIN_NAME, chain->name);
  97         if (ret)
  98                 goto cancel_nest;
  99
 100         nla_nest_end(nlskb, nest2);
 101         nla_nest_end(nlskb, nest);
 102         return ret;
 103
 104 cancel_nest:
 105         nla_nest_cancel(nlskb, nest);
 106         return -EMSGSIZE;
 107 }
 108
 109 static int nfnl_hook_dump_one(struct sk_buff *nlskb,
 110                               const struct nfnl_dump_hook_data *ctx,
 111                               const struct nf_hook_ops *ops,
 112                               unsigned int seq)
 113 {
 114         u16 event = nfnl_msg_type(NFNL_SUBSYS_HOOK, NFNL_MSG_HOOK_GET);
 115         unsigned int portid = NETLINK_CB(nlskb).portid;
 116         struct nlmsghdr *nlh;
 117         int ret = -EMSGSIZE;
 118 #ifdef CONFIG_KALLSYMS
 119         char sym[KSYM_SYMBOL_LEN];
 120         char *module_name;
 121 #endif
 122         nlh = nfnl_msg_put(nlskb, portid, seq, event,
 123                            NLM_F_MULTI, ops->pf, NFNETLINK_V0, 0);
 124         if (!nlh)
 125                 goto nla_put_failure;
 126
 127 #ifdef CONFIG_KALLSYMS
 128         ret = snprintf(sym, sizeof(sym), "%ps", ops->hook);
 129         if (ret >= sizeof(sym)) {
 130                 ret = -EINVAL;
 131                 goto nla_put_failure;
 132         }
 133
 134         module_name = strstr(sym, " [");
 135         if (module_name) {
 136                 char *end;
 137
 138                 module_name += 2;
 139                 end = strchr(module_name, ']');
 140                 if (end) {
 141                         *end = 0;
 142
 143                         ret = nla_put_string(nlskb, NFNLA_HOOK_MODULE_NAME, module_name);
 144                         if (ret)
 145                                 goto nla_put_failure;
 146                 }
 147         }
 148
 149         ret = nla_put_string(nlskb, NFNLA_HOOK_FUNCTION_NAME, sym);
 150         if (ret)
 151                 goto nla_put_failure;
 152 #endif
 153
 154         ret = nla_put_be32(nlskb, NFNLA_HOOK_HOOKNUM, htonl(ops->hooknum));
 155         if (ret)
 156                 goto nla_put_failure;
 157
 158         ret = nla_put_be32(nlskb, NFNLA_HOOK_PRIORITY, htonl(ops->priority));
 159         if (ret)
 160                 goto nla_put_failure;
 161
 162         ret = nfnl_hook_put_nft_chain_info(nlskb, ctx, seq, ops);
 163         if (ret)
 164                 goto nla_put_failure;
 165
 166         nlmsg_end(nlskb, nlh);
 167         return 0;
 168 nla_put_failure:
 169         nlmsg_trim(nlskb, nlh);
 170         return ret;
 171 }
 172
 173 static const struct nf_hook_entries *
 174 nfnl_hook_entries_head(u8 pf, unsigned int hook, struct net *net, const char *dev)
 175 {
 176         const struct nf_hook_entries *hook_head = NULL;
 177         struct net_device *netdev;
 178
 179         switch (pf) {
 180         case NFPROTO_IPV4:
 181                 if (hook >= ARRAY_SIZE(net->nf.hooks_ipv4))
 182                         return ERR_PTR(-EINVAL);
 183                 hook_head = rcu_dereference(net->nf.hooks_ipv4[hook]);
 184                 break;
 185         case NFPROTO_IPV6:
 186                 if (hook >= ARRAY_SIZE(net->nf.hooks_ipv6))
 187                         return ERR_PTR(-EINVAL);
 188                 hook_head = rcu_dereference(net->nf.hooks_ipv6[hook]);
 189                 break;
 190         case NFPROTO_ARP:
 191 #ifdef CONFIG_NETFILTER_FAMILY_ARP
 192                 if (hook >= ARRAY_SIZE(net->nf.hooks_arp))
 193                         return ERR_PTR(-EINVAL);
 194                 hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
 195 #endif
 196                 break;
 197         case NFPROTO_BRIDGE:
 198 #ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 199                 if (hook >= ARRAY_SIZE(net->nf.hooks_bridge))
 200                         return ERR_PTR(-EINVAL);
 201                 hook_head = rcu_dereference(net->nf.hooks_bridge[hook]);
 202 #endif
 203                 break;
 204 #if IS_ENABLED(CONFIG_DECNET)
 205         case NFPROTO_DECNET:
 206                 if (hook >= ARRAY_SIZE(net->nf.hooks_decnet))
 207                         return ERR_PTR(-EINVAL);
 208                 hook_head = rcu_dereference(net->nf.hooks_decnet[hook]);
 209                 break;
 210 #endif
 211 #ifdef CONFIG_NETFILTER_INGRESS
 212         case NFPROTO_NETDEV:
 213                 if (hook != NF_NETDEV_INGRESS)
 214                         return ERR_PTR(-EOPNOTSUPP);
 215
 216                 if (!dev)
 217                         return ERR_PTR(-ENODEV);
 218
 219                 netdev = dev_get_by_name_rcu(net, dev);
 220                 if (!netdev)
 221                         return ERR_PTR(-ENODEV);
 222
 223                 return rcu_dereference(netdev->nf_hooks_ingress);
 224 #endif
 225         default:
 226                 return ERR_PTR(-EPROTONOSUPPORT);
 227         }
 228
 229         return hook_head;
 230 }
 231
 232 static int nfnl_hook_dump(struct sk_buff *nlskb,
 233                           struct netlink_callback *cb)
 234 {
 235         struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
 236         struct nfnl_dump_hook_data *ctx = cb->data;
 237         int err, family = nfmsg->nfgen_family;
 238         struct net *net = sock_net(nlskb->sk);
 239         struct nf_hook_ops * const *ops;
 240         const struct nf_hook_entries *e;
 241         unsigned int i = cb->args[0];
 242
 243         rcu_read_lock();
 244
 245         e = nfnl_hook_entries_head(family, ctx->hook, net, ctx->devname);
 246         if (!e)
 247                 goto done;
 248
 249         if (IS_ERR(e)) {
 250                 cb->seq++;
 251                 goto done;
 252         }
 253
 254         if ((unsigned long)e != ctx->headv || i >= e->num_hook_entries)
 255                 cb->seq++;
 256
 257         ops = nf_hook_entries_get_hook_ops(e);
 258
 259         for (; i < e->num_hook_entries; i++) {
 260                 err = nfnl_hook_dump_one(nlskb, ctx, ops[i], cb->seq);
 261                 if (err)
 262                         break;
 263         }
 264
 265 done:
 266         nl_dump_check_consistent(cb, nlmsg_hdr(nlskb));
 267         rcu_read_unlock();
 268         cb->args[0] = i;
 269         return nlskb->len;
 270 }
 271
 272 static int nfnl_hook_dump_start(struct netlink_callback *cb)
 273 {
 274         const struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
 275         const struct nlattr * const *nla = cb->data;
 276         struct nfnl_dump_hook_data *ctx = NULL;
 277         struct net *net = sock_net(cb->skb->sk);
 278         u8 family = nfmsg->nfgen_family;
 279         char name[IFNAMSIZ] = "";
 280         const void *head;
 281         u32 hooknum;
 282
 283         hooknum = ntohl(nla_get_be32(nla[NFNLA_HOOK_HOOKNUM]));
 284         if (hooknum > 255)
 285                 return -EINVAL;
 286
 287         if (family == NFPROTO_NETDEV) {
 288                 if (!nla[NFNLA_HOOK_DEV])
 289                         return -EINVAL;
 290
 291                 nla_strscpy(name, nla[NFNLA_HOOK_DEV], sizeof(name));
 292         }
 293
 294         rcu_read_lock();
 295         /* Not dereferenced; for consistency check only */
 296         head = nfnl_hook_entries_head(family, hooknum, net, name);
 297         rcu_read_unlock();
 298
 299         if (head && IS_ERR(head))
 300                 return PTR_ERR(head);
 301
 302         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 303         if (!ctx)
 304                 return -ENOMEM;
 305
 306         strscpy(ctx->devname, name, sizeof(ctx->devname));
 307         ctx->headv = (unsigned long)head;
 308         ctx->hook = hooknum;
 309
 310         cb->seq = 1;
 311         cb->data = ctx;
 312
 313         return 0;
 314 }
 315
 316 static int nfnl_hook_dump_stop(struct netlink_callback *cb)
 317 {
 318         kfree(cb->data);
 319         return 0;
 320 }
 321
 322 static int nfnl_hook_get(struct sk_buff *skb,
 323                          const struct nfnl_info *info,
 324                          const struct nlattr * const nla[])
 325 {
 326         if (!nla[NFNLA_HOOK_HOOKNUM])
 327                 return -EINVAL;
 328
 329         if (info->nlh->nlmsg_flags & NLM_F_DUMP) {
 330                 struct netlink_dump_control c = {
 331                         .start = nfnl_hook_dump_start,
 332                         .done = nfnl_hook_dump_stop,
 333                         .dump = nfnl_hook_dump,
 334                         .module = THIS_MODULE,
 335                         .data = (void *)nla,
 336                 };
 337
 338                 return nf_netlink_dump_start_rcu(info->sk, skb, info->nlh, &c);
 339         }
 340
 341         return -EOPNOTSUPP;
 342 }
 343
 344 static const struct nfnl_callback nfnl_hook_cb[NFNL_MSG_HOOK_MAX] = {
 345         [NFNL_MSG_HOOK_GET] = {
 346                 .call           = nfnl_hook_get,
 347                 .type           = NFNL_CB_RCU,
 348                 .attr_count     = NFNLA_HOOK_MAX,
 349                 .policy         = nfnl_hook_nla_policy
 350         },
 351 };
 352
 353 static const struct nfnetlink_subsystem nfhook_subsys = {
 354         .name                           = "nfhook",
 355         .subsys_id                      = NFNL_SUBSYS_HOOK,
 356         .cb_count                       = NFNL_MSG_HOOK_MAX,
 357         .cb                             = nfnl_hook_cb,
 358 };
 359
 360 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_HOOK);
 361
 362 static int __init nfnetlink_hook_init(void)
 363 {
 364         return nfnetlink_subsys_register(&nfhook_subsys);
 365 }
 366
 367 static void __exit nfnetlink_hook_exit(void)
 368 {
 369         nfnetlink_subsys_unregister(&nfhook_subsys);
 370 }
 371
 372 module_init(nfnetlink_hook_init);
 373 module_exit(nfnetlink_hook_exit);
 374
 375 MODULE_LICENSE("GPL");
 376 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
 377 MODULE_DESCRIPTION("nfnetlink_hook: list registered netfilter hooks");