net/netfilter/nfnetlink_osf.c

   1 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   2 #include <linux/module.h>
   3 #include <linux/kernel.h>
   4
   5 #include <linux/capability.h>
   6 #include <linux/if.h>
   7 #include <linux/inetdevice.h>
   8 #include <linux/ip.h>
   9 #include <linux/list.h>
  10 #include <linux/rculist.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/slab.h>
  13 #include <linux/tcp.h>
  14
  15 #include <net/ip.h>
  16 #include <net/tcp.h>
  17
  18 #include <linux/netfilter/nfnetlink.h>
  19 #include <linux/netfilter/x_tables.h>
  20 #include <net/netfilter/nf_log.h>
  21 #include <linux/netfilter/nfnetlink_osf.h>
  22
  23 /*
  24  * Indexed by dont-fragment bit.
  25  * It is the only constant value in the fingerprint.
  26  */
  27 struct list_head nf_osf_fingers[2];
  28 EXPORT_SYMBOL_GPL(nf_osf_fingers);
  29
  30 static inline int nf_osf_ttl(const struct sk_buff *skb,
  31                              int ttl_check, unsigned char f_ttl)
  32 {
  33         const struct iphdr *ip = ip_hdr(skb);
  34
  35         if (ttl_check != -1) {
  36                 if (ttl_check == NF_OSF_TTL_TRUE)
  37                         return ip->ttl == f_ttl;
  38                 if (ttl_check == NF_OSF_TTL_NOCHECK)
  39                         return 1;
  40                 else if (ip->ttl <= f_ttl)
  41                         return 1;
  42                 else {
  43                         struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
  44                         int ret = 0;
  45
  46                         for_ifa(in_dev) {
  47                                 if (inet_ifa_match(ip->saddr, ifa)) {
  48                                         ret = (ip->ttl == f_ttl);
  49                                         break;
  50                                 }
  51                         }
  52                         endfor_ifa(in_dev);
  53
  54                         return ret;
  55                 }
  56         }
  57
  58         return ip->ttl == f_ttl;
  59 }
  60
  61 struct nf_osf_hdr_ctx {
  62         bool                    df;
  63         u16                     window;
  64         u16                     totlen;
  65         const unsigned char     *optp;
  66         unsigned int            optsize;
  67 };
  68
  69 static bool nf_osf_match_one(const struct sk_buff *skb,
  70                              const struct nf_osf_user_finger *f,
  71                              int ttl_check,
  72                              struct nf_osf_hdr_ctx *ctx)
  73 {
  74         const __u8 *optpinit = ctx->optp;
  75         unsigned int check_WSS = 0;
  76         int fmatch = FMATCH_WRONG;
  77         int foptsize, optnum;
  78         u16 mss = 0;
  79
  80         if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
  81                 return false;
  82
  83         /*
  84          * Should not happen if userspace parser was written correctly.
  85          */
  86         if (f->wss.wc >= OSF_WSS_MAX)
  87                 return false;
  88
  89         /* Check options */
  90
  91         foptsize = 0;
  92         for (optnum = 0; optnum < f->opt_num; ++optnum)
  93                 foptsize += f->opt[optnum].length;
  94
  95         if (foptsize > MAX_IPOPTLEN ||
  96             ctx->optsize > MAX_IPOPTLEN ||
  97             ctx->optsize != foptsize)
  98                 return false;
  99
 100         check_WSS = f->wss.wc;
 101
 102         for (optnum = 0; optnum < f->opt_num; ++optnum) {
 103                 if (f->opt[optnum].kind == *ctx->optp) {
 104                         __u32 len = f->opt[optnum].length;
 105                         const __u8 *optend = ctx->optp + len;
 106
 107                         fmatch = FMATCH_OK;
 108
 109                         switch (*ctx->optp) {
 110                         case OSFOPT_MSS:
 111                                 mss = ctx->optp[3];
 112                                 mss <<= 8;
 113                                 mss |= ctx->optp[2];
 114
 115                                 mss = ntohs((__force __be16)mss);
 116                                 break;
 117                         case OSFOPT_TS:
 118                                 break;
 119                         }
 120
 121                         ctx->optp = optend;
 122                 } else
 123                         fmatch = FMATCH_OPT_WRONG;
 124
 125                 if (fmatch != FMATCH_OK)
 126                         break;
 127         }
 128
 129         if (fmatch != FMATCH_OPT_WRONG) {
 130                 fmatch = FMATCH_WRONG;
 131
 132                 switch (check_WSS) {
 133                 case OSF_WSS_PLAIN:
 134                         if (f->wss.val == 0 || ctx->window == f->wss.val)
 135                                 fmatch = FMATCH_OK;
 136                         break;
 137                 case OSF_WSS_MSS:
 138                         /*
 139                          * Some smart modems decrease mangle MSS to
 140                          * SMART_MSS_2, so we check standard, decreased
 141                          * and the one provided in the fingerprint MSS
 142                          * values.
 143                          */
 144 #define SMART_MSS_1     1460
 145 #define SMART_MSS_2     1448
 146                         if (ctx->window == f->wss.val * mss ||
 147                             ctx->window == f->wss.val * SMART_MSS_1 ||
 148                             ctx->window == f->wss.val * SMART_MSS_2)
 149                                 fmatch = FMATCH_OK;
 150                         break;
 151                 case OSF_WSS_MTU:
 152                         if (ctx->window == f->wss.val * (mss + 40) ||
 153                             ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
 154                             ctx->window == f->wss.val * (SMART_MSS_2 + 40))
 155                                 fmatch = FMATCH_OK;
 156                         break;
 157                 case OSF_WSS_MODULO:
 158                         if ((ctx->window % f->wss.val) == 0)
 159                                 fmatch = FMATCH_OK;
 160                         break;
 161                 }
 162         }
 163
 164         if (fmatch != FMATCH_OK)
 165                 ctx->optp = optpinit;
 166
 167         return fmatch == FMATCH_OK;
 168 }
 169
 170 static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
 171                                                 const struct sk_buff *skb,
 172                                                 const struct iphdr *ip,
 173                                                 unsigned char *opts,
 174                                                 struct tcphdr *_tcph)
 175 {
 176         const struct tcphdr *tcp;
 177
 178         tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), _tcph);
 179         if (!tcp)
 180                 return NULL;
 181
 182         if (!tcp->syn)
 183                 return NULL;
 184
 185         ctx->totlen = ntohs(ip->tot_len);
 186         ctx->df = ntohs(ip->frag_off) & IP_DF;
 187         ctx->window = ntohs(tcp->window);
 188
 189         if (tcp->doff * 4 > sizeof(struct tcphdr)) {
 190                 ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
 191
 192                 ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
 193                                 sizeof(struct tcphdr), ctx->optsize, opts);
 194         }
 195
 196         return tcp;
 197 }
 198
 199 bool
 200 nf_osf_match(const struct sk_buff *skb, u_int8_t family,
 201              int hooknum, struct net_device *in, struct net_device *out,
 202              const struct nf_osf_info *info, struct net *net,
 203              const struct list_head *nf_osf_fingers)
 204 {
 205         const struct iphdr *ip = ip_hdr(skb);
 206         const struct nf_osf_user_finger *f;
 207         unsigned char opts[MAX_IPOPTLEN];
 208         const struct nf_osf_finger *kf;
 209         int fcount = 0, ttl_check;
 210         int fmatch = FMATCH_WRONG;
 211         struct nf_osf_hdr_ctx ctx;
 212         const struct tcphdr *tcp;
 213         struct tcphdr _tcph;
 214
 215         memset(&ctx, 0, sizeof(ctx));
 216
 217         tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
 218         if (!tcp)
 219                 return false;
 220
 221         ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : -1;
 222
 223         list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
 224
 225                 f = &kf->finger;
 226
 227                 if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
 228                         continue;
 229
 230                 if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
 231                         continue;
 232
 233                 fmatch = FMATCH_OK;
 234
 235                 fcount++;
 236
 237                 if (info->flags & NF_OSF_LOG)
 238                         nf_log_packet(net, family, hooknum, skb,
 239                                       in, out, NULL,
 240                                       "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
 241                                       f->genre, f->version, f->subtype,
 242                                       &ip->saddr, ntohs(tcp->source),
 243                                       &ip->daddr, ntohs(tcp->dest),
 244                                       f->ttl - ip->ttl);
 245
 246                 if ((info->flags & NF_OSF_LOG) &&
 247                     info->loglevel == NF_OSF_LOGLEVEL_FIRST)
 248                         break;
 249         }
 250
 251         if (!fcount && (info->flags & NF_OSF_LOG))
 252                 nf_log_packet(net, family, hooknum, skb, in, out, NULL,
 253                               "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
 254                               &ip->saddr, ntohs(tcp->source),
 255                               &ip->daddr, ntohs(tcp->dest));
 256
 257         if (fcount)
 258                 fmatch = FMATCH_OK;
 259
 260         return fmatch == FMATCH_OK;
 261 }
 262 EXPORT_SYMBOL_GPL(nf_osf_match);
 263
 264 const char *nf_osf_find(const struct sk_buff *skb,
 265                         const struct list_head *nf_osf_fingers)
 266 {
 267         const struct iphdr *ip = ip_hdr(skb);
 268         const struct nf_osf_user_finger *f;
 269         unsigned char opts[MAX_IPOPTLEN];
 270         const struct nf_osf_finger *kf;
 271         struct nf_osf_hdr_ctx ctx;
 272         const struct tcphdr *tcp;
 273         const char *genre = NULL;
 274         struct tcphdr _tcph;
 275
 276         memset(&ctx, 0, sizeof(ctx));
 277
 278         tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
 279         if (!tcp)
 280                 return NULL;
 281
 282         list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
 283                 f = &kf->finger;
 284                 if (!nf_osf_match_one(skb, f, -1, &ctx))
 285                         continue;
 286
 287                 genre = f->genre;
 288                 break;
 289         }
 290
 291         return genre;
 292 }
 293 EXPORT_SYMBOL_GPL(nf_osf_find);
 294
 295 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = {
 296         [OSF_ATTR_FINGER]       = { .len = sizeof(struct nf_osf_user_finger) },
 297 };
 298
 299 static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl,
 300                                  struct sk_buff *skb, const struct nlmsghdr *nlh,
 301                                  const struct nlattr * const osf_attrs[],
 302                                  struct netlink_ext_ack *extack)
 303 {
 304         struct nf_osf_user_finger *f;
 305         struct nf_osf_finger *kf = NULL, *sf;
 306         int err = 0;
 307
 308         if (!capable(CAP_NET_ADMIN))
 309                 return -EPERM;
 310
 311         if (!osf_attrs[OSF_ATTR_FINGER])
 312                 return -EINVAL;
 313
 314         if (!(nlh->nlmsg_flags & NLM_F_CREATE))
 315                 return -EINVAL;
 316
 317         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 318
 319         kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
 320         if (!kf)
 321                 return -ENOMEM;
 322
 323         memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
 324
 325         list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
 326                 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
 327                         continue;
 328
 329                 kfree(kf);
 330                 kf = NULL;
 331
 332                 if (nlh->nlmsg_flags & NLM_F_EXCL)
 333                         err = -EEXIST;
 334                 break;
 335         }
 336
 337         /*
 338          * We are protected by nfnl mutex.
 339          */
 340         if (kf)
 341                 list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
 342
 343         return err;
 344 }
 345
 346 static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl,
 347                                     struct sk_buff *skb,
 348                                     const struct nlmsghdr *nlh,
 349                                     const struct nlattr * const osf_attrs[],
 350                                     struct netlink_ext_ack *extack)
 351 {
 352         struct nf_osf_user_finger *f;
 353         struct nf_osf_finger *sf;
 354         int err = -ENOENT;
 355
 356         if (!capable(CAP_NET_ADMIN))
 357                 return -EPERM;
 358
 359         if (!osf_attrs[OSF_ATTR_FINGER])
 360                 return -EINVAL;
 361
 362         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 363
 364         list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
 365                 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
 366                         continue;
 367
 368                 /*
 369                  * We are protected by nfnl mutex.
 370                  */
 371                 list_del_rcu(&sf->finger_entry);
 372                 kfree_rcu(sf, rcu_head);
 373
 374                 err = 0;
 375                 break;
 376         }
 377
 378         return err;
 379 }
 380
 381 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = {
 382         [OSF_MSG_ADD]   = {
 383                 .call           = nfnl_osf_add_callback,
 384                 .attr_count     = OSF_ATTR_MAX,
 385                 .policy         = nfnl_osf_policy,
 386         },
 387         [OSF_MSG_REMOVE]        = {
 388                 .call           = nfnl_osf_remove_callback,
 389                 .attr_count     = OSF_ATTR_MAX,
 390                 .policy         = nfnl_osf_policy,
 391         },
 392 };
 393
 394 static const struct nfnetlink_subsystem nfnl_osf_subsys = {
 395         .name                   = "osf",
 396         .subsys_id              = NFNL_SUBSYS_OSF,
 397         .cb_count               = OSF_MSG_MAX,
 398         .cb                     = nfnl_osf_callbacks,
 399 };
 400
 401 static int __init nfnl_osf_init(void)
 402 {
 403         int err = -EINVAL;
 404         int i;
 405
 406         for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
 407                 INIT_LIST_HEAD(&nf_osf_fingers[i]);
 408
 409         err = nfnetlink_subsys_register(&nfnl_osf_subsys);
 410         if (err < 0) {
 411                 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
 412                 goto err_out_exit;
 413         }
 414         return 0;
 415
 416 err_out_exit:
 417         return err;
 418 }
 419
 420 static void __exit nfnl_osf_fini(void)
 421 {
 422         struct nf_osf_finger *f;
 423         int i;
 424
 425         nfnetlink_subsys_unregister(&nfnl_osf_subsys);
 426
 427         rcu_read_lock();
 428         for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
 429                 list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
 430                         list_del_rcu(&f->finger_entry);
 431                         kfree_rcu(f, rcu_head);
 432                 }
 433         }
 434         rcu_read_unlock();
 435
 436         rcu_barrier();
 437 }
 438
 439 module_init(nfnl_osf_init);
 440 module_exit(nfnl_osf_fini);
 441
 442 MODULE_LICENSE("GPL");