net/netfilter/nfnetlink_osf.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   3 #include <linux/module.h>
   4 #include <linux/kernel.h>
   5
   6 #include <linux/capability.h>
   7 #include <linux/if.h>
   8 #include <linux/inetdevice.h>
   9 #include <linux/ip.h>
  10 #include <linux/list.h>
  11 #include <linux/rculist.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/slab.h>
  14 #include <linux/tcp.h>
  15
  16 #include <net/ip.h>
  17 #include <net/tcp.h>
  18
  19 #include <linux/netfilter/nfnetlink.h>
  20 #include <linux/netfilter/x_tables.h>
  21 #include <net/netfilter/nf_log.h>
  22 #include <linux/netfilter/nfnetlink_osf.h>
  23
  24 /*
  25  * Indexed by dont-fragment bit.
  26  * It is the only constant value in the fingerprint.
  27  */
  28 struct list_head nf_osf_fingers[2];
  29 EXPORT_SYMBOL_GPL(nf_osf_fingers);
  30
  31 static inline int nf_osf_ttl(const struct sk_buff *skb,
  32                              int ttl_check, unsigned char f_ttl)
  33 {
  34         struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
  35         const struct iphdr *ip = ip_hdr(skb);
  36         int ret = 0;
  37
  38         if (ttl_check == NF_OSF_TTL_TRUE)
  39                 return ip->ttl == f_ttl;
  40         if (ttl_check == NF_OSF_TTL_NOCHECK)
  41                 return 1;
  42         else if (ip->ttl <= f_ttl)
  43                 return 1;
  44
  45         for_ifa(in_dev) {
  46                 if (inet_ifa_match(ip->saddr, ifa)) {
  47                         ret = (ip->ttl == f_ttl);
  48                         break;
  49                 }
  50         }
  51
  52         endfor_ifa(in_dev);
  53
  54         return ret;
  55 }
  56
  57 struct nf_osf_hdr_ctx {
  58         bool                    df;
  59         u16                     window;
  60         u16                     totlen;
  61         const unsigned char     *optp;
  62         unsigned int            optsize;
  63 };
  64
  65 static bool nf_osf_match_one(const struct sk_buff *skb,
  66                              const struct nf_osf_user_finger *f,
  67                              int ttl_check,
  68                              struct nf_osf_hdr_ctx *ctx)
  69 {
  70         const __u8 *optpinit = ctx->optp;
  71         unsigned int check_WSS = 0;
  72         int fmatch = FMATCH_WRONG;
  73         int foptsize, optnum;
  74         u16 mss = 0;
  75
  76         if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
  77                 return false;
  78
  79         /*
  80          * Should not happen if userspace parser was written correctly.
  81          */
  82         if (f->wss.wc >= OSF_WSS_MAX)
  83                 return false;
  84
  85         /* Check options */
  86
  87         foptsize = 0;
  88         for (optnum = 0; optnum < f->opt_num; ++optnum)
  89                 foptsize += f->opt[optnum].length;
  90
  91         if (foptsize > MAX_IPOPTLEN ||
  92             ctx->optsize > MAX_IPOPTLEN ||
  93             ctx->optsize != foptsize)
  94                 return false;
  95
  96         check_WSS = f->wss.wc;
  97
  98         for (optnum = 0; optnum < f->opt_num; ++optnum) {
  99                 if (f->opt[optnum].kind == *ctx->optp) {
 100                         __u32 len = f->opt[optnum].length;
 101                         const __u8 *optend = ctx->optp + len;
 102
 103                         fmatch = FMATCH_OK;
 104
 105                         switch (*ctx->optp) {
 106                         case OSFOPT_MSS:
 107                                 mss = ctx->optp[3];
 108                                 mss <<= 8;
 109                                 mss |= ctx->optp[2];
 110
 111                                 mss = ntohs((__force __be16)mss);
 112                                 break;
 113                         case OSFOPT_TS:
 114                                 break;
 115                         }
 116
 117                         ctx->optp = optend;
 118                 } else
 119                         fmatch = FMATCH_OPT_WRONG;
 120
 121                 if (fmatch != FMATCH_OK)
 122                         break;
 123         }
 124
 125         if (fmatch != FMATCH_OPT_WRONG) {
 126                 fmatch = FMATCH_WRONG;
 127
 128                 switch (check_WSS) {
 129                 case OSF_WSS_PLAIN:
 130                         if (f->wss.val == 0 || ctx->window == f->wss.val)
 131                                 fmatch = FMATCH_OK;
 132                         break;
 133                 case OSF_WSS_MSS:
 134                         /*
 135                          * Some smart modems decrease mangle MSS to
 136                          * SMART_MSS_2, so we check standard, decreased
 137                          * and the one provided in the fingerprint MSS
 138                          * values.
 139                          */
 140 #define SMART_MSS_1     1460
 141 #define SMART_MSS_2     1448
 142                         if (ctx->window == f->wss.val * mss ||
 143                             ctx->window == f->wss.val * SMART_MSS_1 ||
 144                             ctx->window == f->wss.val * SMART_MSS_2)
 145                                 fmatch = FMATCH_OK;
 146                         break;
 147                 case OSF_WSS_MTU:
 148                         if (ctx->window == f->wss.val * (mss + 40) ||
 149                             ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
 150                             ctx->window == f->wss.val * (SMART_MSS_2 + 40))
 151                                 fmatch = FMATCH_OK;
 152                         break;
 153                 case OSF_WSS_MODULO:
 154                         if ((ctx->window % f->wss.val) == 0)
 155                                 fmatch = FMATCH_OK;
 156                         break;
 157                 }
 158         }
 159
 160         if (fmatch != FMATCH_OK)
 161                 ctx->optp = optpinit;
 162
 163         return fmatch == FMATCH_OK;
 164 }
 165
 166 static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
 167                                                 const struct sk_buff *skb,
 168                                                 const struct iphdr *ip,
 169                                                 unsigned char *opts)
 170 {
 171         const struct tcphdr *tcp;
 172         struct tcphdr _tcph;
 173
 174         tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
 175         if (!tcp)
 176                 return NULL;
 177
 178         if (!tcp->syn)
 179                 return NULL;
 180
 181         ctx->totlen = ntohs(ip->tot_len);
 182         ctx->df = ntohs(ip->frag_off) & IP_DF;
 183         ctx->window = ntohs(tcp->window);
 184
 185         if (tcp->doff * 4 > sizeof(struct tcphdr)) {
 186                 ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
 187
 188                 ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
 189                                 sizeof(struct tcphdr), ctx->optsize, opts);
 190         }
 191
 192         return tcp;
 193 }
 194
 195 bool
 196 nf_osf_match(const struct sk_buff *skb, u_int8_t family,
 197              int hooknum, struct net_device *in, struct net_device *out,
 198              const struct nf_osf_info *info, struct net *net,
 199              const struct list_head *nf_osf_fingers)
 200 {
 201         const struct iphdr *ip = ip_hdr(skb);
 202         const struct nf_osf_user_finger *f;
 203         unsigned char opts[MAX_IPOPTLEN];
 204         const struct nf_osf_finger *kf;
 205         int fcount = 0, ttl_check;
 206         int fmatch = FMATCH_WRONG;
 207         struct nf_osf_hdr_ctx ctx;
 208         const struct tcphdr *tcp;
 209
 210         memset(&ctx, 0, sizeof(ctx));
 211
 212         tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
 213         if (!tcp)
 214                 return false;
 215
 216         ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;
 217
 218         list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
 219
 220                 f = &kf->finger;
 221
 222                 if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
 223                         continue;
 224
 225                 if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
 226                         continue;
 227
 228                 fmatch = FMATCH_OK;
 229
 230                 fcount++;
 231
 232                 if (info->flags & NF_OSF_LOG)
 233                         nf_log_packet(net, family, hooknum, skb,
 234                                       in, out, NULL,
 235                                       "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
 236                                       f->genre, f->version, f->subtype,
 237                                       &ip->saddr, ntohs(tcp->source),
 238                                       &ip->daddr, ntohs(tcp->dest),
 239                                       f->ttl - ip->ttl);
 240
 241                 if ((info->flags & NF_OSF_LOG) &&
 242                     info->loglevel == NF_OSF_LOGLEVEL_FIRST)
 243                         break;
 244         }
 245
 246         if (!fcount && (info->flags & NF_OSF_LOG))
 247                 nf_log_packet(net, family, hooknum, skb, in, out, NULL,
 248                               "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
 249                               &ip->saddr, ntohs(tcp->source),
 250                               &ip->daddr, ntohs(tcp->dest));
 251
 252         if (fcount)
 253                 fmatch = FMATCH_OK;
 254
 255         return fmatch == FMATCH_OK;
 256 }
 257 EXPORT_SYMBOL_GPL(nf_osf_match);
 258
 259 bool nf_osf_find(const struct sk_buff *skb,
 260                  const struct list_head *nf_osf_fingers,
 261                  const int ttl_check, struct nf_osf_data *data)
 262 {
 263         const struct iphdr *ip = ip_hdr(skb);
 264         const struct nf_osf_user_finger *f;
 265         unsigned char opts[MAX_IPOPTLEN];
 266         const struct nf_osf_finger *kf;
 267         struct nf_osf_hdr_ctx ctx;
 268         const struct tcphdr *tcp;
 269
 270         memset(&ctx, 0, sizeof(ctx));
 271
 272         tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
 273         if (!tcp)
 274                 return false;
 275
 276         list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
 277                 f = &kf->finger;
 278                 if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
 279                         continue;
 280
 281                 data->genre = f->genre;
 282                 data->version = f->version;
 283                 break;
 284         }
 285
 286         return true;
 287 }
 288 EXPORT_SYMBOL_GPL(nf_osf_find);
 289
 290 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = {
 291         [OSF_ATTR_FINGER]       = { .len = sizeof(struct nf_osf_user_finger) },
 292 };
 293
 294 static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl,
 295                                  struct sk_buff *skb, const struct nlmsghdr *nlh,
 296                                  const struct nlattr * const osf_attrs[],
 297                                  struct netlink_ext_ack *extack)
 298 {
 299         struct nf_osf_user_finger *f;
 300         struct nf_osf_finger *kf = NULL, *sf;
 301         int err = 0;
 302
 303         if (!capable(CAP_NET_ADMIN))
 304                 return -EPERM;
 305
 306         if (!osf_attrs[OSF_ATTR_FINGER])
 307                 return -EINVAL;
 308
 309         if (!(nlh->nlmsg_flags & NLM_F_CREATE))
 310                 return -EINVAL;
 311
 312         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 313
 314         kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
 315         if (!kf)
 316                 return -ENOMEM;
 317
 318         memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
 319
 320         list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
 321                 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
 322                         continue;
 323
 324                 kfree(kf);
 325                 kf = NULL;
 326
 327                 if (nlh->nlmsg_flags & NLM_F_EXCL)
 328                         err = -EEXIST;
 329                 break;
 330         }
 331
 332         /*
 333          * We are protected by nfnl mutex.
 334          */
 335         if (kf)
 336                 list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
 337
 338         return err;
 339 }
 340
 341 static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl,
 342                                     struct sk_buff *skb,
 343                                     const struct nlmsghdr *nlh,
 344                                     const struct nlattr * const osf_attrs[],
 345                                     struct netlink_ext_ack *extack)
 346 {
 347         struct nf_osf_user_finger *f;
 348         struct nf_osf_finger *sf;
 349         int err = -ENOENT;
 350
 351         if (!capable(CAP_NET_ADMIN))
 352                 return -EPERM;
 353
 354         if (!osf_attrs[OSF_ATTR_FINGER])
 355                 return -EINVAL;
 356
 357         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 358
 359         list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
 360                 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
 361                         continue;
 362
 363                 /*
 364                  * We are protected by nfnl mutex.
 365                  */
 366                 list_del_rcu(&sf->finger_entry);
 367                 kfree_rcu(sf, rcu_head);
 368
 369                 err = 0;
 370                 break;
 371         }
 372
 373         return err;
 374 }
 375
 376 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = {
 377         [OSF_MSG_ADD]   = {
 378                 .call           = nfnl_osf_add_callback,
 379                 .attr_count     = OSF_ATTR_MAX,
 380                 .policy         = nfnl_osf_policy,
 381         },
 382         [OSF_MSG_REMOVE]        = {
 383                 .call           = nfnl_osf_remove_callback,
 384                 .attr_count     = OSF_ATTR_MAX,
 385                 .policy         = nfnl_osf_policy,
 386         },
 387 };
 388
 389 static const struct nfnetlink_subsystem nfnl_osf_subsys = {
 390         .name                   = "osf",
 391         .subsys_id              = NFNL_SUBSYS_OSF,
 392         .cb_count               = OSF_MSG_MAX,
 393         .cb                     = nfnl_osf_callbacks,
 394 };
 395
 396 static int __init nfnl_osf_init(void)
 397 {
 398         int err = -EINVAL;
 399         int i;
 400
 401         for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
 402                 INIT_LIST_HEAD(&nf_osf_fingers[i]);
 403
 404         err = nfnetlink_subsys_register(&nfnl_osf_subsys);
 405         if (err < 0) {
 406                 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
 407                 goto err_out_exit;
 408         }
 409         return 0;
 410
 411 err_out_exit:
 412         return err;
 413 }
 414
 415 static void __exit nfnl_osf_fini(void)
 416 {
 417         struct nf_osf_finger *f;
 418         int i;
 419
 420         nfnetlink_subsys_unregister(&nfnl_osf_subsys);
 421
 422         rcu_read_lock();
 423         for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
 424                 list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
 425                         list_del_rcu(&f->finger_entry);
 426                         kfree_rcu(f, rcu_head);
 427                 }
 428         }
 429         rcu_read_unlock();
 430
 431         rcu_barrier();
 432 }
 433
 434 module_init(nfnl_osf_init);
 435 module_exit(nfnl_osf_fini);
 436
 437 MODULE_LICENSE("GPL");