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         const struct in_ifaddr *ifa;
  37         int ret = 0;
  38
  39         if (ttl_check == NF_OSF_TTL_TRUE)
  40                 return ip->ttl == f_ttl;
  41         if (ttl_check == NF_OSF_TTL_NOCHECK)
  42                 return 1;
  43         else if (ip->ttl <= f_ttl)
  44                 return 1;
  45
  46         in_dev_for_each_ifa_rcu(ifa, in_dev) {
  47                 if (inet_ifa_match(ip->saddr, ifa)) {
  48                         ret = (ip->ttl == f_ttl);
  49                         break;
  50                 }
  51         }
  52
  53         return ret;
  54 }
  55
  56 struct nf_osf_hdr_ctx {
  57         bool                    df;
  58         u16                     window;
  59         u16                     totlen;
  60         const unsigned char     *optp;
  61         unsigned int            optsize;
  62 };
  63
  64 static bool nf_osf_match_one(const struct sk_buff *skb,
  65                              const struct nf_osf_user_finger *f,
  66                              int ttl_check,
  67                              struct nf_osf_hdr_ctx *ctx)
  68 {
  69         const __u8 *optpinit = ctx->optp;
  70         unsigned int check_WSS = 0;
  71         int fmatch = FMATCH_WRONG;
  72         int foptsize, optnum;
  73         u16 mss = 0;
  74
  75         if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
  76                 return false;
  77
  78         /*
  79          * Should not happen if userspace parser was written correctly.
  80          */
  81         if (f->wss.wc >= OSF_WSS_MAX)
  82                 return false;
  83
  84         /* Check options */
  85
  86         foptsize = 0;
  87         for (optnum = 0; optnum < f->opt_num; ++optnum)
  88                 foptsize += f->opt[optnum].length;
  89
  90         if (foptsize > MAX_IPOPTLEN ||
  91             ctx->optsize > MAX_IPOPTLEN ||
  92             ctx->optsize != foptsize)
  93                 return false;
  94
  95         check_WSS = f->wss.wc;
  96
  97         for (optnum = 0; optnum < f->opt_num; ++optnum) {
  98                 if (f->opt[optnum].kind == *ctx->optp) {
  99                         __u32 len = f->opt[optnum].length;
 100                         const __u8 *optend = ctx->optp + len;
 101
 102                         fmatch = FMATCH_OK;
 103
 104                         switch (*ctx->optp) {
 105                         case OSFOPT_MSS:
 106                                 mss = ctx->optp[3];
 107                                 mss <<= 8;
 108                                 mss |= ctx->optp[2];
 109
 110                                 mss = ntohs((__force __be16)mss);
 111                                 break;
 112                         case OSFOPT_TS:
 113                                 break;
 114                         }
 115
 116                         ctx->optp = optend;
 117                 } else
 118                         fmatch = FMATCH_OPT_WRONG;
 119
 120                 if (fmatch != FMATCH_OK)
 121                         break;
 122         }
 123
 124         if (fmatch != FMATCH_OPT_WRONG) {
 125                 fmatch = FMATCH_WRONG;
 126
 127                 switch (check_WSS) {
 128                 case OSF_WSS_PLAIN:
 129                         if (f->wss.val == 0 || ctx->window == f->wss.val)
 130                                 fmatch = FMATCH_OK;
 131                         break;
 132                 case OSF_WSS_MSS:
 133                         /*
 134                          * Some smart modems decrease mangle MSS to
 135                          * SMART_MSS_2, so we check standard, decreased
 136                          * and the one provided in the fingerprint MSS
 137                          * values.
 138                          */
 139 #define SMART_MSS_1     1460
 140 #define SMART_MSS_2     1448
 141                         if (ctx->window == f->wss.val * mss ||
 142                             ctx->window == f->wss.val * SMART_MSS_1 ||
 143                             ctx->window == f->wss.val * SMART_MSS_2)
 144                                 fmatch = FMATCH_OK;
 145                         break;
 146                 case OSF_WSS_MTU:
 147                         if (ctx->window == f->wss.val * (mss + 40) ||
 148                             ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
 149                             ctx->window == f->wss.val * (SMART_MSS_2 + 40))
 150                                 fmatch = FMATCH_OK;
 151                         break;
 152                 case OSF_WSS_MODULO:
 153                         if ((ctx->window % f->wss.val) == 0)
 154                                 fmatch = FMATCH_OK;
 155                         break;
 156                 }
 157         }
 158
 159         if (fmatch != FMATCH_OK)
 160                 ctx->optp = optpinit;
 161
 162         return fmatch == FMATCH_OK;
 163 }
 164
 165 static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
 166                                                 const struct sk_buff *skb,
 167                                                 const struct iphdr *ip,
 168                                                 unsigned char *opts,
 169                                                 struct tcphdr *_tcph)
 170 {
 171         const struct tcphdr *tcp;
 172
 173         tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), _tcph);
 174         if (!tcp)
 175                 return NULL;
 176
 177         if (!tcp->syn)
 178                 return NULL;
 179
 180         ctx->totlen = ntohs(ip->tot_len);
 181         ctx->df = ntohs(ip->frag_off) & IP_DF;
 182         ctx->window = ntohs(tcp->window);
 183
 184         if (tcp->doff * 4 > sizeof(struct tcphdr)) {
 185                 ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
 186
 187                 ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
 188                                 sizeof(struct tcphdr), ctx->optsize, opts);
 189                 if (!ctx->optp)
 190                         return NULL;
 191         }
 192
 193         return tcp;
 194 }
 195
 196 bool
 197 nf_osf_match(const struct sk_buff *skb, u_int8_t family,
 198              int hooknum, struct net_device *in, struct net_device *out,
 199              const struct nf_osf_info *info, struct net *net,
 200              const struct list_head *nf_osf_fingers)
 201 {
 202         const struct iphdr *ip = ip_hdr(skb);
 203         const struct nf_osf_user_finger *f;
 204         unsigned char opts[MAX_IPOPTLEN];
 205         const struct nf_osf_finger *kf;
 206         int fcount = 0, ttl_check;
 207         int fmatch = FMATCH_WRONG;
 208         struct nf_osf_hdr_ctx ctx;
 209         const struct tcphdr *tcp;
 210         struct tcphdr _tcph;
 211
 212         memset(&ctx, 0, sizeof(ctx));
 213
 214         tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
 215         if (!tcp)
 216                 return false;
 217
 218         ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;
 219
 220         list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
 221
 222                 f = &kf->finger;
 223
 224                 if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
 225                         continue;
 226
 227                 if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
 228                         continue;
 229
 230                 fmatch = FMATCH_OK;
 231
 232                 fcount++;
 233
 234                 if (info->flags & NF_OSF_LOG)
 235                         nf_log_packet(net, family, hooknum, skb,
 236                                       in, out, NULL,
 237                                       "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
 238                                       f->genre, f->version, f->subtype,
 239                                       &ip->saddr, ntohs(tcp->source),
 240                                       &ip->daddr, ntohs(tcp->dest),
 241                                       f->ttl - ip->ttl);
 242
 243                 if ((info->flags & NF_OSF_LOG) &&
 244                     info->loglevel == NF_OSF_LOGLEVEL_FIRST)
 245                         break;
 246         }
 247
 248         if (!fcount && (info->flags & NF_OSF_LOG))
 249                 nf_log_packet(net, family, hooknum, skb, in, out, NULL,
 250                               "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
 251                               &ip->saddr, ntohs(tcp->source),
 252                               &ip->daddr, ntohs(tcp->dest));
 253
 254         if (fcount)
 255                 fmatch = FMATCH_OK;
 256
 257         return fmatch == FMATCH_OK;
 258 }
 259 EXPORT_SYMBOL_GPL(nf_osf_match);
 260
 261 bool nf_osf_find(const struct sk_buff *skb,
 262                  const struct list_head *nf_osf_fingers,
 263                  const int ttl_check, struct nf_osf_data *data)
 264 {
 265         const struct iphdr *ip = ip_hdr(skb);
 266         const struct nf_osf_user_finger *f;
 267         unsigned char opts[MAX_IPOPTLEN];
 268         const struct nf_osf_finger *kf;
 269         struct nf_osf_hdr_ctx ctx;
 270         const struct tcphdr *tcp;
 271         struct tcphdr _tcph;
 272         bool found = false;
 273
 274         memset(&ctx, 0, sizeof(ctx));
 275
 276         tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
 277         if (!tcp)
 278                 return false;
 279
 280         list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
 281                 f = &kf->finger;
 282                 if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
 283                         continue;
 284
 285                 data->genre = f->genre;
 286                 data->version = f->version;
 287                 found = true;
 288                 break;
 289         }
 290
 291         return found;
 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 sk_buff *skb,
 300                                  const struct nfnl_info *info,
 301                                  const struct nlattr * const osf_attrs[])
 302 {
 303         struct nf_osf_user_finger *f;
 304         struct nf_osf_finger *kf = NULL, *sf;
 305         int err = 0;
 306
 307         if (!capable(CAP_NET_ADMIN))
 308                 return -EPERM;
 309
 310         if (!osf_attrs[OSF_ATTR_FINGER])
 311                 return -EINVAL;
 312
 313         if (!(info->nlh->nlmsg_flags & NLM_F_CREATE))
 314                 return -EINVAL;
 315
 316         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 317
 318         if (f->opt_num > ARRAY_SIZE(f->opt))
 319                 return -EINVAL;
 320
 321         if (!memchr(f->genre, 0, MAXGENRELEN) ||
 322             !memchr(f->subtype, 0, MAXGENRELEN) ||
 323             !memchr(f->version, 0, MAXGENRELEN))
 324                 return -EINVAL;
 325
 326         kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
 327         if (!kf)
 328                 return -ENOMEM;
 329
 330         memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
 331
 332         list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
 333                 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
 334                         continue;
 335
 336                 kfree(kf);
 337                 kf = NULL;
 338
 339                 if (info->nlh->nlmsg_flags & NLM_F_EXCL)
 340                         err = -EEXIST;
 341                 break;
 342         }
 343
 344         /*
 345          * We are protected by nfnl mutex.
 346          */
 347         if (kf)
 348                 list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
 349
 350         return err;
 351 }
 352
 353 static int nfnl_osf_remove_callback(struct sk_buff *skb,
 354                                     const struct nfnl_info *info,
 355                                     const struct nlattr * const osf_attrs[])
 356 {
 357         struct nf_osf_user_finger *f;
 358         struct nf_osf_finger *sf;
 359         int err = -ENOENT;
 360
 361         if (!capable(CAP_NET_ADMIN))
 362                 return -EPERM;
 363
 364         if (!osf_attrs[OSF_ATTR_FINGER])
 365                 return -EINVAL;
 366
 367         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 368
 369         list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
 370                 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
 371                         continue;
 372
 373                 /*
 374                  * We are protected by nfnl mutex.
 375                  */
 376                 list_del_rcu(&sf->finger_entry);
 377                 kfree_rcu(sf, rcu_head);
 378
 379                 err = 0;
 380                 break;
 381         }
 382
 383         return err;
 384 }
 385
 386 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = {
 387         [OSF_MSG_ADD]   = {
 388                 .call           = nfnl_osf_add_callback,
 389                 .type           = NFNL_CB_MUTEX,
 390                 .attr_count     = OSF_ATTR_MAX,
 391                 .policy         = nfnl_osf_policy,
 392         },
 393         [OSF_MSG_REMOVE]        = {
 394                 .call           = nfnl_osf_remove_callback,
 395                 .type           = NFNL_CB_MUTEX,
 396                 .attr_count     = OSF_ATTR_MAX,
 397                 .policy         = nfnl_osf_policy,
 398         },
 399 };
 400
 401 static const struct nfnetlink_subsystem nfnl_osf_subsys = {
 402         .name                   = "osf",
 403         .subsys_id              = NFNL_SUBSYS_OSF,
 404         .cb_count               = OSF_MSG_MAX,
 405         .cb                     = nfnl_osf_callbacks,
 406 };
 407
 408 static int __init nfnl_osf_init(void)
 409 {
 410         int err = -EINVAL;
 411         int i;
 412
 413         for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
 414                 INIT_LIST_HEAD(&nf_osf_fingers[i]);
 415
 416         err = nfnetlink_subsys_register(&nfnl_osf_subsys);
 417         if (err < 0) {
 418                 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
 419                 goto err_out_exit;
 420         }
 421         return 0;
 422
 423 err_out_exit:
 424         return err;
 425 }
 426
 427 static void __exit nfnl_osf_fini(void)
 428 {
 429         struct nf_osf_finger *f;
 430         int i;
 431
 432         nfnetlink_subsys_unregister(&nfnl_osf_subsys);
 433
 434         rcu_read_lock();
 435         for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
 436                 list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
 437                         list_del_rcu(&f->finger_entry);
 438                         kfree_rcu(f, rcu_head);
 439                 }
 440         }
 441         rcu_read_unlock();
 442
 443         rcu_barrier();
 444 }
 445
 446 module_init(nfnl_osf_init);
 447 module_exit(nfnl_osf_fini);
 448
 449 MODULE_LICENSE("GPL");
 450 MODULE_DESCRIPTION("Passive OS fingerprint matching");
 451 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);