net/netfilter/nft_exthdr.c

   1 /*
   2  * Copyright (c) 2008 Patrick McHardy <kaber@trash.net>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * Development of this code funded by Astaro AG (http://www.astaro.com/)
   9  */
  10
  11 #include <asm/unaligned.h>
  12 #include <linux/kernel.h>
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15 #include <linux/netlink.h>
  16 #include <linux/netfilter.h>
  17 #include <linux/netfilter/nf_tables.h>
  18 #include <net/netfilter/nf_tables.h>
  19 #include <net/tcp.h>
  20
  21 struct nft_exthdr {
  22         u8                      type;
  23         u8                      offset;
  24         u8                      len;
  25         u8                      op;
  26         enum nft_registers      dreg:8;
  27         enum nft_registers      sreg:8;
  28         u8                      flags;
  29 };
  30
  31 static unsigned int optlen(const u8 *opt, unsigned int offset)
  32 {
  33         /* Beware zero-length options: make finite progress */
  34         if (opt[offset] <= TCPOPT_NOP || opt[offset + 1] == 0)
  35                 return 1;
  36         else
  37                 return opt[offset + 1];
  38 }
  39
  40 static void nft_exthdr_ipv6_eval(const struct nft_expr *expr,
  41                                  struct nft_regs *regs,
  42                                  const struct nft_pktinfo *pkt)
  43 {
  44         struct nft_exthdr *priv = nft_expr_priv(expr);
  45         u32 *dest = &regs->data[priv->dreg];
  46         unsigned int offset = 0;
  47         int err;
  48
  49         err = ipv6_find_hdr(pkt->skb, &offset, priv->type, NULL, NULL);
  50         if (priv->flags & NFT_EXTHDR_F_PRESENT) {
  51                 *dest = (err >= 0);
  52                 return;
  53         } else if (err < 0) {
  54                 goto err;
  55         }
  56         offset += priv->offset;
  57
  58         dest[priv->len / NFT_REG32_SIZE] = 0;
  59         if (skb_copy_bits(pkt->skb, offset, dest, priv->len) < 0)
  60                 goto err;
  61         return;
  62 err:
  63         regs->verdict.code = NFT_BREAK;
  64 }
  65
  66 static void *
  67 nft_tcp_header_pointer(const struct nft_pktinfo *pkt,
  68                        unsigned int len, void *buffer, unsigned int *tcphdr_len)
  69 {
  70         struct tcphdr *tcph;
  71
  72         if (!pkt->tprot_set || pkt->tprot != IPPROTO_TCP)
  73                 return NULL;
  74
  75         tcph = skb_header_pointer(pkt->skb, pkt->xt.thoff, sizeof(*tcph), buffer);
  76         if (!tcph)
  77                 return NULL;
  78
  79         *tcphdr_len = __tcp_hdrlen(tcph);
  80         if (*tcphdr_len < sizeof(*tcph) || *tcphdr_len > len)
  81                 return NULL;
  82
  83         return skb_header_pointer(pkt->skb, pkt->xt.thoff, *tcphdr_len, buffer);
  84 }
  85
  86 static void nft_exthdr_tcp_eval(const struct nft_expr *expr,
  87                                 struct nft_regs *regs,
  88                                 const struct nft_pktinfo *pkt)
  89 {
  90         u8 buff[sizeof(struct tcphdr) + MAX_TCP_OPTION_SPACE];
  91         struct nft_exthdr *priv = nft_expr_priv(expr);
  92         unsigned int i, optl, tcphdr_len, offset;
  93         u32 *dest = &regs->data[priv->dreg];
  94         struct tcphdr *tcph;
  95         u8 *opt;
  96
  97         tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff, &tcphdr_len);
  98         if (!tcph)
  99                 goto err;
 100
 101         opt = (u8 *)tcph;
 102         for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) {
 103                 optl = optlen(opt, i);
 104
 105                 if (priv->type != opt[i])
 106                         continue;
 107
 108                 if (i + optl > tcphdr_len || priv->len + priv->offset > optl)
 109                         goto err;
 110
 111                 offset = i + priv->offset;
 112                 if (priv->flags & NFT_EXTHDR_F_PRESENT) {
 113                         *dest = 1;
 114                 } else {
 115                         dest[priv->len / NFT_REG32_SIZE] = 0;
 116                         memcpy(dest, opt + offset, priv->len);
 117                 }
 118
 119                 return;
 120         }
 121
 122 err:
 123         if (priv->flags & NFT_EXTHDR_F_PRESENT)
 124                 *dest = 0;
 125         else
 126                 regs->verdict.code = NFT_BREAK;
 127 }
 128
 129 static void nft_exthdr_tcp_set_eval(const struct nft_expr *expr,
 130                                     struct nft_regs *regs,
 131                                     const struct nft_pktinfo *pkt)
 132 {
 133         u8 buff[sizeof(struct tcphdr) + MAX_TCP_OPTION_SPACE];
 134         struct nft_exthdr *priv = nft_expr_priv(expr);
 135         unsigned int i, optl, tcphdr_len, offset;
 136         struct tcphdr *tcph;
 137         u8 *opt;
 138         u32 src;
 139
 140         tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff, &tcphdr_len);
 141         if (!tcph)
 142                 return;
 143
 144         opt = (u8 *)tcph;
 145         for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) {
 146                 union {
 147                         u8 octet;
 148                         __be16 v16;
 149                         __be32 v32;
 150                 } old, new;
 151
 152                 optl = optlen(opt, i);
 153
 154                 if (priv->type != opt[i])
 155                         continue;
 156
 157                 if (i + optl > tcphdr_len || priv->len + priv->offset > optl)
 158                         return;
 159
 160                 if (!skb_make_writable(pkt->skb, pkt->xt.thoff + i + priv->len))
 161                         return;
 162
 163                 tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff,
 164                                               &tcphdr_len);
 165                 if (!tcph)
 166                         return;
 167
 168                 src = regs->data[priv->sreg];
 169                 offset = i + priv->offset;
 170
 171                 switch (priv->len) {
 172                 case 2:
 173                         old.v16 = get_unaligned((u16 *)(opt + offset));
 174                         new.v16 = src;
 175
 176                         switch (priv->type) {
 177                         case TCPOPT_MSS:
 178                                 /* increase can cause connection to stall */
 179                                 if (ntohs(old.v16) <= ntohs(new.v16))
 180                                         return;
 181                         break;
 182                         }
 183
 184                         if (old.v16 == new.v16)
 185                                 return;
 186
 187                         put_unaligned(new.v16, (u16*)(opt + offset));
 188                         inet_proto_csum_replace2(&tcph->check, pkt->skb,
 189                                                  old.v16, new.v16, false);
 190                         break;
 191                 case 4:
 192                         new.v32 = src;
 193                         old.v32 = get_unaligned((u32 *)(opt + offset));
 194
 195                         if (old.v32 == new.v32)
 196                                 return;
 197
 198                         put_unaligned(new.v32, (u32*)(opt + offset));
 199                         inet_proto_csum_replace4(&tcph->check, pkt->skb,
 200                                                  old.v32, new.v32, false);
 201                         break;
 202                 default:
 203                         WARN_ON_ONCE(1);
 204                         break;
 205                 }
 206
 207                 return;
 208         }
 209 }
 210
 211 static const struct nla_policy nft_exthdr_policy[NFTA_EXTHDR_MAX + 1] = {
 212         [NFTA_EXTHDR_DREG]              = { .type = NLA_U32 },
 213         [NFTA_EXTHDR_TYPE]              = { .type = NLA_U8 },
 214         [NFTA_EXTHDR_OFFSET]            = { .type = NLA_U32 },
 215         [NFTA_EXTHDR_LEN]               = { .type = NLA_U32 },
 216         [NFTA_EXTHDR_FLAGS]             = { .type = NLA_U32 },
 217 };
 218
 219 static int nft_exthdr_init(const struct nft_ctx *ctx,
 220                            const struct nft_expr *expr,
 221                            const struct nlattr * const tb[])
 222 {
 223         struct nft_exthdr *priv = nft_expr_priv(expr);
 224         u32 offset, len, flags = 0, op = NFT_EXTHDR_OP_IPV6;
 225         int err;
 226
 227         if (!tb[NFTA_EXTHDR_DREG] ||
 228             !tb[NFTA_EXTHDR_TYPE] ||
 229             !tb[NFTA_EXTHDR_OFFSET] ||
 230             !tb[NFTA_EXTHDR_LEN])
 231                 return -EINVAL;
 232
 233         err = nft_parse_u32_check(tb[NFTA_EXTHDR_OFFSET], U8_MAX, &offset);
 234         if (err < 0)
 235                 return err;
 236
 237         err = nft_parse_u32_check(tb[NFTA_EXTHDR_LEN], U8_MAX, &len);
 238         if (err < 0)
 239                 return err;
 240
 241         if (tb[NFTA_EXTHDR_FLAGS]) {
 242                 err = nft_parse_u32_check(tb[NFTA_EXTHDR_FLAGS], U8_MAX, &flags);
 243                 if (err < 0)
 244                         return err;
 245
 246                 if (flags & ~NFT_EXTHDR_F_PRESENT)
 247                         return -EINVAL;
 248         }
 249
 250         if (tb[NFTA_EXTHDR_OP]) {
 251                 err = nft_parse_u32_check(tb[NFTA_EXTHDR_OP], U8_MAX, &op);
 252                 if (err < 0)
 253                         return err;
 254         }
 255
 256         priv->type   = nla_get_u8(tb[NFTA_EXTHDR_TYPE]);
 257         priv->offset = offset;
 258         priv->len    = len;
 259         priv->dreg   = nft_parse_register(tb[NFTA_EXTHDR_DREG]);
 260         priv->flags  = flags;
 261         priv->op     = op;
 262
 263         return nft_validate_register_store(ctx, priv->dreg, NULL,
 264                                            NFT_DATA_VALUE, priv->len);
 265 }
 266
 267 static int nft_exthdr_tcp_set_init(const struct nft_ctx *ctx,
 268                                    const struct nft_expr *expr,
 269                                    const struct nlattr * const tb[])
 270 {
 271         struct nft_exthdr *priv = nft_expr_priv(expr);
 272         u32 offset, len, flags = 0, op = NFT_EXTHDR_OP_IPV6;
 273         int err;
 274
 275         if (!tb[NFTA_EXTHDR_SREG] ||
 276             !tb[NFTA_EXTHDR_TYPE] ||
 277             !tb[NFTA_EXTHDR_OFFSET] ||
 278             !tb[NFTA_EXTHDR_LEN])
 279                 return -EINVAL;
 280
 281         if (tb[NFTA_EXTHDR_DREG] || tb[NFTA_EXTHDR_FLAGS])
 282                 return -EINVAL;
 283
 284         err = nft_parse_u32_check(tb[NFTA_EXTHDR_OFFSET], U8_MAX, &offset);
 285         if (err < 0)
 286                 return err;
 287
 288         err = nft_parse_u32_check(tb[NFTA_EXTHDR_LEN], U8_MAX, &len);
 289         if (err < 0)
 290                 return err;
 291
 292         if (offset < 2)
 293                 return -EOPNOTSUPP;
 294
 295         switch (len) {
 296         case 2: break;
 297         case 4: break;
 298         default:
 299                 return -EOPNOTSUPP;
 300         }
 301
 302         err = nft_parse_u32_check(tb[NFTA_EXTHDR_OP], U8_MAX, &op);
 303         if (err < 0)
 304                 return err;
 305
 306         priv->type   = nla_get_u8(tb[NFTA_EXTHDR_TYPE]);
 307         priv->offset = offset;
 308         priv->len    = len;
 309         priv->sreg   = nft_parse_register(tb[NFTA_EXTHDR_SREG]);
 310         priv->flags  = flags;
 311         priv->op     = op;
 312
 313         return nft_validate_register_load(priv->sreg, priv->len);
 314 }
 315
 316 static int nft_exthdr_dump_common(struct sk_buff *skb, const struct nft_exthdr *priv)
 317 {
 318         if (nla_put_u8(skb, NFTA_EXTHDR_TYPE, priv->type))
 319                 goto nla_put_failure;
 320         if (nla_put_be32(skb, NFTA_EXTHDR_OFFSET, htonl(priv->offset)))
 321                 goto nla_put_failure;
 322         if (nla_put_be32(skb, NFTA_EXTHDR_LEN, htonl(priv->len)))
 323                 goto nla_put_failure;
 324         if (nla_put_be32(skb, NFTA_EXTHDR_FLAGS, htonl(priv->flags)))
 325                 goto nla_put_failure;
 326         if (nla_put_be32(skb, NFTA_EXTHDR_OP, htonl(priv->op)))
 327                 goto nla_put_failure;
 328         return 0;
 329
 330 nla_put_failure:
 331         return -1;
 332 }
 333
 334 static int nft_exthdr_dump(struct sk_buff *skb, const struct nft_expr *expr)
 335 {
 336         const struct nft_exthdr *priv = nft_expr_priv(expr);
 337
 338         if (nft_dump_register(skb, NFTA_EXTHDR_DREG, priv->dreg))
 339                 return -1;
 340
 341         return nft_exthdr_dump_common(skb, priv);
 342 }
 343
 344 static int nft_exthdr_dump_set(struct sk_buff *skb, const struct nft_expr *expr)
 345 {
 346         const struct nft_exthdr *priv = nft_expr_priv(expr);
 347
 348         if (nft_dump_register(skb, NFTA_EXTHDR_SREG, priv->sreg))
 349                 return -1;
 350
 351         return nft_exthdr_dump_common(skb, priv);
 352 }
 353
 354 static struct nft_expr_type nft_exthdr_type;
 355 static const struct nft_expr_ops nft_exthdr_ipv6_ops = {
 356         .type           = &nft_exthdr_type,
 357         .size           = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
 358         .eval           = nft_exthdr_ipv6_eval,
 359         .init           = nft_exthdr_init,
 360         .dump           = nft_exthdr_dump,
 361 };
 362
 363 static const struct nft_expr_ops nft_exthdr_tcp_ops = {
 364         .type           = &nft_exthdr_type,
 365         .size           = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
 366         .eval           = nft_exthdr_tcp_eval,
 367         .init           = nft_exthdr_init,
 368         .dump           = nft_exthdr_dump,
 369 };
 370
 371 static const struct nft_expr_ops nft_exthdr_tcp_set_ops = {
 372         .type           = &nft_exthdr_type,
 373         .size           = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
 374         .eval           = nft_exthdr_tcp_set_eval,
 375         .init           = nft_exthdr_tcp_set_init,
 376         .dump           = nft_exthdr_dump_set,
 377 };
 378
 379 static const struct nft_expr_ops *
 380 nft_exthdr_select_ops(const struct nft_ctx *ctx,
 381                       const struct nlattr * const tb[])
 382 {
 383         u32 op;
 384
 385         if (!tb[NFTA_EXTHDR_OP])
 386                 return &nft_exthdr_ipv6_ops;
 387
 388         if (tb[NFTA_EXTHDR_SREG] && tb[NFTA_EXTHDR_DREG])
 389                 return ERR_PTR(-EOPNOTSUPP);
 390
 391         op = ntohl(nla_get_be32(tb[NFTA_EXTHDR_OP]));
 392         switch (op) {
 393         case NFT_EXTHDR_OP_TCPOPT:
 394                 if (tb[NFTA_EXTHDR_SREG])
 395                         return &nft_exthdr_tcp_set_ops;
 396                 if (tb[NFTA_EXTHDR_DREG])
 397                         return &nft_exthdr_tcp_ops;
 398                 break;
 399         case NFT_EXTHDR_OP_IPV6:
 400                 if (tb[NFTA_EXTHDR_DREG])
 401                         return &nft_exthdr_ipv6_ops;
 402                 break;
 403         }
 404
 405         return ERR_PTR(-EOPNOTSUPP);
 406 }
 407
 408 static struct nft_expr_type nft_exthdr_type __read_mostly = {
 409         .name           = "exthdr",
 410         .select_ops     = nft_exthdr_select_ops,
 411         .policy         = nft_exthdr_policy,
 412         .maxattr        = NFTA_EXTHDR_MAX,
 413         .owner          = THIS_MODULE,
 414 };
 415
 416 static int __init nft_exthdr_module_init(void)
 417 {
 418         return nft_register_expr(&nft_exthdr_type);
 419 }
 420
 421 static void __exit nft_exthdr_module_exit(void)
 422 {
 423         nft_unregister_expr(&nft_exthdr_type);
 424 }
 425
 426 module_init(nft_exthdr_module_init);
 427 module_exit(nft_exthdr_module_exit);
 428
 429 MODULE_LICENSE("GPL");
 430 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
 431 MODULE_ALIAS_NFT_EXPR("exthdr");