netfilter: nft_exthdr: add TCP option matching

This patch implements the kernel side of the TCP option patch.

Signed-off-by: Manuel Messner <mm@skelett.io>
Reviewed-by: Florian Westphal <fw@strlen.de>
Acked-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 3e60ed7..2079515 100644 (file)
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -709,13 +709,27 @@ enum nft_exthdr_flags {
 };
 
 /**
- * enum nft_exthdr_attributes - nf_tables IPv6 extension header expression netlink attributes
+ * enum nft_exthdr_op - nf_tables match options
+ *
+ * @NFT_EXTHDR_OP_IPV6: match against ipv6 extension headers
+ * @NFT_EXTHDR_OP_TCP: match against tcp options
+ */
+enum nft_exthdr_op {
+       NFT_EXTHDR_OP_IPV6,
+       NFT_EXTHDR_OP_TCPOPT,
+       __NFT_EXTHDR_OP_MAX
+};
+#define NFT_EXTHDR_OP_MAX      (__NFT_EXTHDR_OP_MAX - 1)
+
+/**
+ * enum nft_exthdr_attributes - nf_tables extension header expression netlink attributes
  *
  * @NFTA_EXTHDR_DREG: destination register (NLA_U32: nft_registers)
  * @NFTA_EXTHDR_TYPE: extension header type (NLA_U8)
  * @NFTA_EXTHDR_OFFSET: extension header offset (NLA_U32)
  * @NFTA_EXTHDR_LEN: extension header length (NLA_U32)
  * @NFTA_EXTHDR_FLAGS: extension header flags (NLA_U32)
+ * @NFTA_EXTHDR_OP: option match type (NLA_U8)
  */
 enum nft_exthdr_attributes {
        NFTA_EXTHDR_UNSPEC,
@@ -724,6 +738,7 @@ enum nft_exthdr_attributes {
        NFTA_EXTHDR_OFFSET,
        NFTA_EXTHDR_LEN,
        NFTA_EXTHDR_FLAGS,
+       NFTA_EXTHDR_OP,
        __NFTA_EXTHDR_MAX
 };
 #define NFTA_EXTHDR_MAX                (__NFTA_EXTHDR_MAX - 1)

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index ea479ed..9b28864 100644 (file)
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -467,10 +467,10 @@ config NF_TABLES_NETDEV
          This option enables support for the "netdev" table.
 
 config NFT_EXTHDR
-       tristate "Netfilter nf_tables IPv6 exthdr module"
+       tristate "Netfilter nf_tables exthdr module"
        help
          This option adds the "exthdr" expression that you can use to match
-         IPv6 extension headers.
+         IPv6 extension headers and tcp options.
 
 config NFT_META
        tristate "Netfilter nf_tables meta module"

diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index a89e5ab..c308920 100644 (file)
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -15,20 +15,29 @@
 #include <linux/netfilter.h>
 #include <linux/netfilter/nf_tables.h>
 #include <net/netfilter/nf_tables.h>
-// FIXME:
-#include <net/ipv6.h>
+#include <net/tcp.h>
 
 struct nft_exthdr {
        u8                      type;
        u8                      offset;
        u8                      len;
+       u8                      op;
        enum nft_registers      dreg:8;
        u8                      flags;
 };
 
-static void nft_exthdr_eval(const struct nft_expr *expr,
-                           struct nft_regs *regs,
-                           const struct nft_pktinfo *pkt)
+static unsigned int optlen(const u8 *opt, unsigned int offset)
+{
+       /* Beware zero-length options: make finite progress */
+       if (opt[offset] <= TCPOPT_NOP || opt[offset + 1] == 0)
+               return 1;
+       else
+               return opt[offset + 1];
+}
+
+static void nft_exthdr_ipv6_eval(const struct nft_expr *expr,
+                                struct nft_regs *regs,
+                                const struct nft_pktinfo *pkt)
 {
        struct nft_exthdr *priv = nft_expr_priv(expr);
        u32 *dest = &regs->data[priv->dreg];
@@ -52,6 +61,53 @@ err:
        regs->verdict.code = NFT_BREAK;
 }
 
+static void nft_exthdr_tcp_eval(const struct nft_expr *expr,
+                               struct nft_regs *regs,
+                               const struct nft_pktinfo *pkt)
+{
+       u8 buff[sizeof(struct tcphdr) + MAX_TCP_OPTION_SPACE];
+       struct nft_exthdr *priv = nft_expr_priv(expr);
+       unsigned int i, optl, tcphdr_len, offset;
+       u32 *dest = &regs->data[priv->dreg];
+       struct tcphdr *tcph;
+       u8 *opt;
+
+       if (!pkt->tprot_set || pkt->tprot != IPPROTO_TCP)
+               goto err;
+
+       tcph = skb_header_pointer(pkt->skb, pkt->xt.thoff, sizeof(*tcph), buff);
+       if (!tcph)
+               goto err;
+
+       tcphdr_len = __tcp_hdrlen(tcph);
+       if (tcphdr_len < sizeof(*tcph))
+               goto err;
+
+       tcph = skb_header_pointer(pkt->skb, pkt->xt.thoff, tcphdr_len, buff);
+       if (!tcph)
+               goto err;
+
+       opt = (u8 *)tcph;
+       for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) {
+               optl = optlen(opt, i);
+
+               if (priv->type != opt[i])
+                       continue;
+
+               if (i + optl > tcphdr_len || priv->len + priv->offset > optl)
+                       goto err;
+
+               offset = i + priv->offset;
+               dest[priv->len / NFT_REG32_SIZE] = 0;
+               memcpy(dest, opt + offset, priv->len);
+
+               return;
+       }
+
+err:
+       regs->verdict.code = NFT_BREAK;
+}
+
 static const struct nla_policy nft_exthdr_policy[NFTA_EXTHDR_MAX + 1] = {
        [NFTA_EXTHDR_DREG]              = { .type = NLA_U32 },
        [NFTA_EXTHDR_TYPE]              = { .type = NLA_U8 },
@@ -65,13 +121,13 @@ static int nft_exthdr_init(const struct nft_ctx *ctx,
                           const struct nlattr * const tb[])
 {
        struct nft_exthdr *priv = nft_expr_priv(expr);
-       u32 offset, len, flags = 0;
+       u32 offset, len, flags = 0, op = NFT_EXTHDR_OP_IPV6;
        int err;
 
-       if (tb[NFTA_EXTHDR_DREG] == NULL ||
-           tb[NFTA_EXTHDR_TYPE] == NULL ||
-           tb[NFTA_EXTHDR_OFFSET] == NULL ||
-           tb[NFTA_EXTHDR_LEN] == NULL)
+       if (!tb[NFTA_EXTHDR_DREG] ||
+           !tb[NFTA_EXTHDR_TYPE] ||
+           !tb[NFTA_EXTHDR_OFFSET] ||
+           !tb[NFTA_EXTHDR_LEN])
                return -EINVAL;
 
        err = nft_parse_u32_check(tb[NFTA_EXTHDR_OFFSET], U8_MAX, &offset);
@@ -91,11 +147,18 @@ static int nft_exthdr_init(const struct nft_ctx *ctx,
                        return -EINVAL;
        }
 
+       if (tb[NFTA_EXTHDR_OP]) {
+               err = nft_parse_u32_check(tb[NFTA_EXTHDR_OP], U8_MAX, &op);
+               if (err < 0)
+                       return err;
+       }
+
        priv->type   = nla_get_u8(tb[NFTA_EXTHDR_TYPE]);
        priv->offset = offset;
        priv->len    = len;
        priv->dreg   = nft_parse_register(tb[NFTA_EXTHDR_DREG]);
        priv->flags  = flags;
+       priv->op     = op;
 
        return nft_validate_register_store(ctx, priv->dreg, NULL,
                                           NFT_DATA_VALUE, priv->len);
@@ -115,6 +178,8 @@ static int nft_exthdr_dump(struct sk_buff *skb, const struct nft_expr *expr)
                goto nla_put_failure;
        if (nla_put_be32(skb, NFTA_EXTHDR_FLAGS, htonl(priv->flags)))
                goto nla_put_failure;
+       if (nla_put_be32(skb, NFTA_EXTHDR_OP, htonl(priv->op)))
+               goto nla_put_failure;
        return 0;
 
 nla_put_failure:
@@ -122,17 +187,45 @@ nla_put_failure:
 }
 
 static struct nft_expr_type nft_exthdr_type;
-static const struct nft_expr_ops nft_exthdr_ops = {
+static const struct nft_expr_ops nft_exthdr_ipv6_ops = {
+       .type           = &nft_exthdr_type,
+       .size           = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
+       .eval           = nft_exthdr_ipv6_eval,
+       .init           = nft_exthdr_init,
+       .dump           = nft_exthdr_dump,
+};
+
+static const struct nft_expr_ops nft_exthdr_tcp_ops = {
        .type           = &nft_exthdr_type,
        .size           = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
-       .eval           = nft_exthdr_eval,
+       .eval           = nft_exthdr_tcp_eval,
        .init           = nft_exthdr_init,
        .dump           = nft_exthdr_dump,
 };
 
+static const struct nft_expr_ops *
+nft_exthdr_select_ops(const struct nft_ctx *ctx,
+                     const struct nlattr * const tb[])
+{
+       u32 op;
+
+       if (!tb[NFTA_EXTHDR_OP])
+               return &nft_exthdr_ipv6_ops;
+
+       op = ntohl(nla_get_u32(tb[NFTA_EXTHDR_OP]));
+       switch (op) {
+       case NFT_EXTHDR_OP_TCPOPT:
+               return &nft_exthdr_tcp_ops;
+       case NFT_EXTHDR_OP_IPV6:
+               return &nft_exthdr_ipv6_ops;
+       }
+
+       return ERR_PTR(-EOPNOTSUPP);
+}
+
 static struct nft_expr_type nft_exthdr_type __read_mostly = {
        .name           = "exthdr",
-       .ops            = &nft_exthdr_ops,
+       .select_ops     = &nft_exthdr_select_ops,
        .policy         = nft_exthdr_policy,
        .maxattr        = NFTA_EXTHDR_MAX,
        .owner          = THIS_MODULE,