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netfilter: nft_exthdr: add TCP option matching
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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>
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@manuelmessner @ummakynes
manuelmessner authored and ummakynes committed Feb 8, 2017
1 parent edee4f1 commit 935b7f6
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Showing 3 changed files with 124 additions and 16 deletions.
17 changes: 16 additions & 1 deletion include/uapi/linux/netfilter/nf_tables.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand All @@ -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)
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4 changes: 2 additions & 2 deletions net/netfilter/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -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"
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119 changes: 106 additions & 13 deletions net/netfilter/nft_exthdr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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];
Expand All @@ -52,6 +61,53 @@ static void nft_exthdr_eval(const struct nft_expr *expr,
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 },
Expand All @@ -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);
Expand All @@ -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);
Expand All @@ -115,24 +178,54 @@ 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:
return -1;
}

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,
Expand Down

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