[RFC,nf-next,3/3] netfilter: exthdr: early set support

Message ID 20170630172848.18196-3-fw@strlen.de
State RFC
Delegated to: Pablo Neira
Headers show

Commit Message

Florian Westphal June 30, 2017, 5:28 p.m.
This allows setting 2 and 4 byte quantities in the tcp option space.
This allows native replacement for xt_TCPMSS in nf_tables.

Todo:
-TCPOPTSTRIP equivalent
-possibly restrict write support so we can't generate
invalid options (e.g., don't allow write to kind,len).

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 include/uapi/linux/netfilter/nf_tables.h |   4 +-
 net/netfilter/nft_exthdr.c               | 161 ++++++++++++++++++++++++++++++-
 2 files changed, 162 insertions(+), 3 deletions(-)

Patch

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 683f6f88fcac..4766f5091b5f 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -731,7 +731,8 @@  enum nft_exthdr_op {
  * @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)
+ * @NFTA_EXTHDR_OP: option match type (NLA_U32)
+ * @NFTA_EXTHDR_SREG: option match type (NLA_U32)
  */
 enum nft_exthdr_attributes {
 	NFTA_EXTHDR_UNSPEC,
@@ -741,6 +742,7 @@  enum nft_exthdr_attributes {
 	NFTA_EXTHDR_LEN,
 	NFTA_EXTHDR_FLAGS,
 	NFTA_EXTHDR_OP,
+	NFTA_EXTHDR_SREG,
 	__NFTA_EXTHDR_MAX
 };
 #define NFTA_EXTHDR_MAX		(__NFTA_EXTHDR_MAX - 1)
diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index e3a6eebe7e0c..214211699f8d 100644
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -8,6 +8,7 @@ 
  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  */
 
+#include <asm/unaligned.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/module.h>
@@ -23,6 +24,7 @@  struct nft_exthdr {
 	u8			len;
 	u8			op;
 	enum nft_registers	dreg:8;
+	enum nft_registers	sreg:8;
 	u8			flags;
 };
 
@@ -124,6 +126,88 @@  static void nft_exthdr_tcp_eval(const struct nft_expr *expr,
 		regs->verdict.code = NFT_BREAK;
 }
 
+static void nft_exthdr_tcp_set_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;
+	struct tcphdr *tcph;
+	u8 *opt;
+	u32 src;
+
+	tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff, &tcphdr_len);
+	if (!tcph)
+		return;
+
+	opt = (u8 *)tcph;
+	for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) {
+		union {
+			u8 octet;
+			__be16 v16;
+			__be32 v32;
+		} old, new;
+
+		optl = optlen(opt, i);
+
+		if (priv->type != opt[i])
+			continue;
+
+		if (i + optl > tcphdr_len || priv->len + priv->offset > optl)
+			return;
+
+		if (!skb_make_writable(pkt->skb, pkt->xt.thoff + i + priv->len))
+			return;
+
+		tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff,
+					      &tcphdr_len);
+		if (!tcph)
+			return;
+
+		src = regs->data[priv->sreg];
+		offset = i + priv->offset;
+
+		switch (priv->len) {
+		case 2:
+			old.v16 = get_unaligned((u16 *)(opt + offset));
+			new.v16 = src;
+
+			if (old.v16 == new.v16)
+				return;
+
+			switch (priv->type) {
+			case TCPOPT_MSS:
+				/* increase can cause connection to stall */
+				if (ntohs(old.v16) <= ntohs(new.v16))
+					return;
+			break;
+			}
+
+			put_unaligned(new.v16, (u16*)(opt + offset));
+			inet_proto_csum_replace2(&tcph->check, pkt->skb,
+						 old.v16, new.v16, false);
+			break;
+		case 4:
+			new.v32 = src;
+			old.v32 = get_unaligned((u32 *)(opt + offset));
+
+			if (old.v32 == new.v32)
+				return;
+
+			put_unaligned(new.v32, (u32*)(opt + offset));
+			inet_proto_csum_replace4(&tcph->check, pkt->skb,
+						 old.v32, new.v32, false);
+			break;
+		default:
+			WARN_ON_ONCE(1);
+			break;
+		}
+
+		return;
+	}
+}
+
 static const struct nla_policy nft_exthdr_policy[NFTA_EXTHDR_MAX + 1] = {
 	[NFTA_EXTHDR_DREG]		= { .type = NLA_U32 },
 	[NFTA_EXTHDR_TYPE]		= { .type = NLA_U8 },
@@ -180,6 +264,52 @@  static int nft_exthdr_init(const struct nft_ctx *ctx,
 					   NFT_DATA_VALUE, priv->len);
 }
 
+static int nft_exthdr_tcp_set_init(const struct nft_ctx *ctx,
+				   const struct nft_expr *expr,
+				   const struct nlattr * const tb[])
+{
+	struct nft_exthdr *priv = nft_expr_priv(expr);
+	u32 offset, len, flags = 0, op = NFT_EXTHDR_OP_IPV6;
+	int err;
+
+	if (!tb[NFTA_EXTHDR_SREG] ||
+	    !tb[NFTA_EXTHDR_TYPE] ||
+	    !tb[NFTA_EXTHDR_OFFSET] ||
+	    !tb[NFTA_EXTHDR_LEN])
+		return -EINVAL;
+
+	if (tb[NFTA_EXTHDR_DREG] || tb[NFTA_EXTHDR_FLAGS])
+		return -EINVAL;
+
+	err = nft_parse_u32_check(tb[NFTA_EXTHDR_OFFSET], U8_MAX, &offset);
+	if (err < 0)
+		return err;
+
+	err = nft_parse_u32_check(tb[NFTA_EXTHDR_LEN], U8_MAX, &len);
+	if (err < 0)
+		return err;
+
+	switch (len) {
+	case 2: break;
+	case 4: break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	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->sreg   = nft_parse_register(tb[NFTA_EXTHDR_SREG]);
+	priv->flags  = flags;
+	priv->op     = op;
+
+	return nft_validate_register_load(priv->sreg, priv->len);
+}
+
 static int nft_exthdr_dump_common(struct sk_buff *skb, const struct nft_exthdr *priv)
 {
 	if (nla_put_u8(skb, NFTA_EXTHDR_TYPE, priv->type))
@@ -208,6 +338,16 @@  static int nft_exthdr_dump(struct sk_buff *skb, const struct nft_expr *expr)
 	return nft_exthdr_dump_common(skb, priv);
 }
 
+static int nft_exthdr_dump_set(struct sk_buff *skb, const struct nft_expr *expr)
+{
+	const struct nft_exthdr *priv = nft_expr_priv(expr);
+
+	if (nft_dump_register(skb, NFTA_EXTHDR_SREG, priv->sreg))
+		return -1;
+
+	return nft_exthdr_dump_common(skb, priv);
+}
+
 static struct nft_expr_type nft_exthdr_type;
 static const struct nft_expr_ops nft_exthdr_ipv6_ops = {
 	.type		= &nft_exthdr_type,
@@ -225,6 +365,14 @@  static const struct nft_expr_ops nft_exthdr_tcp_ops = {
 	.dump		= nft_exthdr_dump,
 };
 
+static const struct nft_expr_ops nft_exthdr_tcp_set_ops = {
+	.type		= &nft_exthdr_type,
+	.size		= NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
+	.eval		= nft_exthdr_tcp_set_eval,
+	.init		= nft_exthdr_tcp_set_init,
+	.dump		= nft_exthdr_dump_set,
+};
+
 static const struct nft_expr_ops *
 nft_exthdr_select_ops(const struct nft_ctx *ctx,
 		      const struct nlattr * const tb[])
@@ -234,12 +382,21 @@  nft_exthdr_select_ops(const struct nft_ctx *ctx,
 	if (!tb[NFTA_EXTHDR_OP])
 		return &nft_exthdr_ipv6_ops;
 
+	if (tb[NFTA_EXTHDR_SREG] && tb[NFTA_EXTHDR_DREG])
+		return ERR_PTR(-EOPNOTSUPP);
+
 	op = ntohl(nla_get_u32(tb[NFTA_EXTHDR_OP]));
 	switch (op) {
 	case NFT_EXTHDR_OP_TCPOPT:
-		return &nft_exthdr_tcp_ops;
+		if (tb[NFTA_EXTHDR_SREG])
+			return &nft_exthdr_tcp_set_ops;
+		if (tb[NFTA_EXTHDR_DREG])
+			return &nft_exthdr_tcp_ops;
+		break;
 	case NFT_EXTHDR_OP_IPV6:
-		return &nft_exthdr_ipv6_ops;
+		if (tb[NFTA_EXTHDR_DREG])
+			return &nft_exthdr_ipv6_ops;
+		break;
 	}
 
 	return ERR_PTR(-EOPNOTSUPP);