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Message-Id: <1481147576-5690-29-git-send-email-pablo@netfilter.org>
Date: Wed, 7 Dec 2016 22:52:34 +0100
From: Pablo Neira Ayuso <pablo@...filter.org>
To: netfilter-devel@...r.kernel.org
Cc: davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCH 28/50] netfilter: nft_payload: layer 4 checksum adjustment for pseudoheader fields
This patch adds a new flag that signals the kernel to update layer 4
checksum if the packet field belongs to the layer 4 pseudoheader. This
implicitly provides stateless NAT 1:1 that is useful under very specific
usecases.
Since rules mangling layer 3 fields that are part of the pseudoheader
may potentially convey any layer 4 packet, we have to deal with the
layer 4 checksum adjustment using protocol specific code.
This patch adds support for TCP, UDP and ICMPv6, since they include the
pseudoheader in the layer 4 checksum calculation. ICMP doesn't, so we
can skip it.
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
include/net/netfilter/nf_tables_core.h | 1 +
include/uapi/linux/netfilter/nf_tables.h | 6 ++
net/netfilter/nft_payload.c | 107 +++++++++++++++++++++++++++++--
3 files changed, 109 insertions(+), 5 deletions(-)
diff --git a/include/net/netfilter/nf_tables_core.h b/include/net/netfilter/nf_tables_core.h
index 862373d4ea9d..8f690effec37 100644
--- a/include/net/netfilter/nf_tables_core.h
+++ b/include/net/netfilter/nf_tables_core.h
@@ -45,6 +45,7 @@ struct nft_payload_set {
enum nft_registers sreg:8;
u8 csum_type;
u8 csum_offset;
+ u8 csum_flags;
};
extern const struct nft_expr_ops nft_payload_fast_ops;
diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 14e5f619167e..f030e59aa2ec 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -659,6 +659,10 @@ enum nft_payload_csum_types {
NFT_PAYLOAD_CSUM_INET,
};
+enum nft_payload_csum_flags {
+ NFT_PAYLOAD_L4CSUM_PSEUDOHDR = (1 << 0),
+};
+
/**
* enum nft_payload_attributes - nf_tables payload expression netlink attributes
*
@@ -669,6 +673,7 @@ enum nft_payload_csum_types {
* @NFTA_PAYLOAD_SREG: source register to load data from (NLA_U32: nft_registers)
* @NFTA_PAYLOAD_CSUM_TYPE: checksum type (NLA_U32)
* @NFTA_PAYLOAD_CSUM_OFFSET: checksum offset relative to base (NLA_U32)
+ * @NFTA_PAYLOAD_CSUM_FLAGS: checksum flags (NLA_U32)
*/
enum nft_payload_attributes {
NFTA_PAYLOAD_UNSPEC,
@@ -679,6 +684,7 @@ enum nft_payload_attributes {
NFTA_PAYLOAD_SREG,
NFTA_PAYLOAD_CSUM_TYPE,
NFTA_PAYLOAD_CSUM_OFFSET,
+ NFTA_PAYLOAD_CSUM_FLAGS,
__NFTA_PAYLOAD_MAX
};
#define NFTA_PAYLOAD_MAX (__NFTA_PAYLOAD_MAX - 1)
diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index 98fb5d7b8087..36d2b1096546 100644
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -1,5 +1,6 @@
/*
* Copyright (c) 2008-2009 Patrick McHardy <kaber@...sh.net>
+ * Copyright (c) 2016 Pablo Neira Ayuso <pablo@...filter.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
@@ -17,6 +18,10 @@
#include <linux/netfilter/nf_tables.h>
#include <net/netfilter/nf_tables_core.h>
#include <net/netfilter/nf_tables.h>
+/* For layer 4 checksum field offset. */
+#include <linux/tcp.h>
+#include <linux/udp.h>
+#include <linux/icmpv6.h>
/* add vlan header into the user buffer for if tag was removed by offloads */
static bool
@@ -164,6 +169,87 @@ const struct nft_expr_ops nft_payload_fast_ops = {
.dump = nft_payload_dump,
};
+static inline void nft_csum_replace(__sum16 *sum, __wsum fsum, __wsum tsum)
+{
+ *sum = csum_fold(csum_add(csum_sub(~csum_unfold(*sum), fsum), tsum));
+ if (*sum == 0)
+ *sum = CSUM_MANGLED_0;
+}
+
+static bool nft_payload_udp_checksum(struct sk_buff *skb, unsigned int thoff)
+{
+ struct udphdr *uh, _uh;
+
+ uh = skb_header_pointer(skb, thoff, sizeof(_uh), &_uh);
+ if (!uh)
+ return false;
+
+ return uh->check;
+}
+
+static int nft_payload_l4csum_offset(const struct nft_pktinfo *pkt,
+ struct sk_buff *skb,
+ unsigned int *l4csum_offset)
+{
+ switch (pkt->tprot) {
+ case IPPROTO_TCP:
+ *l4csum_offset = offsetof(struct tcphdr, check);
+ break;
+ case IPPROTO_UDP:
+ if (!nft_payload_udp_checksum(skb, pkt->xt.thoff))
+ return -1;
+ /* Fall through. */
+ case IPPROTO_UDPLITE:
+ *l4csum_offset = offsetof(struct udphdr, check);
+ break;
+ case IPPROTO_ICMPV6:
+ *l4csum_offset = offsetof(struct icmp6hdr, icmp6_cksum);
+ break;
+ default:
+ return -1;
+ }
+
+ *l4csum_offset += pkt->xt.thoff;
+ return 0;
+}
+
+static int nft_payload_l4csum_update(const struct nft_pktinfo *pkt,
+ struct sk_buff *skb,
+ __wsum fsum, __wsum tsum)
+{
+ int l4csum_offset;
+ __sum16 sum;
+
+ /* If we cannot determine layer 4 checksum offset or this packet doesn't
+ * require layer 4 checksum recalculation, skip this packet.
+ */
+ if (nft_payload_l4csum_offset(pkt, skb, &l4csum_offset) < 0)
+ return 0;
+
+ if (skb_copy_bits(skb, l4csum_offset, &sum, sizeof(sum)) < 0)
+ return -1;
+
+ /* Checksum mangling for an arbitrary amount of bytes, based on
+ * inet_proto_csum_replace*() functions.
+ */
+ if (skb->ip_summed != CHECKSUM_PARTIAL) {
+ nft_csum_replace(&sum, fsum, tsum);
+ if (skb->ip_summed == CHECKSUM_COMPLETE) {
+ skb->csum = ~csum_add(csum_sub(~(skb->csum), fsum),
+ tsum);
+ }
+ } else {
+ sum = ~csum_fold(csum_add(csum_sub(csum_unfold(sum), fsum),
+ tsum));
+ }
+
+ if (!skb_make_writable(skb, l4csum_offset + sizeof(sum)) ||
+ skb_store_bits(skb, l4csum_offset, &sum, sizeof(sum)) < 0)
+ return -1;
+
+ return 0;
+}
+
static void nft_payload_set_eval(const struct nft_expr *expr,
struct nft_regs *regs,
const struct nft_pktinfo *pkt)
@@ -204,14 +290,15 @@ static void nft_payload_set_eval(const struct nft_expr *expr,
fsum = skb_checksum(skb, offset, priv->len, 0);
tsum = csum_partial(src, priv->len, 0);
- sum = csum_fold(csum_add(csum_sub(~csum_unfold(sum), fsum),
- tsum));
- if (sum == 0)
- sum = CSUM_MANGLED_0;
+ nft_csum_replace(&sum, fsum, tsum);
if (!skb_make_writable(skb, csum_offset + sizeof(sum)) ||
skb_store_bits(skb, csum_offset, &sum, sizeof(sum)) < 0)
goto err;
+
+ if (priv->csum_flags &&
+ nft_payload_l4csum_update(pkt, skb, fsum, tsum) < 0)
+ goto err;
}
if (!skb_make_writable(skb, max(offset + priv->len, 0)) ||
@@ -240,6 +327,15 @@ static int nft_payload_set_init(const struct nft_ctx *ctx,
if (tb[NFTA_PAYLOAD_CSUM_OFFSET])
priv->csum_offset =
ntohl(nla_get_be32(tb[NFTA_PAYLOAD_CSUM_OFFSET]));
+ if (tb[NFTA_PAYLOAD_CSUM_FLAGS]) {
+ u32 flags;
+
+ flags = ntohl(nla_get_be32(tb[NFTA_PAYLOAD_CSUM_FLAGS]));
+ if (flags & ~NFT_PAYLOAD_L4CSUM_PSEUDOHDR)
+ return -EINVAL;
+
+ priv->csum_flags = flags;
+ }
switch (priv->csum_type) {
case NFT_PAYLOAD_CSUM_NONE:
@@ -262,7 +358,8 @@ static int nft_payload_set_dump(struct sk_buff *skb, const struct nft_expr *expr
nla_put_be32(skb, NFTA_PAYLOAD_LEN, htonl(priv->len)) ||
nla_put_be32(skb, NFTA_PAYLOAD_CSUM_TYPE, htonl(priv->csum_type)) ||
nla_put_be32(skb, NFTA_PAYLOAD_CSUM_OFFSET,
- htonl(priv->csum_offset)))
+ htonl(priv->csum_offset)) ||
+ nla_put_be32(skb, NFTA_PAYLOAD_CSUM_FLAGS, htonl(priv->csum_flags)))
goto nla_put_failure;
return 0;
--
2.1.4
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