From: Davide Caratti <dcaratti@xxxxxxxxxx>
nftables payload statements are used to mangle SCTP headers, but they can
only replace the Internet Checksum. As a consequence, nftables rules that
mangle sport/dport/vtag in SCTP headers potentially generate packets that
are discarded by the receiver, unless the CRC-32C is "offloaded" (e.g the
rule mangles a skb having 'ip_summed' equal to 'CHECKSUM_PARTIAL'.
Fix this extending uAPI definitions and L4 checksum update function, in a
way that userspace programs (e.g. nft) can instruct the kernel to compute
CRC-32C in SCTP headers. Also ensure that LIBCRC32C is built if NF_TABLES
is 'y' or 'm' in the kernel build configuration.
Signed-off-by: Davide Caratti <dcaratti@xxxxxxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
NB: I accidentally pushed the userspace side to nftables.git already,
my bad. Here is the kernel part.
include/uapi/linux/netfilter/nf_tables.h | 2 ++
net/netfilter/Kconfig | 1 +
net/netfilter/nft_payload.c | 28 ++++++++++++++++++++++++
3 files changed, 31 insertions(+)
diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 352ee51707a1..98272cb5f617 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -749,10 +749,12 @@ enum nft_payload_bases {
*
* @NFT_PAYLOAD_CSUM_NONE: no checksumming
* @NFT_PAYLOAD_CSUM_INET: internet checksum (RFC 791)
+ * @NFT_PAYLOAD_CSUM_SCTP: CRC-32c, for use in SCTP header (RFC 3309)
*/
enum nft_payload_csum_types {
NFT_PAYLOAD_CSUM_NONE,
NFT_PAYLOAD_CSUM_INET,
+ NFT_PAYLOAD_CSUM_SCTP,
};
enum nft_payload_csum_flags {
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 25313c29d799..52370211e46b 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -441,6 +441,7 @@ endif # NF_CONNTRACK
config NF_TABLES
select NETFILTER_NETLINK
+ select LIBCRC32C
tristate "Netfilter nf_tables support"
help
nftables is the new packet classification framework that intends to
diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index 7a2e59638499..dcd3c7b8a367 100644
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -22,6 +22,7 @@
#include <linux/icmpv6.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
+#include <net/sctp/checksum.h>
static bool nft_payload_rebuild_vlan_hdr(const struct sk_buff *skb, int mac_off,
struct vlan_ethhdr *veth)
@@ -484,6 +485,19 @@ static int nft_payload_l4csum_offset(const struct nft_pktinfo *pkt,
return 0;
}
+static int nft_payload_csum_sctp(struct sk_buff *skb, int offset)
+{
+ struct sctphdr *sh;
+
+ if (skb_ensure_writable(skb, offset + sizeof(*sh)))
+ return -1;
+
+ sh = (struct sctphdr *)(skb->data + offset);
+ sh->checksum = sctp_compute_cksum(skb, offset);
+ skb->ip_summed = CHECKSUM_UNNECESSARY;
+ return 0;
+}
+
static int nft_payload_l4csum_update(const struct nft_pktinfo *pkt,
struct sk_buff *skb,
__wsum fsum, __wsum tsum)
@@ -587,6 +601,13 @@ static void nft_payload_set_eval(const struct nft_expr *expr,
skb_store_bits(skb, offset, src, priv->len) < 0)
goto err;
+ if (priv->csum_type == NFT_PAYLOAD_CSUM_SCTP &&
+ pkt->tprot == IPPROTO_SCTP &&
+ skb->ip_summed != CHECKSUM_PARTIAL) {
+ if (nft_payload_csum_sctp(skb, pkt->xt.thoff))
+ goto err;
+ }
+
return;
err:
regs->verdict.code = NFT_BREAK;
@@ -623,6 +644,13 @@ static int nft_payload_set_init(const struct nft_ctx *ctx,
case NFT_PAYLOAD_CSUM_NONE:
case NFT_PAYLOAD_CSUM_INET:
break;
+ case NFT_PAYLOAD_CSUM_SCTP:
+ if (priv->base != NFT_PAYLOAD_TRANSPORT_HEADER)
+ return -EINVAL;
+
+ if (priv->csum_offset != offsetof(struct sctphdr, checksum))
+ return -EINVAL;
+ break;
default:
return -EOPNOTSUPP;
}
--
2.26.2
