1 files changed, 92 insertions, 0 deletions
diff --git a/net/ipv4/netfilter/arpt_mangle.c b/net/ipv4/netfilter/arpt_mangle.c
new file mode 100644
index 000000000..a4e07e5e9
--- /dev/null
+++ b/net/ipv4/netfilter/arpt_mangle.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* module that allows mangling of the arp payload */
+#include <linux/module.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter_arp/arpt_mangle.h>
+#include <net/sock.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
+MODULE_DESCRIPTION("arptables arp payload mangle target");
+
+static unsigned int
+target(struct sk_buff *skb, const struct xt_action_param *par)
+{
+	const struct arpt_mangle *mangle = par->targinfo;
+	const struct arphdr *arp;
+	unsigned char *arpptr;
+	int pln, hln;
+
+	if (skb_ensure_writable(skb, skb->len))
+		return NF_DROP;
+
+	arp = arp_hdr(skb);
+	arpptr = skb_network_header(skb) + sizeof(*arp);
+	pln = arp->ar_pln;
+	hln = arp->ar_hln;
+	/* We assume that pln and hln were checked in the match */
+	if (mangle->flags & ARPT_MANGLE_SDEV) {
+		if (ARPT_DEV_ADDR_LEN_MAX < hln ||
+		   (arpptr + hln > skb_tail_pointer(skb)))
+			return NF_DROP;
+		memcpy(arpptr, mangle->src_devaddr, hln);
+	}
+	arpptr += hln;
+	if (mangle->flags & ARPT_MANGLE_SIP) {
+		if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
+		   (arpptr + pln > skb_tail_pointer(skb)))
+			return NF_DROP;
+		memcpy(arpptr, &mangle->u_s.src_ip, pln);
+	}
+	arpptr += pln;
+	if (mangle->flags & ARPT_MANGLE_TDEV) {
+		if (ARPT_DEV_ADDR_LEN_MAX < hln ||
+		   (arpptr + hln > skb_tail_pointer(skb)))
+			return NF_DROP;
+		memcpy(arpptr, mangle->tgt_devaddr, hln);
+	}
+	arpptr += hln;
+	if (mangle->flags & ARPT_MANGLE_TIP) {
+		if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
+		   (arpptr + pln > skb_tail_pointer(skb)))
+			return NF_DROP;
+		memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
+	}
+	return mangle->target;
+}
+
+static int checkentry(const struct xt_tgchk_param *par)
+{
+	const struct arpt_mangle *mangle = par->targinfo;
+
+	if (mangle->flags & ~ARPT_MANGLE_MASK ||
+	    !(mangle->flags & ARPT_MANGLE_MASK))
+		return -EINVAL;
+
+	if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
+	   mangle->target != XT_CONTINUE)
+		return -EINVAL;
+	return 0;
+}
+
+static struct xt_target arpt_mangle_reg __read_mostly = {
+	.name		= "mangle",
+	.family		= NFPROTO_ARP,
+	.target		= target,
+	.targetsize	= sizeof(struct arpt_mangle),
+	.checkentry	= checkentry,
+	.me		= THIS_MODULE,
+};
+
+static int __init arpt_mangle_init(void)
+{
+	return xt_register_target(&arpt_mangle_reg);
+}
+
+static void __exit arpt_mangle_fini(void)
+{
+	xt_unregister_target(&arpt_mangle_reg);
+}
+
+module_init(arpt_mangle_init);
+module_exit(arpt_mangle_fini);