Fixed MTP to work with TWRP

net/ipv4/ip_forward.c

@@ -0,0 +1,158 @@
+/*
+ * INET		An implementation of the TCP/IP protocol suite for the LINUX
+ *		operating system.  INET is implemented using the  BSD Socket
+ *		interface as the means of communication with the user level.
+ *
+ *		The IP forwarding functionality.
+ *
+ * Authors:	see ip.c
+ *
+ * Fixes:
+ *		Many		:	Split from ip.c , see ip_input.c for
+ *					history.
+ *		Dave Gregorich	:	NULL ip_rt_put fix for multicast
+ *					routing.
+ *		Jos Vos		:	Add call_out_firewall before sending,
+ *					use output device for accounting.
+ *		Jos Vos		:	Call forward firewall after routing
+ *					(always use output device).
+ *		Mike McLagan	:	Routing by source
+ */
+
+#include <linux/types.h>
+#include <linux/mm.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <linux/icmp.h>
+#include <linux/netdevice.h>
+#include <linux/slab.h>
+#include <net/sock.h>
+#include <net/ip.h>
+#include <net/tcp.h>
+#include <net/udp.h>
+#include <net/icmp.h>
+#include <linux/tcp.h>
+#include <linux/udp.h>
+#include <linux/netfilter_ipv4.h>
+#include <net/checksum.h>
+#include <linux/route.h>
+#include <net/route.h>
+#include <net/xfrm.h>
+
+static bool ip_may_fragment(const struct sk_buff *skb)
+{
+	return unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0) ||
+		skb->ignore_df;
+}
+
+static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
+{
+	if (skb->len <= mtu)
+		return false;
+
+	if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)
+		return false;
+
+	return true;
+}
+
+
+static int ip_forward_finish(struct sk_buff *skb)
+{
+	struct ip_options *opt	= &(IPCB(skb)->opt);
+
+	IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS);
+	IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len);
+
+	if (unlikely(opt->optlen))
+		ip_forward_options(skb);
+
+	return dst_output(skb);
+}
+
+int ip_forward(struct sk_buff *skb)
+{
+	u32 mtu;
+	struct iphdr *iph;	/* Our header */
+	struct rtable *rt;	/* Route we use */
+	struct ip_options *opt	= &(IPCB(skb)->opt);
+
+	/* that should never happen */
+	if (skb->pkt_type != PACKET_HOST)
+		goto drop;
+
+	if (unlikely(skb->sk))
+		goto drop;
+
+	if (skb_warn_if_lro(skb))
+		goto drop;
+
+	if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
+		goto drop;
+
+	if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
+		return NET_RX_SUCCESS;
+
+	skb_forward_csum(skb);
+
+	/*
+	 *	According to the RFC, we must first decrease the TTL field. If
+	 *	that reaches zero, we must reply an ICMP control message telling
+	 *	that the packet's lifetime expired.
+	 */
+	if (ip_hdr(skb)->ttl <= 1)
+		goto too_many_hops;
+
+	if (!xfrm4_route_forward(skb))
+		goto drop;
+
+	rt = skb_rtable(skb);
+
+	if (opt->is_strictroute && rt->rt_uses_gateway)
+		goto sr_failed;
+
+	IPCB(skb)->flags |= IPSKB_FORWARDED;
+	mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
+	if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, mtu)) {
+		IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
+		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
+			  htonl(mtu));
+		goto drop;
+	}
+
+	/* We are about to mangle packet. Copy it! */
+	if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
+		goto drop;
+	iph = ip_hdr(skb);
+
+	/* Decrease ttl after skb cow done */
+	ip_decrease_ttl(iph);
+
+	/*
+	 *	We now generate an ICMP HOST REDIRECT giving the route
+	 *	we calculated.
+	 */
+	if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr &&
+	    !skb_sec_path(skb))
+		ip_rt_send_redirect(skb);
+
+	skb->priority = rt_tos2priority(iph->tos);
+
+	return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev,
+		       rt->dst.dev, ip_forward_finish);
+
+sr_failed:
+	/*
+	 *	Strict routing permits no gatewaying
+	 */
+	 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
+	 goto drop;
+
+too_many_hops:
+	/* Tell the sender its packet died... */
+	IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS);
+	icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
+drop:
+	kfree_skb(skb);
+	return NET_RX_DROP;
+}