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Commit d0daebc3 authored by Thomas Graf's avatar Thomas Graf Committed by David S. Miller
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ipv4: Add interface option to enable routing of 127.0.0.0/8 



Routing of 127/8 is tradtionally forbidden, we consider
packets from that address block martian when routing and do
not process corresponding ARP requests.

This is a sane default but renders a huge address space
practically unuseable.

The RFC states that no address within the 127/8 block should
ever appear on any network anywhere but it does not forbid
the use of such addresses outside of the loopback device in
particular. For example to address a pool of virtual guests
behind a load balancer.

This patch adds a new interface option 'route_localnet'
enabling routing of the 127/8 address block and processing
of ARP requests on a specific interface.

Note that for the feature to work, the default local route
covering 127/8 dev lo needs to be removed.

Example:
  $ sysctl -w net.ipv4.conf.eth0.route_localnet=1
  $ ip route del 127.0.0.0/8 dev lo table local
  $ ip addr add 127.1.0.1/16 dev eth0
  $ ip route flush cache

V2: Fix invalid check to auto flush cache (thanks davem)

Signed-off-by: default avatarThomas Graf <tgraf@suug.ch>
Acked-by: default avatarNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0440507b

Documentation/networking/ip-sysctl.txt

+5 −0
Original line number Diff line number Diff line
@@ -862,6 +862,11 @@ accept_local - BOOLEAN 
	local interfaces over the wire and have them accepted properly.

	default FALSE



route_localnet - BOOLEAN

	Do not consider loopback addresses as martian source or destination

	while routing. This enables the use of 127/8 for local routing purposes.

	default FALSE



rp_filter - INTEGER

	0 - No source validation.

	1 - Strict mode as defined in RFC3704 Strict Reverse Path

include/linux/inetdevice.h

+2 −0
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ enum 
	IPV4_DEVCONF_ACCEPT_LOCAL,

	IPV4_DEVCONF_SRC_VMARK,

	IPV4_DEVCONF_PROXY_ARP_PVLAN,

	IPV4_DEVCONF_ROUTE_LOCALNET,

	__IPV4_DEVCONF_MAX

};
@@ -131,6 +132,7 @@ static inline void ipv4_devconf_setall(struct in_device *in_dev) 
#define IN_DEV_PROMOTE_SECONDARIES(in_dev) \

					IN_DEV_ORCONF((in_dev), \

						      PROMOTE_SECONDARIES)

#define IN_DEV_ROUTE_LOCALNET(in_dev)	IN_DEV_ORCONF(in_dev, ROUTE_LOCALNET)



#define IN_DEV_RX_REDIRECTS(in_dev) \

	((IN_DEV_FORWARD(in_dev) && \

net/ipv4/arp.c

+2 −1
Original line number Diff line number Diff line
@@ -790,7 +790,8 @@ static int arp_process(struct sk_buff *skb) 
 *	Check for bad requests for 127.x.x.x and requests for multicast

 *	addresses.  If this is one such, delete it.

 */

	if (ipv4_is_loopback(tip) || ipv4_is_multicast(tip))

	if (ipv4_is_multicast(tip) ||

	    (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip)))

		goto out;



/*

net/ipv4/devinet.c

+4 −1
Original line number Diff line number Diff line
@@ -1500,7 +1500,8 @@ static int devinet_conf_proc(ctl_table *ctl, int write, 


		if (cnf == net->ipv4.devconf_dflt)

			devinet_copy_dflt_conf(net, i);

		if (i == IPV4_DEVCONF_ACCEPT_LOCAL - 1)

		if (i == IPV4_DEVCONF_ACCEPT_LOCAL - 1 ||

		    i == IPV4_DEVCONF_ROUTE_LOCALNET - 1)

			if ((new_value == 0) && (old_value != 0))

				rt_cache_flush(net, 0);

	}
@@ -1617,6 +1618,8 @@ static struct devinet_sysctl_table { 
					      "force_igmp_version"),

		DEVINET_SYSCTL_FLUSHING_ENTRY(PROMOTE_SECONDARIES,

					      "promote_secondaries"),

		DEVINET_SYSCTL_FLUSHING_ENTRY(ROUTE_LOCALNET,

					      "route_localnet"),

	},

};

net/ipv4/route.c

+21 −9
Original line number Diff line number Diff line
@@ -1960,7 +1960,11 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr, 
		return -EINVAL;



	if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr) ||

	    ipv4_is_loopback(saddr) || skb->protocol != htons(ETH_P_IP))

	    skb->protocol != htons(ETH_P_IP))

		goto e_inval;



	if (likely(!IN_DEV_ROUTE_LOCALNET(in_dev)))

		if (ipv4_is_loopback(saddr))

			goto e_inval;



	if (ipv4_is_zeronet(saddr)) {
@@ -2203,8 +2207,7 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr, 
	   by fib_lookup.

	 */



	if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr) ||

	    ipv4_is_loopback(saddr))

	if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr))

		goto martian_source;



	if (ipv4_is_lbcast(daddr) || (saddr == 0 && daddr == 0))
@@ -2216,9 +2219,17 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr, 
	if (ipv4_is_zeronet(saddr))

		goto martian_source;



	if (ipv4_is_zeronet(daddr) || ipv4_is_loopback(daddr))

	if (ipv4_is_zeronet(daddr))

		goto martian_destination;



	if (likely(!IN_DEV_ROUTE_LOCALNET(in_dev))) {

		if (ipv4_is_loopback(daddr))

			goto martian_destination;



		if (ipv4_is_loopback(saddr))

			goto martian_source;

	}



	/*

	 *	Now we are ready to route packet.

	 */
@@ -2457,6 +2468,11 @@ static struct rtable *__mkroute_output(const struct fib_result *res, 
	u16 type = res->type;

	struct rtable *rth;



	in_dev = __in_dev_get_rcu(dev_out);

	if (!in_dev)

		return ERR_PTR(-EINVAL);



	if (likely(!IN_DEV_ROUTE_LOCALNET(in_dev)))

		if (ipv4_is_loopback(fl4->saddr) && !(dev_out->flags & IFF_LOOPBACK))

			return ERR_PTR(-EINVAL);
@@ -2470,10 +2486,6 @@ static struct rtable *__mkroute_output(const struct fib_result *res, 
	if (dev_out->flags & IFF_LOOPBACK)

		flags |= RTCF_LOCAL;



	in_dev = __in_dev_get_rcu(dev_out);

	if (!in_dev)

		return ERR_PTR(-EINVAL);



	if (type == RTN_BROADCAST) {

		flags |= RTCF_BROADCAST | RTCF_LOCAL;

		fi = NULL;