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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: Thomas Graf <tgraf@suug.ch>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Thomas Graf 2012-06-12 00:44:01 +00:00 committed by David S. Miller
parent 0440507bbc
commit d0daebc3d6
5 changed files with 34 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
Documentation/networking/ip-sysctl.txt
View File

@ -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

2
include/linux/inetdevice.h
View File

@ -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) && \

3
net/ipv4/arp.c
View File

@ -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;
/*

5
net/ipv4/devinet.c
View File

@ -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"),
},
};

30
net/ipv4/route.c
View File

@ -1960,9 +1960,13 @@ 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)) {
if (!ipv4_is_local_multicast(daddr))
goto e_inval;
@ -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.
*/
@ -2457,9 +2468,14 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
u16 type = res->type;
struct rtable *rth;
if (ipv4_is_loopback(fl4->saddr) && !(dev_out->flags & IFF_LOOPBACK))
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);
if (ipv4_is_lbcast(fl4->daddr))
type = RTN_BROADCAST;
else if (ipv4_is_multicast(fl4->daddr))
@ -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;