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ipv4/icmp: redirect messages can use the ingress daddr as source

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This patch allows configuring how the source address of ICMP
redirect messages is selected; by default the old behaviour is
retained, while setting icmp_redirects_use_orig_daddr force the
usage of the destination address of the packet that caused the
redirect.

The new behaviour fits closely the RFC 5798 section 8.1.1, and fix the
following scenario:

Two machines are set up with VRRP to act as routers out of a subnet,
they have IPs x.x.x.1/24 and x.x.x.2/24, with VRRP holding on to
x.x.x.254/24.

If a host in said subnet needs to get an ICMP redirect from the VRRP
router, i.e. to reach a destination behind a different gateway, the
source IP in the ICMP redirect is chosen as the primary IP on the
interface that the packet arrived at, i.e. x.x.x.1 or x.x.x.2.

The host will then ignore said redirect, due to RFC 1122 section 3.2.2.2,
and will continue to use the wrong next-op.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2015-10-09 14:34:31 +02:00 committed by David S. Miller
parent 0944d6b5a2
commit e2ca690b65
4 changed files with 33 additions and 3 deletions
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19
Documentation/networking/ip-sysctl.txt
View File

@ -884,8 +884,8 @@ icmp_ignore_bogus_error_responses - BOOLEAN
icmp_errors_use_inbound_ifaddr - BOOLEAN
If zero, icmp error messages are sent with the primary address of
the exiting interface.
If zero, icmp error messages except redirects are sent with the primary
address of the exiting interface.
If non-zero, the message will be sent with the primary address of
the interface that received the packet that caused the icmp error.
@ -897,8 +897,23 @@ icmp_errors_use_inbound_ifaddr - BOOLEAN
then the primary address of the first non-loopback interface that
has one will be used regardless of this setting.
The source address selection of icmp redirect messages is controlled by
icmp_errors_use_inbound_ifaddr.
Default: 0
icmp_redirects_use_orig_daddr - BOOLEAN
If zero, icmp redirect messages are sent using the address specified for
other icmp errors by icmp_errors_use_inbound_ifaddr.
If non-zero, the message will be sent with the destination address of
the packet that caused the icmp redirect.
This behaviour is the preferred one on VRRP routers (see RFC 5798
section 8.1.1).
Default: 0
igmp_max_memberships - INTEGER
Change the maximum number of multicast groups we can subscribe to.
Default: 20

1
include/net/netns/ipv4.h
View File

@ -74,6 +74,7 @@ struct netns_ipv4 {
int sysctl_icmp_ratelimit;
int sysctl_icmp_ratemask;
int sysctl_icmp_errors_use_inbound_ifaddr;
int sysctl_icmp_redirects_use_orig_daddr;
struct local_ports ip_local_ports;

9
net/ipv4/icmp.c
View File

@ -659,7 +659,9 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
*/
saddr = iph->daddr;
if (!(rt->rt_flags & RTCF_LOCAL)) {
if (!((type == ICMP_REDIRECT) &&
net->ipv4.sysctl_icmp_redirects_use_orig_daddr) &&
!(rt->rt_flags & RTCF_LOCAL)) {
struct net_device *dev = NULL;
rcu_read_lock();
@ -1222,6 +1224,11 @@ static int __net_init icmp_sk_init(struct net *net)
net->ipv4.sysctl_icmp_ratemask = 0x1818;
net->ipv4.sysctl_icmp_errors_use_inbound_ifaddr = 0;
/* Control paramerer - use the daddr of originating packets as saddr
* in redirect messages?
*/
net->ipv4.sysctl_icmp_redirects_use_orig_daddr = 0;
return 0;
fail:

7
net/ipv4/sysctl_net_ipv4.c
View File

@ -817,6 +817,13 @@ static struct ctl_table ipv4_net_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "icmp_redirects_use_orig_daddr",
.data = &init_net.ipv4.sysctl_icmp_redirects_use_orig_daddr,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "icmp_ratelimit",
.data = &init_net.ipv4.sysctl_icmp_ratelimit,