sctp: Sysctl configuration for IPv4 Address Scoping

This patch introduces a new sysctl option to make IPv4 Address Scoping
configurable <draft-stewart-tsvwg-sctp-ipv4-00.txt>.

In networking environments where DNAT rules in iptables prerouting
chains convert destination IP's to link-local/private IP addresses,
SCTP connections fail to establish as the INIT chunk is dropped by the
kernel due to address scope match failure.
For example to support overlapping IP addresses (same IP address with
different vlan id) a Layer-5 application listens on link local IP's,
and there is a DNAT rule that maps the destination IP to a link local
IP. Such applications never get the SCTP INIT if the address-scoping
draft is strictly followed.

This sysctl configuration allows SCTP to function in such
unconventional networking environments.

Sysctl options:
0 - Disable IPv4 address scoping draft altogether
1 - Enable IPv4 address scoping (default, current behavior)
2 - Enable address scoping but allow IPv4 private addresses in init/init-ack
3 - Enable address scoping but allow IPv4 link local address in init/init-ack

Signed-off-by: Bhaskar Dutta <bhaskar.dutta@globallogic.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index 63eabbc71298..ab7151da120f 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -51,6 +51,7 @@ static int timer_max = 86400000; /* ms in one day */
 static int int_max = INT_MAX;
 static int sack_timer_min = 1;
 static int sack_timer_max = 500;
+static int addr_scope_max = 3; /* check sctp_scope_policy_t in include/net/sctp/constants.h for max entries */
 
 extern int sysctl_sctp_mem[3];
 extern int sysctl_sctp_rmem[3];
@@ -272,6 +273,17 @@ static ctl_table sctp_table[] = {
                 .proc_handler   = proc_dointvec,
                 .strategy       = sysctl_intvec
         },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "addr_scope_policy",
+                .data           = &sctp_scope_policy,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &zero,
+                .extra2         = &addr_scope_max,
+        },
         { .ctl_name = 0 }
 };