net: ipv6: Add sysctl entry to disable MTU updates from RA
The kernel forcefully applies MTU values received in router
advertisements provided the new MTU is less than the current. This
behavior is undesirable when the user space is managing the MTU. Instead
a sysctl flag 'accept_ra_mtu' is introduced such that the user space
can control whether or not RA provided MTU updates should be applied. The
default behavior is unchanged; user space must explicitly set this flag
to 0 for RA MTUs to be ignored.
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d6b4f5d..7dcc065e 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -201,6 +201,7 @@
.disable_ipv6 = 0,
.accept_dad = 1,
.suppress_frag_ndisc = 1,
+ .accept_ra_mtu = 1,
};
static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
@@ -238,6 +239,7 @@
.disable_ipv6 = 0,
.accept_dad = 1,
.suppress_frag_ndisc = 1,
+ .accept_ra_mtu = 1,
};
/* Check if a valid qdisc is available */
@@ -4380,6 +4382,7 @@
array[DEVCONF_NDISC_NOTIFY] = cnf->ndisc_notify;
array[DEVCONF_SUPPRESS_FRAG_NDISC] = cnf->suppress_frag_ndisc;
array[DEVCONF_ACCEPT_RA_FROM_LOCAL] = cnf->accept_ra_from_local;
+ array[DEVCONF_ACCEPT_RA_MTU] = cnf->accept_ra_mtu;
}
static inline size_t inet6_ifla6_size(void)
@@ -5259,6 +5262,13 @@
.proc_handler = proc_dointvec,
},
{
+ .procname = "accept_ra_mtu",
+ .data = &ipv6_devconf.accept_ra_mtu,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+ {
/* sentinel */
}
},
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 6828667..8a9d7c1 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1348,7 +1348,7 @@
}
}
- if (ndopts.nd_opts_mtu) {
+ if (ndopts.nd_opts_mtu && in6_dev->cnf.accept_ra_mtu) {
__be32 n;
u32 mtu;
