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net: ipv6: Add sysctl entry to disable MTU updates from RA

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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>
This commit is contained in:
Harout Hedeshian 2015-01-20 10:06:05 -07:00 committed by David S. Miller
parent 46a93af29f
commit c2943f1453
5 changed files with 20 additions and 1 deletions
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7
Documentation/networking/ip-sysctl.txt
View File

@ -1287,6 +1287,13 @@ accept_ra_rtr_pref - BOOLEAN
Functional default: enabled if accept_ra is enabled.
disabled if accept_ra is disabled.
accept_ra_mtu - BOOLEAN
Apply the MTU value specified in RA option 5 (RFC4861). If
disabled, the MTU specified in the RA will be ignored.
Functional default: enabled if accept_ra is enabled.
disabled if accept_ra is disabled.
accept_redirects - BOOLEAN
Accept Redirects.

1
include/linux/ipv6.h
View File

@ -52,6 +52,7 @@ struct ipv6_devconf {
__s32 force_tllao;
__s32 ndisc_notify;
__s32 suppress_frag_ndisc;
__s32 accept_ra_mtu;
void *sysctl;
};

1
include/uapi/linux/ipv6.h
View File

@ -169,6 +169,7 @@ enum {
DEVCONF_SUPPRESS_FRAG_NDISC,
DEVCONF_ACCEPT_RA_FROM_LOCAL,
DEVCONF_USE_OPTIMISTIC,
DEVCONF_ACCEPT_RA_MTU,
DEVCONF_MAX
};

10
net/ipv6/addrconf.c
View File

@ -201,6 +201,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
.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 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
.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 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
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)
@ -5258,6 +5261,13 @@ static struct addrconf_sysctl_table
.mode = 0644,
.proc_handler = proc_dointvec,
},
{
.procname = "accept_ra_mtu",
.data = &ipv6_devconf.accept_ra_mtu,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
{
/* sentinel */
}

2
net/ipv6/ndisc.c
View File

@ -1348,7 +1348,7 @@ static void ndisc_router_discovery(struct sk_buff *skb)
}
}
if (ndopts.nd_opts_mtu) {
if (ndopts.nd_opts_mtu && in6_dev->cnf.accept_ra_mtu) {
__be32 n;
u32 mtu;