[PATCH 3.4 087/107] ipv6: addrconf: validate new MTU before applying it

lizf
2016-03-16T08:12:37Z

From: Marcelo Leitner <mleitner@redhat.com>

3.4.111-rc1 review patch. If anyone has any objections, please let me know.

------------------

commit 77751427a1ff25b27d47a4c36b12c3c8667855ac upstream.

Currently we don't check if the new MTU is valid or not and this allows
one to configure a smaller than minimum allowed by RFCs or even bigger
than interface own MTU, which is a problem as it may lead to packet
drops.

If you have a daemon like NetworkManager running, this may be exploited
by remote attackers by forging RA packets with an invalid MTU, possibly
leading to a DoS. (NetworkManager currently only validates for values
too small, but not for too big ones.)

The fix is just to make sure the new value is valid. That is, between
IPV6_MIN_MTU and interface's MTU.

Note that similar check is already performed at
ndisc_router_discovery(), for when kernel itself parses the RA.

Signed-off-by: Marcelo Ricardo Leitner <mleitner@redhat.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
net/ipv6/addrconf.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index be58760..b6c236b 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4340,6 +4340,21 @@ int addrconf_sysctl_forward(ctl_table *ctl, int write,
return ret;
}

+static
+int addrconf_sysctl_mtu(struct ctl_table *ctl, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct inet6_dev *idev = ctl->extra1;
+ int min_mtu = IPV6_MIN_MTU;
+ struct ctl_table lctl;
+
+ lctl = *ctl;
+ lctl.extra1 = &min_mtu;
+ lctl.extra2 = idev ? &idev->dev->mtu : NULL;
+
+ return proc_dointvec_minmax(&lctl, write, buffer, lenp, ppos);
+}
+
static void dev_disable_change(struct inet6_dev *idev)
{
if (!idev || !idev->dev)
@@ -4449,7 +4464,7 @@ static struct addrconf_sysctl_table
.data = &ipv6_devconf.mtu6,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec,
+ .proc_handler = addrconf_sysctl_mtu,
},
{
.procname = "accept_ra",
--
1.9.1