Patch "ipv6: addrconf: validate new MTU before applying it" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

ipv6: addrconf: validate new MTU before applying it

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ipv6-addrconf-validate-new-mtu-before-applying-it.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marcelo Leitner <[email protected]>
Date: Mon, 23 Feb 2015 11:17:13 -0300
Subject: ipv6: addrconf: validate new MTU before applying it

From: Marcelo Leitner <[email protected]>

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.

---
 net/ipv6/addrconf.c |   17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

@@ -4793,6 +4793,21 @@ int addrconf_sysctl_forward(struct ctl_t
 	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)
 {
 	struct netdev_notifier_info info;

@@ -4944,7 +4959,7 @@ 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",

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/ipv6-addrconf-validate-new-mtu-before-applying-it.patch