From 77751427a1ff25b27d47a4c36b12c3c8667855ac Mon Sep 17 00:00:00 2001 From: Marcelo Leitner Date: Mon, 23 Feb 2015 11:17:13 -0300 Subject: [PATCH] ipv6: addrconf: validate new MTU before applying it 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 Signed-off-by: Sabrina Dubroca Signed-off-by: David S. Miller --- 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 98e4a63d72bb..b6030025f411 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -4903,6 +4903,21 @@ int addrconf_sysctl_forward(struct 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) { struct netdev_notifier_info info; @@ -5054,7 +5069,7 @@ 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", -- 2.20.1