Messages in this thread Patch in this message | | | From | Jiri Slaby <> | Subject | [PATCH 3.12 70/72] ipv6: addrconf: validate new MTU before applying it | Date | Mon, 23 Nov 2015 14:12:31 +0100 |
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From: Marcelo Leitner <mleitner@redhat.com>
3.12-stable 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: Jiri Slaby <jslaby@suse.cz> --- 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 87f1a70bd234..38540a3ed92f 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -4656,6 +4656,21 @@ 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; @@ -4767,7 +4782,7 @@ 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", -- 2.6.3
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