From: Marcelo Leitner Date: Mon, 23 Feb 2015 14:17:13 +0000 (-0300) Subject: ipv6: addrconf: validate new MTU before applying it X-Git-Tag: v3.4.111~21 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=59c8392ffcf3d6e39dcdd558e0354afc545f4c91;p=thirdparty%2Fkernel%2Fstable.git ipv6: addrconf: validate new MTU before applying it 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 Signed-off-by: Sabrina Dubroca Signed-off-by: David S. Miller Signed-off-by: Zefan Li --- diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index be5876079a8e7..b6c236bd23260 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",