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ipv6: addrconf: validate new MTU before applying it

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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>
This commit is contained in:
Marcelo Leitner 2015-02-23 11:17:13 -03:00 committed by David S. Miller
parent 8d4ac39df0
commit 77751427a1
1 changed files with 16 additions and 1 deletions
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17
net/ipv6/addrconf.c
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@ -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",