3.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Marcelo Leitner <mleitner@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: "Charles (Chas) Williams" <3chas3@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv6/addrconf.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -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",
--
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