macsec: avoid to set wrong mtu

[ Upstream commit 7f327080364abccf923fa5a5b24e038eb0ba1407 ]

When a macsec interface is created, the mtu is calculated with the lower
interface's mtu value.
If the mtu of lower interface is lower than the length, which is needed
by macsec interface, macsec's mtu value will be overflowed.
So, if the lower interface's mtu is too low, macsec interface's mtu
should be set to 0.

Test commands:
    ip link add dummy0 mtu 10 type dummy
    ip link add macsec0 link dummy0 type macsec
    ip link show macsec0

Before:
    11: macsec0@dummy0: <BROADCAST,MULTICAST,M-DOWN> mtu 4294967274
After:
    11: macsec0@dummy0: <BROADCAST,MULTICAST,M-DOWN> mtu 0

Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 5959e8817a1b8d3b96d2eb8f5ddae17123810758..926e2eb528fd42dd4c3e909e56d7bd06dd221654 100644 (file)
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -3209,11 +3209,11 @@ static int macsec_newlink(struct net *net, struct net_device *dev,
                          struct netlink_ext_ack *extack)
 {
        struct macsec_dev *macsec = macsec_priv(dev);
+       rx_handler_func_t *rx_handler;
+       u8 icv_len = DEFAULT_ICV_LEN;
        struct net_device *real_dev;
-       int err;
+       int err, mtu;
        sci_t sci;
-       u8 icv_len = DEFAULT_ICV_LEN;
-       rx_handler_func_t *rx_handler;
 
        if (!tb[IFLA_LINK])
                return -EINVAL;
@@ -3229,7 +3229,11 @@ static int macsec_newlink(struct net *net, struct net_device *dev,
 
        if (data && data[IFLA_MACSEC_ICV_LEN])
                icv_len = nla_get_u8(data[IFLA_MACSEC_ICV_LEN]);
-       dev->mtu = real_dev->mtu - icv_len - macsec_extra_len(true);
+       mtu = real_dev->mtu - icv_len - macsec_extra_len(true);
+       if (mtu < 0)
+               dev->mtu = 0;
+       else
+               dev->mtu = mtu;
 
        rx_handler = rtnl_dereference(real_dev->rx_handler);
        if (rx_handler && rx_handler != macsec_handle_frame)