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macsec: avoid to set wrong mtu 

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: c09440f7dc ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Taehee Yoo 2020-04-23 13:40:47 +00:00 committed by David S. Miller
parent c651b461b5
commit 7f32708036
1 changed files with 9 additions and 5 deletions
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14
drivers/net/macsec.c
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@ -4002,11 +4002,11 @@ static int macsec_newlink(struct net *net, struct net_device *dev,
struct netlink_ext_ack *extack)
{
struct macsec_dev *macsec = macsec_priv(dev);
struct net_device *real_dev;
int err;
sci_t sci;
u8 icv_len = DEFAULT_ICV_LEN;
rx_handler_func_t *rx_handler;
u8 icv_len = DEFAULT_ICV_LEN;
struct net_device *real_dev;
int err, mtu;
sci_t sci;
if (!tb[IFLA_LINK])
return -EINVAL;
@ -4033,7 +4033,11 @@ 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)