net: check dev->addr_len for dev_set_mac_address()

Historically, dev_ifsioc() uses struct sockaddr as mac
address definition, this is why dev_set_mac_address()
accepts a struct sockaddr pointer as input but now we
have various types of mac addresse whose lengths
are up to MAX_ADDR_LEN, longer than struct sockaddr,
and saved in dev->addr_len.

It is too late to fix dev_ifsioc() due to API
compatibility, so just reject those larger than
sizeof(struct sockaddr), otherwise we would read
and use some random bytes from kernel stack.

Fortunately, only a few IPv6 tunnel devices have addr_len
larger than sizeof(struct sockaddr) and they don't support
ndo_set_mac_addr(). But with team driver, in lb mode, they
can still be enslaved to a team master and make its mac addr
length as the same.

Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev_ioctl.c

@@ -263,6 +263,8 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
 		return dev_set_mtu(dev, ifr->ifr_mtu);
 
 	case SIOCSIFHWADDR:
+		if (dev->addr_len > sizeof(struct sockaddr))
+			return -EINVAL;
 		return dev_set_mac_address(dev, &ifr->ifr_hwaddr);
 
 	case SIOCSIFHWBROADCAST: