rtnetlink: fix data overflow in rtnl_calcit()

"ip addr show" command execute error when we have a physical
network card with a large number of VFs

The return value of if_nlmsg_size() in rtnl_calcit() will exceed
range of u16 data type when any network cards has a larger number of
VFs. rtnl_vfinfo_size() will significant increase needed dump size when
the value of num_vfs is larger.

Eventually we get a wrong value of min_ifinfo_dump_size because of overflow
which decides the memory size needed by netlink dump and netlink_dump()
will return -EMSGSIZE because of not enough memory was allocated.

So fix it by promoting  min_dump_alloc data type to u32 to
avoid whole netlink message size overflow and it's also align
with the data type of struct netlink_callback{}.min_dump_alloc
which is assigned by return value of rtnl_calcit()
Signed-off-by: Di Zhu <zhudi21@huawei.com>
Link: https://lore.kernel.org/r/20201021020053.1401-1-zhudi21@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netlink.h

@@ -240,7 +240,7 @@ struct netlink_dump_control {
 	int (*done)(struct netlink_callback *);
 	void *data;
 	struct module *module;
-	u16 min_dump_alloc;
+	u32 min_dump_alloc;
 };
 
 int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,

net/core/rtnetlink.c

@@ -3709,13 +3709,13 @@ static int rtnl_dellinkprop(struct sk_buff *skb, struct nlmsghdr *nlh,
 	return rtnl_linkprop(RTM_DELLINKPROP, skb, nlh, extack);
 }
 
-static u16 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
+static u32 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
 {
 	struct net *net = sock_net(skb->sk);
-	struct net_device *dev;
+	size_t min_ifinfo_dump_size = 0;
 	struct nlattr *tb[IFLA_MAX+1];
 	u32 ext_filter_mask = 0;
-	u16 min_ifinfo_dump_size = 0;
+	struct net_device *dev;
 	int hdrlen;
 
 	/* Same kernel<->userspace interface hack as in rtnl_dump_ifinfo. */
@@ -3735,9 +3735,8 @@ static u16 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
 	 */
 	rcu_read_lock();
 	for_each_netdev_rcu(net, dev) {
-		min_ifinfo_dump_size = max_t(u16, min_ifinfo_dump_size,
-					     if_nlmsg_size(dev,
-						           ext_filter_mask));
+		min_ifinfo_dump_size = max(min_ifinfo_dump_size,
+					   if_nlmsg_size(dev, ext_filter_mask));
 	}
 	rcu_read_unlock();
 
@@ -5494,7 +5493,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (kind == 2 && nlh->nlmsg_flags&NLM_F_DUMP) {
 		struct sock *rtnl;
 		rtnl_dumpit_func dumpit;
-		u16 min_dump_alloc = 0;
+		u32 min_dump_alloc = 0;
 
 		link = rtnl_get_link(family, type);
 		if (!link || !link->dumpit) {