rtnl: stats - add missing netlink message size checks

[ Upstream commit 4775cc1f ]

We miss to check if the netlink message is actually big enough to contain
a struct if_stats_msg.

Add a check to prevent userland from sending us short messages that would
make us access memory beyond the end of the message.

Fixes: 10c9ead9 ("rtnetlink: add new RTM_GETSTATS message to dump...")
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/core/rtnetlink.c

@@ -3886,6 +3886,9 @@ static int rtnl_stats_get(struct sk_buff *skb, struct nlmsghdr *nlh)
 	u32 filter_mask;
 	int err;
 
+	if (nlmsg_len(nlh) < sizeof(*ifsm))
+		return -EINVAL;
+
 	ifsm = nlmsg_data(nlh);
 	if (ifsm->ifindex > 0)
 		dev = __dev_get_by_index(net, ifsm->ifindex);
@@ -3935,6 +3938,9 @@ static int rtnl_stats_dump(struct sk_buff *skb, struct netlink_callback *cb)
 
 	cb->seq = net->dev_base_seq;
 
+	if (nlmsg_len(cb->nlh) < sizeof(*ifsm))
+		return -EINVAL;
+
 	ifsm = nlmsg_data(cb->nlh);
 	filter_mask = ifsm->filter_mask;
 	if (!filter_mask)