net: rtnetlink: add bulk delete support flag

Add a new rtnl flag (RTNL_FLAG_BULK_DEL_SUPPORTED) which is used to
verify that the delete operation allows bulk object deletion. Also emit
a warning if anyone tries to set it for non-delete kind.
Suggested-by: NDavid Ahern <dsahern@kernel.org>
Signed-off-by: NNikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/rtnetlink.h

@@ -10,7 +10,8 @@ typedef int (*rtnl_doit_func)(struct sk_buff *, struct nlmsghdr *,
 typedef int (*rtnl_dumpit_func)(struct sk_buff *, struct netlink_callback *);
 
 enum rtnl_link_flags {
-	RTNL_FLAG_DOIT_UNLOCKED = BIT(0),
+	RTNL_FLAG_DOIT_UNLOCKED		= BIT(0),
+	RTNL_FLAG_BULK_DEL_SUPPORTED	= BIT(1),
 };
 
 enum rtnl_kinds {

net/core/rtnetlink.c

@@ -249,6 +249,8 @@ static int rtnl_register_internal(struct module *owner,
 	if (dumpit)
 		link->dumpit = dumpit;
 
+	WARN_ON(rtnl_msgtype_kind(msgtype) != RTNL_KIND_DEL &&
+		(flags & RTNL_FLAG_BULK_DEL_SUPPORTED));
 	link->flags |= flags;
 
 	/* publish protocol:msgtype */
@@ -6009,6 +6011,12 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 	}
 
 	flags = link->flags;
+	if (kind == RTNL_KIND_DEL && (nlh->nlmsg_flags & NLM_F_BULK) &&
+	    !(flags & RTNL_FLAG_BULK_DEL_SUPPORTED)) {
+		NL_SET_ERR_MSG(extack, "Bulk delete is not supported");
+		goto err_unlock;
+	}
+
 	if (flags & RTNL_FLAG_DOIT_UNLOCKED) {
 		doit = link->doit;
 		rcu_read_unlock();