[PATCH net-next] net:sched: add gkprio scheduler

[Nishanth Devarajan <ndev2021@gmail.com>]

net/sched: add gkprio scheduler

Gkprio (Gatekeeper Priority Queue) is a queueing discipline that prioritizes
IPv4 and IPv6 packets accordingly to their DSCP field. Although Gkprio can be
employed in any QoS scenario in which a higher DSCP field means a higher
priority packet, Gkprio was concieved as a solution for denial-of-service
defenses that need to route packets with different priorities.

Signed-off-by: Nishanth Devarajan <ndev2021@gmail.com>
Reviewed-by: Cody Doucette <doucette@bu.edu>
Reviewed-by: Michel Machado <michel@digirati.com.br>
Reviewed-by: Sachin Paryani <sachin.paryani@gmail.com>
---
 include/uapi/linux/pkt_sched.h |  11 ++
 net/sched/Kconfig              |  13 ++
 net/sched/Makefile             |   1 +
 net/sched/sch_gkprio.c         | 316 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 341 insertions(+)
 create mode 100644 net/sched/sch_gkprio.c

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 37b5096..de8b5ca 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -124,6 +124,17 @@ struct tc_fifo_qopt {
 	__u32	limit;	/* Queue length: bytes for bfifo, packets for pfifo */
 };
 
+/* GKPRIO section */
+
+struct tc_gkprio_qopt {
+	__u32	limit; 	    	/* Queue length in packets. */
+	__u16	noip_dfltp; 	/* Default priority for non-IP packets. */
+
+	/* Stats. */
+	__u16 highest_prio; 	/* Highest priority currently in queue.  */
+	__u16 lowest_prio;  	/* Lowest priority currently in queue. */
+};
+
 /* PRIO section */
 
 #define TCQ_PRIO_BANDS	16
diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index a01169f..9c47857 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -240,6 +240,19 @@ config NET_SCH_MQPRIO
 
 	  If unsure, say N.
 
+config NET_SCH_GKPRIO
+	tristate "Gatekeeper priority queue scheduler (GKPRIO)"
+	help
+	  Say Y here if you want to use the Gatekeeper priority queue
+	  scheduler. This schedules packets according to priorities based on
+	  the DSCP (IPv4) and DS (IPv6) fields, which is useful for request
+	  packets in DoS mitigation systems such as Gatekeeper.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called sch_gkprio.
+
+	  If unsure, say N.
+
 config NET_SCH_CHOKE
 	tristate "CHOose and Keep responsive flow scheduler (CHOKE)"
 	help
diff --git a/net/sched/Makefile b/net/sched/Makefile
index 8811d38..93a1fdb 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_NET_SCH_NETEM)	+= sch_netem.o
 obj-$(CONFIG_NET_SCH_DRR)	+= sch_drr.o
 obj-$(CONFIG_NET_SCH_PLUG)	+= sch_plug.o
 obj-$(CONFIG_NET_SCH_MQPRIO)	+= sch_mqprio.o
+obj-$(CONFIG_NET_SCH_GKPRIO)	+= sch_gkprio.o
 obj-$(CONFIG_NET_SCH_CHOKE)	+= sch_choke.o
 obj-$(CONFIG_NET_SCH_QFQ)	+= sch_qfq.o
 obj-$(CONFIG_NET_SCH_CODEL)	+= sch_codel.o
diff --git a/net/sched/sch_gkprio.c b/net/sched/sch_gkprio.c
new file mode 100644
index 0000000..ad1227c
--- /dev/null
+++ b/net/sched/sch_gkprio.c
@@ -0,0 +1,316 @@
+/*
+ * net/sched/sch_gkprio.c  Gatekeeper Priority Queue.
+ *
+ *		This program is free software; you can redistribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ * Authors:	Nishanth Devarajan, <ndev_2021@gmail.com>
+ *	        original idea by Michel Machado, Cody Doucette, and Qiaobin Fu
+ */
+
+#include <linux/string.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <net/pkt_sched.h>
+#include <net/sch_generic.h>
+#include <net/inet_ecn.h>
+
+/* Packets are assigned priorities [0, 63] due to the IP DSCP field limits. */
+#define GKPRIO_MAX_PRIORITY 64
+
+/*	  Gatekeeper Priority Queue
+ *	=================================
+ *
+ * This qdisc schedules a packet according to the value (0-63) of its DSCP
+ * (IPv4) or DS (IPv6) field, where a higher value places the packet closer
+ * to the exit of the queue. Non-IP packets are assigned a default priority
+ * specified to GKPRIO; if none is specified, default priority is set
+ * to 0. When the queue is full, the lowest priority packet in the queue is
+ * dropped to make room for the packet to be added if it has higher priority.
+ * If the packet to be added has lower priority than all packets in the queue,
+ * it is dropped.
+ *
+ * Without the Gatekeeper priority queue, queue length limits must be imposed
+ * for individual queues, and there is no easy way to enforce a global queue
+ * length limit across all priorities. With the Gatekeeper queue, a global
+ * queue length limit can be enforced while not restricting the queue lengths
+ * of individual priorities.
+ *
+ * This is especially useful for a denial-of-service defense system; like
+ * Gatekeeper, which prioritizes packets in flows that demonstrate expected
+ * behavior of legitimate users. The queue is flexible to allow any number
+ * of packets of any priority up to the global limit of the scheduler
+ * without risking resource overconsumption by a flood of low priority packets.
+ *
+ * The Gatekeper standalone codebase is found here:
+ *
+ *		https://github.com/AltraMayor/gatekeeper
+ */
+
+struct gkprio_sched_data {
+	/* Parameters. */
+	u32 max_limit;
+	u16 noip_dfltp;
+
+	/* Queue state. */
+	struct sk_buff_head qdiscs[GKPRIO_MAX_PRIORITY];
+	u16 highest_prio;
+	u16 lowest_prio;
+};
+
+static u16 calc_new_high_prio(const struct gkprio_sched_data *q)
+{
+	int prio;
+
+	for (prio = q->highest_prio - 1; prio >= q->lowest_prio; prio--) {
+		if (!skb_queue_empty(&q->qdiscs[prio]))
+			return prio;
+	}
+
+	/* GK queue is empty, return 0 (default highest priority setting). */
+	return 0;
+}
+
+static u16 calc_new_low_prio(const struct gkprio_sched_data *q)
+{
+	int prio;
+
+	for (prio = q->lowest_prio + 1; prio <= q->highest_prio; prio++) {
+		if (!skb_queue_empty(&q->qdiscs[prio]))
+			return prio;
+	}
+
+	/* GK queue is empty, return GKPRIO_MAX_PRIORITY - 1
+	 * (default lowest priority setting).
+	 */
+	return GKPRIO_MAX_PRIORITY - 1;
+}
+
+static int gkprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
+			  struct sk_buff **to_free)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	struct sk_buff_head *qdisc;
+	struct sk_buff_head *lp_qdisc;
+	struct sk_buff *to_drop;
+	int wlen;
+	u16 prio, lp;
+
+	/* Obtain the priority of @skb. */
+	wlen = skb_network_offset(skb);
+	switch (tc_skb_protocol(skb)) {
+	case htons(ETH_P_IP):
+		wlen += sizeof(struct iphdr);
+		if (!pskb_may_pull(skb, wlen))
+			goto drop;
+		prio = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
+		break;
+
+	case htons(ETH_P_IPV6):
+		wlen += sizeof(struct ipv6hdr);
+		if (!pskb_may_pull(skb, wlen))
+			goto drop;
+		prio = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
+		break;
+
+	default:
+		prio = q->noip_dfltp;
+		break;
+	}
+
+	qdisc = &q->qdiscs[prio];
+
+	if (sch->q.qlen < q->max_limit) {
+		__skb_queue_tail(qdisc, skb);
+		qdisc_qstats_backlog_inc(sch, skb);
+
+		/* Check to update highest and lowest priorities. */
+		if (prio > q->highest_prio)
+			q->highest_prio = prio;
+
+		if (prio < q->lowest_prio)
+			q->lowest_prio = prio;
+
+		sch->q.qlen++;
+		return NET_XMIT_SUCCESS;
+	}
+
+	/* If this packet has the lowest priority, drop it. */
+	lp = q->lowest_prio;
+	if (prio <= lp)
+		return qdisc_drop(skb, sch, to_free);
+
+	/* Drop the packet at the tail of the lowest priority qdisc. */
+	lp_qdisc = &q->qdiscs[lp];
+	to_drop = __skb_dequeue_tail(lp_qdisc);
+	BUG_ON(!to_drop);
+	qdisc_qstats_backlog_dec(sch, to_drop);
+	qdisc_drop(to_drop, sch, to_free);
+
+	__skb_queue_tail(qdisc, skb);
+	qdisc_qstats_backlog_inc(sch, skb);
+
+	/* Check to update highest and lowest priorities. */
+	if (skb_queue_empty(lp_qdisc)) {
+		if (q->lowest_prio == q->highest_prio) {
+			BUG_ON(sch->q.qlen);
+			q->lowest_prio = prio;
+			q->highest_prio = prio;
+		} else {
+			q->lowest_prio = calc_new_low_prio(q);
+		}
+	}
+
+	if (prio > q->highest_prio)
+		q->highest_prio = prio;
+
+	return NET_XMIT_SUCCESS;
+drop:
+	qdisc_drop(skb, sch, to_free);
+	return NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+}
+
+static struct sk_buff *gkprio_dequeue(struct Qdisc *sch)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	struct sk_buff_head *hpq = &q->qdiscs[q->highest_prio];
+	struct sk_buff *skb = __skb_dequeue(hpq);
+
+	if (unlikely(!skb))
+		return NULL;
+
+	sch->q.qlen--;
+	qdisc_qstats_backlog_dec(sch, skb);
+	qdisc_bstats_update(sch, skb);
+
+	/* Update highest priority field. */
+	if (skb_queue_empty(hpq)) {
+		if (q->lowest_prio == q->highest_prio) {
+			BUG_ON(sch->q.qlen);
+			q->highest_prio = 0;
+			q->lowest_prio = GKPRIO_MAX_PRIORITY - 1;
+		} else {
+			q->highest_prio = calc_new_high_prio(q);
+		}
+	}
+	return skb;
+}
+
+static int gkprio_change(struct Qdisc *sch, struct nlattr *opt,
+			struct netlink_ext_ack *extack)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	struct tc_gkprio_qopt *ctl = nla_data(opt);
+	unsigned int min_limit = 1;
+
+	if (ctl->limit == (typeof(ctl->limit))-1)
+		q->max_limit = max(qdisc_dev(sch)->tx_queue_len, min_limit);
+	else if (ctl->limit < 1 || ctl->limit > qdisc_dev(sch)->tx_queue_len)
+		return -EINVAL;
+	else
+		q->max_limit = ctl->limit;
+
+	if (ctl->noip_dfltp == (typeof(ctl->noip_dfltp))-1)
+		q->noip_dfltp = 0;
+	else if (ctl->noip_dfltp >= GKPRIO_MAX_PRIORITY)
+		return -EINVAL;
+	else
+		q->noip_dfltp = ctl->noip_dfltp;
+
+	return 0;
+}
+
+static int gkprio_init(struct Qdisc *sch, struct nlattr *opt,
+			struct netlink_ext_ack *extack)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	int prio;
+	unsigned int min_limit = 1;
+
+	/* Initialise all queues, one for each possible priority. */
+	for (prio = 0; prio < GKPRIO_MAX_PRIORITY; prio++)
+		__skb_queue_head_init(&q->qdiscs[prio]);
+
+	q->highest_prio = 0;
+	q->lowest_prio = GKPRIO_MAX_PRIORITY - 1;
+	if (!opt) {
+		q->max_limit = max(qdisc_dev(sch)->tx_queue_len, min_limit);
+		q->noip_dfltp = 0;
+		return 0;
+	}
+	return gkprio_change(sch, opt, extack);
+}
+
+static int gkprio_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	struct tc_gkprio_qopt opt;
+
+	opt.limit = q->max_limit;
+	opt.noip_dfltp = q->noip_dfltp;
+	opt.highest_prio = q->highest_prio;
+	opt.lowest_prio = q->lowest_prio;
+
+	if (nla_put(skb, TCA_OPTIONS, sizeof(opt), &opt))
+		return -1;
+
+	return skb->len;
+}
+
+static void gkprio_reset(struct Qdisc *sch)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	int prio;
+
+	sch->qstats.backlog = 0;
+	sch->q.qlen = 0;
+
+	for (prio = 0; prio < GKPRIO_MAX_PRIORITY; prio++)
+		__skb_queue_purge(&q->qdiscs[prio]);
+	q->highest_prio = 0;
+	q->lowest_prio = GKPRIO_MAX_PRIORITY - 1;
+}
+
+static void gkprio_destroy(struct Qdisc *sch)
+{
+	struct gkprio_sched_data *q = qdisc_priv(sch);
+	int prio;
+
+	for (prio = 0; prio < GKPRIO_MAX_PRIORITY; prio++)
+		__skb_queue_purge(&q->qdiscs[prio]);
+}
+
+struct Qdisc_ops gkprio_qdisc_ops __read_mostly = {
+	.id		=	"gkprio",
+	.priv_size	=	sizeof(struct gkprio_sched_data),
+	.enqueue	=	gkprio_enqueue,
+	.dequeue	=	gkprio_dequeue,
+	.peek		=	qdisc_peek_dequeued,
+	.init		=	gkprio_init,
+	.reset		=	gkprio_reset,
+	.change		=	gkprio_change,
+	.dump		=	gkprio_dump,
+	.destroy	=	gkprio_destroy,
+	.owner		=	THIS_MODULE,
+};
+
+static int __init gkprio_module_init(void)
+{
+	return register_qdisc(&gkprio_qdisc_ops);
+}
+
+static void __exit gkprio_module_exit(void)
+{
+	unregister_qdisc(&gkprio_qdisc_ops);
+}
+
+module_init(gkprio_module_init)
+module_exit(gkprio_module_exit)
+
+MODULE_LICENSE("GPL");
-- 
1.9.1