Merge: sched: sch_cake: add bounds checks to host bulk flow fairness counts

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/698

JIRA: https://issues.redhat.com/browse/RHEL-77316
CVE: CVE-2025-21647
Tested: compile only

Signed-off-by: Xin Long <lxin@redhat.com>

Approved-by: Marcelo Ricardo Leitner <mleitner@redhat.com>
Approved-by: Toke Høiland-Jørgensen <toke@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Julio Faracco <jfaracco@redhat.com>

Author: jcfaracco

net/sched/sch_cake.c

@@ -627,6 +627,63 @@ static bool cake_ddst(int flow_mode)
 	return (flow_mode & CAKE_FLOW_DUAL_DST) == CAKE_FLOW_DUAL_DST;
 }
 
+static void cake_dec_srchost_bulk_flow_count(struct cake_tin_data *q,
+					     struct cake_flow *flow,
+					     int flow_mode)
+{
+	if (likely(cake_dsrc(flow_mode) &&
+		   q->hosts[flow->srchost].srchost_bulk_flow_count))
+		q->hosts[flow->srchost].srchost_bulk_flow_count--;
+}
+
+static void cake_inc_srchost_bulk_flow_count(struct cake_tin_data *q,
+					     struct cake_flow *flow,
+					     int flow_mode)
+{
+	if (likely(cake_dsrc(flow_mode) &&
+		   q->hosts[flow->srchost].srchost_bulk_flow_count < CAKE_QUEUES))
+		q->hosts[flow->srchost].srchost_bulk_flow_count++;
+}
+
+static void cake_dec_dsthost_bulk_flow_count(struct cake_tin_data *q,
+					     struct cake_flow *flow,
+					     int flow_mode)
+{
+	if (likely(cake_ddst(flow_mode) &&
+		   q->hosts[flow->dsthost].dsthost_bulk_flow_count))
+		q->hosts[flow->dsthost].dsthost_bulk_flow_count--;
+}
+
+static void cake_inc_dsthost_bulk_flow_count(struct cake_tin_data *q,
+					     struct cake_flow *flow,
+					     int flow_mode)
+{
+	if (likely(cake_ddst(flow_mode) &&
+		   q->hosts[flow->dsthost].dsthost_bulk_flow_count < CAKE_QUEUES))
+		q->hosts[flow->dsthost].dsthost_bulk_flow_count++;
+}
+
+static u16 cake_get_flow_quantum(struct cake_tin_data *q,
+				 struct cake_flow *flow,
+				 int flow_mode)
+{
+	u16 host_load = 1;
+
+	if (cake_dsrc(flow_mode))
+		host_load = max(host_load,
+				q->hosts[flow->srchost].srchost_bulk_flow_count);
+
+	if (cake_ddst(flow_mode))
+		host_load = max(host_load,
+				q->hosts[flow->dsthost].dsthost_bulk_flow_count);
+
+	/* The get_random_u16() is a way to apply dithering to avoid
+	 * accumulating roundoff errors
+	 */
+	return (q->flow_quantum * quantum_div[host_load] +
+		get_random_u16()) >> 16;
+}
+
 static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
 		     int flow_mode, u16 flow_override, u16 host_override)
 {
@@ -773,10 +830,8 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
 		allocate_dst = cake_ddst(flow_mode);
 
 		if (q->flows[outer_hash + k].set == CAKE_SET_BULK) {
-			if (allocate_src)
-				q->hosts[q->flows[reduced_hash].srchost].srchost_bulk_flow_count--;
-			if (allocate_dst)
-				q->hosts[q->flows[reduced_hash].dsthost].dsthost_bulk_flow_count--;
+			cake_dec_srchost_bulk_flow_count(q, &q->flows[outer_hash + k], flow_mode);
+			cake_dec_dsthost_bulk_flow_count(q, &q->flows[outer_hash + k], flow_mode);
 		}
 found:
 		/* reserve queue for future packets in same flow */
@@ -801,9 +856,10 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
 			q->hosts[outer_hash + k].srchost_tag = srchost_hash;
 found_src:
 			srchost_idx = outer_hash + k;
-			if (q->flows[reduced_hash].set == CAKE_SET_BULK)
-				q->hosts[srchost_idx].srchost_bulk_flow_count++;
 			q->flows[reduced_hash].srchost = srchost_idx;
+
+			if (q->flows[reduced_hash].set == CAKE_SET_BULK)
+				cake_inc_srchost_bulk_flow_count(q, &q->flows[reduced_hash], flow_mode);
 		}
 
 		if (allocate_dst) {
@@ -824,9 +880,10 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
 			q->hosts[outer_hash + k].dsthost_tag = dsthost_hash;
 found_dst:
 			dsthost_idx = outer_hash + k;
-			if (q->flows[reduced_hash].set == CAKE_SET_BULK)
-				q->hosts[dsthost_idx].dsthost_bulk_flow_count++;
 			q->flows[reduced_hash].dsthost = dsthost_idx;
+
+			if (q->flows[reduced_hash].set == CAKE_SET_BULK)
+				cake_inc_dsthost_bulk_flow_count(q, &q->flows[reduced_hash], flow_mode);
 		}
 	}
 
@@ -1839,10 +1896,6 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 	/* flowchain */
 	if (!flow->set || flow->set == CAKE_SET_DECAYING) {
-		struct cake_host *srchost = &b->hosts[flow->srchost];
-		struct cake_host *dsthost = &b->hosts[flow->dsthost];
-		u16 host_load = 1;
-
 		if (!flow->set) {
 			list_add_tail(&flow->flowchain, &b->new_flows);
 		} else {
@@ -1852,31 +1905,17 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		flow->set = CAKE_SET_SPARSE;
 		b->sparse_flow_count++;
 
-		if (cake_dsrc(q->flow_mode))
-			host_load = max(host_load, srchost->srchost_bulk_flow_count);
-
-		if (cake_ddst(q->flow_mode))
-			host_load = max(host_load, dsthost->dsthost_bulk_flow_count);
-
-		flow->deficit = (b->flow_quantum *
-				 quantum_div[host_load]) >> 16;
+		flow->deficit = cake_get_flow_quantum(b, flow, q->flow_mode);
 	} else if (flow->set == CAKE_SET_SPARSE_WAIT) {
-		struct cake_host *srchost = &b->hosts[flow->srchost];
-		struct cake_host *dsthost = &b->hosts[flow->dsthost];
-
 		/* this flow was empty, accounted as a sparse flow, but actually
 		 * in the bulk rotation.
 		 */
 		flow->set = CAKE_SET_BULK;
 		b->sparse_flow_count--;
 		b->bulk_flow_count++;
 
-		if (cake_dsrc(q->flow_mode))
-			srchost->srchost_bulk_flow_count++;
-
-		if (cake_ddst(q->flow_mode))
-			dsthost->dsthost_bulk_flow_count++;
-
+		cake_inc_srchost_bulk_flow_count(b, flow, q->flow_mode);
+		cake_inc_dsthost_bulk_flow_count(b, flow, q->flow_mode);
 	}
 
 	if (q->buffer_used > q->buffer_max_used)
@@ -1933,13 +1972,11 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 {
 	struct cake_sched_data *q = qdisc_priv(sch);
 	struct cake_tin_data *b = &q->tins[q->cur_tin];
-	struct cake_host *srchost, *dsthost;
 	ktime_t now = ktime_get();
 	struct cake_flow *flow;
 	struct list_head *head;
 	bool first_flow = true;
 	struct sk_buff *skb;
-	u16 host_load;
 	u64 delay;
 	u32 len;
 
@@ -2039,11 +2076,6 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 	q->cur_flow = flow - b->flows;
 	first_flow = false;
 
-	/* triple isolation (modified DRR++) */
-	srchost = &b->hosts[flow->srchost];
-	dsthost = &b->hosts[flow->dsthost];
-	host_load = 1;
-
 	/* flow isolation (DRR++) */
 	if (flow->deficit <= 0) {
 		/* Keep all flows with deficits out of the sparse and decaying
@@ -2055,11 +2087,8 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 				b->sparse_flow_count--;
 				b->bulk_flow_count++;
 
-				if (cake_dsrc(q->flow_mode))
-					srchost->srchost_bulk_flow_count++;
-
-				if (cake_ddst(q->flow_mode))
-					dsthost->dsthost_bulk_flow_count++;
+				cake_inc_srchost_bulk_flow_count(b, flow, q->flow_mode);
+				cake_inc_dsthost_bulk_flow_count(b, flow, q->flow_mode);
 
 				flow->set = CAKE_SET_BULK;
 			} else {
@@ -2071,19 +2100,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 			}
 		}
 
-		if (cake_dsrc(q->flow_mode))
-			host_load = max(host_load, srchost->srchost_bulk_flow_count);
-
-		if (cake_ddst(q->flow_mode))
-			host_load = max(host_load, dsthost->dsthost_bulk_flow_count);
-
-		WARN_ON(host_load > CAKE_QUEUES);
-
-		/* The get_random_u16() is a way to apply dithering to avoid
-		 * accumulating roundoff errors
-		 */
-		flow->deficit += (b->flow_quantum * quantum_div[host_load] +
-				  get_random_u16()) >> 16;
+		flow->deficit += cake_get_flow_quantum(b, flow, q->flow_mode);
 		list_move_tail(&flow->flowchain, &b->old_flows);
 
 		goto retry;
@@ -2107,11 +2124,8 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 				if (flow->set == CAKE_SET_BULK) {
 					b->bulk_flow_count--;
 
-					if (cake_dsrc(q->flow_mode))
-						srchost->srchost_bulk_flow_count--;
-
-					if (cake_ddst(q->flow_mode))
-						dsthost->dsthost_bulk_flow_count--;
+					cake_dec_srchost_bulk_flow_count(b, flow, q->flow_mode);
+					cake_dec_dsthost_bulk_flow_count(b, flow, q->flow_mode);
 
 					b->decaying_flow_count++;
 				} else if (flow->set == CAKE_SET_SPARSE ||
@@ -2129,12 +2143,8 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 				else if (flow->set == CAKE_SET_BULK) {
 					b->bulk_flow_count--;
 
-					if (cake_dsrc(q->flow_mode))
-						srchost->srchost_bulk_flow_count--;
-
-					if (cake_ddst(q->flow_mode))
-						dsthost->dsthost_bulk_flow_count--;
-
+					cake_dec_srchost_bulk_flow_count(b, flow, q->flow_mode);
+					cake_dec_dsthost_bulk_flow_count(b, flow, q->flow_mode);
 				} else
 					b->decaying_flow_count--;