netdev - [Patch net v2 2/3] net_sched: hfsc: Fix a potential UAF in hfsc

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Message-Id: <20250417184732.943057-3-xiyou.wangcong@gmail.com>
Date: Thu, 17 Apr 2025 11:47:31 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: jhs@...atatu.com,
	jiri@...nulli.us,
	gerrard.tai@...rlabs.sg,
	Cong Wang <xiyou.wangcong@...il.com>
Subject: [Patch net v2 2/3] net_sched: hfsc: Fix a potential UAF in hfsc_dequeue() too

Similarly to the previous patch, we need to safe guard hfsc_dequeue()
too. But for this one, we don't have a reliable reproducer.

Fixes: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 ("Linux-2.6.12-rc2")
Reported-by: Gerrard Tai <gerrard.tai@...rlabs.sg>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/sched/sch_hfsc.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index b368ac0595d5..6c8ef826cec0 100644
--- a/net/sched/sch_hfsc.c
+++ b/net/sched/sch_hfsc.c
@@ -1641,10 +1641,16 @@ hfsc_dequeue(struct Qdisc *sch)
 		if (cl->qdisc->q.qlen != 0) {
 			/* update ed */
 			next_len = qdisc_peek_len(cl->qdisc);
-			if (realtime)
-				update_ed(cl, next_len);
-			else
-				update_d(cl, next_len);
+			/* Check queue length again since some qdisc implementations
+			 * (e.g., netem/codel) might empty the queue during the peek
+			 * operation.
+			 */
+			if (cl->qdisc->q.qlen != 0) {
+				if (realtime)
+					update_ed(cl, next_len);
+				else
+					update_d(cl, next_len);
+			}
 		} else {
 			/* the class becomes passive */
 			eltree_remove(cl);
-- 
2.34.1