Commit 37694786 authored by Cong Wang's avatar Cong Wang Committed by Jakub Kicinski
Browse files

sch_htb: make htb_deactivate() idempotent 



Alan reported a NULL pointer dereference in htb_next_rb_node()
after we made htb_qlen_notify() idempotent.

It turns out in the following case it introduced some regression:

htb_dequeue_tree():
  |-> fq_codel_dequeue()
    |-> qdisc_tree_reduce_backlog()
      |-> htb_qlen_notify()
        |-> htb_deactivate()
  |-> htb_next_rb_node()
  |-> htb_deactivate()

For htb_next_rb_node(), after calling the 1st htb_deactivate(), the
clprio[prio]->ptr could be already set to  NULL, which means
htb_next_rb_node() is vulnerable here.

For htb_deactivate(), although we checked qlen before calling it, in
case of qlen==0 after qdisc_tree_reduce_backlog(), we may call it again
which triggers the warning inside.

To fix the issues here, we need to:

1) Make htb_deactivate() idempotent, that is, simply return if we
   already call it before.
2) Make htb_next_rb_node() safe against ptr==NULL.

Many thanks to Alan for testing and for the reproducer.

Fixes: 5ba8b837 ("sch_htb: make htb_qlen_notify() idempotent")
Reported-by: default avatarAlan J. Wylie <alan@wylie.me.uk>
Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
Link: https://patch.msgid.link/20250428232955.1740419-2-xiyou.wangcong@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent ebd297a2

net/sched/sch_htb.c

+6 −9
Original line number Diff line number Diff line
@@ -348,6 +348,7 @@ static void htb_add_to_wait_tree(struct htb_sched *q, 
 */

static inline void htb_next_rb_node(struct rb_node **n)

{

	if (*n)

		*n = rb_next(*n);

}
@@ -609,8 +610,8 @@ static inline void htb_activate(struct htb_sched *q, struct htb_class *cl) 
 */

static inline void htb_deactivate(struct htb_sched *q, struct htb_class *cl)

{

	WARN_ON(!cl->prio_activity);



	if (!cl->prio_activity)

		return;

	htb_deactivate_prios(q, cl);

	cl->prio_activity = 0;

}
@@ -1485,8 +1486,6 @@ static void htb_qlen_notify(struct Qdisc *sch, unsigned long arg) 
{

	struct htb_class *cl = (struct htb_class *)arg;



	if (!cl->prio_activity)

		return;

	htb_deactivate(qdisc_priv(sch), cl);

}
@@ -1740,7 +1739,6 @@ static int htb_delete(struct Qdisc *sch, unsigned long arg, 
	if (cl->parent)

		cl->parent->children--;



	if (cl->prio_activity)

	htb_deactivate(q, cl);



	if (cl->cmode != HTB_CAN_SEND)
@@ -1949,7 +1947,6 @@ static int htb_change_class(struct Qdisc *sch, u32 classid, 
			/* turn parent into inner node */

			qdisc_purge_queue(parent->leaf.q);

			parent_qdisc = parent->leaf.q;

			if (parent->prio_activity)

			htb_deactivate(q, parent);



			/* remove from evt list because of level change */