Commit a6bd339d authored by Fernando Fernandez Mancera's avatar Fernando Fernandez Mancera Committed by Jakub Kicinski
Browse files

net_sched: fix skb memory leak in deferred qdisc drops 



When the network stack cleans up the deferred list via qdisc_run_end(),
it operates on the root qdisc. If the root qdisc do not implement the
TCQ_F_DEQUEUE_DROPS flag the packets queue to free are never freed and
gets stranded on the child's local to_free list.

Fix this by making qdisc_dequeue_drop() aware of the root qdisc. It
fetches the root qdisc and check for the TCQ_F_DEQUEUE_DROPS flag. If
the flag is present, the packet is appended directly to the root's
to_free list. Otherwise, drop it directly as it was done before the
optimization was implemented.

Fixes: a6efc273 ("net_sched: use qdisc_dequeue_drop() in cake, codel, fq_codel")
Reported-by: default avatarDamilola Bello <damilola@aterlo.com>
Closes: https://lore.kernel.org/netdev/CAPgFtOLaedBMU0f_BxV2bXftTJSmJr018Q5uozOo5vVo6b9tjw@mail.gmail.com/


Signed-off-by: default avatarFernando Fernandez Mancera <fmancera@suse.de>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260408100044.4530-1-fmancera@suse.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 656121b1

include/net/sch_generic.h

+13 −3
Original line number Diff line number Diff line
@@ -1170,12 +1170,22 @@ static inline void tcf_kfree_skb_list(struct sk_buff *skb) 
static inline void qdisc_dequeue_drop(struct Qdisc *q, struct sk_buff *skb,

				      enum skb_drop_reason reason)

{

	struct Qdisc *root;



	DEBUG_NET_WARN_ON_ONCE(!(q->flags & TCQ_F_DEQUEUE_DROPS));

	DEBUG_NET_WARN_ON_ONCE(q->flags & TCQ_F_NOLOCK);



	rcu_read_lock();

	root = qdisc_root_sleeping(q);



	if (root->flags & TCQ_F_DEQUEUE_DROPS) {

		tcf_set_drop_reason(skb, reason);

	skb->next = q->to_free;

	q->to_free = skb;

		skb->next = root->to_free;

		root->to_free = skb;

	} else {

		kfree_skb_reason(skb, reason);

	}

	rcu_read_unlock();

}



/* Instead of calling kfree_skb() while root qdisc lock is held,