From: Chia-Yu Chang <[email protected]>
Fix dualpi2_change() to correctly enforce updated limit and memlimit values
after a configuration change of the dualpi2 qdisc.
Before this patch, dualpi2_change() always attempted to dequeue packets via
the root qdisc (C-queue) when reducing backlog or memory usage, and
unconditionally assumed that a valid skb will be returned. When traffic
classification results in packets being queued in the L-queue while the
C-queue is empty, this leads to a NULL skb dereference during limit or
memlimit enforcement.
This is fixed by first dequeuing from the C-queue path if it is non-empty.
Once the C-queue is empty, packets are dequeued directly from the L-queue.
Return values from qdisc_dequeue_internal() are checked for both queues. When
dequeuing from the L-queue, the parent qdisc qlen and backlog counters are
updated explicitly to keep overall qdisc statistics consistent.
Fixes: 320d031ad6e4 ("sched: Struct definition and parsing of dualpi2 qdisc")
Reported-by: "Kito Xu (veritas501)" <[email protected]>
Signed-off-by: Chia-Yu Chang <[email protected]>
---
net/sched/sch_dualpi2.c | 30 +++++++++++++++++++++++++-----
1 file changed, 25 insertions(+), 5 deletions(-)
diff --git a/net/sched/sch_dualpi2.c b/net/sched/sch_dualpi2.c
index fe6f5e889625..5fcec5e6e97d 100644
--- a/net/sched/sch_dualpi2.c
+++ b/net/sched/sch_dualpi2.c
@@ -868,11 +868,31 @@ static int dualpi2_change(struct Qdisc *sch, struct
nlattr *opt,
old_backlog = sch->qstats.backlog;
while (qdisc_qlen(sch) > sch->limit ||
q->memory_used > q->memory_limit) {
- struct sk_buff *skb = qdisc_dequeue_internal(sch, true);
-
- q->memory_used -= skb->truesize;
- qdisc_qstats_backlog_dec(sch, skb);
- rtnl_qdisc_drop(skb, sch);
+ int c_len = qdisc_qlen(sch) - qdisc_qlen(q->l_queue);
+ struct sk_buff *skb = NULL;
+
+ if (c_len) {
+ skb = qdisc_dequeue_internal(sch, true);
+ if (!skb)
+ break;
+ q->memory_used -= skb->truesize;
+ rtnl_qdisc_drop(skb, sch);
+ } else if (qdisc_qlen(q->l_queue)) {
+ skb = qdisc_dequeue_internal(q->l_queue, true);
+ if (!skb)
+ break;
+ /* Keep the overall qdisc stats consistent */
+ --sch->q.qlen;
+ qdisc_qstats_backlog_dec(sch, skb);
+
+ q->memory_used -= skb->truesize;
+ rtnl_qdisc_drop(skb, q->l_queue);
+
+ /* After incrementing the drop counter for the L-queue
+ via rtnl_qdisc_drop(), update the parent qdisc
+ drop counter via qdisc_qstats_drop(sch) */
+ qdisc_qstats_drop(sch);
+ }
}
qdisc_tree_reduce_backlog(sch, old_qlen - qdisc_qlen(sch),
old_backlog - sch->qstats.backlog);
--
2.34.1
