5.4-stable review patch. If anyone has any objections, please let me know.
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From: Victor Nogueira victor@mojatatu.com
[ Upstream commit f99a3fbf023e20b626be4b0f042463d598050c9a ]
As described in Gerrard's report [1], there are use cases where a netem child qdisc will make the parent qdisc's enqueue callback reentrant. In the case of drr, there won't be a UAF, but the code will add the same classifier to the list twice, which will cause memory corruption.
In addition to checking for qlen being zero, this patch checks whether the class was already added to the active_list (cl_is_active) before adding to the list to cover for the reentrant case.
[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-...
Fixes: 37d9cf1a3ce3 ("sched: Fix detection of empty queues in child qdiscs") Acked-by: Jamal Hadi Salim jhs@mojatatu.com Signed-off-by: Victor Nogueira victor@mojatatu.com Link: https://patch.msgid.link/20250425220710.3964791-2-victor@mojatatu.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/sched/sch_drr.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c index 07a2b0b354954..1a05718063426 100644 --- a/net/sched/sch_drr.c +++ b/net/sched/sch_drr.c @@ -36,6 +36,11 @@ struct drr_sched { struct Qdisc_class_hash clhash; };
+static bool cl_is_active(struct drr_class *cl) +{ + return !list_empty(&cl->alist); +} + static struct drr_class *drr_find_class(struct Qdisc *sch, u32 classid) { struct drr_sched *q = qdisc_priv(sch); @@ -344,7 +349,6 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct drr_sched *q = qdisc_priv(sch); struct drr_class *cl; int err = 0; - bool first;
cl = drr_classify(skb, sch, &err); if (cl == NULL) { @@ -354,7 +358,6 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch, return err; }
- first = !cl->qdisc->q.qlen; err = qdisc_enqueue(skb, cl->qdisc, to_free); if (unlikely(err != NET_XMIT_SUCCESS)) { if (net_xmit_drop_count(err)) { @@ -364,7 +367,7 @@ static int drr_enqueue(struct sk_buff *skb, struct Qdisc *sch, return err; }
- if (first) { + if (!cl_is_active(cl)) { list_add_tail(&cl->alist, &q->active); cl->deficit = cl->quantum; }