gred_enqueue() admits a packet when the current backlog plus the packet length fits within the queue limit: sch->qstats.backlog + qdisc_pkt_len(skb) <= sch->limit (default VQ) gred_backlog(t, q, sch) + qdisc_pkt_len(skb) <= q->limit (configured VQ) sch->qstats.backlog and q->backlog are u32, and qdisc_pkt_len() returns unsigned int, so both sums are computed in 32 bits and wrap at 2^32. Once the true backlog exceeds 4 GiB the wrapped sum becomes small and admission keeps succeeding, so the queue grows without bound and the kernel can be driven to OOM. Promote the sums to u64 so admission stops once the true backlog exceeds the limit. The limit is u32, so the bounded queue stays below 2^32 and the stored u32 backlog never wraps. Fixes: a3eb95f891d6 ("net_sched: gred: add TCA_GRED_LIMIT attribute") Reported-by: vega@nebusec.ai Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim --- net/sched/sch_gred.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_gred.c b/net/sched/sch_gred.c index fcc1a4c03636..f04f425c6c44 100644 --- a/net/sched/sch_gred.c +++ b/net/sched/sch_gred.c @@ -179,7 +179,7 @@ static int gred_enqueue(struct sk_buff *skb, struct Qdisc *sch, * if no default DP has been configured. This * allows for DP flows to be left untouched. */ - if (likely(sch->qstats.backlog + qdisc_pkt_len(skb) <= + if (likely((u64)sch->qstats.backlog + qdisc_pkt_len(skb) <= sch->limit)) return qdisc_enqueue_tail(skb, sch); else @@ -244,7 +244,7 @@ static int gred_enqueue(struct sk_buff *skb, struct Qdisc *sch, break; } - if (gred_backlog(t, q, sch) + qdisc_pkt_len(skb) <= q->limit) { + if ((u64)gred_backlog(t, q, sch) + qdisc_pkt_len(skb) <= q->limit) { q->backlog += qdisc_pkt_len(skb); return qdisc_enqueue_tail(skb, sch); } -- 2.34.1