In cake_overhead(), the header length up to the transport layer is computed using logic borrowed from qdisc_pkt_len_segs_init(): /* borrowed from qdisc_pkt_len_segs_init() */ if (!skb->encapsulation) hdr_len = skb_transport_offset(skb); else hdr_len = skb_inner_transport_offset(skb); However, cake_overhead() suffers from several issues: 1. When segs == 0 (e.g. from dodgy GSO packets where gso_segs is not recomputed), the multi-segment arithmetic underflows: (segs - 1) wraps to 4294967295, causing cake_calc_overhead() * (segs - 1) to produce an enormous length. When charged in cake_advance_shaper(), time_next_packet is pushed decades into the future, permanently stalling the CAKE dequeue queue. Fix this by returning cake_calc_overhead(q, len, off) for segs <= 1. 2. When the transport header was never set, skb->transport_header holds the sentinel value ~0U. skb_transport_offset() returns ~65535, which is not caught by a negative offset check. skb_header_pointer() fails, and hdr_len stays ~65535, charging ~66 KB per segment to the shaper. Fix this by mirroring qdisc_pkt_len_segs_init() and checking unlikely(!skb_transport_header_was_set(skb)). 3. Both skb_transport_offset() and skb_inner_transport_offset() return signed int, but hdr_len is declared as unsigned int. If post-enqueue mangling (such as BPF packet trimming via bpf_skb_net_shrink()) produces a negative offset, hdr_len wraps to near UINT_MAX, causing corrupted header length accounting. Fix this by declaring hdr_len as int and falling back to cake_calc_overhead(q, len, off) if hdr_len is negative. Fixes: a41851bea7bf ("net: account for encap headers in qdisc pkt len") Cc: stable@vger.kernel.org Signed-off-by: Yuchao Zhang --- v2: - Accurately describe the impact as shaper accounting corruption / stall rather than OOB read past the allocation per Sashiko review. - Fix pre-existing high-severity integer underflow when segs == 0 by checking segs <= 1. - Import companion check !skb_transport_header_was_set(skb) from qdisc_pkt_len_segs_init() to prevent unset transport header sentinel (~0U) from inflating packet length to ~66 KB. net/sched/sch_cake.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c index dc93267029e7..45969c1b95fc 100644 --- a/net/sched/sch_cake.c +++ b/net/sched/sch_cake.c @@ -1413,21 +1413,28 @@ static u32 cake_calc_overhead(struct cake_sched_data *qd, u32 len, u32 off) static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *skb) { const struct skb_shared_info *shinfo = skb_shinfo(skb); - unsigned int hdr_len, last_len = 0; + unsigned int last_len = 0; u32 off = skb_network_offset(skb); u16 segs = qdisc_pkt_segs(skb); u32 len = qdisc_pkt_len(skb); + int hdr_len; WRITE_ONCE(q->avg_netoff, cake_ewma(q->avg_netoff, off << 16, 8)); - if (segs == 1) + if (segs <= 1) return cake_calc_overhead(q, len, off); /* borrowed from qdisc_pkt_len_segs_init() */ - if (!skb->encapsulation) + if (!skb->encapsulation) { + if (unlikely(!skb_transport_header_was_set(skb))) + return cake_calc_overhead(q, len, off); hdr_len = skb_transport_offset(skb); - else + } else { hdr_len = skb_inner_transport_offset(skb); + } + + if (unlikely(hdr_len < 0)) + return cake_calc_overhead(q, len, off); /* + transport layer */ if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | -- 2.53.0