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() does not validate the computed offset: 1. When the transport header was never set, skb->transport_header holds the sentinel value ~0U. skb_transport_offset() returns ~65535. skb_header_pointer() subsequently fails, leaving hdr_len as ~65535, charging ~66 KB per segment to the shaper. Mirror qdisc_pkt_len_segs_init() by returning cake_calc_overhead() when unlikely(!skb_transport_header_was_set(skb)). 2. While qdisc_pkt_len_segs_init() runs at the start of __dev_queue_xmit(), packet headers may be adjusted before cake_overhead() is reached: - in sch_handle_egress() via tc/BPF egress filters; - inside cake_enqueue() via cake_classify() -> tcf_classify() (e.g. act_bpf, act_pedit, act_mpls, act_vlan). For example, bpf_skb_adjust_room(..., BPF_ADJ_ROOM_MAC) invokes bpf_skb_net_hdr_pop(), which pulls skb->data forward and re-syncs transport_header only when it aliased network_header, i.e. when no transport header had been parsed. If a transport header had been parsed, its offset is left where it was while skb->data moves forward, so skb_transport_offset() becomes old_offset - len and can turn negative. Since hdr_len was declared as unsigned int, a negative offset wraps around to near UINT_MAX, corrupting header length accounting. Declare hdr_len as int and fall back to cake_calc_overhead(q, len, off) if unlikely(hdr_len < 0). Fixes: a729b7f0bd5b ("sch_cake: Add overhead compensation support to the rate shaper") Cc: stable@vger.kernel.org Signed-off-by: Yuchao Zhang --- v3: - Split from v2 into a standalone patch with its own Fixes: tag (a729b7f0bd5b) per Simon Horman and Sashiko review. - Clarify header mangling ordering (sch_handle_egress() and cake_classify() before cake_overhead()) rather than inaccurate "post-enqueue mangling" wording per Sashiko review. - Link to v2: https://lore.kernel.org/netdev/20260922084124.36858-1-ndaugoing@gmail.com/ - Link to v1: https://lore.kernel.org/netdev/20260917122153.62722-1-ndaugoing@gmail.com/ net/sched/sch_cake.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c index b0d604a7052a..45969c1b95fc 100644 --- a/net/sched/sch_cake.c +++ b/net/sched/sch_cake.c @@ -1413,10 +1413,11 @@ 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)); @@ -1424,10 +1425,16 @@ static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *skb) 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