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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Jamal Hadi Salim , Jiri Pirko , cake@lists.bufferbloat.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Yuchao Zhang Subject: [PATCH net v3 0/2] net/sched: sch_cake: prevent shaper corruption and stall in cake_overhead() Date: Sun, 27 Sep 2026 21:10:07 +0800 Message-ID: <20260927131009.24250-1-ndaugoing@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This series addresses two issues in cake_overhead() that can lead to corrupted rate shaper accounting or long dequeue stalls: Patch 1 fixes an integer underflow when segs == 0. When an skb with segs == 0 (such as dodgy GSO packets where gso_segs is not recomputed) reaches cake_overhead(), (segs - 1) wraps around to UINT32_MAX, multiplying per-segment overhead by ~4.29 billion and returning a length close to 4.29 GB. cake_advance_shaper() then charges that length to the shaper, stalling the dequeue queue for tens of seconds at 1 Gbit/s, and for minutes to hours at lower rates. This was introduced by commit c5d34f4583ea ("net_sched: cake: use qdisc_pkt_segs()"). Patch 2 validates the transport header offset computed in cake_overhead(). When the transport header was never set, skb_transport_offset() returns the ~0U sentinel (~65535), which inflates shaper accounting by ~66 KB per segment. Furthermore, if preceding egress BPF filters (e.g. sch_handle_egress()) or cake classifier actions (e.g. act_bpf trimming headers via bpf_skb_adjust_room(BPF_ADJ_ROOM_MAC)) leave the transport header stale (bpf_skb_net_hdr_pop() only re-syncs it when it aliased network_header), skb_transport_offset() can become negative. Because hdr_len was declared as unsigned int, a negative offset wraps to near UINT_MAX. Patch 2 checks !skb_transport_header_was_set() and ensures hdr_len >= 0. Both hunks date back to commit a729b7f0bd5b ("sch_cake: Add overhead compensation support to the rate shaper"), so they share a single Fixes: tag and stable range. Changes in v3: - Split the v2 patch into a 2-patch series per Simon Horman and Sashiko AI review so each logical fix carries its own accurate Fixes: tag and matches proper stable tree backport ranges: - Patch 1 Fixes: c5d34f4583ea ("net_sched: cake: use qdisc_pkt_segs()") - Patch 2 Fixes: a729b7f0bd5b ("sch_cake: Add overhead compensation support to the rate shaper") - Clarify the timing and code paths where header mangling can occur (sch_handle_egress() and cake_classify() before cake_overhead()) rather than inaccurate "post-enqueue mangling" wording. - Link to v2: https://lore.kernel.org/netdev/20260922084124.36858-1-ndaugoing@gmail.com/ Changes in v2: - Accurately describe the impact as shaper accounting corruption / stall rather than OOB read past the allocation. - Fix 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. - Link to v1: https://lore.kernel.org/netdev/20260917122153.62722-1-ndaugoing@gmail.com/ Yuchao Zhang (2): net/sched: sch_cake: fix shaper stall on segs == 0 in cake_overhead() net/sched: sch_cake: validate transport header offset in cake_overhead() net/sched/sch_cake.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) -- 2.53.0