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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , Jamal Hadi Salim , Jiri Pirko , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, zjamg Subject: [PATCH 0/2] net: fix negative transport offset handling in GSO pkt len calculation Date: Thu, 17 Sep 2026 20:21:51 +0800 Message-ID: <20260917122153.62722-1-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 Hi, This series fixes an out-of-bounds read and kernel crash in qdisc_pkt_len_segs_init() (and similar borrowed logic in sch_cake) when processing packets whose transport offset has become negative. Both skb_transport_offset() and skb_inner_transport_offset() return a signed int. However, qdisc_pkt_len_segs_init() stores the offset into an unsigned int hdr_len. When an encapsulated or tagged packet has undergone header operations (such as skb_vlan_untag() pulling stacked VLAN tags without updating inner_transport_header, or other header stripping that advances skb->data past the transport header), the computed offset becomes negative. Converting this negative int to unsigned int results in a value near UINT_MAX (e.g. 0xFFFFFFF0). Consequently: 1. pskb_may_pull(skb, hdr_len + sizeof(struct tcphdr)) computes 0xFFFFFFF0 + 20, which wraps around in 32-bit unsigned arithmetic to 4. This passes the check if skb->len >= 4, completely defeating the guard. 2. th = (const struct tcphdr *)(skb->data + hdr_len) zero-extends hdr_len to 64 bits, producing a wild pointer ~4 GiB past skb->data. 3. __tcp_hdrlen(th) dereferences th->doff at that address, triggering an immediate translation fault / KASAN wild-memory-access panic. Patch 1 declares hdr_len as int and drops packets with negative offset via SKB_DROP_REASON_SKB_BAD_GSO. Patch 2 fixes the corresponding logic borrowed in sch_cake. Thanks, zjamg zjamg (2): net: fix OOB read in qdisc_pkt_len_segs_init() on negative transport offset net/sched: sch_cake: check negative transport offset in cake_overhead() net/core/dev.c | 5 ++++- net/sched/sch_cake.c | 6 +++++- 2 files changed, 9 insertions(+), 2 deletions(-) -- 2.53.0