Linux kernel BPF tc_skb_cb state collision in cls_bpf_classify

CVE-2025-68200 is a Linux kernel vulnerability in the BPF/networking path affecting cls_bpf_classify(). A faulty interaction between net_sched control-block storage in struct tc_skb_cb and BPF data pointer handling introduced a state collision, allowing cls_bpf_classify() to modify tc_skb_cb(skb)->drop_reason unexpectedly. This can trigger a kernel warning in sk_skb_reason_drop() / __sk_skb_reason_drop() in net/core/skbuff.c. The issue stems from the interaction between the tc control block changes introduced by commit ec624fe740b4 and BPF data/data_end wiring from commit db58ba459202; later addition of drop_reason made the collision observable. The fix adds bpf_prog_run_data_pointers() to save and restore net_sched storage that collides with BPF data_meta/data_end.