In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject non-negative offsets in stack_slot_obj_get_spi()
bpf_get_spi() computes (-off - 1) / BPF_REG_SIZE using C division, which truncates toward zero. For off == 0, this produces spi 0, the same index used by the valid stack slot at fp-8.
stack_slot_obj_get_spi() currently checks alignment and the resulting spi bounds, but does not reject the non-negative offset itself. It can therefore validate a PTR_TO_STACK register holding fp+0 against an iterator stored at fp-8 even though the runtime receives the actual fp+0 pointer. An effectful iterator kfunc can then interpret memory outside the BPF stack as iterator state.
Reject non-negative offsets before converting the offset to an spi. All valid stack objects begin at a negative offset from the frame pointer.
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