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And veth re-stamps the Rx queues. > > > > > > What do you mean by 're-stamps' in this case? > > > > > > > > > > > I am not sure if re-stamps will have ill effects. > > > > > > > > The allocation and deallocation for this issue happens while > > > > processing the same packet (receive skb -> skb_pp_cow_data -> > > > > page_pool alloc ... __bpf_prog_run -> bpf_xdp_adjust_tail). > > > > > > > > IIUC, if the veth re-stamps the RX queue to MEM_TYPE_PAGE_POOL > > > > skb_pp_cow_data will proceed to allocate from page_pool and > > > > bpf_xdp_adjust_tail will correctly free from page_pool. > > > > > > netif_get_rxqueue() gives you a pointer the netstack queue, not the driver > > > one. Then you take the xdp_rxq from there. Do we even register memory > > > model for these queues? Or am I missing something here. > > > > > Ah, yes, you are right. So my comment in the commit message about > TUN/TAP registering a page shared memory model is wrong. But I think > the fix is still correct for the reported syzkaller issue. From > bpf_prog_run_generic_xdp: > > rxqueue = netif_get_rxqueue(skb); > xdp_init_buff(xdp, frame_sz, rxq: &rxqueue->xdp_rxq); > > So xdp_buff's rxq is set to the netstack queue for the generic XDP > hook. And adding the check in netif_skb_check_for_xdp based on the > netstack queue should be correct, right? Per my limited understanding your change is making skb_cow_data_for_xdp() a dead code as I don't see mem model being registered for these stack queues - netif_alloc_rx_queues() only calls xdp_rxq_info_reg() and mem.type defaults to MEM_TYPE_PAGE_SHARED as it's defined as 0, which means it's never going to be MEM_TYPE_PAGE_POOL. IMHO that single case where we rewrite skb to memory backed by page pool should have it reflected in mem.type so __xdp_return() potentially used in bpf helpers could act correctly. > > > > We're in generic XDP hook where driver specifics should not matter here > > > IMHO. > > > > Well, IDK how helpful the flow below would be but: > > > > veth_xdp_xmit() -> [ptr ring] -> veth_xdp_rcv() -> veth_xdp_rcv_one() > > | > > | xdp_convert_frame_to_buff() <-' > > ( "re-stamps" ;) -> | xdp->rxq = &rq->xdp_rxq; > > can eat frags but now rxq | bpf_prog_run_xdp() > > is veth's | > > > > I just glanced at the code so >50% changes I'm wrong, but that's what > > I meant. > > Thanks for the clarification, I thought that "re-stamps" means the: > > xdp->rxq->mem.type = frame->mem_type; > > from veth_xdp_rcv_one in the XDP_TX/XDP_REDIRECT cases. > > And yes, now I think the same issue can happen because veth sets the > memory model to MEM_TYPE_PAGE_SHARED but veth_convert_skb_to_xdp_buff > calls skb_pp_cow_data that uses page_pool for allocations. I'll try to > see if I can adapt the syzkaller repro to trigger it for confirmation. That is a good catch.