net: flush skb_defer_nodes in dev_cpu_dead()

Summary

In the Linux kernel, the following vulnerability has been resolved: net: flush skb_defer_nodes in dev_cpu_dead() When a CPU goes offline, dev_cpu_dead() drains its softnet queues (completion_queue, output_queue, poll_list, process_queue, and input_pkt_queue), but leaves net_hotdata.skb_defer_nodes untouched. If oldcpu goes offline while holding pending skbs in its skb_defer_nodes lists (e.g. below the sysctl_skb_defer_max >> 1 IPI threshold, or if the IPI races with CPU teardown), those skbs remain stranded until oldcpu is brought back online. If any of these skbs hold page_pool fragments, page_pool_destroy() will stall indefinitely waiting for inflight pages to be returned when a netdev or driver is torn down while oldcpu is offline. Additionally, if smp_call_function_single_async() fails in kick_defer_list_purge() because the target CPU went offline, reset defer_ipi_scheduled to 0 so future IPI kicks are not blocked when the CPU comes back online. Also, if oldcpu was the last online CPU on its NUMA node, drain that node's slot across all CPUs so no skbs deferred from that node remain stranded on idle remote CPUs (or if the node itself is subsequently offlined). Finally, in skb_attempt_defer_free(), re-check cpu_online(cpu) and whether the caller migrated CPUs after llist_add(), flushing the node list if so, to close the preemption TOCTOU race against CPU/node teardown.

Timeline

1. Oct 18, 2026, 3:18 PM UTCCVE published
2. Oct 19, 2026, 9:21 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 68822bdf76f10c3dc80609d4e2cdc1e847429086 · fixed in c68f4157463448a76893223e117170be8374d773; From 68822bdf76f10c3dc80609d4e2cdc1e847429086 · fixed in 06e3f54e8b22040ada01a28343badf1990b4dd7d

• Linux Linux

  5.19

• KernelLinux

  From 5.19.0 · fixed in 7.2.9

References 2