Use-after-free in Linux kernel netfilter nft_set_pipapo garbage collection
CVE-2026-23351 is a use-after-free vulnerability in the Linux kernel netfilter subsystem, specifically in the nftables pipapo set backend (nft_set_pipapo). According to the provided kernel fix description, the flaw occurs during garbage collection of expired elements. Under a large number of expired elements, commit-time garbage collection can run for an extended period in a non-preemptible context. During this process, expired elements may remain visible through the live copy of the data structure to both the packet-processing path and userspace dump operations. The issue arises because elements could be queued for freeing before the commit phase has progressed far enough to swap clone and live pointers, allowing readers to observe freed elements. The fix splits garbage collection into distinct unlink and reclaim phases to ensure elements are first detached from visibility before reclamation.
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