CVE-2026-23231

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: fix use-after-free in nf_tables_addchain()

nf_tables_addchain() publishes the chain to table->chains via
list_add_tail_rcu() (in nft_chain_add()) before registering hooks.
If nf_tables_register_hook() then fails, the error path calls
nft_chain_del() (list_del_rcu()) followed by nf_tables_chain_destroy()
with no RCU grace period in between.

This creates two use-after-free conditions:

1) Control-plane: nf_tables_dump_chains() traverses table->chains
under rcu_read_lock(). A concurrent dump can still be walking
the chain when the error path frees it.

2) Packet path: for NFPROTO_INET, nf_register_net_hook() briefly
installs the IPv4 hook before IPv6 registration fails. Packets
entering nft_do_chain() via the transient IPv4 hook can still be
dereferencing chain->blob_gen_X when the error path frees the
chain.

Add synchronize_rcu() between nft_chain_del() and the chain destroy
so that all RCU readers -- both dump threads and in-flight packet
evaluation -- have finished before the chain is freed.