From d644b23afe1ef509c9961a6d84a093c2587edf02 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=A9r=C3=A9my=20Jean?= Date: Tue, 18 Aug 2026 20:00:15 +0000 Subject: [PATCH] netfilter: flowtable: publish HW_DEAD after worker is done MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit flow_offload_work_del() sets NF_FLOW_HW_DEAD before the work handler clears NF_FLOW_HW_PENDING. Once a flow is both HW_DYING and HW_DEAD, a concurrent garbage collection pass can remove it and schedule it for RCU freeing. The offload worker holds neither an RCU read lock nor a reference to the flow. If it is preempted after publishing HW_DEAD, the RCU callback can free the flow before the worker resumes and clears HW_PENDING, resulting in a use-after-free. Move HW_DEAD publication to the common worker epilogue after the pending bit is cleared, making it the final flow access by destroy work. Order all preceding flow accesses before publishing the bit that allows garbage collection to free the object. Fixes: 2c8897953f3b ("netfilter: flowtable: Add pending bit for offload work") Assisted-by: Codex:gpt-5 Signed-off-by: Jérémy Jean Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_flow_table_offload.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c index 801a3dd9ceea..6757fd89c1f1 100644 --- a/net/netfilter/nf_flow_table_offload.c +++ b/net/netfilter/nf_flow_table_offload.c @@ -995,7 +995,6 @@ static void flow_offload_work_del(struct flow_offload_work *offload) flow_offload_tuple_del(offload, FLOW_OFFLOAD_DIR_ORIGINAL); if (test_bit(NF_FLOW_HW_BIDIRECTIONAL, &offload->flow->flags)) flow_offload_tuple_del(offload, FLOW_OFFLOAD_DIR_REPLY); - set_bit(NF_FLOW_HW_DEAD, &offload->flow->flags); } static void flow_offload_tuple_stats(struct flow_offload_work *offload, @@ -1059,6 +1058,12 @@ static void flow_offload_work_handler(struct work_struct *work) } clear_bit(NF_FLOW_HW_PENDING, &offload->flow->flags); + if (offload->cmd == FLOW_CLS_DESTROY) { + /* Publish after the worker's last flow access. */ + smp_mb__before_atomic(); + set_bit(NF_FLOW_HW_DEAD, &offload->flow->flags); + } + kfree(offload); }