[PATCH net 11/13] netfilter: flowtable: publish GC-visible tuple last

[Pablo Neira Ayuso <pablo@netfilter.org>]

From: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>

nf_flow_table_iterate() only treats original-direction tuple nodes as
owning entries. Publishing the original node first lets GC observe and
free a flow while flow_offload_add() is still inserting the reply node.
Publish the reply node first and the original node last so GC never
sees a partially installed flow.

KASAN can trigger slab-use-after-free read and write reports in the
flowtable/rhashtable path (rht_deferred_worker, jhash, flow_offload_del,
flow_offload_lookup, etc.).

Fixes: ac2a66665e23 ("netfilter: add generic flow table infrastructure")
Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>
Assisted-by: Codex:gpt-5
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_flow_table_core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
index b66e65439341..8b1165f2b5a4 100644
--- a/net/netfilter/nf_flow_table_core.c
+++ b/net/netfilter/nf_flow_table_core.c
@@ -332,17 +332,18 @@ int flow_offload_add(struct nf_flowtable *flow_table, struct flow_offload *flow)
 	flow->timeout = nf_flowtable_time_stamp + flow_offload_get_timeout(flow);
 
 	err = rhashtable_insert_fast(&flow_table->rhashtable,
-				     &flow->tuplehash[0].node,
+				     &flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].node,
 				     nf_flow_offload_rhash_params);
 	if (err < 0)
 		return err;
 
+	/* GC only iterates original-direction entries; publish original last. */
 	err = rhashtable_insert_fast(&flow_table->rhashtable,
-				     &flow->tuplehash[1].node,
+				     &flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].node,
 				     nf_flow_offload_rhash_params);
 	if (err < 0) {
 		rhashtable_remove_fast(&flow_table->rhashtable,
-				       &flow->tuplehash[0].node,
+				       &flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].node,
 				       nf_flow_offload_rhash_params);
 		return err;
 	}
-- 
2.47.3