| Message ID | 20220707193056.29833-1-fw@strlen.de |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | [nf-next] netfilter: flowtable: prefer refcount_inc | expand |
On Thu, Jul 07, 2022 at 09:30:56PM +0200, Florian Westphal wrote: > With refcount_inc_not_zero, we'd also need a smp_rmb or similar, > followed by a test of the CONFIRMED bit. > > However, the ct pointer is taken from skb->_nfct, its refcount must > not be 0 (else, we'd already have a use-after-free bug). > > Use refcount_inc() instead to clarify the ct refcount is expected to > be at least 1. Applied, thanks
diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c index f2def06d1070..cca2358c10a1 100644 --- a/net/netfilter/nf_flow_table_core.c +++ b/net/netfilter/nf_flow_table_core.c @@ -53,14 +53,14 @@ struct flow_offload *flow_offload_alloc(struct nf_conn *ct) { struct flow_offload *flow; - if (unlikely(nf_ct_is_dying(ct) || - !refcount_inc_not_zero(&ct->ct_general.use))) + if (unlikely(nf_ct_is_dying(ct))) return NULL; flow = kzalloc(sizeof(*flow), GFP_ATOMIC); if (!flow) - goto err_ct_refcnt; + return NULL; + refcount_inc(&ct->ct_general.use); flow->ct = ct; flow_offload_fill_dir(flow, FLOW_OFFLOAD_DIR_ORIGINAL); @@ -72,11 +72,6 @@ struct flow_offload *flow_offload_alloc(struct nf_conn *ct) __set_bit(NF_FLOW_DNAT, &flow->flags); return flow; - -err_ct_refcnt: - nf_ct_put(ct); - - return NULL; } EXPORT_SYMBOL_GPL(flow_offload_alloc);
With refcount_inc_not_zero, we'd also need a smp_rmb or similar, followed by a test of the CONFIRMED bit. However, the ct pointer is taken from skb->_nfct, its refcount must not be 0 (else, we'd already have a use-after-free bug). Use refcount_inc() instead to clarify the ct refcount is expected to be at least 1. Signed-off-by: Florian Westphal <fw@strlen.de> --- A followp to 'netfilter: conntrack: fix crash due to confirmed bit load reordering', but target next as current code works fine.