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netfilter: flowtable: prefer refcount_inc 

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>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2022-07-07 21:30:56 +02:00 committed by Pablo Neira Ayuso
parent 5787db7c90
commit f02e7dc4cf
1 changed files with 3 additions and 8 deletions
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11
net/netfilter/nf_flow_table_core.c
View File

@ -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);