In the Linux kernel, the following vulnerability has been resolved:
netfilter: nft_flow_offload: drop flowtable reference on init error path
nft_flow_offload_init() bumps the flowtable use count with
nft_use_inc() before calling nf_ct_netns_get(). When the latter
fails, the error is returned as-is and the reference is leaked.
The upper layers do not balance it either: nf_tables_newexpr()
clears expr->ops when the expression init callback fails, so the
nft_expr_more() iteration in nft_rule_expr_deactivate() and
nf_tables_rule_destroy() stops right before the failed expression
and its ->destroy callback, which would drop the reference, never
runs.
Each failed rule addition therefore leaks one flowtable reference
and the flowtable can no longer be removed: NFT_MSG_DELFLOWTABLE
keeps reporting -EBUSY even though no rule references it.
Save the nf_ct_netns_get() return value and undo the nft_use_inc()
when it fails, restoring the inc/dec pairing within
nft_flow_offload_init() itself.
