Re: [PATCH 4.4 38/97] netfilter: xt_CT: fix refcnt leak on error path

[Ben Hutchings]

On Fri, 2018-03-23 at 10:54 +0100, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.ÂÂIf anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Gao Feng <fgao@xxxxxxxxxx>
> 
> 
> [ Upstream commit 470acf55a021713869b9bcc967268ac90c8a0fac ]
[...]
> --- a/net/netfilter/xt_CT.c
> +++ b/net/netfilter/xt_CT.c
> @@ -168,8 +168,10 @@ xt_ct_set_timeout(struct nf_conn *ct, co
> Â		goto err_put_timeout;
> Â	}
> Â	timeout_ext = nf_ct_timeout_ext_add(ct, timeout, GFP_ATOMIC);
> -	if (timeout_ext == NULL)
> +	if (!timeout_ext) {
> Â		ret = -ENOMEM;
> +		goto err_put_timeout;
> +	}
> Â
> Â	rcu_read_unlock();
> Â	return ret;

This part looks fine.

> @@ -201,6 +203,7 @@ static int xt_ct_tg_check(const struct x
> > Â			ÂÂstruct xt_ct_target_info_v1 *info)
> Â{
> Â	struct nf_conntrack_zone zone;
> +	struct nf_conn_help *help;
> Â	struct nf_conn *ct;
> Â	int ret = -EOPNOTSUPP;
> Â
> @@ -249,7 +252,7 @@ static int xt_ct_tg_check(const struct x
> Â	if (info->timeout[0]) {
> Â		ret = xt_ct_set_timeout(ct, par, info->timeout);
> Â		if (ret < 0)
> -			goto err3;
> +			goto err4;
> Â	}
> Â	__set_bit(IPS_CONFIRMED_BIT, &ct->status);
> Â	nf_conntrack_get(&ct->ct_general);
> @@ -257,6 +260,10 @@ out:
> Â	info->ct = ct;
> Â	return 0;
> Â
> +err4:
> +	help = nfct_help(ct);
> +	if (help)
> +		module_put(help->helper->me);
> Âerr3:
> Â	nf_ct_tmpl_free(ct);
> Âerr2:

This does not.  nf_ct_tmpl_free() calls nf_ct_ext_destroy() which I
think will call back into xt_ct_tg_destroy().  So I think the module
reference is already dropped here and we mustn't do it twice.  Am I
missing something?

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.