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Date: Mon, 12 Mar 2018 16:58:38 -0700
From: Joe Perches <joe@...ches.com>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>, Pablo Neira Ayuso
<pablo@...filter.org>, Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>, Florian
Westphal <fw@...len.de>, "David S. Miller" <davem@...emloft.net>
Cc: netfilter-devel@...r.kernel.org, coreteam@...filter.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Kernel Hardening
<kernel-hardening@...ts.openwall.com>, Kees Cook <keescook@...omium.org>,
"Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: Re: [PATCH] netfilter: cttimeout: remove VLA usage
On Mon, 2018-03-12 at 18:14 -0500, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wvla, remove VLA and replace it
> with dynamic memory allocation.
>
> From a security viewpoint, the use of Variable Length Arrays can be
> a vector for stack overflow attacks. Also, in general, as the code
> evolves it is easy to lose track of how big a VLA can get. Thus, we
> can end up having segfaults that are hard to debug.
>
> Also, fixed as part of the directive to remove all VLAs from
[]
> diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
[]
> @@ -51,19 +51,27 @@ ctnl_timeout_parse_policy(void *timeouts,
> const struct nf_conntrack_l4proto *l4proto,
> struct net *net, const struct nlattr *attr)
> {
> + struct nlattr **tb;
> int ret = 0;
>
> - if (likely(l4proto->ctnl_timeout.nlattr_to_obj)) {
> - struct nlattr *tb[l4proto->ctnl_timeout.nlattr_max+1];
> + if (!l4proto->ctnl_timeout.nlattr_to_obj)
> + return 0;
Why not
if unlikely(!...)
>
> - ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max,
> - attr, l4proto->ctnl_timeout.nla_policy,
> - NULL);
> - if (ret < 0)
> - return ret;
> + tb = kcalloc(l4proto->ctnl_timeout.nlattr_max + 1, sizeof(*tb),
> + GFP_KERNEL);
kmalloc_array?
>
> - ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
> - }
> + if (!tb)
> + return -ENOMEM;
> +
> + ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max, attr,
> + l4proto->ctnl_timeout.nla_policy, NULL);
> + if (ret < 0)
> + goto err;
> +
> + ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
> +
> +err:
> + kfree(tb);
> return ret;
> }
>
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