netdev - Re: [PATCH] netfilter: fix possible ZERO_SIZE

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Message-ID: <20160601092711.GB2711@salvia>
Date:	Wed, 1 Jun 2016 11:27:11 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Xiubo Li <lixiubo@...s.chinamobile.com>
Cc:	kaber@...sh.net, kadlec@...ckhole.kfki.hu, davem@...emloft.net,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: fix possible ZERO_SIZE_PTR pointer
 dereferencing error.

On Wed, Jun 01, 2016 at 04:34:28PM +0800, Xiubo Li wrote:
> Since we cannot make sure the 'hook_mask' will always be none zero
> here. If it equals to zero, the num_hooks will be zero too, and then
> kmalloc() will return ZERO_SIZE_PTR, which is (void *)16.
> 
> Then the following error check will fails:
>   ops = kmalloc(sizeof(*ops) * num_hooks, GFP_KERNEL);
>   if (ops == NULL)
>           return ERR_PTR(-ENOMEM);
> 
> So this patch fix this with just doing the zero check before calling
> kmalloc() is called.
> 
> Maybe the case above will never happen here, but in theory.
> 
> Signed-off-by: Xiubo Li <lixiubo@...s.chinamobile.com>
> ---
>  net/netfilter/x_tables.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index c8a0b7d..4df8e38 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -1185,6 +1185,9 @@ struct nf_hook_ops *xt_hook_link(const struct xt_table *table, nf_hookfn *fn)

What kernel version are you using? I don't see xt_hook_link() in the
development tree.

>  	struct nf_hook_ops *ops;
>  	int ret;
>  
> +	if (!num_hooks)
> +		return ERR_PTR(-EINVAL);
> +
>  	ops = kmalloc(sizeof(*ops) * num_hooks, GFP_KERNEL);
>  	if (ops == NULL)
>  		return ERR_PTR(-ENOMEM);
> -- 
> 1.8.3.1
> 
> 
>