netdev - Re: [PATCH 03/26] netfilter: x_tables: fix possible ZERO_SIZE

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Message-ID: <46b1bb67-6261-c641-ce21-61c23beab191@cogentembedded.com>
Date:	Wed, 6 Jul 2016 21:11:28 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>,
	netfilter-devel@...r.kernel.org
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH 03/26] netfilter: x_tables: fix possible ZERO_SIZE_PTR
 pointer dereferencing error.

Hello.

On 07/06/2016 05:23 PM, Pablo Neira Ayuso wrote:

> From: Xiubo Li <lixiubo@...s.chinamobile.com>
>
> Since we cannot make sure that the 'hook_mask' will always be none
> zero here.

    Non-zero, you mean?

> 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 will fix this with just doing the zero check before
> kmalloc() is called.
>
> Maybe the case above will never happen here, but in theory.
>
> Signed-off-by: Xiubo Li <lixiubo@...s.chinamobile.com>
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> ---
>  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 c69c892..8aff34e 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -1460,6 +1460,9 @@ xt_hook_ops_alloc(const struct xt_table *table, nf_hookfn *fn)
>  	uint8_t hooknum;
>  	struct nf_hook_ops *ops;
>
> +	if (!num_hooks)
> +		return ERR_PTR(-EINVAL);
> +
>  	ops = kmalloc(sizeof(*ops) * num_hooks, GFP_KERNEL);

    BTW, asking to be kcalloc() instead?

[...]

MBR, Sergei