netdev - Re: [PATCH v2] netfilter: properly initialize xt_table

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Date:   Thu, 17 May 2018 02:55:42 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Florian Westphal <fw@...len.de>
Cc:     Michal Kubecek <mkubecek@...e.cz>, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] netfilter: properly initialize xt_table_info structure



On 05/17/2018 02:34 AM, Greg Kroah-Hartman wrote:
> When allocating a xt_table_info structure, we should be clearing out the
> full amount of memory that was allocated, not just the "header" of the
> structure.  Otherwise odd values could be passed to userspace, which is
> not a good thing.
> 
> Cc: stable <stable@...r.kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> v2: use kvzalloc instead of kvmalloc/memset pair, as suggested by Michal Kubecek
> 
>  net/netfilter/x_tables.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index cb7cb300c3bc..cd22bb9b66f3 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -1183,11 +1183,10 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size)
>  	 * than shoot all processes down before realizing there is nothing
>  	 * more to reclaim.
>  	 */
> -	info = kvmalloc(sz, GFP_KERNEL | __GFP_NORETRY);
> +	info = kvzalloc(sz, GFP_KERNEL | __GFP_NORETRY);
>  	if (!info)
>  		return NULL;
>  
> -	memset(info, 0, sizeof(*info));
>  	info->size = size;
>  	return info;
>  }
> 

I am curious, what particular path does not later overwrite the whole zone ?

Do not get me wrong, this is not fast path, but these blobs can be huge.