Re: [PATCH nf] netfilter: conntrack: avoid integer overflow when resizing

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Sun, Apr 24, 2016 at 01:18:21AM +0200, Florian Westphal wrote:
> Can overflow so we might allocate very small table when bucket count is
> high on a 32bit platform.
> 
> Note: resize is only possible from init_netns.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  net/netfilter/nf_conntrack_core.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index 2bbb962..11daca5 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -1563,8 +1563,15 @@ void *nf_ct_alloc_hashtable(unsigned int *sizep, int nulls)
>  	unsigned int nr_slots, i;
>  	size_t sz;
>  
> +	if (*sizep > (UINT_MAX / sizeof(struct hlist_nulls_head)))
> +		return NULL;

*sizep gets initially set to the number of buckets.

>  	BUILD_BUG_ON(sizeof(struct hlist_nulls_head) != sizeof(struct hlist_head));
>  	nr_slots = *sizep = roundup(*sizep, PAGE_SIZE / sizeof(struct hlist_nulls_head));

Then, this value is divided by the number of hlist heads that fit into
a page.

> +
> +	if (nr_slots > (UINT_MAX / sizeof(struct hlist_nulls_head)))
> +		return NULL;

So, isn't is enough with this sole check? I might be missing anything.

> +
>  	sz = nr_slots * sizeof(struct hlist_nulls_head);
>  	hash = (void *)__get_free_pages(GFP_KERNEL | __GFP_NOWARN | __GFP_ZERO,
>  					get_order(sz));
> -- 
> 2.7.3
> 
> --
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