netdev - Re: [PATCH] netfilter: ipset: Fix overflow before widen in the bitmap_ip

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Date:   Wed, 11 Jan 2023 11:19:47 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Gavrilov Ilia <Ilia.Gavrilov@...otecs.ru>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "coreteam@...filter.org" <coreteam@...filter.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org>
Subject: Re: [PATCH] netfilter: ipset: Fix overflow before widen in the
 bitmap_ip_create() function.

Hi Gavrilov,

On Mon, Jan 09, 2023 at 11:54:02AM +0000, Gavrilov Ilia wrote:
> When first_ip is 0, last_ip is 0xFFFFFFF, and netmask is 31, the value of
> an arithmetic expression 2 << (netmask - mask_bits - 1) is subject
> to overflow due to a failure casting operands to a larger data type
> before performing the arithmetic.
> 
> Note that it's harmless since the value will be checked at the next step.

Do you mean 0xFFFFFFFF (8 rather than 8 'F's) ?
If so, I agree with this patch.

> Found by InfoTeCS on behalf of Linux Verification Center
> (linuxtesting.org) with SVACE.
> 
> Fixes: b9fed748185a ("netfilter: ipset: Check and reject crazy /0 input parameters")
> Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@...otecs.ru>
> ---
>  net/netfilter/ipset/ip_set_bitmap_ip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/ipset/ip_set_bitmap_ip.c b/net/netfilter/ipset/ip_set_bitmap_ip.c
> index a8ce04a4bb72..b8f0fb37378f 100644
> --- a/net/netfilter/ipset/ip_set_bitmap_ip.c
> +++ b/net/netfilter/ipset/ip_set_bitmap_ip.c
> @@ -309,7 +309,7 @@ bitmap_ip_create(struct net *net, struct ip_set *set, struct nlattr *tb[],
>  
>  		pr_debug("mask_bits %u, netmask %u\n", mask_bits, netmask);
>  		hosts = 2 << (32 - netmask - 1);

I think that hosts also overflows, in the case you have described.
Although it also doesn't matter for the same reason you state.
But from a correctness point of view perhaps it should also be addressed?

> -		elements = 2 << (netmask - mask_bits - 1);
> +		elements = 2UL << (netmask - mask_bits - 1);
>  	}
>  	if (elements > IPSET_BITMAP_MAX_RANGE + 1)
>  		return -IPSET_ERR_BITMAP_RANGE_SIZE;
> -- 
> 2.30.2
>