Re: [PATCH v2] netfilter: ipset: Fix overflow before widen in the bitmap_ip_create() function.

[Simon Horman]

On Wed, Jan 11, 2023 at 11:57:39AM +0000, Gavrilov Ilia wrote:
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> 
> When first_ip is 0, last_ip is 0xFFFFFFFF, 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.
> 
> 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@xxxxxxxxxxx>

Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>

> ---
> v2: Fix typo of the last_ip value in the description. Fix the expression for 'hosts'.
>  net/netfilter/ipset/ip_set_bitmap_ip.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/ipset/ip_set_bitmap_ip.c b/net/netfilter/ipset/ip_set_bitmap_ip.c
> index a8ce04a4bb72..e4fa00abde6a 100644
> --- a/net/netfilter/ipset/ip_set_bitmap_ip.c
> +++ b/net/netfilter/ipset/ip_set_bitmap_ip.c
> @@ -308,8 +308,8 @@ bitmap_ip_create(struct net *net, struct ip_set *set, struct nlattr *tb[],
>                         return -IPSET_ERR_BITMAP_RANGE;
> 
>                 pr_debug("mask_bits %u, netmask %u\n", mask_bits, netmask);
> -               hosts = 2 << (32 - netmask - 1);
> -               elements = 2 << (netmask - mask_bits - 1);
> +               hosts = 2U << (32 - netmask - 1);
> +               elements = 2UL << (netmask - mask_bits - 1);
>         }
>         if (elements > IPSET_BITMAP_MAX_RANGE + 1)
>                 return -IPSET_ERR_BITMAP_RANGE_SIZE;
> --
> 2.30.2