Re: [PATCH nft 1/2] segtree: Fix range_mask_len() for subnet ranges exceeding unsigned int

[Phil Sutter <phil@nwl.cc>]

On Thu, May 06, 2021 at 12:23:13AM +0200, Stefano Brivio wrote:
> As concatenated ranges are fetched from kernel sets and displayed to
> the user, range_mask_len() evaluates whether the range is suitable for
> display as netmask, and in that case it calculates the mask length by
> right-shifting the endpoints until no set bits are left, but in the
> existing version the temporary copies of the endpoints are derived by
> copying their unsigned int representation, which doesn't suffice for
> IPv6 netmask lengths, in general.
> 
> PetrB reports that, after inserting a /56 subnet in a concatenated set
> element, it's listed as a /64 range. In fact, this happens for any
> IPv6 mask shorter than 64 bits.
> 
> Fix this issue by simply sourcing the range endpoints provided by the
> caller and setting the temporary copies with mpz_init_set(), instead
> of fetching the unsigned int representation. The issue only affects
> displaying of the masks, setting elements already works as expected.
> 

Fixes: 8ac2f3b2fca38 ("src: Add support for concatenated set ranges")

> Reported-by: PetrB <petr.boltik@gmail.com>
> Bugzilla: https://bugzilla.netfilter.org/show_bug.cgi?id=1520
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> ---
>  src/segtree.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/segtree.c b/src/segtree.c
> index ad199355532e..353a0053ebc0 100644
> --- a/src/segtree.c
> +++ b/src/segtree.c
> @@ -838,8 +838,8 @@ static int range_mask_len(const mpz_t start, const mpz_t end, unsigned int len)
>  	mpz_t tmp_start, tmp_end;
>  	int ret;
>  
> -	mpz_init_set_ui(tmp_start, mpz_get_ui(start));
> -	mpz_init_set_ui(tmp_end, mpz_get_ui(end));
> +	mpz_init_set(tmp_start, start);
> +	mpz_init_set(tmp_end, end);

The old code is a bit funny, was there a specific reason why you
exported the values into a C variable intermediately?

Cheers, Phil