Thread: Re: PATCH: Disallow a netmask of zero unless the IP is also all zeroes

Greg Sabino Mullane <htamfids@gmail.com> writes:
> I say "of course" but few people (even tech ones) know the distinction.
> (Nor should they have to! But that's for a nearby thread). This patch aims
> to prevent this very bad footgun by only allowing a /0 if the IP consists
> of only zeroes. It works for ipv4 and ipv6.

More generally, should we reject if the netmask causes *any* nonzero
IP bits to be ignored?  Our CIDR type already imposes that rule:

regression=# select '1.2.3.4/24'::cidr;
ERROR:  invalid cidr value: "1.2.3.4/24"
LINE 1: select '1.2.3.4/24'::cidr;
               ^
DETAIL:  Value has bits set to right of mask.

I'm a bit distressed to realize that hba.c isn't using cidr_in.
Maybe we should try to share code instead of duplicating yet more.

            regards, tom lane

> On 11 Feb 2025, at 21:25, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> I'm a bit distressed to realize that hba.c isn't using cidr_in.
> Maybe we should try to share code instead of duplicating yet more.

+1.  I have a note along these lines on my never-shrinking TODO, I think it
would be great if we took a stab at that.

--
Daniel Gustafsson

On 2/11/25 9:25 PM, Tom Lane wrote:
> Greg Sabino Mullane <htamfids@gmail.com> writes:
>> I say "of course" but few people (even tech ones) know the distinction.
>> (Nor should they have to! But that's for a nearby thread). This patch aims
>> to prevent this very bad footgun by only allowing a /0 if the IP consists
>> of only zeroes. It works for ipv4 and ipv6.
> 
> More generally, should we reject if the netmask causes *any* nonzero
> IP bits to be ignored?  Our CIDR type already imposes that rule:

+1 From me too. I think we should fix the general issue rather than 
special casing /0.

Andreas