Re: [iptables PATCH] nft: Fix for broken address mask match detection

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

On Mon, Sep 28, 2020 at 07:05:47PM +0200, Phil Sutter wrote:
> Trying to decide whether a bitwise expression is needed to match parts
> of a source or destination address only, add_addr() checks if all bytes
> in 'mask' are 0xff or not. The check is apparently broken though as each
> byte in 'mask' is cast to a signed char before comparing against 0xff,
> therefore the bitwise is always added:
> 
> | # ./bad/iptables-nft -A foo -s 10.0.0.1 -j ACCEPT
> | # ./good/iptables-nft -A foo -s 10.0.0.2 -j ACCEPT
> | # nft --debug=netlink list chain ip filter foo
> | ip filter foo 5
> |   [ payload load 4b @ network header + 12 => reg 1 ]
> |   [ bitwise reg 1 = (reg=1 & 0xffffffff ) ^ 0x00000000 ]
> |   [ cmp eq reg 1 0x0100000a ]
> |   [ counter pkts 0 bytes 0 ]
> |   [ immediate reg 0 accept ]
> |
> | ip filter foo 6 5
> |   [ payload load 4b @ network header + 12 => reg 1 ]
> |   [ cmp eq reg 1 0x0200000a ]
> |   [ counter pkts 0 bytes 0 ]
> |   [ immediate reg 0 accept ]
> |
> | table ip filter {
> | 	chain foo {
> | 		ip saddr 10.0.0.1 counter packets 0 bytes 0 accept
> | 		ip saddr 10.0.0.2 counter packets 0 bytes 0 accept
> | 	}
> | }
> 
> Fix the cast, safe an extra op and gain 100% performance in ideal cases.

LGTM.