Re: [PATCH] netfilter: use fwmark_reflect in nf_send_reset

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

Hi Pau,

On Fri, Dec 16, 2016 at 11:03:27AM +0100, Pau Espin Pedrol wrote:
> Otherwise, RST packets generated by ipt_REJECT always have mark 0 when
> the routing is checked later in the same code path.

Your patch works fine, I can see mark is reflected to TCP RST for
packets that are generated by netfilter.

However, it seems fwmark_reflect is broken here for TCP RST that are
generated by the stack, or at least I don't manage to trigger the
reflection with current git tree.

Using this simple ruleset to mark input packets:

# nft list ruleset
table ip x {
        chain y {
                type filter hook output priority 0; policy accept;
                log prefix "output: "
        }

        chain z {
                type filter hook input priority 0; policy accept;
                mark set 0x00000001
                log prefix "input: "
        }
}

Note input packets shows mark 0x1:

Dec 23 15:07:37 salvia kernel: [14895.204591] input: IN=eth0 OUT=
MAC=... SRC=192.168.12.1 DST=192.168.12.195 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=27691 DF
PROTO=TCP SPT=36341 DPT=24 WINDOW=14600 RES=0x00 SYN URGP=0 MARK=0x1 

however, output shows no mark, so no reflection is going on:

Dec 23 15:07:37 salvia kernel: [14895.204643] output: IN= OUT=eth0
SRC=192.168.12.195 DST=192.168.12.1 LEN=40 TOS=0x00 PREC=0x00 TTL=64
ID=52846 DF PROTO=TCP SPT=24 DPT=36341 WINDOW=0 RES=0x00 ACK RST
URGP=0 

fwmark_reflect works perfectly fine with ICMP:

Dec 23 15:11:21 salvia kernel: [15119.556780] input: IN=eth0 OUT=
MAC=... SRC=192.168.12.1 DST=192.168.12.195 LEN=84 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=ICMP
TYPE=8 CODE=0 ID=5429 SEQ=2 MARK=0x1
 
Dec 23 15:11:21 salvia kernel: [15119.556822] output: IN= OUT=eth0
SRC=192.168.2.195 DST=192.168.2.1 LEN=84 TOS=0x00 PREC=0x00 TTL=64
ID=25617 PROTO=ICMP TYPE=0 CODE=0 ID=5429 SEQ=2 MARK=0x1 

Thanks.