Re: [PATCH] firewall: Accept traffic on loopback interface if source and destination are within 127.0.0.0/8 only

[Michael Tremer <michael.tremer@ipfire.org>]

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Hi,

Because it is the shortest path.

My system here has 192.168.190.1 on green0:

[root(a)fw01 ~]# ip route get 192.168.190.1
local 192.168.190.1 dev lo table local src 192.168.190.1 uid 0
    cache <local>

-Michael

> On 19 May 2020, at 14:06, Peter Müller <peter.mueller(a)ipfire.org> wrote:
> 
> Hello Matthias, hello list,
> 
> why is that traffic passing through the loopback interface?!
> 
> Thanks, and best regards,
> Peter Müller
> 
>> Hi,
>> 
>> perhaps its only me, but after applying this patch for testing purposes
>> I don't see any (redirected) urlfilter block pages anymore.
>> 
>> Only the firewall logs are telling me:
>> 
>> ...
>> REJECT_INPUT lo TCP 192.168.100.254 53464 192.168.100.254 81
>> ...
>> 
>> I had to build a new "Incoming Firewall Access" rule (INPUTFW) allowing
>> TCP traffic from (e.g.) 192.168.100.254/32 to GREEN (192.168.100.254) to
>> TCP port 81 to see a block page again...
>> 
>> Only me?
>> 
>> Best,
>> Matthias
>> 
>> On 14.05.2020 12:36, Michael Tremer wrote:
>>> Hello,
>>> 
>>> This is indeed *very* unlikely, but I am okay with this patch being accepted.
>>> 
>>> Acked-by: Michael Tremer <michael.tremer(a)ipfire.org>
>>> 
>>> Best,
>>> -Michael
>>> 
>>>> On 13 May 2020, at 21:21, Peter Müller <peter.mueller(a)ipfire.org> wrote:
>>>> 
>>>> This ensures traffic on the loopback interface matches the IPv4
>>>> loopback characteristics (source and destination are within 127.0.0.0/8)
>>>> and prevents any damage in the unlikely case of non-loopback traffic
>>>> being injected/emitted (in)to the loopback interface.
>>>> 
>>>> Cc: Arne Fitzenreiter <arne.fitzenreiter(a)ipfire.org>
>>>> Cc: Michael Tremer <michael.tremer(a)ipfire.org>
>>>> Signed-off-by: Peter Müller <peter.mueller(a)ipfire.org>
>>>> ---
>>>> src/initscripts/system/firewall | 6 +++---
>>>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>>> 
>>>> diff --git a/src/initscripts/system/firewall b/src/initscripts/system/firewall
>>>> index 00512d9fa..409aaf7a9 100644
>>>> --- a/src/initscripts/system/firewall
>>>> +++ b/src/initscripts/system/firewall
>>>> @@ -219,10 +219,10 @@ iptables_init() {
>>>> 	iptables -A INPUT -j ICMPINPUT
>>>> 	iptables -A ICMPINPUT -p icmp --icmp-type 8 -j ACCEPT
>>>> 
>>>> -	# Accept everything on loopback
>>>> +	# Accept everything on loopback if both source and destination are within 127.0.0.0/8
>>>> 	iptables -N LOOPBACK
>>>> -	iptables -A LOOPBACK -i lo -j ACCEPT
>>>> -	iptables -A LOOPBACK -o lo -j ACCEPT
>>>> +	iptables -A LOOPBACK -i lo -s 127.0.0.0/8 -d 127.0.0.0/8 -j ACCEPT
>>>> +	iptables -A LOOPBACK -o lo -s 127.0.0.0/8 -d 127.0.0.0/8 -j ACCEPT
>>>> 
>>>> 	# Filter all packets with loopback addresses on non-loopback interfaces.
>>>> 	iptables -A LOOPBACK -s 127.0.0.0/8 -j DROP
>>>> -- 
>>>> 2.26.1
>>> 
>>