Re: [pve-devel] [PATCH v1 pve-firewall] fix #7068: show rule comments in iptables output

[Robert Obkircher <r.obkircher@proxmox.com>]

On 12/5/25 12:58, Stefan Hanreich wrote:
> Tested this in a similar vein as the nftables one:
> * "normal" comments
> * comments that are too long
> * comments that are too long and do not truncate nicely at the 255
> boundary
> * comments in security groups
> * emojis in comments
>
> afaict the PVECOMMENT: prefix is merely visual? it doesn't serve any
> functional purpose? At least a quick monkey-patch removing it didn't
> break anything and judging from the source code it seems fine as well.
> Imo it would be fine then to completely omit it then (even in the case
> where rule comments start with PVESIG).

I think the parser in iptables_get_chains would at least temporarily set 
an invalid signature on the chain and only override it later because the 
real PVESIG: rule is always present and printed last. Relying on that 
seemed a bit sketchy.

>
> mb someone with more experience with perl and utf-8 can chime in on the
> truncation logic?
>
> Tested-by: Stefan Hanreich <s.hanreich@proxmox.com>
>
> On 12/1/25 1:33 PM, Robert Obkircher wrote:
>> Use the iptables comment extension to include comments from the UI.
>> Prefix them with "PVECOMMENT:" to avoid interfering with the existing
>> "PVESIG:$sig" comments, which are used to store signatures for change
>> detection.
>>
>> The total length of the (unescaped) comments is limited to 255 utf8
>> bytes. According to the man page it could be up to 256 characters, but
>> the actual implementation seems to zero terminate the buffer before
>> saving. For example, the following command produces a 255 char comment
>> ending in 'a':
>> iptables -A PVEFW-HOST-IN -m comment --comment $(python3 -c "print('ab'*256)")
>>
>> Unlike the iptables command, this version truncates to valid utf8.
>>
>> Signed-off-by: Robert Obkircher <r.obkircher@proxmox.com>
>> ---
>>   src/PVE/Firewall.pm | 17 ++++++++++++++++-
>>   1 file changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/PVE/Firewall.pm b/src/PVE/Firewall.pm
>> index 93f8c34..688829a 100644
>> --- a/src/PVE/Firewall.pm
>> +++ b/src/PVE/Firewall.pm
>> @@ -2271,6 +2271,20 @@ sub ipt_gen_src_or_dst_match {
>>       return $match;
>>   }
>>   
>> +sub print_ipt_comment {
>> +    my ($comment) = @_;
>> +    return "" if !defined($comment) || $comment eq "";
>> +    $comment = encode("utf8", $comment, Encode::LEAVE_SRC);
>> +    $comment = "PVECOMMENT:$comment"; # avoid any confusion with PVESIG comments
>> +
>> +    # man iptables-extensions says 256 chars, but the code only saves 255
>> +    $comment = substr($comment, 0, 255);
>> +    $comment = encode('utf8', decode('utf8', $comment, Encode::FB_QUIET | Encode::LEAVE_SRC));
>> +
>> +    $comment =~ s/[\\"']/\\$1/g; # escape logic from xtables_save_string
>> +    return " -m comment --comment \"$comment\""; # never omit quotes because of the colon
>> +}
>> +
>>   # convert a %rule to an array of iptables commands
>>   sub ipt_rule_to_cmds {
>>       my ($rule, $chain, $ipversion, $cluster_conf, $fw_conf, $vmid) = @_;
>> @@ -2375,7 +2389,8 @@ sub ipt_rule_to_cmds {
>>           my $logaction = get_log_rule_base($chain, $vmid, $rule->{logmsg}, $loglevel);
>>           push @iptcmds, "-A $chain $matchstr $logaction";
>>       }
>> -    push @iptcmds, "-A $chain $matchstr $targetstr";
>> +    my $comment = print_ipt_comment($rule->{comment});
>> +    push @iptcmds, "-A $chain $matchstr $targetstr$comment";
>>       return @iptcmds;
>>   }
>>   
>


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