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

[Stefan Hanreich <s.hanreich@proxmox.com>]

On 12/5/25 2:02 PM, Robert Obkircher wrote:
> 
> 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.

Do you mean the 'unknown' signature? Seems like this happens due to this
line here in the parser callback [1]. The other regex matches only
`PVESIG:` comments anyway.

If we remove the prefix, adding a comment with a `PVESIG:` prefix would
do that, I guess?

[1]
https://git.proxmox.com/?p=pve-firewall.git;a=blob;f=src/PVE/Firewall.pm;h=93f8c34466fd61bc646439275597aa24b8718053;hb=HEAD#l2093

>>
>> 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

seems like there is still an issue here - setting the comment `###"` I
get several:

Use of uninitialized value $1 in concatenation (.) or string at
/usr/share/perl5/PVE/Firewall.pm line 2284.

Can be easily checked via `pve-firewall compile`.

>>> +    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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