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

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

superseded-by: 
https://lore.proxmox.com/pve-devel/20251215150906.257151-1-r.obkircher@proxmox.com/

On 12/9/25 11:21, Robert Obkircher wrote:
>
> On 12/5/25 14:58, Stefan Hanreich wrote:
>>
>> 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 
>>
> I meant that without a prefix the other regex would match user 
> comments as well. E.g if I remove
>
> -    $comment = "PVECOMMENT:$comment"; # avoid any confusion with 
> PVESIG comments
>
> and add:
>
>          } elsif ($line =~ 
> m/^-A\s+(\S+)\s.*--comment\s+\"PVESIG:(\S+)\"/) {
>              my ($chain, $sig) = ($1, $2);
>              return if !&$is_pvefw_chain($chain);
> +            print "$chain := $sig \n";
>              $res->{$chain} = $sig;
>
> a rule like -A PVEFW-HOST-IN  -j RETURN -m comment --comment 
> "PVESIG:abc" briefly sets $res->{chain} to abc:
>
> PVEFW-HOST-IN := abc
> PVEFW-HOST-IN := KeS6hbQXz4tEHemQqhJqOqWEWBA
>
>
>>>> mb someone with more experience with perl and utf-8 can chime in on 
>>>> the
>>>> truncation logic?
>>>>
>>>> Tested-by: Stefan Hanreich <s.hanreich@proxmox.com>
>>>>
>>>> On 12/1/25 1:33 PM, Robert Obkircher wrote:
>>>>> Use the iptables comment extension to include comments from the UI.
>>>>> Prefix them with "PVECOMMENT:" to avoid interfering with the existing
>>>>> "PVESIG:$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 $1 in concatenation (.) or string at
>> /usr/share/perl5/PVE/Firewall.pm line 2284.
>>
>> Can be easily checked via `pve-firewall compile`.
> I think this had nothing to do with '#', I just forgot the capture 
> group in the substitution.
>>
>>>>> +    return " -m comment --comment \"$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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