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 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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