Re: [PATCH 3/3] oe.gpg_sign: support obs-signd

Mark Hatle
2016-01-22T14:09:25Z

On 1/22/16 4:43 AM, Markus Lehtonen wrote:
> Hi Mark,
>
>
>
> (CC'd the mailing list which was accidentally dropped from my previous email)
>
> On 21/01/16 17:21, "Mark Hatle" <mark.hatle@windriver.com> wrote:
>
>> On 1/21/16 5:20 AM, Markus Lehtonen wrote:
>>> On Wed, 2016-01-13 at 12:28 +0200, Markus Lehtonen wrote:
>>>> On Tue, 2016-01-12 at 18:24 +0200, Markus Lehtonen wrote:
>>>>> Hi Mark,
>>>>>
>>>>> Thank you for your review! Comments below.
>>>>>
>>>>> On Mon, 2016-01-11 at 10:33 -0600, Mark Hatle wrote:
>>>
>>> [...SNIP...]
>>>
>>>>>>
>>>>>> Why are you removing existing signatures? I believe for many cases this is
>>>>>> actually incorrect.
>>>>>>
>>>>>> RPM (5) has the ability to have an endless number of signatures within a given
>>>>>> package. The package SHOULD included the internal non-repudiable signature...
>>>>>>
>>>>>> (to refresh memory) all RPM 5 packages include an internal non-repudiable
>>>>>> signature. Think of this as an extended md5sum, sha256sum, etc. It doesn't
>>>>>> change that a package is 'authentic' in any way (often the purpose of signatures
>>>>>> like what this code is doing), but instead keeps a high reliability way to sign
>>>>>> and verify the package is signed properly.
>>>>>>
>>>>>> This is used for validation if the system doing the install does not have the
>>>>>> public key that the package was signed with.
>>>>>>
>>>>>> ... as well as one or more repudiable signatures that can be used to verify that
>>>>>> it's "authentic" in some way. A system could very easily have OSV, OEM, and ISV
>>>>>> keys install on them. You can program RPM in such a way that it will refused to
>>>>>> install packages with unknown authentication keys or the non-repudiable key as well.
>>>>>>
>>>>>> So, I believe running delsign is wrong. If the obs-signd can't handle ADDING
>>>>>> signatures to packages, then I'd say it is broken and should be fixed in some
>>>>>> way -- or at least the signature deletion code should be optional.
>>>>>
>>>>> Yes, unfortunately this is currently the limitation of obs-signd. It
>>>>> refuses to sign if there are signatures present in the rpm package.
>>>>> Using --delsign is "unfortunate" consequence of this and that should've
>>>>> probably been described in a comment. Making signature deletion a
>>>>> configurable setting is hopefully a decent resolution for now. I will
>>>>> send a new version of the patchset later.
>>>>
>>>> Backing up a bit here. I did some quick testing and it seems that RPM5
>>>> does not support multiple signatures (anymore?). Doing --addsign seems
>>>> to overwrite the existing signatures similarly to --resign. Support for
>>>> multiple signatures were removed from RPM4 years ago.
>>>>
>>>> In this light, doing --delsign should be ok. What do you think?
>>>
>>> Hi Mark. Do you have any comments to the above? I'd like to get this
>>> patchset out of my hands :)
>>
>> RPM5 does have multiple signatures, but only allows one of each of the three
>> types to be installed. The delsign shouldn't be used as it might remove the
>> wrong signature.
>
> AFAIU, rpm only allows one signature so be present. The file format allows that, but, the rpm tool does not (anymore). For example, rpm --addsign will remove an existing DSA signature when adding an RSA signature. The SHA1 / MD5 digests are not touched by --delsign.
>
>
>> (Three types are DSA/RSA, ECDSA, and simple SHA256 or similar.)
>
> I didn't know that rpm(5?) supports ECDSA signatures.
>
>
>> But making the --delsign optional I think is the best approach. (It would be
>> better to move it to the obs-sign script itself -- but I can live with doing it
>> on the OE side since people are trying to use their owns systems.)
>
> I still believe that making it optional is just worthless and complicates things because doing rpm --addsign has exactly the same effect.
>
>
>> The alternative would be to not call the script 'obs-sign', but instead call an
>> arbitrarily named (and defined in a bitbake variable) script.. Then THAT script
>> can do the del and call the obs-sign.)
>
> Hmm, I probably don't like this idea that much. This user-written script would need to be a bit more complex as a it needs to support multiple operations (signrpm, detach sign, export pubkey). Of course, I could write a default script and put it under scripts/ but somehow feels more complex than needed.

The more I look at this, the more I think that makes sense.

I've had some of my (WR Linux) release guys look at this, and the obs-sign
mechanism will not work for us. So we're going to have to write some custom
signing code anyway. It will be much easier if there is a generic interface.
The previous thought was to use the obs-sign "interface", but write our own...
but at that point OBS has nothing to do with it.. It's just really being used as
a signing interface.

I'm assuming at this point that we're not alone in this need. I've talked to a
variety of commercial people and they all have slightly different signing
policies and mechanisms. Everything from, we don't sign the packages but check
separate checksums -- to we sign locally with a local keyring key -- to we sign
locally with a special in-memory key -- to after every package is built we have
to upload the package to an (internal password protected) FTP/HTTP site and
trigger it to be signed, then once signed we download it. (And of course OBS
specific signing...)

I think in this case an external script makes this all much easier for someone
to implement their specific policy and procedures, especially with a defined
API. Including default scripts with this as useful runners or examples would
definitely be a part of the work in my mind.

--Mark

>
> Thanks,
> Markus
>
>