Messages in this thread | | | Date | Wed, 12 Jan 2022 21:15:38 +0100 | From | "Maciej S. Szmigiero" <> | Subject | Re: [PATCH 00/14] KEYS: Add support for PGP keys and signatures |
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On 12.01.2022 10:16, Roberto Sassu wrote: >> From: Maciej S. Szmigiero [mailto:mail@maciej.szmigiero.name] >> Sent: Tuesday, January 11, 2022 9:33 PM >> On 11.01.2022 19:03, Roberto Sassu wrote: >>> Support for PGP keys and signatures was proposed by David long time ago, >>> before the decision of using PKCS#7 for kernel modules signatures >>> verification was made. After that, there has been not enough interest to >>> support PGP too. >>> >>> Lately, when discussing a proposal of introducing fsverity signatures in >>> Fedora [1], developers expressed their preference on not having a separate >>> key for signing, which would complicate the management of the distribution. >>> They would be more in favor of using the same PGP key, currently used for >>> signing RPM headers, also for file-based signatures (not only fsverity, but >>> also IMA ones). >> >> Aren't PGP keys simply RSA / ECC / EdDSA keys with additional metadata? >> Can't they be unwrapped from their (complex) PGP format in userspace and >> loaded raw into the kernel, in a similar way as they are sometimes used >> for SSH authentication? > > Probably, this would be possible by introducing a new asymmetric > key subtype parsing PGP keys and signatures in a more simple format, > after conversion by user space. But still, a parser would be required. > To be honest, I would prefer to implement (actually David did) a > parser following an RFC, than developing a new one.
A parser in userspace is preferred to one in kernel since if there is a bug somewhere its consequences are much less severe. And experience shows that parsers are especially prone to bugs. A userspace implementation can also be tightly sandboxed for extra security.
There are many existing OpenPGP parsing libraries to choose from.
>> This will save us from having to add complex parsers (a well-known source >> of bugs) into the kernel - I guess there aren't any plans to add an >> in-kernel PGP Web of Trust implementation. > > I extensively tested the implementation with an ad-hoc fault injector, > to see if the code can correctly handle errors. I also developed a > fuzzer to corrupt the data before it is read by the kernel. Finally, > I checked that there are not memory leaks. But I agree, there could > still be bugs. > > If you mean that a key can be added to the kernel if is vouched for > by another key in the built-in keyring, I actually implemented this > (was missing in the original implementation). Some keyrings, e.g. .ima, > have this restriction. > > The way this works is that, whenever you add a PGP key to the > kernel, the parser takes not only the public key and the user ID, > but also its signature by the same or another PGP key. > > The signature is verified when the key is added to the keyring > with that restriction, and only if the verification is successful > the key can be added.
I understand but it would be great to make use as much as possible of the existing in-kernel signature verification mechanisms.
> Roberto
Thanks, Maciej
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