docs: verify integrity of image hash sums

[pohly]

https://clearlinux.org/documentation/clear-linux/get-started/bare-metal-install#verify-the-integrity-of-the-clear-linux-image documents how to verify the integrity of the downloaded image file. What's missing is documentation on how to verify the integrity of the SHA512SUMS file.

The files are signed, so presumably some gpg invocation will do that. But what key needs to be trusted?

[phmccarty]

I'm not sure where the actual documentation exists for this on clearlinux.org, but this blog post describes how to verify the SHA512SUMS file:

https://clearlinux.org/blogs/security-software-update-clear-linux-os-intel-architecture

$ openssl smime -verify -in [image]-SHA512SUMS.sig -inform der -content sha512sum.out -CAfile ClearLinuxRoot.pem -out /dev/null

[pohly]

Patrick McCarty <notifications@github.com> writes:

I'm not sure where the actual documentation exists for this on clearlinux.org,

The right place to document this IMHO is the link I had in my initial description. That's also what the download directory links to.

but this blog post describes how to verify the SHA512SUMS file: https://clearlinux.org/blogs/security-software-update-clear-linux-os-intel-architecture

Thanks, that does indeed explain it.

[phmccarty]

The right place to document this IMHO is the link I had in my initial description. That's also what the download directory links to.

I agree. I will prepare a PR to update the docs accordingly.

[pohly]

Patrick McCarty <notifications@github.com> writes:

https://clearlinux.org/blogs/security-software-update-clear-linux-os-intel-architecture ``` $ openssl smime -verify -in [image]-SHA512SUMS.sig -inform der -content sha512sum.out -CAfile ClearLinuxRoot.pem -out /dev/null ```

I tried that with the .pem and images+sig from 22840, but it fails for me (Debian Stable, OpenSSL 1.1.0f): $ openssl smime -verify -in clear-22840-kvm.img.xz-SHA512SUMS.sig -inform der -content sha512sum.out -CAfile ../test/ClearLinuxRoot.pem -out /dev/null Verification failure 140263623320832:error:21075075:PKCS7 routines:PKCS7_verify:certificate verify error:../crypto/pkcs7/pk7_smime.c:285:Verify error:unsupported certificate purpose Am I the first one who is paranoid enough to try this, or is it related to my version of OpenSSL? ;-}

[phmccarty]

Am I the first one who is paranoid enough to try this, or is it related to my version of OpenSSL? ;-}

I see the verification fail with openssl 1.1.0h on Arch Linux, and it succeeds with openssl 1.0.2o on Clear Linux. My guess is that it's an incompatibility between 1.0.x and 1.1.x :-(

[ahkok]

Why can't sha512sum be used instead? That should hopefully not be affected by openssl versions.

[pohly]

sha512sum does get used to verify the integrity of the image. But to prevent attacks, one first has to verify the integrity of the checksum file. Otherwise an attacker could modify the image and then update the checksum file accordingly.

I'm not sure how important it is to have these signatures. But apparently they were considered important enough to set up something, so probably it is worth fixing the mechanism.

[pohly]

The sha512sum -c command from https://clearlinux.org/documentation/clear-linux/get-started/bare-metal-install#verify-the-integrity-of-the-clear-linux-image also no longer works because the SHA512SUMS from release 23290 (current latest) contains an absolute path. It used to contain just the file name:

$ sha512sum -c clear-$version-kvm.img.xz-SHA512SUMS
sha512sum: /home/releases/www/23290/clear/clear-23290-kvm.img.xz: No such file or directory
/home/releases/www/23290/clear/clear-23290-kvm.img.xz: FAILED open or read
sha512sum: WARNING: 1 listed file could not be read

[alexjch]

A change to speed up the build caused the inclusion of the file path. We fixed the issue in the tree and this will be working as documented this afternoon after the late morning build goes out (any valid release version >= 23310 will work as documented)

[iphutch]

Closing as docs PR was merged

[mcastelino]

@phmccarty @iphutch I see this issue happening again with clear-29690-cloud.img.xz

/cc @pohly

[phmccarty]

@mcastelino The verification of clear-29690-cloud.img.xz-SHA512SUMS.sig passes for me on Clear. I see from the referenced issue that your environment is Ubuntu 18.04, so that may the reason for verification failure, due to the (likely) different versions of openssl in use.