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SubjectRe: [RFC PATCH v5 1/1] Add dm verity root hash pkcs7 sig validation.

On Thu, 27 Jun 2019, Milan Broz wrote:

> Hi,
> I tried to test test the patch, two comments below.
> On 19/06/2019 21:10, Jaskaran Khurana wrote:
>> The verification is to support cases where the roothash is not secured by
>> Trusted Boot, UEFI Secureboot or similar technologies.
>> One of the use cases for this is for dm-verity volumes mounted after boot,
>> the root hash provided during the creation of the dm-verity volume has to
>> be secure and thus in-kernel validation implemented here will be used
>> before we trust the root hash and allow the block device to be created.
>> The signature being provided for verification must verify the root hash and
>> must be trusted by the builtin keyring for verification to succeed.
>> The hash is added as a key of type "user" and the description is passed to
>> the kernel so it can look it up and use it for verification.
>> Kernel commandline parameter will indicate whether to check (only if
>> specified) or force (for all dm verity volumes) roothash signature
>> verification.
>> Kernel commandline: dm_verity.verify_sig=1 or 2 for check/force root hash
>> signature validation respectively.
> 1) I think the switch should be just boolean - enforce signatures for all dm-verity targets
> (with default to false/off).
> The rest should be handled by simple logic - if the root_hash_sig_key_desc option
> is specified, the signature MUST be validated in the constructor, all errors should cause
> failure (bad reference in keyring, bad signature, etc).
> (Now it ignores for example bad reference to the keyring, this is quite misleading.)
> If a user wants to activate a dm-verity device without a signature, just remove
> optional argument referencing the signature.
> (This is not possible with dm_verity.verify_sig set to true/on.)
> 2) All DM targets must provide the same mapping table status ("dmsetup table"
> command) as initially configured.
> The output of the command should be directly usable as mapping table constructor.
> Your patch is missing that part, I tried to fix it, add-on patch is here
> (feel free to fold it in your patch)
> Thanks,
> Milan
Hello Milan,

Thanks for testing and reviewing this. I will take care of the above
comments change it to a boolean and for the second point merge the add-on
patch that you shared.


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