Re: [dm-devel] [RFC] dm-crypt: add ability to use keys from the kernel key retention service

[Andrey Ryabinin]

On 08/10/2016 02:16 PM, Ondrej Kozina wrote:
> On 08/09/2016 03:56 PM, Andrey Ryabinin wrote:
> 
> Hi Andrey,
> 
> I'm definitely in favour of dm-crypt with support for kernel keyring service, but I think this patch do lack in addressing few issues:
> 
> Currently the dm-crypt guarantees that on remove ioctl command the volume key gets deleted from both crypto layer and device-mapper subsystem without exception. I believe we should stick to the guarantee. At least let's provide an option that would immediately invalidate the key passed via key description on table destruction. Or on last table destruction that would reach dm-crypt internal reference count on such key equal to zero. Each table key has at least single copy in crypto layer anyway... This is no big deal on live system (copy in crypto layer) but after proper system shutdown there should be no key in system memory (coldboot risk mitigation).
> 

Hmm... I don't think that the kernel should do this (delete keys from keyring).
It makes sense that remove command wipes the keys added by create command.
But create command doesn't add keys to the keyring, so it would be odd if remove command clear such key.
It sound like a userspace's responsibility to manage such keys.

> While it may sound contradicting my claim about guaranteed key destruction I'd like to be able to perform table load (imagine admin wants to resize dm-crypt device) without need of reuploading the key every time. Even when such user/admin has no access to already active volume key put in a keyring. IOW it doesn't matter what keyring the key was originally anchored in. (Re)load of table with valid key description should always pass).
> 

Well, at first we'll  need to understand how to perform table load without asking the key every time.
But, for that case, it shouldn't matter whether the key passed directly or placed in keyring.


> The uspace part is about to land in cryptsetup 2.0 hopefully later this year. Most probably the kernel keyring will be used with other features of 2.0 release apart from loading dm-crypt mappings.
> 
> Last but not least: Mind me asking where do you plan to use it? In case we come with different implementation I'd like to reassure it'll be still of use to you.
> 

Our plan is to use this for encrypting containers.

> Regards Ondrej