On Mon, Aug 09, 2021 at 12:00:40PM +0200, Ahmad Fatoum wrote: > Hello Jarkko, > > On 09.08.21 11:44, Jarkko Sakkinen wrote: > > On Fri, Aug 06, 2021 at 05:09:28PM +0200, Ahmad Fatoum wrote: > >> Kernel trusted keys don't require userspace knowledge of the raw key > >> material and instead export a sealed blob, which can be persisted to > >> unencrypted storage. Userspace can then load this blob into the kernel, > >> where it's unsealed and from there on usable for kernel crypto. > >> > >> This is incompatible with fscrypt, where userspace is supposed to supply > >> the raw key material. For TPMs, a work around is to do key unsealing in > >> userspace, but this may not be feasible for other trusted key backends. > >> > >> Make it possible to benefit from both fscrypt and trusted key sealing > >> by extending fscrypt_add_key_arg::key_id to hold either the ID of a > >> fscrypt-provisioning or a trusted key. > >> > >> A non fscrypt-provisioning key_id was so far prohibited, so additionally > >> allowing trusted keys won't break backwards compatibility. > >> > >> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> > >> --- > >> Tested with: > >> https://github.com/google/fscryptctl/pull/23 > >> - if (key->type != &key_type_fscrypt_provisioning) > >> - goto bad_key; > >> - payload = key->payload.data[0]; > >> + if (key->type == &key_type_fscrypt_provisioning) { > > > > Why does fscrypt have own key type, and does not extend 'encrypted' with a > > new format [*]? > > See the commit[1] adding it for more information. TL;DR: > > fscrypt maintainers would've preferred keys to be associated with > a "domain". So an encrypted key generated for fscrypt use couldn't be reused > for e.g. dm-crypt. They are wary of fscrypt users being more exposed if their > keys can be used with weaker ciphers via other kernel functionality that could > be used to extract information about the raw key material. > > Eric also mentioned dislike of the possibility of rooting encrypted keys to > user keys. v2 is only restricted to v2, so we didn't discuss this further. > > Restricting the key to fscrypt-only precludes this reuse. > > My commit makes no attempts in changing that. It just adds a new way to pass > raw key material into fscrypt. For more information, see the commit[1] adding > that key type. > > > [*] https://www.kernel.org/doc/html/v5.13/security/keys/trusted-encrypted.html > > [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=93edd392ca OK, so why does the trusted key does not seal a fscrypt key, but instead its key material is directly used? > Cheers, > Ahmad /Jarkko
