KEYS: Provide a function to load keys from a PGP keyring blob

hulk inclusion
category: feature
feature: IMA Digest Lists extension
bugzilla: 46797

-------------------------------------------------

Provide a function to load keys from a PGP keyring blob for use in
initialising the module signing key keyring:

	int preload_pgp_keys(const u8 *pgpdata, size_t pgpdatalen,
			     struct key *keyring);

Descriptions are generated from user ID notes and key fingerprints.  The
keys will actually be identified by the ID calculated from the PGP data
rather than by the description, so this shouldn't be a problem.

The keys are attached to the keyring supplied.

Looking as root in /proc/keys after the module signing keyring has been
loaded:

383a00c1 I------     1 perm 1f030000     0     0 asymmetri \
				Red Hat, Inc. dbeca166: PGP.DSA dbeca166 []

Thanks to Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> for some
pointing out some errors.

Changelog

v0:
- avoid Kconfig circular dependency (Roberto Sassu)
- modify flags passed to key_create_or_update() (Roberto Sassu)
- don't process Public-Subkey packets (Roberto Sassu)

Signed-off-by: David Howells <dhowells@redhat.com>
Co-developed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Tianxing Zhang <zhangtianxing3@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>