KEYS: Add a system blacklist keyring

Add the following:

 (1) A new system keyring that is used to store information about
     blacklisted certificates and signatures.

 (2) A new key type (called 'blacklist') that is used to store a
     blacklisted hash in its description as a hex string.  The key accepts
     no payload.

 (3) The ability to configure a list of blacklisted hashes into the kernel
     at build time.  This is done by setting
     CONFIG_SYSTEM_BLACKLIST_HASH_LIST to the filename of a list of hashes
     that are in the form:

	"<hash>", "<hash>", ..., "<hash>"

     where each <hash> is a hex string representation of the hash and must
     include all necessary leading zeros to pad the hash to the right size.

The above are enabled with CONFIG_SYSTEM_BLACKLIST_KEYRING.

Once the kernel is booted, the blacklist keyring can be listed:

	root@andromeda ~]# keyctl show %:.blacklist
	Keyring
	 723359729 ---lswrv      0     0  keyring: .blacklist
	 676257228 ---lswrv      0     0   \_ blacklist: 123412341234c55c1dcc601ab8e172917706aa32fb5eaf826813547fdf02dd46

The blacklist cannot currently be modified by userspace, but it will be
possible to load it, for example, from the UEFI blacklist database.

A later commit will make it possible to load blacklisted asymmetric keys in
here too.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/certs/Kconfig b/certs/Kconfig
index fc5955f5fc8a..6ce51ede9e9b 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -64,4 +64,22 @@ config SECONDARY_TRUSTED_KEYRING
 	  those keys are not blacklisted and are vouched for by a key built
 	  into the kernel or already in the secondary trusted keyring.
 
+config SYSTEM_BLACKLIST_KEYRING
+	bool "Provide system-wide ring of blacklisted keys"
+	depends on KEYS
+	help
+	  Provide a system keyring to which blacklisted keys can be added.
+	  Keys in the keyring are considered entirely untrusted.  Keys in this
+	  keyring are used by the module signature checking to reject loading
+	  of modules signed with a blacklisted key.
+
+config SYSTEM_BLACKLIST_HASH_LIST
+	string "Hashes to be preloaded into the system blacklist keyring"
+	depends on SYSTEM_BLACKLIST_KEYRING
+	help
+	  If set, this option should be the filename of a list of hashes in the
+	  form "<hash>", "<hash>", ... .  This will be included into a C
+	  wrapper to incorporate the list into the kernel.  Each <hash> should
+	  be a string of hex digits.
+
 endmenu