From: Josh Boyer <jwboyer@fedoraproject.org>
Date: Fri, 26 Oct 2012 12:36:24 -0400
Subject: [PATCH] KEYS: Add a system blacklist keyring

This adds an additional keyring that is used to store certificates that
are blacklisted.  This keyring is searched first when loading signed modules
and if the module's certificate is found, it will refuse to load.  This is
useful in cases where third party certificates are used for module signing.

Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
---
 include/keys/system_keyring.h |  4 ++++
 init/Kconfig                  |  9 +++++++++
 kernel/module_signing.c       | 12 ++++++++++++
 kernel/system_keyring.c       | 17 +++++++++++++++++
 4 files changed, 42 insertions(+)

diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
index 72665eb80692..2c7b80d31366 100644
--- a/include/keys/system_keyring.h
+++ b/include/keys/system_keyring.h
@@ -28,4 +28,8 @@ static inline struct key *get_system_trusted_keyring(void)
 }
 #endif
 
+#ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
+extern struct key *system_blacklist_keyring;
+#endif
+
 #endif /* _KEYS_SYSTEM_KEYRING_H */
diff --git a/init/Kconfig b/init/Kconfig
index af09b4fb43d2..62f6fd191e4f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1752,6 +1752,15 @@ config SYSTEM_TRUSTED_KEYRING
 
 	  Keys in this keyring are used by module signature checking.
 
+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 PROFILING
 	bool "Profiling support"
 	help
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index be5b8fac4bd0..fed815fcdaf2 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -158,6 +158,18 @@ static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
 
 	pr_debug("Look up: \"%s\"\n", id);
 
+#ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
+	key = keyring_search(make_key_ref(system_blacklist_keyring, 1),
+				   &key_type_asymmetric, id);
+	if (!IS_ERR(key)) {
+		/* module is signed with a cert in the blacklist.  reject */
+		pr_err("Module key '%s' is in blacklist\n", id);
+		key_ref_put(key);
+		kfree(id);
+		return ERR_PTR(-EKEYREJECTED);
+	}
+#endif
+
 	key = keyring_search(make_key_ref(system_trusted_keyring, 1),
 			     &key_type_asymmetric, id);
 	if (IS_ERR(key))
diff --git a/kernel/system_keyring.c b/kernel/system_keyring.c
index 875f64e8935b..c15e93f5a418 100644
--- a/kernel/system_keyring.c
+++ b/kernel/system_keyring.c
@@ -20,6 +20,9 @@
 
 struct key *system_trusted_keyring;
 EXPORT_SYMBOL_GPL(system_trusted_keyring);
+#ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
+struct key *system_blacklist_keyring;
+#endif
 
 extern __initconst const u8 system_certificate_list[];
 extern __initconst const unsigned long system_certificate_list_size;
@@ -41,6 +44,20 @@ static __init int system_trusted_keyring_init(void)
 		panic("Can't allocate system trusted keyring\n");
 
 	set_bit(KEY_FLAG_TRUSTED_ONLY, &system_trusted_keyring->flags);
+
+#ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
+	system_blacklist_keyring = keyring_alloc(".system_blacklist_keyring",
+				    KUIDT_INIT(0), KGIDT_INIT(0),
+				    current_cred(),
+				    (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+				    KEY_USR_VIEW | KEY_USR_READ,
+				    KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(system_blacklist_keyring))
+		panic("Can't allocate system blacklist keyring\n");
+
+	set_bit(KEY_FLAG_TRUSTED_ONLY, &system_blacklist_keyring->flags);
+#endif
+
 	return 0;
 }