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, 174 insertions, 0 deletions

diff --git a/certs/blacklist.c b/certs/blacklist.c
new file mode 100644
index 000000000000..3eddce0e307a
--- /dev/null
+++ b/certs/blacklist.c
@@ -0,0 +1,174 @@
+/* System hash blacklist.
+ *
+ * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) "blacklist: "fmt
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/key.h>
+#include <linux/key-type.h>
+#include <linux/sched.h>
+#include <linux/ctype.h>
+#include <linux/err.h>
+#include <linux/seq_file.h>
+#include <keys/system_keyring.h>
+#include "blacklist.h"
+
+static struct key *blacklist_keyring;
+
+/*
+ * The description must be a type prefix, a colon and then an even number of
+ * hex digits.  The hash is kept in the description.
+ */
+static int blacklist_vet_description(const char *desc)
+{
+        int n = 0;
+
+        if (*desc == ':')
+                return -EINVAL;
+        for (; *desc; desc++)
+                if (*desc == ':')
+                        goto found_colon;
+        return -EINVAL;
+
+found_colon:
+        desc++;
+        for (; *desc; desc++) {
+                if (!isxdigit(*desc))
+                        return -EINVAL;
+                n++;
+        }
+
+        if (n == 0 || n & 1)
+                return -EINVAL;
+        return 0;
+}
+
+/*
+ * The hash to be blacklisted is expected to be in the description.  There will
+ * be no payload.
+ */
+static int blacklist_preparse(struct key_preparsed_payload *prep)
+{
+        if (prep->datalen > 0)
+                return -EINVAL;
+        return 0;
+}
+
+static void blacklist_free_preparse(struct key_preparsed_payload *prep)
+{
+}
+
+static void blacklist_describe(const struct key *key, struct seq_file *m)
+{
+        seq_puts(m, key->description);
+}
+
+static struct key_type key_type_blacklist = {
+        .name                   = "blacklist",
+        .vet_description        = blacklist_vet_description,
+        .preparse               = blacklist_preparse,
+        .free_preparse          = blacklist_free_preparse,
+        .instantiate            = generic_key_instantiate,
+        .describe               = blacklist_describe,
+};
+
+/**
+ * mark_hash_blacklisted - Add a hash to the system blacklist
+ * @hash - The hash as a hex string with a type prefix (eg. "tbs:23aa429783")
+ */
+int mark_hash_blacklisted(const char *hash)
+{
+        key_ref_t key;
+
+        key = key_create_or_update(make_key_ref(blacklist_keyring, true),
+                                   "blacklist",
+                                   hash,
+                                   NULL,
+                                   0,
+                                   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
+                                    KEY_USR_VIEW),
+                                   KEY_ALLOC_NOT_IN_QUOTA |
+                                   KEY_ALLOC_BUILT_IN);
+        if (IS_ERR(key)) {
+                pr_err("Problem blacklisting hash (%ld)\n", PTR_ERR(key));
+                return PTR_ERR(key);
+        }
+        return 0;
+}
+
+/**
+ * is_hash_blacklisted - Determine if a hash is blacklisted
+ * @hash: The hash to be checked as a binary blob
+ * @hash_len: The length of the binary hash
+ * @type: Type of hash
+ */
+int is_hash_blacklisted(const u8 *hash, size_t hash_len, const char *type)
+{
+        key_ref_t kref;
+        size_t type_len = strlen(type);
+        char *buffer, *p;
+        int ret = 0;
+
+        buffer = kmalloc(type_len + 1 + hash_len * 2 + 1, GFP_KERNEL);
+        if (!buffer)
+                return -ENOMEM;
+        p = memcpy(buffer, type, type_len);
+        p += type_len;
+        *p++ = ':';
+        bin2hex(p, hash, hash_len);
+        p += hash_len * 2;
+        *p = 0;
+
+        kref = keyring_search(make_key_ref(blacklist_keyring, true),
+                              &key_type_blacklist, buffer);
+        if (!IS_ERR(kref)) {
+                key_ref_put(kref);
+                ret = -EKEYREJECTED;
+        }
+
+        kfree(buffer);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(is_hash_blacklisted);
+
+/*
+ * Intialise the blacklist
+ */
+static int __init blacklist_init(void)
+{
+        const char *const *bl;
+
+        if (register_key_type(&key_type_blacklist) < 0)
+                panic("Can't allocate system blacklist key type\n");
+
+        blacklist_keyring =
+                keyring_alloc(".blacklist",
+                              KUIDT_INIT(0), KGIDT_INIT(0),
+                              current_cred(),
+                              (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+                              KEY_USR_VIEW | KEY_USR_READ |
+                              KEY_USR_SEARCH,
+                              KEY_ALLOC_NOT_IN_QUOTA |
+                              KEY_FLAG_KEEP,
+                              NULL, NULL);
+        if (IS_ERR(blacklist_keyring))
+                panic("Can't allocate system blacklist keyring\n");
+
+        for (bl = blacklist_hashes; *bl; bl++)
+                if (mark_hash_blacklisted(*bl) < 0)
+                        pr_err("- blacklisting failed\n");
+        return 0;
+}
+
+/*
+ * Must be initialised before we try and load the keys into the keyring.
+ */
+device_initcall(blacklist_init);