certs/blacklist.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* System hash blacklist.
   3  *
   4  * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #define pr_fmt(fmt) "blacklist: "fmt
   9 #include <linux/module.h>
  10 #include <linux/slab.h>
  11 #include <linux/key.h>
  12 #include <linux/key-type.h>
  13 #include <linux/sched.h>
  14 #include <linux/ctype.h>
  15 #include <linux/err.h>
  16 #include <linux/seq_file.h>
  17 #include <keys/system_keyring.h>
  18 #include "blacklist.h"
  19
  20 static struct key *blacklist_keyring;
  21
  22 /*
  23  * The description must be a type prefix, a colon and then an even number of
  24  * hex digits.  The hash is kept in the description.
  25  */
  26 static int blacklist_vet_description(const char *desc)
  27 {
  28         int n = 0;
  29
  30         if (*desc == ':')
  31                 return -EINVAL;
  32         for (; *desc; desc++)
  33                 if (*desc == ':')
  34                         goto found_colon;
  35         return -EINVAL;
  36
  37 found_colon:
  38         desc++;
  39         for (; *desc; desc++) {
  40                 if (!isxdigit(*desc))
  41                         return -EINVAL;
  42                 n++;
  43         }
  44
  45         if (n == 0 || n & 1)
  46                 return -EINVAL;
  47         return 0;
  48 }
  49
  50 /*
  51  * The hash to be blacklisted is expected to be in the description.  There will
  52  * be no payload.
  53  */
  54 static int blacklist_preparse(struct key_preparsed_payload *prep)
  55 {
  56         if (prep->datalen > 0)
  57                 return -EINVAL;
  58         return 0;
  59 }
  60
  61 static void blacklist_free_preparse(struct key_preparsed_payload *prep)
  62 {
  63 }
  64
  65 static void blacklist_describe(const struct key *key, struct seq_file *m)
  66 {
  67         seq_puts(m, key->description);
  68 }
  69
  70 static struct key_type key_type_blacklist = {
  71         .name                   = "blacklist",
  72         .vet_description        = blacklist_vet_description,
  73         .preparse               = blacklist_preparse,
  74         .free_preparse          = blacklist_free_preparse,
  75         .instantiate            = generic_key_instantiate,
  76         .describe               = blacklist_describe,
  77 };
  78
  79 /**
  80  * mark_hash_blacklisted - Add a hash to the system blacklist
  81  * @hash - The hash as a hex string with a type prefix (eg. "tbs:23aa429783")
  82  */
  83 int mark_hash_blacklisted(const char *hash)
  84 {
  85         key_ref_t key;
  86
  87         key = key_create_or_update(make_key_ref(blacklist_keyring, true),
  88                                    "blacklist",
  89                                    hash,
  90                                    NULL,
  91                                    0,
  92                                    ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
  93                                     KEY_USR_VIEW),
  94                                    KEY_ALLOC_NOT_IN_QUOTA |
  95                                    KEY_ALLOC_BUILT_IN);
  96         if (IS_ERR(key)) {
  97                 pr_err("Problem blacklisting hash (%ld)\n", PTR_ERR(key));
  98                 return PTR_ERR(key);
  99         }
 100         return 0;
 101 }
 102
 103 /**
 104  * is_hash_blacklisted - Determine if a hash is blacklisted
 105  * @hash: The hash to be checked as a binary blob
 106  * @hash_len: The length of the binary hash
 107  * @type: Type of hash
 108  */
 109 int is_hash_blacklisted(const u8 *hash, size_t hash_len, const char *type)
 110 {
 111         key_ref_t kref;
 112         size_t type_len = strlen(type);
 113         char *buffer, *p;
 114         int ret = 0;
 115
 116         buffer = kmalloc(type_len + 1 + hash_len * 2 + 1, GFP_KERNEL);
 117         if (!buffer)
 118                 return -ENOMEM;
 119         p = memcpy(buffer, type, type_len);
 120         p += type_len;
 121         *p++ = ':';
 122         bin2hex(p, hash, hash_len);
 123         p += hash_len * 2;
 124         *p = 0;
 125
 126         kref = keyring_search(make_key_ref(blacklist_keyring, true),
 127                               &key_type_blacklist, buffer, false);
 128         if (!IS_ERR(kref)) {
 129                 key_ref_put(kref);
 130                 ret = -EKEYREJECTED;
 131         }
 132
 133         kfree(buffer);
 134         return ret;
 135 }
 136 EXPORT_SYMBOL_GPL(is_hash_blacklisted);
 137
 138 int is_binary_blacklisted(const u8 *hash, size_t hash_len)
 139 {
 140         if (is_hash_blacklisted(hash, hash_len, "bin") == -EKEYREJECTED)
 141                 return -EPERM;
 142
 143         return 0;
 144 }
 145 EXPORT_SYMBOL_GPL(is_binary_blacklisted);
 146
 147 /*
 148  * Initialise the blacklist
 149  */
 150 static int __init blacklist_init(void)
 151 {
 152         const char *const *bl;
 153
 154         if (register_key_type(&key_type_blacklist) < 0)
 155                 panic("Can't allocate system blacklist key type\n");
 156
 157         blacklist_keyring =
 158                 keyring_alloc(".blacklist",
 159                               KUIDT_INIT(0), KGIDT_INIT(0),
 160                               current_cred(),
 161                               (KEY_POS_ALL & ~KEY_POS_SETATTR) |
 162                               KEY_USR_VIEW | KEY_USR_READ |
 163                               KEY_USR_SEARCH,
 164                               KEY_ALLOC_NOT_IN_QUOTA |
 165                               KEY_FLAG_KEEP,
 166                               NULL, NULL);
 167         if (IS_ERR(blacklist_keyring))
 168                 panic("Can't allocate system blacklist keyring\n");
 169
 170         for (bl = blacklist_hashes; *bl; bl++)
 171                 if (mark_hash_blacklisted(*bl) < 0)
 172                         pr_err("- blacklisting failed\n");
 173         return 0;
 174 }
 175
 176 /*
 177  * Must be initialised before we try and load the keys into the keyring.
 178  */
 179 device_initcall(blacklist_init);