certs/efi_parser.c

   1 /* EFI signature/key/certificate list parser
   2  *
   3  * Copyright (C) 2012, 2016 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #define pr_fmt(fmt) "EFI: "fmt
  13 #include <linux/module.h>
  14 #include <linux/printk.h>
  15 #include <linux/err.h>
  16 #include <linux/efi.h>
  17
  18 /**
  19  * parse_efi_signature_list - Parse an EFI signature list for certificates
  20  * @source: The source of the key
  21  * @data: The data blob to parse
  22  * @size: The size of the data blob
  23  * @get_handler_for_guid: Get the handler func for the sig type (or NULL)
  24  *
  25  * Parse an EFI signature list looking for elements of interest.  A list is
  26  * made up of a series of sublists, where all the elements in a sublist are of
  27  * the same type, but sublists can be of different types.
  28  *
  29  * For each sublist encountered, the @get_handler_for_guid function is called
  30  * with the type specifier GUID and returns either a pointer to a function to
  31  * handle elements of that type or NULL if the type is not of interest.
  32  *
  33  * If the sublist is of interest, each element is passed to the handler
  34  * function in turn.
  35  *
  36  * Error EBADMSG is returned if the list doesn't parse correctly and 0 is
  37  * returned if the list was parsed correctly.  No error can be returned from
  38  * the @get_handler_for_guid function or the element handler function it
  39  * returns.
  40  */
  41 int __init parse_efi_signature_list(
  42         const char *source,
  43         const void *data, size_t size,
  44         efi_element_handler_t (*get_handler_for_guid)(const efi_guid_t *))
  45 {
  46         efi_element_handler_t handler;
  47         unsigned offs = 0;
  48
  49         pr_devel("-->%s(,%zu)\n", __func__, size);
  50
  51         while (size > 0) {
  52                 const efi_signature_data_t *elem;
  53                 efi_signature_list_t list;
  54                 size_t lsize, esize, hsize, elsize;
  55
  56                 if (size < sizeof(list))
  57                         return -EBADMSG;
  58
  59                 memcpy(&list, data, sizeof(list));
  60                 pr_devel("LIST[%04x] guid=%pUl ls=%x hs=%x ss=%x\n",
  61                          offs,
  62                          list.signature_type.b, list.signature_list_size,
  63                          list.signature_header_size, list.signature_size);
  64
  65                 lsize = list.signature_list_size;
  66                 hsize = list.signature_header_size;
  67                 esize = list.signature_size;
  68                 elsize = lsize - sizeof(list) - hsize;
  69
  70                 if (lsize > size) {
  71                         pr_devel("<--%s() = -EBADMSG [overrun @%x]\n",
  72                                  __func__, offs);
  73                         return -EBADMSG;
  74                 }
  75
  76                 if (lsize < sizeof(list) ||
  77                     lsize - sizeof(list) < hsize ||
  78                     esize < sizeof(*elem) ||
  79                     elsize < esize ||
  80                     elsize % esize != 0) {
  81                         pr_devel("- bad size combo @%x\n", offs);
  82                         return -EBADMSG;
  83                 }
  84
  85                 handler = get_handler_for_guid(&list.signature_type);
  86                 if (!handler) {
  87                         data += lsize;
  88                         size -= lsize;
  89                         offs += lsize;
  90                         continue;
  91                 }
  92
  93                 data += sizeof(list) + hsize;
  94                 size -= sizeof(list) + hsize;
  95                 offs += sizeof(list) + hsize;
  96
  97                 for (; elsize > 0; elsize -= esize) {
  98                         elem = data;
  99
 100                         pr_devel("ELEM[%04x]\n", offs);
 101                         handler(source,
 102                                 &elem->signature_data,
 103                                 esize - sizeof(*elem));
 104
 105                         data += esize;
 106                         size -= esize;
 107                         offs += esize;
 108                 }
 109         }
 110
 111         return 0;
 112 }