LXR linux/scripts/extract-module-sig.pl

   1#!/usr/bin/env perl
   2# SPDX-License-Identifier: GPL-2.0
   3#
   4# extract-mod-sig <part> <module-file>
   5#
   6# Reads the module file and writes out some or all of the signature
   7# section to stdout.  Part is the bit to be written and is one of:
   8#
   9#  -0: The unsigned module, no signature data at all
  10#  -a: All of the signature data, including magic number
  11#  -d: Just the descriptor values as a sequence of numbers
  12#  -n: Just the signer's name
  13#  -k: Just the key ID
  14#  -s: Just the crypto signature or PKCS#7 message
  15#
  16use warnings;
  17use strict;
  18
  19die "Format: $0 -[0adnks] module-file >out\n"
  20    if ($#ARGV != 1);
  21
  22my $part = $ARGV[0];
  23my $modfile = $ARGV[1];
  24
  25my $magic_number = "~Module signature appended~\n";
  26
  27#
  28# Read the module contents
  29#
  30open FD, "<$modfile" || die $modfile;
  31binmode(FD);
  32my @st = stat(FD);
  33die "$modfile" unless (@st);
  34my $buf = "";
  35my $len = sysread(FD, $buf, $st[7]);
  36die "$modfile" unless (defined($len));
  37die "Short read on $modfile\n" unless ($len == $st[7]);
  38close(FD) || die $modfile;
  39
  40print STDERR "Read ", $len, " bytes from module file\n";
  41
  42die "The file is too short to have a sig magic number and descriptor\n"
  43    if ($len < 12 + length($magic_number));
  44
  45#
  46# Check for the magic number and extract the information block
  47#
  48my $p = $len - length($magic_number);
  49my $raw_magic = substr($buf, $p);
  50
  51die "Magic number not found at $len\n"
  52    if ($raw_magic ne $magic_number);
  53print STDERR "Found magic number at $len\n";
  54
  55$p -= 12;
  56my $raw_info = substr($buf, $p, 12);
  57
  58my @info = unpack("CCCCCxxxN", $raw_info);
  59my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
  60
  61if ($id_type == 0) {
  62    print STDERR "Found PGP key identifier\n";
  63} elsif ($id_type == 1) {
  64    print STDERR "Found X.509 cert identifier\n";
  65} elsif ($id_type == 2) {
  66    print STDERR "Found PKCS#7/CMS encapsulation\n";
  67} else {
  68    print STDERR "Found unsupported identifier type $id_type\n";
  69}
  70
  71#
  72# Extract the three pieces of info data
  73#
  74die "Insufficient name+kid+sig data in file\n"
  75    unless ($p >= $name_len + $kid_len + $sig_len);
  76
  77$p -= $sig_len;
  78my $raw_sig = substr($buf, $p, $sig_len);
  79$p -= $kid_len;
  80my $raw_kid = substr($buf, $p, $kid_len);
  81$p -= $name_len;
  82my $raw_name = substr($buf, $p, $name_len);
  83
  84my $module_len = $p;
  85
  86if ($sig_len > 0) {
  87    print STDERR "Found $sig_len bytes of signature [";
  88    my $n = $sig_len > 16 ? 16 : $sig_len;
  89    foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
  90        printf STDERR "%02x", $i;
  91    }
  92    print STDERR "]\n";
  93}
  94
  95if ($kid_len > 0) {
  96    print STDERR "Found $kid_len bytes of key identifier [";
  97    my $n = $kid_len > 16 ? 16 : $kid_len;
  98    foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
  99        printf STDERR "%02x", $i;
 100    }
 101    print STDERR "]\n";
 102}
 103
 104if ($name_len > 0) {
 105    print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
 106}
 107
 108#
 109# Produce the requested output
 110#
 111if ($part eq "-0") {
 112    # The unsigned module, no signature data at all
 113    binmode(STDOUT);
 114    print substr($buf, 0, $module_len);
 115} elsif ($part eq "-a") {
 116    # All of the signature data, including magic number
 117    binmode(STDOUT);
 118    print substr($buf, $module_len);
 119} elsif ($part eq "-d") {
 120    # Just the descriptor values as a sequence of numbers
 121    print join(" ", @info), "\n";
 122} elsif ($part eq "-n") {
 123    # Just the signer's name
 124    print STDERR "No signer's name for PKCS#7 message type sig\n"
 125        if ($id_type == 2);
 126    binmode(STDOUT);
 127    print $raw_name;
 128} elsif ($part eq "-k") {
 129    # Just the key identifier
 130    print STDERR "No key ID for PKCS#7 message type sig\n"
 131        if ($id_type == 2);
 132    binmode(STDOUT);
 133    print $raw_kid;
 134} elsif ($part eq "-s") {
 135    # Just the crypto signature or PKCS#7 message
 136    binmode(STDOUT);
 137    print $raw_sig;
 138}
 139