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 #
  16 use warnings;
  17 use strict;
  18
  19 die "Format: $0 -[0adnks] module-file >out\n"
  20     if ($#ARGV != 1);
  21
  22 my $part = $ARGV[0];
  23 my $modfile = $ARGV[1];
  24
  25 my $magic_number = "~Module signature appended~\n";
  26
  27 #
  28 # Read the module contents
  29 #
  30 open FD, "<$modfile" || die $modfile;
  31 binmode(FD);
  32 my @st = stat(FD);
  33 die "$modfile" unless (@st);
  34 my $buf = "";
  35 my $len = sysread(FD, $buf, $st[7]);
  36 die "$modfile" unless (defined($len));
  37 die "Short read on $modfile\n" unless ($len == $st[7]);
  38 close(FD) || die $modfile;
  39
  40 print STDERR "Read ", $len, " bytes from module file\n";
  41
  42 die "The file is too short to have a sig magic number and descriptor\n"
  43     if ($len < 12 + length($magic_number));
  44
  45 #
  46 # Check for the magic number and extract the information block
  47 #
  48 my $p = $len - length($magic_number);
  49 my $raw_magic = substr($buf, $p);
  50
  51 die "Magic number not found at $len\n"
  52     if ($raw_magic ne $magic_number);
  53 print STDERR "Found magic number at $len\n";
  54
  55 $p -= 12;
  56 my $raw_info = substr($buf, $p, 12);
  57
  58 my @info = unpack("CCCCCxxxN", $raw_info);
  59 my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
  60
  61 if ($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 $id_type\n";
  69 }
  70
  71 #
  72 # Extract the three pieces of info data
  73 #
  74 die "Insufficient name+kid+sig data in file\n"
  75     unless ($p >= $name_len + $kid_len + $sig_len);
  76
  77 $p -= $sig_len;
  78 my $raw_sig = substr($buf, $p, $sig_len);
  79 $p -= $kid_len;
  80 my $raw_kid = substr($buf, $p, $kid_len);
  81 $p -= $name_len;
  82 my $raw_name = substr($buf, $p, $name_len);
  83
  84 my $module_len = $p;
  85
  86 if ($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", $i;
  91     }
  92     print STDERR "]\n";
  93 }
  94
  95 if ($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", $i;
 100     }
 101     print STDERR "]\n";
 102 }
 103
 104 if ($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 #
 111 if ($part eq "-0") {
 112     # The unsigned module, no signature data at all
 113     binmode(STDOUT);
 114     print substr($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 }