thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 138 insertions, 0 deletions

diff --git a/scripts/extract-module-sig.pl b/scripts/extract-module-sig.pl
new file mode 100755
index 000000000..36a2f59c4
--- /dev/null
+++ b/scripts/extract-module-sig.pl
@@ -0,0 +1,138 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# extract-mod-sig <part> <module-file>
+#
+# Reads the module file and writes out some or all of the signature
+# section to stdout.  Part is the bit to be written and is one of:
+#
+#  -0: The unsigned module, no signature data at all
+#  -a: All of the signature data, including magic number
+#  -d: Just the descriptor values as a sequence of numbers
+#  -n: Just the signer's name
+#  -k: Just the key ID
+#  -s: Just the crypto signature or PKCS#7 message
+#
+use warnings;
+use strict;
+
+die "Format: $0 -[0adnks] module-file >out\n"
+    if ($#ARGV != 1);
+
+my $part = $ARGV[0];
+my $modfile = $ARGV[1];
+
+my $magic_number = "~Module signature appended~\n";
+
+#
+# Read the module contents
+#
+open FD, "<$modfile" || die $modfile;
+binmode(FD);
+my @st = stat(FD);
+die "$modfile" unless (@st);
+my $buf = "";
+my $len = sysread(FD, $buf, $st[7]);
+die "$modfile" unless (defined($len));
+die "Short read on $modfile\n" unless ($len == $st[7]);
+close(FD) || die $modfile;
+
+print STDERR "Read ", $len, " bytes from module file\n";
+
+die "The file is too short to have a sig magic number and descriptor\n"
+    if ($len < 12 + length($magic_number));
+
+#
+# Check for the magic number and extract the information block
+#
+my $p = $len - length($magic_number);
+my $raw_magic = substr($buf, $p);
+
+die "Magic number not found at $len\n"
+    if ($raw_magic ne $magic_number);
+print STDERR "Found magic number at $len\n";
+
+$p -= 12;
+my $raw_info = substr($buf, $p, 12);
+
+my @info = unpack("CCCCCxxxN", $raw_info);
+my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
+
+if ($id_type == 0) {
+    print STDERR "Found PGP key identifier\n";
+} elsif ($id_type == 1) {
+    print STDERR "Found X.509 cert identifier\n";
+} elsif ($id_type == 2) {
+    print STDERR "Found PKCS#7/CMS encapsulation\n";
+} else {
+    print STDERR "Found unsupported identifier type $id_type\n";
+}
+
+#
+# Extract the three pieces of info data
+#
+die "Insufficient name+kid+sig data in file\n"
+    unless ($p >= $name_len + $kid_len + $sig_len);
+
+$p -= $sig_len;
+my $raw_sig = substr($buf, $p, $sig_len);
+$p -= $kid_len;
+my $raw_kid = substr($buf, $p, $kid_len);
+$p -= $name_len;
+my $raw_name = substr($buf, $p, $name_len);
+
+my $module_len = $p;
+
+if ($sig_len > 0) {
+    print STDERR "Found $sig_len bytes of signature [";
+    my $n = $sig_len > 16 ? 16 : $sig_len;
+    foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
+	printf STDERR "%02x", $i;
+    }
+    print STDERR "]\n";
+}
+
+if ($kid_len > 0) {
+    print STDERR "Found $kid_len bytes of key identifier [";
+    my $n = $kid_len > 16 ? 16 : $kid_len;
+    foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
+	printf STDERR "%02x", $i;
+    }
+    print STDERR "]\n";
+}
+
+if ($name_len > 0) {
+    print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
+}
+
+#
+# Produce the requested output
+#
+if ($part eq "-0") {
+    # The unsigned module, no signature data at all
+    binmode(STDOUT);
+    print substr($buf, 0, $module_len);
+} elsif ($part eq "-a") {
+    # All of the signature data, including magic number
+    binmode(STDOUT);
+    print substr($buf, $module_len);
+} elsif ($part eq "-d") {
+    # Just the descriptor values as a sequence of numbers
+    print join(" ", @info), "\n";
+} elsif ($part eq "-n") {
+    # Just the signer's name
+    print STDERR "No signer's name for PKCS#7 message type sig\n"
+	if ($id_type == 2);
+    binmode(STDOUT);
+    print $raw_name;
+} elsif ($part eq "-k") {
+    # Just the key identifier
+    print STDERR "No key ID for PKCS#7 message type sig\n"
+	if ($id_type == 2);
+    binmode(STDOUT);
+    print $raw_kid;
+} elsif ($part eq "-s") {
+    # Just the crypto signature or PKCS#7 message
+    binmode(STDOUT);
+    print $raw_sig;
+}