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, 235 insertions, 0 deletions

diff --git a/tools/debugging/kernel-chktaint b/tools/debugging/kernel-chktaint
new file mode 100755
index 000000000..e1571c04a
--- /dev/null
+++ b/tools/debugging/kernel-chktaint
@@ -0,0 +1,235 @@
+#! /bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Randy Dunlap <rdunlap@infradead.org>, 2018
+# Thorsten Leemhuis <linux@leemhuis.info>, 2018
+
+usage()
+{
+	cat <<EOF
+usage: ${0##*/}
+       ${0##*/} <int>
+
+Call without parameters to decode /proc/sys/kernel/tainted.
+
+Call with a positive integer as parameter to decode a value you
+retrieved from /proc/sys/kernel/tainted on another system.
+
+EOF
+}
+
+if [ "$1"x != "x" ]; then
+	if  [ "$1"x == "--helpx" ] || [ "$1"x == "-hx" ] ; then
+		usage
+		exit 1
+	elif  [ $1 -ge 0 ] 2>/dev/null ; then
+		taint=$1
+	else
+		echo "Error: Parameter '$1' not a positive integer. Aborting." >&2
+		exit 1
+	fi
+else
+	TAINTFILE="/proc/sys/kernel/tainted"
+	if [ ! -r $TAINTFILE ]; then
+		echo "No file: $TAINTFILE"
+		exit
+	fi
+
+	taint=`cat $TAINTFILE`
+fi
+
+if [ $taint -eq 0 ]; then
+	echo "Kernel not Tainted"
+	exit
+else
+	echo "Kernel is \"tainted\" for the following reasons:"
+fi
+
+T=$taint
+out=
+
+addout() {
+	out=$out$1
+}
+
+if [ `expr $T % 2` -eq 0 ]; then
+	addout "G"
+else
+	addout "P"
+	echo " * proprietary module was loaded (#0)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "F"
+	echo " * module was force loaded (#1)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "S"
+	echo " * kernel running on an out of specification system (#2)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "R"
+	echo " * module was force unloaded (#3)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "M"
+	echo " * processor reported a Machine Check Exception (MCE) (#4)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "B"
+	echo " * bad page referenced or some unexpected page flags (#5)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "U"
+	echo " * taint requested by userspace application (#6)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "D"
+	echo " * kernel died recently, i.e. there was an OOPS or BUG (#7)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "A"
+	echo " * an ACPI table was overridden by user (#8)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "W"
+	echo " * kernel issued warning (#9)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "C"
+	echo " * staging driver was loaded (#10)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "I"
+	echo " * workaround for bug in platform firmware applied (#11)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "O"
+	echo " * externally-built ('out-of-tree') module was loaded  (#12)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "E"
+	echo " * unsigned module was loaded (#13)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "L"
+	echo " * soft lockup occurred (#14)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "K"
+	echo " * kernel has been live patched (#15)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "X"
+	echo " * auxiliary taint, defined for and used by distros (#16)"
+
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "T"
+	echo " * kernel was built with the struct randomization plugin (#17)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "N"
+	echo " * an in-kernel test (such as a KUnit test) has been run (#18)"
+fi
+
+T=`expr $T / 2`
+if [ `expr $T % 2` -eq 0 ]; then
+	addout " "
+else
+	addout "J"
+	echo " * fwctl's mutating debug interface was used (#19)"
+fi
+echo "Raw taint value as int/string: $taint/'$out'"
+
+# report on any tainted loadable modules
+[ "$1" = "" ] && [ -r /sys/module/ ] && \
+	cnt=`grep [A-Z] /sys/module/*/taint | wc -l` || cnt=0
+
+if [ $cnt -ne 0 ]; then
+	echo
+	echo "Tainted modules:"
+	for dir in `ls /sys/module` ; do
+		if [ -r /sys/module/$dir/taint ]; then
+			modtnt=`cat /sys/module/$dir/taint`
+			[ "$modtnt" = "" ] || echo " * $dir ($modtnt)"
+		fi
+	done
+fi
+
+echo
+echo "For a more detailed explanation of the various taint flags see"
+echo " Documentation/admin-guide/tainted-kernels.rst in the Linux kernel sources"
+echo " or https://kernel.org/doc/html/latest/admin-guide/tainted-kernels.html"
+#EOF#