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, 78 insertions, 0 deletions

diff --git a/scripts/ld-version.sh b/scripts/ld-version.sh
new file mode 100755
index 000000000..b9513d224
--- /dev/null
+++ b/scripts/ld-version.sh
@@ -0,0 +1,78 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Print the linker name and its version in a 5 or 6-digit form.
+# Also, perform the minimum version check.
+
+set -e
+
+# Convert the version string x.y.z to a canonical 5 or 6-digit form.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+
+	# If the 2nd or 3rd field is missing, fill it with a zero.
+	#
+	# The 4th field, if present, is ignored.
+	# This occurs in development snapshots as in 2.35.1.20201116
+	echo $((10000 * $1 + 100 * ${2:-0} + ${3:-0}))
+}
+
+orig_args="$@"
+
+# Get the first line of the --version output.
+IFS='
+'
+set -- $(LC_ALL=C "$@" --version)
+
+# Split the line on spaces.
+IFS=' '
+set -- $1
+
+min_tool_version=$(dirname $0)/min-tool-version.sh
+
+if [ "$1" = GNU -a "$2" = ld ]; then
+	shift $(($# - 1))
+	version=$1
+	min_version=$($min_tool_version binutils)
+	name=BFD
+	disp_name="GNU ld"
+elif [ "$1" = GNU -a "$2" = gold ]; then
+	echo "gold linker is not supported as it is not capable of linking the kernel proper." >&2
+	exit 1
+else
+	while [ $# -gt 1 -a "$1" != "LLD" ]; do
+		shift
+	done
+
+	if [ "$1" = LLD ]; then
+		version=$2
+		min_version=$($min_tool_version llvm)
+		name=LLD
+		disp_name=LLD
+	else
+		echo "$orig_args: unknown linker" >&2
+		exit 1
+	fi
+fi
+
+# There may be something after the version, such as a distribution's package
+# release number (like Fedora's "2.34-4.fc32") or punctuation (like LLD briefly
+# added before the "compatible with GNU linkers" string), so remove everything
+# after just numbers and periods.
+version=${version%%[!0-9.]*}
+
+cversion=$(get_canonical_version $version)
+min_cversion=$(get_canonical_version $min_version)
+
+if [ "$cversion" -lt "$min_cversion" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Linker is too old."
+	echo >&2 "***   Your $disp_name version:    $version"
+	echo >&2 "***   Minimum $disp_name version: $min_version"
+	echo >&2 "***"
+	exit 1
+fi
+
+echo $name $cversion