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, 115 insertions, 0 deletions

diff --git a/Documentation/Makefile b/Documentation/Makefile
new file mode 100644
index 000000000..377a44965
--- /dev/null
+++ b/Documentation/Makefile
@@ -0,0 +1,115 @@
+# -*- makefile -*-
+# Makefile for Sphinx documentation
+#
+
+# for cleaning
+subdir- := devicetree/bindings
+
+ifneq ($(MAKECMDGOALS),cleandocs)
+# Check for broken documentation file references
+ifeq ($(CONFIG_WARN_MISSING_DOCUMENTS),y)
+$(shell $(srctree)/tools/docs/documentation-file-ref-check --warn)
+endif
+
+# Check for broken ABI files
+ifeq ($(CONFIG_WARN_ABI_ERRORS),y)
+$(shell $(srctree)/tools/docs/get_abi.py --dir $(srctree)/Documentation/ABI validate)
+endif
+endif
+
+# You can set these variables from the command line.
+SPHINXBUILD   = sphinx-build
+SPHINXOPTS    =
+SPHINXDIRS    = .
+DOCS_THEME    =
+DOCS_CSS      =
+RUSTDOC       =
+PAPER         =
+BUILDDIR      = $(obj)/output
+PDFLATEX      = xelatex
+LATEXOPTS     = -interaction=batchmode -no-shell-escape
+
+PYTHONPYCACHEPREFIX ?= $(abspath $(BUILDDIR)/__pycache__)
+
+# Wrapper for sphinx-build
+
+BUILD_WRAPPER = $(srctree)/tools/docs/sphinx-build-wrapper
+
+# For denylisting "variable font" files
+# Can be overridden by setting as an env variable
+FONTS_CONF_DENY_VF ?= $(HOME)/deny-vf
+
+# User-friendly check for sphinx-build
+HAVE_SPHINX := $(shell if which $(SPHINXBUILD) >/dev/null 2>&1; then echo 1; else echo 0; fi)
+
+ifeq ($(HAVE_SPHINX),0)
+
+.DEFAULT:
+	$(warning The '$(SPHINXBUILD)' command was not found. Make sure you have Sphinx installed and in PATH, or set the SPHINXBUILD make variable to point to the full path of the '$(SPHINXBUILD)' executable.)
+	@echo
+	@$(srctree)/tools/docs/sphinx-pre-install
+	@echo "  SKIP    Sphinx $@ target."
+
+else # HAVE_SPHINX
+
+# Common documentation targets
+htmldocs mandocs infodocs texinfodocs latexdocs epubdocs xmldocs pdfdocs linkcheckdocs:
+	$(Q)PYTHONPYCACHEPREFIX="$(PYTHONPYCACHEPREFIX)" \
+		$(srctree)/tools/docs/sphinx-pre-install --version-check
+	+$(Q)PYTHONPYCACHEPREFIX="$(PYTHONPYCACHEPREFIX)" \
+		$(PYTHON3) $(BUILD_WRAPPER) $@ \
+		--sphinxdirs="$(SPHINXDIRS)" $(RUSTDOC) \
+		--builddir="$(BUILDDIR)" --deny-vf=$(FONTS_CONF_DENY_VF) \
+		--theme=$(DOCS_THEME) --css=$(DOCS_CSS) --paper=$(PAPER)
+
+
+endif
+
+# The following targets are independent of HAVE_SPHINX, and the rules should
+# work or silently pass without Sphinx.
+
+htmldocs-redirects: $(srctree)/Documentation/.renames.txt
+	@tools/docs/gen-redirects.py --output $(BUILDDIR) < $<
+
+refcheckdocs:
+	$(Q)cd $(srctree); tools/docs/documentation-file-ref-check
+
+cleandocs:
+	$(Q)rm -rf $(BUILDDIR)
+
+# Used only on help
+_SPHINXDIRS   = $(shell printf "%s\n" $(patsubst $(srctree)/Documentation/%/index.rst,%,$(wildcard $(srctree)/Documentation/*/index.rst)) | sort -f)
+
+dochelp:
+	@echo  ' Linux kernel internal documentation in different formats from ReST:'
+	@echo  '  htmldocs        - HTML'
+	@echo  '  htmldocs-redirects - generate HTML redirects for moved pages'
+	@echo  '  texinfodocs     - Texinfo'
+	@echo  '  infodocs        - Info'
+	@echo  '  mandocs         - Man pages'
+	@echo  '  latexdocs       - LaTeX'
+	@echo  '  pdfdocs         - PDF'
+	@echo  '  epubdocs        - EPUB'
+	@echo  '  xmldocs         - XML'
+	@echo  '  linkcheckdocs   - check for broken external links'
+	@echo  '                    (will connect to external hosts)'
+	@echo  '  refcheckdocs    - check for references to non-existing files under'
+	@echo  '                    Documentation'
+	@echo  '  cleandocs       - clean all generated files'
+	@echo
+	@echo  '  make SPHINXDIRS="s1 s2" [target] Generate only docs of folder s1, s2'
+	@echo  '  top level values for SPHINXDIRS are:'
+	@echo  '$(_SPHINXDIRS)' | fmt -s -w 75 -g 75 | sed 's/^/    /'
+	@echo  '  you may also use a subdirectory like SPHINXDIRS=userspace-api/media,'
+	@echo  '  provided that there is an index.rst file at the subdirectory.'
+	@echo
+	@echo  '  make DOCS_THEME={sphinx-theme} selects a different Sphinx theme.'
+	@echo
+	@echo  '  make DOCS_CSS={a .css file} adds a DOCS_CSS override file for html/epub output.'
+	@echo
+	@echo  '  make PAPER={a4|letter} Specifies the paper size used for LaTeX/PDF output.'
+	@echo
+	@echo  '  make FONTS_CONF_DENY_VF={path} sets a deny list to block variable Noto CJK fonts'
+	@echo  '  for PDF build. See tools/lib/python/kdoc/latex_fonts.py for more details'
+	@echo
+	@echo  '  Default location for the generated documents is Documentation/output'