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, 157 insertions, 0 deletions

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
new file mode 100644
index 000000000..d7d45067d
--- /dev/null
+++ b/scripts/Makefile.modpost
@@ -0,0 +1,157 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# Module versions
+# ===========================================================================
+#
+# Stage one of module building created the following:
+# a) The individual .o files used for the module
+# b) A <module>.o file which is the .o files above linked together
+# c) A <module>.mod file, listing the name of the preliminary <module>.o file,
+#    plus all .o files
+# d) modules.order, which lists all the modules
+
+# Stage 2 is handled by this file and does the following
+# 1) Find all modules listed in modules.order
+# 2) modpost is then used to
+# 3)  create one <module>.mod.c file per module
+# 4)  create one Module.symvers file with CRC for all exported symbols
+
+# Step 3 is used to place certain information in the module's ELF
+# section, including information such as:
+#   Version magic (see include/linux/vermagic.h for full details)
+#     - Kernel release
+#     - SMP is CONFIG_SMP
+#     - PREEMPT is CONFIG_PREEMPT[_RT]
+#     - GCC Version
+#   Module info
+#     - Module version (MODULE_VERSION)
+#     - Module alias'es (MODULE_ALIAS)
+#     - Module license (MODULE_LICENSE)
+#     - See include/linux/module.h for more details
+
+# Step 4 is solely used to allow module versioning in external modules,
+# where the CRC of each module is retrieved from the Module.symvers file.
+
+PHONY := __modpost
+__modpost:
+
+include $(objtree)/include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+
+MODPOST = $(objtree)/scripts/mod/modpost
+
+modpost-args =										\
+	$(if $(CONFIG_MODULES),-M)							\
+	$(if $(CONFIG_MODVERSIONS),-m)							\
+	$(if $(CONFIG_BASIC_MODVERSIONS),-b)						\
+	$(if $(CONFIG_EXTENDED_MODVERSIONS),-x)						\
+	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
+	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
+	$(if $(KBUILD_MODPOST_WARN),-w)							\
+	$(if $(KBUILD_NSDEPS),-d modules.nsdeps)					\
+	$(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-N)	\
+	$(if $(findstring 1, $(KBUILD_EXTRA_WARN)),-W)					\
+	-o $@
+
+modpost-deps := $(MODPOST)
+
+# 'make -i -k' ignores compile errors, and builds as many modules as possible.
+ifneq ($(findstring i,$(filter-out --%,$(MAKEFLAGS))),)
+modpost-args += -n
+endif
+
+# Read out modules.order to pass in modpost.
+# Otherwise, allmodconfig would fail with "Argument list too long".
+ifdef KBUILD_MODULES
+modpost-args += -T modules.order
+modpost-deps += modules.order
+endif
+
+ifeq ($(KBUILD_EXTMOD),)
+
+# Generate the list of in-tree objects in vmlinux
+# ---------------------------------------------------------------------------
+
+# This is used to retrieve symbol versions generated by genksyms.
+ifdef CONFIG_MODVERSIONS
+vmlinux.symvers Module.symvers: .vmlinux.objs
+endif
+
+# Ignore libgcc.a
+# Some architectures do '$(CC) --print-libgcc-file-name' to borrow libgcc.a
+# from the toolchain, but there is no EXPORT_SYMBOL in it.
+
+quiet_cmd_vmlinux_objs = GEN     $@
+      cmd_vmlinux_objs =		\
+	for f in $(real-prereqs); do	\
+		case $${f} in		\
+		*libgcc.a) ;;		\
+		*) $(AR) t $${f} ;;	\
+		esac			\
+	done > $@
+
+targets += .vmlinux.objs
+.vmlinux.objs: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
+	$(call if_changed,vmlinux_objs)
+
+ifdef CONFIG_TRIM_UNUSED_KSYMS
+ksym-wl := $(CONFIG_UNUSED_KSYMS_WHITELIST)
+ksym-wl := $(if $(filter-out /%, $(ksym-wl)),$(if $(wildcard $(ksym-wl)),,$(srctree)/))$(ksym-wl)
+modpost-args += -t $(addprefix -u , $(ksym-wl))
+modpost-deps += $(ksym-wl)
+endif
+
+ifeq ($(wildcard vmlinux.o),)
+missing-input := vmlinux.o
+output-symdump := modules-only.symvers
+else
+modpost-args += vmlinux.o
+modpost-deps += vmlinux.o
+output-symdump := $(if $(KBUILD_MODULES), Module.symvers, vmlinux.symvers)
+endif
+
+else
+
+# set src + obj - they may be used in the modules's Makefile
+obj := .
+src := $(srcroot)
+
+# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
+include $(kbuild-file)
+
+output-symdump := Module.symvers
+
+ifeq ($(wildcard $(objtree)/Module.symvers),)
+missing-input := $(objtree)/Module.symvers
+else
+modpost-args += -i $(objtree)/Module.symvers
+modpost-deps += $(objtree)/Module.symvers
+endif
+
+modpost-args += -e $(addprefix -i , $(KBUILD_EXTRA_SYMBOLS))
+
+endif # ($(KBUILD_EXTMOD),)
+
+quiet_cmd_modpost = MODPOST $@
+      cmd_modpost = \
+	$(if $(missing-input), \
+		echo >&2 "WARNING: $(missing-input) is missing."; \
+		echo >&2 "         Modules may not have dependencies or modversions."; \
+		echo >&2 "         You may get many unresolved symbol errors."; \
+		echo >&2 "         You can set KBUILD_MODPOST_WARN=1 to turn errors into warning"; \
+		echo >&2 "         if you want to proceed at your own risk.";) \
+	$(MODPOST) $(modpost-args)
+
+targets += $(output-symdump)
+$(output-symdump): $(modpost-deps) FORCE
+	$(call if_changed,modpost)
+
+__modpost: $(output-symdump)
+PHONY += FORCE
+FORCE:
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)