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, 98 insertions, 0 deletions

diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
new file mode 100644
index 000000000..24a3a4fd2
--- /dev/null
+++ b/scripts/Makefile.vmlinux_o
@@ -0,0 +1,98 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+PHONY := __default
+__default: vmlinux.o
+
+include include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+
+# for objtool
+include $(srctree)/scripts/Makefile.lib
+
+# Generate a linker script to ensure correct ordering of initcalls for Clang LTO
+# ---------------------------------------------------------------------------
+
+quiet_cmd_gen_initcalls_lds = GEN     $@
+      cmd_gen_initcalls_lds = \
+	$(PYTHON3) $(srctree)/scripts/jobserver-exec \
+	$(PERL) $(real-prereqs) > $@
+
+.tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
+		vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
+	$(call if_changed,gen_initcalls_lds)
+
+targets := .tmp_initcalls.lds
+
+ifdef CONFIG_LTO_CLANG
+initcalls-lds := .tmp_initcalls.lds
+endif
+
+# objtool for vmlinux.o
+# ---------------------------------------------------------------------------
+#
+# For delay-objtool (IBT or LTO), objtool doesn't run on individual translation
+# units.  Instead it runs on vmlinux.o.
+#
+# For !delay-objtool + CONFIG_NOINSTR_VALIDATION, it runs on both translation
+# units and vmlinux.o, with the latter only used for noinstr/unret validation.
+
+objtool-enabled := $(or $(delay-objtool),$(CONFIG_NOINSTR_VALIDATION))
+
+ifeq ($(delay-objtool),y)
+vmlinux-objtool-args-y					+= $(objtool-args-y)
+else
+vmlinux-objtool-args-$(CONFIG_OBJTOOL_WERROR)		+= --werror
+endif
+
+vmlinux-objtool-args-$(CONFIG_NOINSTR_VALIDATION)	+= --noinstr \
+							   $(if $(or $(CONFIG_MITIGATION_UNRET_ENTRY),$(CONFIG_MITIGATION_SRSO)), --unret)
+
+# Only used for builds initiated by klp-build
+vmlinux-objtool-args-$(if $(KLP_SYMIDS),y)		+= --klp-symids
+
+objtool-args = $(vmlinux-objtool-args-y) --link
+
+# Link of vmlinux.o used for section mismatch analysis
+# ---------------------------------------------------------------------------
+
+vmlinux-o-ld-args-$(CONFIG_BUILTIN_MODULE_RANGES)	+= -Map=$@.map
+
+quiet_cmd_ld_vmlinux.o = LD      $@
+      cmd_ld_vmlinux.o = \
+	$(LD) ${KBUILD_LDFLAGS} -r -o $@ \
+	$(vmlinux-o-ld-args-y) \
+	$(addprefix -T , $(initcalls-lds)) \
+	--whole-archive vmlinux.a --no-whole-archive \
+	--start-group $(KBUILD_VMLINUX_LIBS) --end-group \
+	$(cmd_objtool)
+
+cmd_check_function_names = $(srctree)/scripts/check-function-names.sh $@
+
+define rule_ld_vmlinux.o
+	$(call cmd_and_savecmd,ld_vmlinux.o)
+	$(call cmd,gen_objtooldep)
+	$(call cmd,check_function_names)
+endef
+
+
+vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
+	$(call if_changed_rule,ld_vmlinux.o)
+
+targets += vmlinux.o
+
+# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
+# ---------------------------------------------------------------------------
+
+PHONY += FORCE
+FORCE:
+
+# Read all saved command lines and dependencies for the $(targets) we
+# may be building above, using $(if_changed{,_dep}). As an
+# optimization, we don't need to read them if the target does not
+# exist, we will rebuild anyway in that case.
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)