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, 108 insertions, 0 deletions

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
new file mode 100644
index 000000000..440fb7638
--- /dev/null
+++ b/rust/helpers/helpers.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Non-trivial C macros cannot be used in Rust. Similarly, inlined C functions
+ * cannot be called either. This file explicitly creates functions ("helpers")
+ * that wrap those so that they can be called from Rust.
+ *
+ * Sorted alphabetically.
+ */
+
+#include <linux/compiler_types.h>
+
+#ifdef __BINDGEN__
+// Omit `inline` for bindgen as it ignores inline functions.
+#define __rust_helper
+#else
+// The helper functions are all inline functions.
+//
+// We use `__always_inline` here to bypass LLVM inlining checks, in case the
+// helpers are inlined directly into Rust CGUs.
+//
+// The LLVM inlining checks are false positives:
+// * LLVM doesn't want to inline functions compiled with
+//   `-fno-delete-null-pointer-checks` with code compiled without.
+//   The C CGUs all have this enabled and Rust CGUs don't. Inlining is okay
+//   since this is one of the hardening features that does not change the ABI,
+//   and we shouldn't have null pointer dereferences in these helpers.
+// * LLVM doesn't want to inline functions with different list of builtins. C
+//   side has `-fno-builtin-wcslen`; `wcslen` is not a Rust builtin, so they
+//   should be compatible, but LLVM does not perform inlining due to attributes
+//   mismatch.
+// * clang and Rust doesn't have the exact target string. Clang generates
+//   `+cmov,+cx8,+fxsr` but Rust doesn't enable them (in fact, Rust will
+//   complain if `-Ctarget-feature=+cmov,+cx8,+fxsr` is used). x86-64 always
+//   enable these features, so they are in fact the same target string, but
+//   LLVM doesn't understand this and so inlining is inhibited. This can be
+//   bypassed with `--ignore-tti-inline-compatible`, but this is a hidden
+//   option.
+#define __rust_helper __always_inline
+#endif
+
+#include "atomic.c"
+#include "atomic_ext.c"
+#include "auxiliary.c"
+#include "barrier.c"
+#include "binder.c"
+#include "bitmap.c"
+#include "bitops.c"
+#include "blk.c"
+#include "bug.c"
+#include "build_assert.c"
+#include "build_bug.c"
+#include "clk.c"
+#include "completion.c"
+#include "cpu.c"
+#include "cpufreq.c"
+#include "cpumask.c"
+#include "cred.c"
+#include "device.c"
+#include "dma.c"
+#ifdef CONFIG_DMA_SHARED_BUFFER
+#include "dma-resv.c"
+#endif
+#include "drm.c"
+#include "drm_gpuvm.c"
+#include "err.c"
+#include "fs.c"
+#include "fwctl.c"
+#include "gpu.c"
+#include "interrupt.c"
+#include "io.c"
+#include "irq.c"
+#include "jump_label.c"
+#include "kunit.c"
+#include "list.c"
+#include "maple_tree.c"
+#include "mm.c"
+#include "mutex.c"
+#include "net/genetlink.c"
+#include "of.c"
+#include "page.c"
+#include "pci.c"
+#include "pid_namespace.c"
+#include "platform.c"
+#include "poll.c"
+#include "processor.c"
+#include "property.c"
+#include "pwm.c"
+#include "rbtree.c"
+#include "rcu.c"
+#include "refcount.c"
+#include "regulator.c"
+#include "scatterlist.c"
+#include "security.c"
+#include "serdev.c"
+#include "signal.c"
+#include "slab.c"
+#include "spinlock.c"
+#include "string.c"
+#include "srcu.c"
+#include "sync.c"
+#include "task.c"
+#include "time.c"
+#include "uaccess.c"
+#include "usb.c"
+#include "vmalloc.c"
+#include "wait.c"
+#include "workqueue.c"
+#include "xarray.c"