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, 42 insertions, 0 deletions

diff --git a/include/uapi/asm-generic/poll.h b/include/uapi/asm-generic/poll.h
new file mode 100644
index 000000000..f9c520ce4
--- /dev/null
+++ b/include/uapi/asm-generic/poll.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __ASM_GENERIC_POLL_H
+#define __ASM_GENERIC_POLL_H
+
+/* These are specified by iBCS2 */
+#define POLLIN		0x0001
+#define POLLPRI		0x0002
+#define POLLOUT		0x0004
+#define POLLERR		0x0008
+#define POLLHUP		0x0010
+#define POLLNVAL	0x0020
+
+/* The rest seem to be more-or-less nonstandard. Check them! */
+#define POLLRDNORM	0x0040
+#define POLLRDBAND	0x0080
+#ifndef POLLWRNORM
+#define POLLWRNORM	0x0100
+#endif
+#ifndef POLLWRBAND
+#define POLLWRBAND	0x0200
+#endif
+#ifndef POLLMSG
+#define POLLMSG		0x0400
+#endif
+#ifndef POLLREMOVE
+#define POLLREMOVE	0x1000
+#endif
+#ifndef POLLRDHUP
+#define POLLRDHUP       0x2000
+#endif
+
+#define POLLFREE	(__force __poll_t)0x4000
+
+#define POLL_BUSY_LOOP	(__force __poll_t)0x8000
+
+struct pollfd {
+	int fd;
+	short events;
+	short revents;
+};
+
+#endif	/* __ASM_GENERIC_POLL_H */