commit 13054abb upstream.

Ring buffer implementation in hid_debug_event() and hid_debug_events_read()
is strange allowing lost or corrupted data. After commit 717adfda
("HID: debug: check length before copy_to_user()") it is possible to enter
an infinite loop in hid_debug_events_read() by providing 0 as count, this
locks up a system. Fix this by rewriting the ring buffer implementation
with kfifo and simplify the code.

This fixes CVE-2019-3819.

v2: fix an execution logic and add a comment
v3: use __set_current_state() instead of set_current_state()

Backport to v4.9: some tree-wide patches are missing in v4.9 so
cherry-pick relevant pieces from:
 * 6396bb22 ("treewide: kzalloc() -> kcalloc()")
 * a9a08845 ("vfs: do bulk POLL* -> EPOLL* replacement")
 * 174cd4b1 ("sched/headers: Prepare to move signal wakeup & sigpending
   methods from <linux/sched.h> into <linux/sched/signal.h>")

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1669187
Cc: stable@vger.kernel.org # v4.18+
Fixes: cd667ce2 ("HID: use debugfs for events/reports dumping")
Fixes: 717adfda ("HID: debug: check length before copy_to_user()")
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>