HID: debug: fix the ring buffer implementation

HID: debug: fix the ring buffer implementation

commit 13054abbaa4f1fd4e6f3b4b63439ec033b4c8035 upstream.

Ring buffer implementation in hid_debug_event() and hid_debug_events_read()
is strange allowing lost or corrupted data. After commit 717adfdaf147
("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 v3.18: some (tree-wide) patches are missing in v3.18 so
cherry-pick relevant pieces from:
 * 6396bb221514 ("treewide: kzalloc() -> kcalloc()")
 * a9a08845e9ac ("vfs: do bulk POLL* -> EPOLL* replacement")
 * 92529623d242 ("HID: debug: improve hid_debug_event()")
 * 174cd4b1e5fb ("sched/headers: Prepare to move signal wakeup & sigpending
   methods from <linux/sched.h> into <linux/sched/signal.h>")
 * 8fec02a73e31 ("HID: debug: fix error handling in hid_debug_events_read()")

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1669187
Cc: stable@vger.kernel.org # v4.18+
Fixes: cd667ce24796 ("HID: use debugfs for events/reports dumping")
Fixes: 717adfdaf147 ("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>