usbip: synchronize event handler with sysfs code paths

commit 363eaa3a

 upstream.

Fuzzing uncovered race condition between sysfs code paths in usbip
drivers. Device connect/disconnect code paths initiated through
sysfs interface are prone to races if disconnect happens during
connect and vice versa.

Use sysfs_lock to synchronize event handler with sysfs paths
in usbip drivers.

Cc: stable@vger.kernel.org
Reported-and-tested-by:  <syzbot+a93fba6d384346a761e3@syzkaller.appspotmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/c5c8723d3f29dfe3d759cfaafa7dd16b0dfe2918.1616807117.git.skhan@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>