usbip: synchronize event handler with sysfs code paths

stable inclusion
from stable-5.10.30
commit f06cb4641b15e55c2c7d47c44a57a8c9208b92ef
bugzilla: 51791

--------------------------------

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: NShuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/c5c8723d3f29dfe3d759cfaafa7dd16b0dfe2918.1616807117.git.skhan@linuxfoundation.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: N  Weilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/usb/usbip/usbip_event.c

@@ -70,6 +70,7 @@ static void event_handler(struct work_struct *work)
 	while ((ud = get_event()) != NULL) {
 		usbip_dbg_eh("pending event %lx\n", ud->event);
 
+		mutex_lock(&ud->sysfs_lock);
 		/*
 		 * NOTE: shutdown must come first.
 		 * Shutdown the device.
@@ -90,6 +91,7 @@ static void event_handler(struct work_struct *work)
 			ud->eh_ops.unusable(ud);
 			unset_event(ud, USBIP_EH_UNUSABLE);
 		}
+		mutex_unlock(&ud->sysfs_lock);
 
 		wake_up(&ud->eh_waitq);
 	}