[PATCH 4.9 27/37] usbip: synchronize event handler with sysfs code paths

[Greg Kroah-Hartman]

From: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

commit 363eaa3a450abb4e63bd6e3ad79d1f7a0f717814 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@xxxxxxxxxxxxxxx # 4.9.x
Reported-and-tested-by: syzbot+a93fba6d384346a761e3@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/c5c8723d3f29dfe3d759cfaafa7dd16b0dfe2918.1616807117.git.skhan@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tom Seewald <tseewald@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/usb/usbip/usbip_event.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/usb/usbip/usbip_event.c
+++ b/drivers/usb/usbip/usbip_event.c
@@ -84,6 +84,7 @@ static void event_handler(struct work_st
 	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.
@@ -104,6 +105,7 @@ static void event_handler(struct work_st
 			ud->eh_ops.unusable(ud);
 			unset_event(ud, USBIP_EH_UNUSABLE);
 		}
+		mutex_unlock(&ud->sysfs_lock);
 
 		wake_up(&ud->eh_waitq);
 	}