syzbot is reporting a crash at vhci_shutdown_connection() [1]. It turned
out that it was not a NULL pointer dereference but an ERR_PTR(-EINTR)
pointer dereference, for kthread_create() became killable due to
commit 786235eeba0e1e85 ("kthread: make kthread_create() killable").
When SIGKILLed while attach_store() is calling kthread_get_run(),
ERR_PTR(-EINTR) is stored into vdev->ud.tcp_{rx,tx}, and then
kthread_stop_put() is called on vdev->ud.tcp_{rx,tx} from
vhci_shutdown_connection() because vdev->ud.tcp_{rx,tx} != NULL.
Prior to commit 9720b4bc76a83807 ("staging/usbip: convert to kthread"),
"current" pointer is assigned to vdev->ud.tcp_{rx,tx} by usbip_thread()
kernel thread, and hence vdev->ud.tcp_{rx,tx} != NULL meant a valid task
pointer. Therefore, we should make kthread_get_run() return NULL when
kthread_create() failed.
[1] https://syzkaller.appspot.com/bug?id=c21c07f3d51769405e8efc027bdb927515dcc7d6
Reported-by: syzbot <syzbot+a93fba6d384346a761e3@xxxxxxxxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+bf1a360e305ee719e364@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Fixes: 9720b4bc76a83807 ("staging/usbip: convert to kthread")
Cc: Arnd Bergmann <arnd@xxxxxxxx>
---
drivers/usb/usbip/usbip_common.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/usb/usbip/usbip_common.h b/drivers/usb/usbip/usbip_common.h
index 8be857a4fa13..a7c68097aa1d 100644
--- a/drivers/usb/usbip/usbip_common.h
+++ b/drivers/usb/usbip/usbip_common.h
@@ -286,6 +286,8 @@ struct usbip_device {
if (!IS_ERR(__k)) { \
get_task_struct(__k); \
wake_up_process(__k); \
+ } else { \
+ __k = NULL; \
} \
__k; \
})
--
2.18.4
