On 2/19/21 8:53 AM, Greg Kroah-Hartman wrote:
On Sat, Feb 20, 2021 at 12:08:32AM +0900, Tetsuo Handa wrote:syzbot is reporting an ERR_PTR(-EINTR) pointer dereference at vhci_shutdown_connection() [1], 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 means a valid task pointer. However, this patch does not make kthread_get_run() return NULL when kthread_create() failed, for this patch removes kthread_get_run() in order to fix the other bug described below. syzbot is also reporting a NULL pointer dereference at sock_sendmsg() [2], for lack of serialization between attach_store() and event_handler() causes vhci_shutdown_connection() to observe vdev->ud.tcp_tx == NULL while vdev->ud.tcp_socket != NULL. Please read the reference link for details of this race window. Therefore, this patch does the following things in order to fix reported bugs and other possible bugs. (1) Handle kthread_create() failure (which fixes [1]) by grouping socket lookup, kthread_create() and get_task_struct() into usbip_prepare_threads() function. (2) Serialize usbip_sockfd_store(), detach_store(), attach_store() and ud->eh_ops.{shutdown,reset,unusable}() operations using usbip_event_mutex mutex (which fixes [2]). Introducing such large mutex should be safe because ud->tcp_{tx,rx} must not wait for event_handler() to flush because event_handler() is processed by a singlethreaded workqueue. (3) Add SOCK_STREAM check into usbip_prepare_threads(), for current code is not verifying that a file descriptor passed is actually a stream socket. If the file descriptor passed was a SOCK_DGRAM socket, sock_recvmsg() can't detect end of stream. (4) Don't perform ud->tcp_socket = NULL in vhci_device_reset(). Since ud->tcp_{tx,rx} depend on ud->tcp_socket != NULL whereas ud->tcp_socket and ud->tcp_{tx,rx} are assigned at the same time, it is never safe to reset ud->tcp_socket from vhci_device_reset() without calling kthread_stop_put() from vhci_shutdown_connection(). (5) usbip_sockfd_store() must perform if ({sdev,udc}->ud.status != SDEV_ST_AVAILABLE) { /* misc assignments for attach operation */ {sdev,udc}->ud.status = SDEV_ST_USED; } atomically, or multiple ud->tcp_{tx,rx} are created (which will later cause a crash like [2]) and refcount on ud->tcp_socket is leaked when usbip_sockfd_store() is concurrently called. [1] https://syzkaller.appspot.com/bug?extid=a93fba6d384346a761e3 [2] https://syzkaller.appspot.com/bug?extid=95ce4b142579611ef0a9 Reported-and-tested-by: syzbot <syzbot+a93fba6d384346a761e3@xxxxxxxxxxxxxxxxxxxxxxxxx> Reported-by: syzbot <syzbot+bf1a360e305ee719e364@xxxxxxxxxxxxxxxxxxxxxxxxx> Reported-by: syzbot <syzbot+95ce4b142579611ef0a9@xxxxxxxxxxxxxxxxxxxxxxxxx> References: https://lkml.kernel.org/r/676d4518-0faa-9fab-15db-0db8d216d7fb@xxxxxxxxxxxxxxxxxxx Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Fixes: 9720b4bc76a83807 ("staging/usbip: convert to kthread") --- drivers/usb/usbip/stub_dev.c | 56 ++++++++++++++++++-------------- drivers/usb/usbip/usbip_common.c | 55 +++++++++++++++++++++++++++++++ drivers/usb/usbip/usbip_common.h | 25 +++++++------- drivers/usb/usbip/usbip_event.c | 15 +++++++++ drivers/usb/usbip/vhci_hcd.c | 6 ---- drivers/usb/usbip/vhci_sysfs.c | 50 ++++++++++++++++++++-------- drivers/usb/usbip/vudc_sysfs.c | 50 ++++++++++++++++------------ 7 files changed, 181 insertions(+), 76 deletions(-)What changed from v1? Why isn't that info below the --- line? Please do a v3 with that fixed up.
+1 on this. Also please run the usbip test on your changes: tools/testing/selftests/drivers/usb/usbip/usbip_test.sh thanks, -- Shuah
