[PATCH 1/2] usbip: clear actual_length after a failed receive

[Cheng Yongkang <teel4res@gmail.com>]

vhci_recv_ret_submit() receives the transfer buffer for an IN URB.  When
usbip_recv_xbuff() fails, it sets urb->status to -EPROTO and gives the URB
back, but leaves urb->actual_length at the value supplied by the usbip
peer.  A malicious peer can set actual_length larger than
transfer_buffer_length; usbfs then copies that many bytes from the
kmalloc(transfer_buffer_length) buffer to userspace:

  BUG: KASAN: slab-out-of-bounds in _copy_to_user+0x79/0xb0
  Read of size 88 at addr ...
  copy_urb_data_to_user+0x36f/0x480

Clear actual_length on the failure path so the failed URB never carries a
peer-controlled length.  The URB is completed with -EPROTO and userspace
observes a zero-length, failed transfer.

Fixes: aabb5b833872 ("usbip: Fix error path of vhci_recv_ret_submit()")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Cheng Yongkang <teel4res@gmail.com>
---
 drivers/usb/usbip/vhci_rx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/usbip/vhci_rx.c b/drivers/usb/usbip/vhci_rx.c
index a678e7c..741107a 100644
--- a/drivers/usb/usbip/vhci_rx.c
+++ b/drivers/usb/usbip/vhci_rx.c
@@ -79,6 +79,7 @@ static void vhci_recv_ret_submit(struct vhci_device *vdev,
 	/* recv transfer buffer */
 	if (usbip_recv_xbuff(ud, urb) < 0) {
 		urb->status = -EPROTO;
+		urb->actual_length = 0;
 		goto error;
 	}
 
-- 
2.34.1