CVE-2024-36894 Information

Description

In the Linux kernel the following vulnerability has been resolved:

usb: gadget: f_fs: Fix race between aio_cancel() and AIO request complete

FFS based applications can utilize the aio_cancel() callback to dequeue pending USB requests submitted to the UDC. There is a scenario where the FFS application issues an AIO cancel call while the UDC is handling a soft disconnect. For a DWC3 based implementation the callstack looks like the following:

DWC3 Gadget                               FFS Application

dwc3_gadget_soft_disconnect() … –> dwc3_stop_active_transfers() –> dwc3_gadget_giveback(-ESHUTDOWN) –> ffs_epfile_async_io_complete() ffs_aio_cancel() –> usb_ep_free_request() –> usb_ep_dequeue()

There is currently no locking implemented between the AIO completion handler and AIO cancel so the issue occurs if the completion routine is running in parallel to an AIO cancel call coming from the FFS application. As the completion call frees the USB request (io_data->req) the FFS application is also referencing it for the usb_ep_dequeue() call. This can lead to accessing a stale/hanging pointer.

commit b566d38857fc (�sb: gadget: f_fs: use io_data->status consistently) relocated the usb_ep_free_request() into ffs_epfile_async_io_complete(). However in order to properly implement locking to mitigate this issue the spinlock can’t be added to ffs_epfile_async_io_complete() as usb_ep_dequeue() (if successfully dequeuing a USB request) will call the function driver’s completion handler in the same context. Hence leading into a deadlock.

Fix this issue by moving the usb_ep_free_request() back to ffs_user_copy_worker() and ensuring that it explicitly sets io_data->req to NULL after freeing it within the ffs->eps_lock. This resolves the race condition above as the ffs_aio_cancel() routine will not continue attempting to dequeue a request that has already been freed or the ffs_user_copy_work() not freeing the USB request until the AIO cancel is done referencing it.

This fix depends on commit b566d38857fc (�sb: gadget: f_fs: use io_data->status consistently)

Reference

https://git.kernel.org/stable/c/73c05ad46bb4fbbdb346004651576d1c8dbcffbb https://git.kernel.org/stable/c/d7461830823242702f5d84084bcccb25159003f4 https://git.kernel.org/stable/c/24729b307eefcd7c476065cd7351c1a018082c19