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PUBLISHED

CVE-2024-36894

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

Assigner:Linux (416baaa9-dc9f-4396-8d5f-8c081fb06d67)
Reserved:2024-05-30
Published:2024-05-30
Updated:2024-06-21

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 ("usb: 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 ("usb: gadget: f_fs: use io_data->status consistently")

Product status

Default status
unaffected

2e4c7553cd6f before a0fdccb1c9e0
affected

2e4c7553cd6f before 73c05ad46bb4
affected

2e4c7553cd6f before d74618308232
affected

2e4c7553cd6f before 24729b307eef
affected

Default status
affected

3.15
affected

Any version before 3.15
unaffected

6.1.95
unaffected

6.6.31
unaffected

6.8.10
unaffected

6.9
unaffected

References

https://git.kernel.org/stable/c/a0fdccb1c9e027e3195f947f61aa87d6d0d2ea14

https://git.kernel.org/stable/c/73c05ad46bb4fbbdb346004651576d1c8dbcffbb

https://git.kernel.org/stable/c/d7461830823242702f5d84084bcccb25159003f4

https://git.kernel.org/stable/c/24729b307eefcd7c476065cd7351c1a018082c19

cve.org CVE-2024-36894

nvd.nist.gov CVE-2024-36894

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