Re: [PATCH v2] usb: uas: fix urb unmapping issue when the uas device is remove during ongoing data transfer

[Owen Gu]

Hi Oliver,

I'm following up on my previous patch v2. Could you please provide feedback on it?
If there's anything I can improve, let me know.

Thanks,
Owen Gu

On Wed, Oct 15, 2025 at 11:31:57PM +0800, guhuinan wrote:
> From: Owen Gu <guhuinan@xxxxxxxxxx>
> 
> When a UAS device is unplugged during data transfer, there is
> a probability of a system panic occurring. The root cause is
> an access to an invalid memory address during URB callback handling.
> Specifically, this happens when the dma_direct_unmap_sg() function
> is called within the usb_hcd_unmap_urb_for_dma() interface, but the
> sg->dma_address field is 0 and the sg data structure has already been
> freed.
> 
> The SCSI driver sends transfer commands by invoking uas_queuecommand_lck()
> in uas.c, using the uas_submit_urbs() function to submit requests to USB.
> Within the uas_submit_urbs() implementation, three URBs (sense_urb,
> data_urb, and cmd_urb) are sequentially submitted. Device removal may
> occur at any point during uas_submit_urbs execution, which may result
> in URB submission failure. However, some URBs might have been successfully
> submitted before the failure, and uas_submit_urbs will return the -ENODEV
> error code in this case. The current error handling directly calls
> scsi_done(). In the SCSI driver, this eventually triggers scsi_complete()
> to invoke scsi_end_request() for releasing the sgtable. The successfully
> submitted URBs, when being unlinked to giveback, call
> usb_hcd_unmap_urb_for_dma() in hcd.c, leading to exceptions during sg
> unmapping operations since the sg data structure has already been freed.
> 
> This patch modifies the error condition check in the uas_submit_urbs()
> function. When a UAS device is removed but one or more URBs have already
> been successfully submitted to USB, it avoids immediately invoking
> scsi_done() and save the cmnd to devinfo->cmnd array. If the successfully
> submitted URBs is completed before devinfo->resetting being set, then
> the scsi_done() function will be called within uas_try_complete() after
> all pending URB operations are finalized. Otherwise, the scsi_done()
> function will be called within uas_zap_pending(), which is executed after
> usb_kill_anchored_urbs(). The uas_zap_pending() iterates over
> devinfo->cmnd array, invoking uas_try_complete() for each command to
> finalize their handling.
> 
> Signed-off-by: Yu Chen <chenyu45@xxxxxxxxxx>
> Signed-off-by: Owen Gu <guhuinan@xxxxxxxxxx>
> ---
> v2: Upon uas_submit_urbs() returning -ENODEV despite successful URB
> submission, the cmnd is added to the devinfo->cmnd array before
> exiting uas_queuecommand_lck().
> v1: https://lore.kernel.org/linux-usb/20250930045309.21588-1-guhuinan@xxxxxxxxxx/
> ---
> ---
>  drivers/usb/storage/uas.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
> index 4ed0dc19afe0..45b01df364f7 100644
> --- a/drivers/usb/storage/uas.c
> +++ b/drivers/usb/storage/uas.c
> @@ -698,6 +698,10 @@ static int uas_queuecommand_lck(struct scsi_cmnd *cmnd)
>  	 * of queueing, no matter how fatal the error
>  	 */
>  	if (err == -ENODEV) {
> +		if (cmdinfo->state & (COMMAND_INFLIGHT | DATA_IN_URB_INFLIGHT |
> +				DATA_OUT_URB_INFLIGHT))
> +			goto out;
> +
>  		set_host_byte(cmnd, DID_NO_CONNECT);
>  		scsi_done(cmnd);
>  		goto zombie;
> @@ -711,6 +715,7 @@ static int uas_queuecommand_lck(struct scsi_cmnd *cmnd)
>  		uas_add_work(cmnd);
>  	}
>  
> +out:
>  	devinfo->cmnd[idx] = cmnd;
>  zombie:
>  	spin_unlock_irqrestore(&devinfo->lock, flags);
> -- 
> 2.43.0
>