linux-kernel - Re: [PATCH v3] usb: uas: fix urb unmapping issue when the uas device is remove during ongoing data transfer

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Message-ID: <eb0e0fda-2292-4759-89e7-66e590c4ca83@suse.com>
Date: Mon, 10 Nov 2025 14:23:15 +0100
From: Oliver Neukum <oneukum@...e.com>
To: guhuinan <guhuinan@...omi.com>, Oliver Neukum <oneukum@...e.com>,
 Alan Stern <stern@...land.harvard.edu>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, linux-scsi@...r.kernel.org,
 usb-storage@...ts.one-eyed-alien.net, linux-kernel@...r.kernel.org,
 Yu Chen <chenyu45@...omi.com>, Michal Pecio <michal.pecio@...il.com>
Subject: Re: [PATCH v3] usb: uas: fix urb unmapping issue when the uas device
 is remove during ongoing data transfer

On 04.11.25 07:16, guhuinan wrote:
> From: Owen Gu <guhuinan@...omi.com>
> 
> 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 error handling only takes effect when uas_queuecommand_lck() calls
> uas_submit_urbs() and returns the error value -ENODEV . In this case,
> the device is disconnected, and the flow proceeds to uas_disconnect(),
> where uas_zap_pending() is invoked to call uas_try_complete().
> 
> Signed-off-by: Yu Chen <chenyu45@...omi.com>
> Signed-off-by: Owen Gu <guhuinan@...omi.com>
Acked-by: Oliver Neukum <oneukum@...e.com>> ---
> v3: Add some commit message.
> 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().
> https://lore.kernel.org/linux-usb/20251015153157.11870-1-guhuinan@xiaomi.com/
> v1: https://lore.kernel.org/linux-usb/20250930045309.21588-1-guhuinan@xiaomi.com/
> ---
> ---
>   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);