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

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Message-ID: <6c65094e-81e5-4ce8-8592-9458c51116f7@suse.com>
Date: Tue, 30 Sep 2025 15:22:45 +0200
From: Oliver Neukum <oneukum@...e.com>
To: guhuinan <guhuinan@...omi.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>
Subject: Re: [PATCH] fix urb unmapping issue when the uas device is remove
 during ongoing data transfer

Hi,

On 30.09.25 06:53, 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 completed (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(). Instead, it waits for the successfully submitted URBs to
> complete , and then triggers the scsi_done() function call within
> uas_try_complete() after all pending URB operations are finalized.
> 
> Signed-off-by: Yu Chen <chenyu45@...omi.com>
> Signed-off-by: Owen Gu <guhuinan@...omi.com>
> ---
>   drivers/usb/storage/uas.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
> index 4ed0dc19afe0..6bfc7281f7ad 100644
> --- a/drivers/usb/storage/uas.c
> +++ b/drivers/usb/storage/uas.c
> @@ -699,7 +699,9 @@ static int uas_queuecommand_lck(struct scsi_cmnd *cmnd)
>   	 */
>   	if (err == -ENODEV) {
>   		set_host_byte(cmnd, DID_NO_CONNECT);

Why then set the host byte unconditionally?

> -		scsi_done(cmnd);
> +		if (!(cmdinfo->state & (COMMAND_INFLIGHT | DATA_IN_URB_INFLIGHT |
> +				DATA_OUT_URB_INFLIGHT)))
> +			scsi_done(cmnd);

It would seem to me that in this case you need to make sure
in the completion handlers that scsi_done() is always called,
even if the resetting flag is set.

	Regards
		Oliver