Re: [PATCH 1/2] usb: storage: Fix memory leak in USB bulk transport

[Alan Stern <stern@rowland.harvard.edu>]

On Wed, Oct 29, 2025 at 04:14:13PM -0300, Desnes Nunes wrote:
> A kernel memory leak was identified by the 'ioctl_sg01' test from Linux
> Test Project (LTP). The following bytes were maily observed: 0x53425355.
> 
> When USB storage devices incorrectly skip the data phase with status data,
> the code extracts/validates the CSW from the sg buffer, but fails to clear
> it afterwards. This leaves status protocol data in srb's transfer buffer,
> such as the US_BULK_CS_SIGN 'USBS' signature observed here. Thus, this
> leads to USB protocols leaks to user space through SCSI generic (/dev/sg*)
> interfaces, such as the one seen here when the LTP test requested 512 KiB.
> 
> Fix the leak by zeroing the CSW data in srb's transfer buffer immediately
> after the validation of devices that skip data phase.
> 
> Note: Differently from CVE-2018-1000204, which fixed a big leak by zero-
> ing pages at allocation time, this leak occurs after allocation, when USB
> protocol data is written to already-allocated sg pages.
> 
> Fixes: a45b599ad808 ("scsi: sg: allocate with __GFP_ZERO in sg_build_indirect()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Desnes Nunes <desnesn@redhat.com>
> ---
>  drivers/usb/storage/transport.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
> index 1aa1bd26c81f..8e9f6459e197 100644
> --- a/drivers/usb/storage/transport.c
> +++ b/drivers/usb/storage/transport.c
> @@ -1200,7 +1200,17 @@ int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
>  						US_BULK_CS_WRAP_LEN &&
>  					bcs->Signature ==
>  						cpu_to_le32(US_BULK_CS_SIGN)) {
> +				unsigned char buf[US_BULK_CS_WRAP_LEN];

You don't have to define another buffer here.  bcs is still available
and it is exactly the right size.

Alan Stern

> +
> +				sg = NULL;
> +				offset = 0;
> +				memset(buf, 0, US_BULK_CS_WRAP_LEN);
>  				usb_stor_dbg(us, "Device skipped data phase\n");
> +
> +				if (usb_stor_access_xfer_buf(buf, US_BULK_CS_WRAP_LEN, srb,
> +						&sg, &offset, TO_XFER_BUF) != US_BULK_CS_WRAP_LEN)
> +					usb_stor_dbg(us, "Failed to clear CSW data\n");
> +
>  				scsi_set_resid(srb, transfer_length);
>  				goto skipped_data_phase;
>  			}
> -- 
> 2.51.0
>