RE: [EXTERNAL] [PATCH 1/1] scsi: Fix possible buffer overflows in storvsc_queuecommand

[KY Srinivasan <kys@microsoft.com>]

> -----Original Message-----
> From: Xiaohui Zhang <ruc_zhangxiaohui@163.com>
> Sent: Tuesday, December 8, 2020 5:19 AM
> To: Xiaohui Zhang <ruc_zhangxiaohui@163.com>; KY Srinivasan
> <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Stephen
> Hemminger <sthemmin@microsoft.com>; Wei Liu <wei.liu@kernel.org>;
> James E.J. Bottomley <jejb@linux.ibm.com>; Martin K. Petersen
> <martin.petersen@oracle.com>; linux-hyperv@vger.kernel.org; linux-
> scsi@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: [EXTERNAL] [PATCH 1/1] scsi: Fix possible buffer overflows in
> storvsc_queuecommand
> 
> From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
> 
> storvsc_queuecommand() calls memcpy() without checking the destination size
> may trigger a buffer overflower, which a local user could use to cause denial of
> service or the execution of arbitrary code.
> Fix it by putting the length check before calling memcpy().
> 
> Signed-off-by: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
> ---
>  drivers/scsi/storvsc_drv.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c index
> 0c65fbd41..09b60a4c0 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1729,6 +1729,8 @@ static int storvsc_queuecommand(struct Scsi_Host
> *host, struct scsi_cmnd *scmnd)
> 
>  	vm_srb->cdb_length = scmnd->cmd_len;
> 
> +	if (vm_srb->cdb_length > STORVSC_MAX_CMD_LEN)
> +		vm_srb->cdb_length = STORVSC_MAX_CMD_LEN;
>  	memcpy(vm_srb->cdb, scmnd->cmnd, vm_srb->cdb_length);

The data  structure is sized correctly to handle the max command length. Besides
your check is bogus - you cannot truncate the command!

K. Y
> 
>  	sgl = (struct scatterlist *)scsi_sglist(scmnd);
> --
> 2.17.1